ACIDS AND BASES - StudyTime NZ...Acids and Bases 27 Defining Acids and Bases 27 pH Scale 29...

NCEA | Walkthrough Guide

ACIDS AND BASES

DISTANCE/TIME GRAPHS AND AVERAGE SPEED

dist.miles

timehours

12

34

5

8

6

4

2

Smaller Surface → Larger pressure

Level 1SCIENCE

AcidBase

WaterSalt

HCl + NaOHH2O + NaCl

TT TtTt

Tt

Tt

TT

t

t

tt

Introduction 3

Atoms 4

Atomic Structure 4Opposites attract: how electrons and protons interact 5Electron configuration 6The periodic table 8Quick Questions 10

Ions 10

Valence Shells 11Forming Ions 12Ionic Bonds 13Ionic Compounds 14Quick Questions 17

Rates of Reaction 18

Reaction Rate 18Collision Theory 19Activation Energy 20Measuring Reaction Rate 21Reaction Rate Graphs 21Concentration 22Temperature 23Surface Area 24Catalysts 26Quick Questions 27

Acids and Bases 27

Defining Acids and Bases 27pH Scale 29Indicators 30Linking pH, indicators and acids and bases 31Neutralisation Reactions 32Balancing equations 34How to physically make your desired salt in the lab 36Quick Questions 36

Key Terms 37

Level 1 Science | Acids and Bases

Level 1 Science | Acids and Bases | © Inspiration Education Limited 2018. All rights reserved.3


You’ve probably heard the term ‘Chemistry’ before. It’s the thing the main characters have in movies, and what you think you might have with that classmate you’re too afraid to talk to.

Although you may have covered it in science in earlier years, there’s a chance this is the first time you’ve really been able to explore it. So, you’re in luck! This external teaches you all about what makes up the universe around us. Sound intense? We promise you’ll be fine. It turns out everything around us is made up of tiny particles which have more in common than you’d think.

What we’ll be covering in this walkthrough guide

As we work through this standard, you’ll encounter these tiny particles (which we’ll call atoms), their alter egos, ‘ions’ and the symbols, methods and equations we use to give them meaning. You’ll come out ready for the exams, and confidently able to drop words like ‘indicators’ and ‘pH’ when you finally go on that date you’ve been holding out for.

A word about exam strategy

Chemistry is one of those subjects that seems really hard, but a good mark in acids and bases is definitely achievable.

Broadly speaking, questions in acids and bases are usually discussion based questions or involve writing and balancing equations.

Our advice? Get really good at writing and balancing equations. Make sure you can do all the writing and balancing equations questions from previous exam papers. There’s generally two writing and balancing equations in each year’s exam (but NCEA can always change the format, so take our advice cautiously).

Also, one that always creeps up in exams is explaining the practical steps to producing a salt. Unfortunately, lots of students haven’t studied this, and end up missing an easy Merit or Excellence mark. To help, we make it the very last thing we cover in this guide.

Here at StudyTime, we’re pretty much GCs (good citizens), so to help you out, we’ve made this guide in plain English as much as we can. We’ve also included a glossary for some of the key terms that you’ll need to master for your exam.

INTRODUCTION

4 Level 1 Science | Acids and Bases| © Inspiration Education Limited 2018. All rights reserved.


ATOMSThere’s that word again! A fluffy textbook will tell you that atoms are the ‘essence of life’ - and, well, it is actually true. From the chair you are sitting on, to the rubber of your shoes, every single thing can be broken into tiny particles called ‘atoms’. You can’t see them - and for now you’ll have to trust us, but we promise that’s all there is to it!

As we work through this topic, we’ll gear you up with the tools to talk about, categorise and discuss what it really means to be an atom.

Just to hold us accountable, here’s what we’ll run through:

What an atom actually is - and how to break down the structure of one.How to use the periodic table - and what all the numbers on it really mean.What an electron is, and what that means to an atom. The magic of the outer electrons, and why they are so special to atoms.

Atomic Structure

So I just told you that everything is made up of atoms. Tiny particles which, through different interactions and characteristics, can combine to form everything around us.

An atom is the defining structure of an element.

But where do these different characteristics come from? What makes the chair you’re sitting on different from the bottom of your shoe?

It turns out atoms have a structure - and the way that this structure works in each individual atom dictates what it will eventually become.

If learning key words first off scares you (or bores you), then focus on understanding the concepts the first time around, and then memorise the definitions so you can explain it the way the NCEA wants you to.

However, the language we use isn’t always something you can directly write in yourexam. When this is the case, we offer a more scientific definition or explanation (in ahandy blue box) underneath. These boxes are trickier to understand on your first readthrough, but contain language you are allowed to write in your exam. Look out forthem to make sure you stay on target!



How atoms are structured

Let’s break it down. Pretend you get super-strength vision overnight, and you can suddenly zoom into what makes up an atom. Here’s what you’ll see:

nucleus

electron

neutronsprotons

e

Smack bang right in the centre of all atoms is a teensy-tiny “nucleus”. It’s made up of two types of particles:

1. The positively-charged protons2. The uncharged neutrons

We’ll come back to this idea a bit later on, but basically the number of protons tells us what kind of atom we have; whether it is it a hydrogen atom, a helium atom, a lithium atom, and so on. Pretty much, discussing the number of protons an atom has is like discussing its personality.

Unlike the tightly packed contents of the nucleus, the electrons do their own thing on the outskirts. You can think of electrons as constantly whizzing around, orbiting the nucleus, similar to how the planets orbit around the sun. But they do this in a nice orderly fashion, with electrons only staying within a certain electron “shell”.

2nd electron shell

1st electron shell

valence electron

e

e e

e

e

e

Opposites attract: how electrons and protons interact

As any cliche romantic will tell you, opposites attract. So, negatively-charged electrons are attracted to the positively-charged protons. The actual term for this is electrostatic attraction.

+++ + +

+

+ +++++



In fact, electrostatic attraction is the very reason these atoms can actually hold themselves together!

Electrostatic attraction is name for the attractive forces holding atoms together - and allowing them to exist in compact structures.

So, that’s it; atoms are made of a dense nucleus of protons and neutrons, which is in turn orbited by electrons in specific electron shells.

STOP AND CHECK:

Turn your book over and see if you can remember:

The structure of an atom – have a go at drawing it! How electrons orbit the nucleus.

Try to explain it in your own words.

Electron Configuration

Let’s have a closer look at the electrons whizzing around the nucleus. Rather than having a higgledy-piggledy mess of electrons, the electrons orbit in specific rings called ‘electron shells’. These shells look like Saturn’s rings, and all the electrons in each shell tend to stick to their own path as they travel around the nucleus.

The ‘2,8,8’ rule

These shells aren’t equal - and each can hold a different number of electrons. The 1st electron shell can hold up to 2 electrons and is the closest to the nucleus. The 2nd and 3rd electron shells can hold up to 8 electrons each, and are a little further away. So, how many electrons does each atom have in total? It turns out it differs between atoms!

The main idea you can rely on is that, in a normal atom, there are equal numbers of protons and electrons.

Because they have the same number of positive and negative charges, atoms are neutral – everything balances. The number of protons depends on the element (or type of atom), and therefore all uncharged atoms of the same element will have the same number of electrons.

For example, nitrogen (N) is number 7 in the periodic table, and has 7 protons, and 7 electrons.



So, how do these electrons fit into the atom? Imagine throwing electrons into the atom, one by one. They’ll start filling up the 1st electron shell, and when that’s full they’ll start filling up the 2nd electron shell, and so on.

An electron shell is an organised group of electrons orbiting the nucleus. Different atoms have different numbers of electron shells, and electrons within each one.

The number of electrons in each electron shell is the electron configuration. It would look a little something like this:

Carbon

• 6 protons• 6 neutrons• 6 electrons

ee

ee

ee

Electron configuration: (2,4)

Sodium

• 11 protons• 12 neutrons• 11 electrons

ee

ee

ee

e

e e

ee

Electron configuration: (2,8,1)

STOP AND CHECK:

Turn your book over and see if you can write out the electron configuration, using your Periodic Table, for:

Carbon (C) Oxygen (O) Sodium (Na)



The Periodic TableThe Periodic Table is more than just a poster to remind you that you’re in a science classroom. It turns out it’s actually an incredibly clever and useful tool to work out everything you need to know about atoms.

nitrogen

14.007N

7

helium

He4.0026

2

neon

Ne20.180

10fluorine

F18.998

9oxygen

O15.999

8carbon

C12.011

6boron

B10.811

5

argon

Ar39.948

18chlorine

Cl35.453

17sulfur

S32.065

16phosphorus

P30.974

15silicon

Si28.086

14aluminium

Al26.982

13

krypton

Kr83.798

36bromine

Br79.904

35selenium

Se78.96

34arsenic

As74.922

33germanium

Ge72.64

32gallium

Ga69.723

31zinc

Zn65.38

30copper

Cu63.546

29nickel

Ni58.693

28cobalt

Co58.933

27iron

Fe55.845

26manganese

Mn54.938

25chromium

Cr51.996

24vanadium

V50.942

23titanium

Ti47.867

22scandium

Sc44.956

21calcium

Ca40.078

20potassium

K39.098

19

magnesium

Mg24.305

12sodium

Na22.990

11

beryllium

Be9.0122

4lithium

Li6.941

3

hydrogen

H1.0079

1

1 18

2

3 4 5 6 7 8 9 10 11 12

13 14 15 16 17

xenon

Xe131.29

54iodine

I126.90

53tellurium

Te127.60

52antimony

Sb121.76

51tin

Sn118.71

50indium

In114.82

49cadmium

Cd112.41

48silver

Ag107.87

47palladium

Pd106.42

46rhodium

Rh102.91

45ruthenium

Ru101.07

44technetium

Tc[98]

43molybdenum

Mo95.96

42niobium

Nb92.906

41zirconium

Zr91.224

40yttrium

Y88.906

39

Lanthanite

57-71

strontium

Sr87.62

38rubidium

Rb85.468

37

radon

Rn[222]

86astatine

At[210]

85polonium

Po[209]

84bismuth

Bi208.98

83lead

Pb207.2

82

dysprosium

Dy162.50

66terbium

Tb158.93

65gadolinium

Gd157.25

64europium

Eu151.96

63samarium

Sm150.36

62promethium

Pm[145]

61neodymium

Nd144.24

60praseodymium

Pr140.91

59cerium

Ce140.12

58lanthanum

La138.91

57

barium

Ba137.33

56caesium

Cs132.91

55

roentgenium

Rg[272]

111darmstadtium

Ds[271]

110meitnerium

Mt[268]

109hassium

Hs[277]

108bohrium

Bh[264]

107seaborgium

Sg[266]

106dubnium

Db[262]

105rutherfordium

Rf[261]

104radium

Ra[226]

88francium

Fr[223]

87

lutetium

Lu174.97

71ytterbium

Yb173.05

70thulium

Tm168.93

69erbium

Er167.26

68holmium

Ho164.93

67

thallium

Tl204.38

81mercury

Hg200.59

80

ununoctium

Uuo294

118ununseptium

Uus294

117livermorium

Lv293

116ununpentium

Uup288

115flerovium

Fl289

114ununtrum

Uut284

113copernicium

Cn277

112

gold

Au196.97

79platinum

Pt195.08

78iridium

Ir192.22

77osmium

Os190.23

76rhenium

Re186.21

75tungsten

W183.84

74tantalum

Ta180.95

73hafnium

Hf178.49

72

berkelium

Bk[247]

97lawrencium

Lr[262]

103nobelium

No[259]

102mendelevium

Md[258]

101fermium

Fm[257]

100einsteinium

Es[252]

99californium

Cf[251]

98curium

Cm[247]

96americium

Am[243]

95plutonium

Pu[244]

94neptunium

Np[237]

93uranium

U238.03

92protactinium

Pa231.04

91thorium

Th232.04

90actinium

Ac[227]

89

Alkali metal Alkali earth metal Transition metal Basic metal Semimetal Nonmetal Halogen Noble Glas Lanthanite Actinide

89-103

Actinide

Here are the main parts of the periodic table:

Namehydrogen

H1.0079

1 Atomic number

Chemical symbol

Mass number

Chemical ‘symbols’: These are really just shortened versions of the name for each element - for example, Magnesium is a little too big to write in the box, so we give it the abbreviation ‘Mg’. A very special number in the top left corner called the ‘atomic number’. This number is important, as it tells you what the number of protons is (and therefore the number of electrons) you need to draw. A smaller number in the bottom of the square called the ‘mass number’. This number tells you how many particles are in the nucleus. If you’ve been following along, you’ll know this will just be the number of protons added to the number of neutrons!



Using the atomic number from the Periodic table, you can work out the number of protons in each element. Then, using your new Chemistry knowledge, you can simply remember that the number of electrons is the same as this - and you’re ready to draw an atom!

Electrons are really tiny, so the mass number is the number of neutrons + the number of protons, you can determine the number of neutrons by subtracting the atomic number from the mass number. As an equation: neutrons = mass number - atomic number.

But wait, there’s more…

It turns out the periodic table is even more clever than you thought! It is organised into rows (called periods), going left to right, and columns (called groups), going up and down.

By counting the number of periods, you can work out the number of electron shells the atoms have. For example, all the elements in the 2nd period have 2 electron shells. By counting the groups, you can work out the number of electrons in the very outer of these shells. So, all the atoms in Group (or column) 1 have 1 electron in their last shell.

Unfortunately, there is a little trick you must learn for the higher groups (to the right of the periodic table).

For example, fluorine (F) is in group 17 but it only has an atomic number of 9. This means, there is no way it has 17 valence electrons! It actually has 7 valence electrons. When dealing with groups in their teens (groups 13-18) remember to minus 10 from the group number to get the valence number.

1 18

2

3 4 5 6 7 8 9 10 11 12

13 14 15 16 17fluorine

F18.998

9

17-10 = 7 (Valence number)



STOP AND CHECK:

Turn your book over and see if you can calculate the number of protons, neutrons and electrons (using the Periodic Table) for:

Lithium (Li) Fluorine (F) Magnesium (Mg)

What group do each of these atoms belong to – how many valence electrons will they have?

Quick Questions How do you calculate the number of protons an element has, using its atomic

number? How do you calculate the number of electrons and neutrons an element has,

usings its atomic and mass numbers? How many electrons are in the first three shells of an atom? Draw an atom, and label the key structural components of it.

IONS Hopefully by now, you’re getting comfortable with the idea of atoms. But, remember how we said they had an alter ego?

Remember that one of the key rules we talked about with atoms is that they always have a neutral charge. To recap, this means an equal number of protons and electrons.

--

-Atom

++

+=

Don’t worry, this rule is still always true for atoms. In fact, when this isn’t true anymore, we give atoms another name - ions.

Ions have a different number of protons and electrons, and therefore have a positive or negative charge to them.

An ion is a molecule with an electrical charge due to a loss or gain of at least one electron

?



We’ll talk for a bit about ions and nail off the following points:

What a ‘valence shell’ is - and why they are important when it comes to talking about ions.How ions come about. The ‘ionic bond’ - and how it relates to the formation of ionsHow ions come together to create millions of different compounds.

Valence Shells

What the heck is a valence shell?

Valence shells sound fancy, but, if you’ve followed along so far, they won’t be too much extra to wrap your head around. If you think back to those electron shells we talked about when we discussed atoms, just remember that the ‘valence shell’ is simply the shell on the very outside. Another way of thinking about it, is that it’s the biggest.

The valence shell is the outermost electron shell of an atom

Why is this shell more important than the others? It turns out, a lot of the properties we associate with atoms come down to the number of electrons in the valence shell.

Think of valence electrons as marbles. If you begin to lose your marbles you’ve lost your mind, you start to act crazy, and you slowly become insane. For atoms, when they have a full valence electron shell they have a full set of marbles; they’re stable.

So, we don’t really have to worry about atoms with a full valence shell. However, when the valence shell is not full, we have a couple of things to talk about.

- -

-

--

--

-

- -

-- -

Stable Unstable

This is because atoms are determined to become stable. An atom without a full valence shell will desperately try to make its outer shell full. It can do this in a couple of ways, which we’ll go through in the next couple of sections:



1. Sharing valence electrons with another atom so that they both have a full shell (forming a covalent bond). 2. Gaining or losing valence electrons and forming ions.

STOP AND CHECK:


The importance of valence electrons. The two main ways that atoms can get a full valence shell.


Forming Ions

The last group (or column) on the periodic table contains very special atoms. They’re special because they already have a full valence shell, have their full set of marbles, and are stable. This is why they just sit around on the couch and don’t get involved in reactions with other atoms.

For the majority of other atoms, though, they’re a few marbles short. If they’re close enough (4 or more valence electrons) they try to find other electrons around them to fill their shells. If they have less than four electrons, they give up a little, and choose to empty out their last shell instead.

e

e

e

e

e

e

e

e

e e

e

e

e

e

e

e

e

e

e e

eI’m out

valence shell

valenceelectron

full valence shell

loses valence electron

e

e

e

e

e

e

e

e

e

e e

e

e

e

e

e

e

e

e

e e

unfilledvalence shell full valence shell

gain electron



Because electrons are negative by nature, ambitious atoms that go out in search of new electrons end up gaining more negative charges. Because the number of protons hasn’t changed, the atom ends up becoming negatively charged overall.

In a similar way, the atoms that lose electrons surrender a negative charge. Once again, because the number of protons doesn’t change, they are left positively charged overall.

Interpreting the charge of an ion

Not only is the sign (positive or negative) important, but the size of the charge is important too. The number of electrons gained or lost tells us the size of the charge.

If the atom loses 1 electron or gains 1 electron it has a charge of 1- or 1+ .

If the atom loses 2 electrons or gains 2 electrons it has a charge of 2- or 2+ .

As soon as this happens, drop all talk of atoms - you’ve got yourself an ion.

Let that sink in. An ion is just an atom that has lost or gained at least one electron - and therefore gained a charge.

Beyond the word switch, there’s a couple of things you need to know about writing out ions:

An ‘ionic symbol’ is just your abbreviation from the periodic table, followed by the charge written out in tiny letters next to it (For example, the Magnesium ion is Mg2+)For a charge of -1 or +1 you can drop the 1 and just write out the sign (i.e Cl-).

STOP AND CHECK:


How positive ions are formed and why they have a positive charge. How negative are formed and why they have a negative charge.


Ionic Bonds

Righty-ho, so far, we know that atoms will lose or gain electrons in order to get a full valence shell. They can either toss ‘em away or hunt for more. But where do they get these extra electrons from, and where do they go when the atom abandons them?



Turns out electrons aren’t just floating around in space waiting to be collected. Atoms get electrons from other atoms. Atoms with 1 or 2 valence electrons who want to get rid of them simply donate them to atoms in need.

So, imagine that one atom donates its electrons to another atom. Both of them now have a full valence shell. Because the first atom gave up the electrons, it has a positive charge. The second atom, which gained the electrons, has a negative charge. And what does this charge mean? We are now able to call them ions.

The super cool thing is that, because positive charges attract negative charges, the positive ion is attracted to the negative ion, and they decide to stay side by side. This attraction is called an ionic bond, and forms the basis of all kinds of chemical interactions.

An ionic bond is an interaction caused by the attraction between a negatively charged ion, and the positively charged ion it gained its electrons from.

e

e

e

e

e

e

e

e

e e

e

e

e

e

e

e

e

e

ee

positive and negative charges attract-+

e

e

e

e

e

e

e

e

ee

e

e

e

e

e

e

e

e

ee

STOP AND CHECK:


How ionic bonds are formed.


Ionic Compounds

When at least two ions are held together by an ionic bond you get what is called an ionic compound. Here’s a handy life-hack: the ionic compounds you’ll be learning about contain at least one metal atom (an atom from Group 1 or 2, or aluminium) and at least one non-metal atom (any atom from Group 4 onwards).



Lots and lots of similar pairs of ions can come together, throw a party, and form an ionic solid. Table salt is an ionic compound of sodium and chloride ions. In those grains of salt you pour over your chips, each one contains millions and billions of sodium and chloride ions all bonded together through the giving and taking of electrons.

An ionic compound is a structure comprised of ions held together by ionic bonds

When an ionic compound forms, it is important that we give it a name.

Here’s how it works.

Naming ionic compounds

1. Take the name of the metal, and leave it exactly how it is. This is the first part of the name of your organic compound

2. Take the name of the non-metal and make a decision:

If the atom name normally ends in “-ine”, like fluorine, you replace it with “-ide” instead, like fluoride. If the atom name normally ends in “-gen” or “-ogen”, like oxygen or nitrogen, you replace it with “-ide” as well, like oxide or nitride.The sulphur ion is called sulphide. Sometimes you will encounter non-metal ions that have two or three elements in them. If they have two, they will end in -ide (like hydroxide), if they have more they will most likely end in -ate (like nitrate)

3. Name your mix of positive and negative ions by placing the name of the metal in front of your modified non-metal. For example table salt, which is made up of sodium and chlorine becomes sodium chloride.

The ‘table of ions’ AKA your ticket to NCEA glory

In your exam, you’ll be given a handy reference list known as a ‘table of ions’. This list gives you the symbol of the ions you may need to talk about. There’s no need to memorise the symbols - but you do need to know the names of each symbol off by heart.



Here’s a list of all the symbols you’ll need to know and their respective names:

Name Symbol ChargeHydroxide OH- -1Nitrate NO3

- -1Bicarbonate or hydrogen carbonate

HCO3- -1

Carbonate CO32- -2

Sulphate SO42- -2

Phosphate PO43- -3

Ammonium NH4+ +1

Element Ion ChargeSilver Ag+ +1

Copper Cu2+ +2Lead Pb2+ +2Iron Fe2+ or Fe3+ +2 or +3Barium Ba2+ +2Zinc Zn2+ +2

Being able to use the table of ions in the exam is the key to unlocking a few of the excellence questions. So, make sure you spend some time learning how to recognise ions by their ionic symbol.

Writing the symbols for ionic compounds

Now that we have the naming sorted, you need to work out how to write the name of ionic compounds using their symbols.

The key thing to remember is that all ionic compounds need to be balanced. This means that there needs to be the right number of positive and negative ions to create a compound with no charge itself.

With some compounds, this is a lot easier than others! We’ll start with an easy case:

Sodium chloride is made of sodium ions (Na+) and chloride ions (Cl-). Both ions have equal sized charges (+1 and -1), which means you just need 1 of each to balance out charges. So, the ionic formula is simply written by placing each atomic symbol side by side, leaving you with NaCl.



But what do you do when things don’t balance out so naturally? If you are magnesium and desperately want to get rid of two valence electrons, but you have to donate to chlorine - who is only able to take on one, what do you do?

It’s simple! You ask chlorine to bring a mate - and give one electron to each chlorine atom. This ratio of one magnesium to two chlorine ions must be reflected in the formula for the compound. This is simply done by putting a little ‘2’ next to the Cl atom.

Here’s a recap:

Magnesium chloride is made of magnesium ions (Mg2+) and chloride ions (Cl-). magnesium has a charge of +2 while chloride has a charge of -1. So, you need 2 chloride ions to balance out the charges. This gives it the ionic formula: MgCl2.

Sometimes an ionic compound will contain more than two atoms, a good example is copper hydroxide, which is made of an Cu+ and OH- ions, when they form an ionic compound we simply put the hydroxide ion in brackets to show that there are two hydroxide ions to make copper hydroxide, Cu(OH)2. Everything is balanced, just as it should be.

A quick way to write ionic compounds: Swap n’ Drop

A really quick and easy method for writing the ionic fomulae is to use a method called ‘swap and drop‘. The steps couldn’t be more simple, start with your ions, let’s say iron (III) and nitrate and take the charge from the top, swap it to the other ion and drop it down to be the number of that ion.

It should also be noted that because the charge of nitrate is 1-, we leave this out in the final compound. This will leave you with a compound that is neutral, because we need three 1- nitrate ions to balance out the 3+ charges of the iron ion. It is really important that you understand why this method works and not just how to do the swap n’ drop.

Fe3+ NO3-

Fe(NO3)3

1. Write the charge

2. Swap and Drop



STOP AND CHECK:

Turn your book over and see if you can figure out the ionic formula for:

Sodium fluoride Magnesium oxide Lithium carbonate And if you’re feeling brave: aluminium oxide

Once you finish that, have a go at working out the proper name for these ions:

AlCl3 FeO and Fe2O3 – why are there two different formulae?


Quick Questions Why the heck are valence shells and their electrons so important? Why do atoms want full valence electrons? How are ions formed, and why do they have a charge? I heard that a special bond forms between ions; what’s that all about? What is the overall charge of ionic compounds? Also, what’s this “ionic formula”–

how do you figure that out?

?

Level 1 Science | Acids and Basest | © Inspiration Education Limited 2018. All rights reserved.19


RATES OF REACTIONHalfway there: two topics down, two more to go! Here’s a few things you should get out of this section:

You’ve heard of reactions, but how about reaction rates? How reactions work, and how this relates to something we call ‘collision theory’. The importance of activation energy, and how it dictates whether reactions happen at all.How to measure the rate of a reaction, and interpret it on funky graphs.Learn how to crack the world of chemistry by speeding up reaction rates using concentration, surface area, temperature or catalysts.

Reaction RateHere’s a little secret: a chemical reaction is simply the process of taking a couple of chemicals (which we’ll call reactants), and combining them in a way that makes them change into something else (which we’ll call products).

Think of it as baking - you throw in some reactants (the flour and sugar), and out of it comes the product (a cake).

Chemistry is all about chemical reactions. Some reactions are over in the blink of an eye, while others crawl along as slowly as a snail. This all comes down to the reaction rate.

The rate of the reaction is simply how long it takes the product to form (or the reactants to all be used up).

Complete

20 Level 1 Science | Acids and Basest| © Inspiration Education Limited 2018. All rights reserved.


STOP AND CHECK:


How to define the reaction rate.


Collision Theory

So, how do these reactions actually happen?

It turns out it’s a lot less complicated than you may think. The particles in a reaction (the reactant atoms or molecules) are like mindless drones, aimlessly roaming around inside the container. They might gently bump into the walls of the container or into other particles. Occasionally, they might even bump into each other.

If the reactant particles crash and collide in the right orientation and with enough energy for a successful collision to occur, changes begin to take place, and we might have a reaction on our hands.

A successful reaction occurs when particles collide with sufficient energy, at the correct orientation

Successful collisions between particles

CRASH

AA

B

B

A

B

Where are we going?

a collision

product

Ultimately the factors that affect the reaction rate also affect how often these collisions occur between reactants. This idea has a fitting name: Collision Theory.



STOP AND CHECK:


What makes a reaction, or collision, successful.


Activation Energy

If you’ve ever been to a school dance you may have experienced the initial awkwardness when nobody wants to dance with each other. Eventually there’s a brave kid who takes one for the team and makes the first move. Chemical reactions are a bit like this, they need a push in the right direction to get the party started.

This push is called the activation energy and all chemical reactions have this.

The activation energy is the minimum amount of energy required for a reaction to occur.

A failure to reach this amount of energy results in no cake - and the equivalent to a sad pile of sugar and eggs in the bottom of a mixing bowl.

AB

AB

activationenergy

particles need a push in energyto reach activation energy

reactants

reaction time

ENERGY

product C

+

STOP AND CHECK:


What activation energy even means.




Measuring Reaction Rate

You’ve most probably guessed that it’s a tad difficult to sit there with a stopwatch and count how many individual particles collide and react. Personally, I’ve never tried but I assume it’s impossible. Instead, we can measure a few more practical things:

How quickly gas is produced (gas can be a product of a reaction).How quickly the mass of reactants decreases (or the mass of product increases). The time it takes for a certain colour to appear or disappear (reactants and products can be different colours). The time it takes for a solid reactant to vanish (may be reacting to form something which can dissolve).

STOP AND CHECK:


A few ways that you could measure the reaction rate.


Reaction Rate Graphs

Once you measure the reaction rate somehow, you can plot it on a graph.

On the y-axis (the vertical one) you’ve got the thing you measured: the amount of gas produced, the mass of the reactant or product, or the height of the cake as it rises.On the x-axis (the horizontal one) there is time.

The steepness of the line, or the gradient, indicates how fast the reaction rate is: the steeper the line, the faster the reaction rate. A perfectly horizontal line means that nothing is happening, and our reaction has reached a halt.

For all reactions, the rate will decrease over time. In other words, the gradient of the line flattens out until it becomes totally horizontal. This means that over time less and less reactions happen.

This is because, as the atoms collide and form products, the number of available particles begins to decrease. Essentially there are less and less reactants for reactions to actually happen! Once all the reactants are gone no more reactions happen and the reaction rate hits zero.



STOP AND CHECK:

Turn your book over and see if you can draw your own reaction rate curve and explain what’s happening when the line is steep, not-so-steep, and when it is horizontal.

Can you remember:

Why reaction rates slow down and reach zero eventually.


Concentration

The concentration is the amount of a particular substance present in a given volume. Basically, it tells how much ‘stuff’ we have in our sample.

1 L

0.5 L

1 L

concentration = 5 particles per L

concentration = 10 particles per L

concentration = 5 particles per 0.5 L or 10 particles per L

To increase the concentration, you need to chuck more reactant particles into the container.

As the concentration increases, things can start to become more and more hectic. Because it has become more crowded, as the particles cruise around there’s less free space and it becomes more likely that they’ll crash and collide with another particle. If they collide with enough of a bang – in the correct orientation and with enough energy – a successful reaction between them will occur. With more reactions occurring in a given time the reaction rate increases.

Increaseconcentration

more reactions occur in the same amount of time

ahh, I’m aboutto crash



To decrease the concentration, you need to take away some reactant particles from the container. As the concentration decreases, the environment gets more and more peaceful. With more room to move, particles are less likely to crash and collide into one another. Less successful reactions will occur and so the reaction rate decreases.

Decreaseconcentration

less reactions occur in the same amount of time

wow, where iseveryone?

STOP AND CHECK:


How concentration affects the reaction rate.


Temperature

The temperature is the amount of heat energy present per particle. The more we crank up the heat - the more energy our particles will gain.

Cold temperature Hot temperature

brrr, too coldto move!



This increase in temperature is pretty important for two distinct reasons:

Kinetic Energy

As we said before, as things get hot and steamy the reactant particles start to get fired up. More heat energy means more kinetic energy, and the faster they’re moving, the sooner they’ll meet another reactant, and the more likely a collision will occur. Because they’re also moving at high speeds it’s going to be a high-impact crash. This means the greater the temperature, the more successful collisions, and therefore reactions, are likely to occur.

Activation Energy

Reactions don’t start until reactants manage to get over the energy barrier. In other words, they need to reach the activation energy! The more heat energy we pump into the system the more likely it is for particles to have that minimum amount of energy required. So, if the temperature rises, reactions will start happening sooner and so the reaction rate increases.

STOP AND CHECK:


How temperature affects the reaction rate.


Surface Area

Solid substances are said to be 3-dimensional: they have a height, width and length. They have atoms chillin’ on the outside, and atoms cosy in the inside. The single layer of atoms on the very outside make up the surface, and the total area of all the surface layers of the solid substance is (surprise, surprise) the surface area. You only need to worry about the surface area for solids. Gases don’t have a surface area and you can’t really change the surface area of liquids.

1 m

1 m

surface of a cube

6 faces of a cube

area of the surface (one face) = 1 x 1 = 1 m2

total area of a cube = 6 x 1 m2 = 6 m2



The surface area is super important when it comes to reaction rates, so make sure you read carefully! The particles which make up the surface layer are the only ones that can collide and react with other particles to produce products. Only when the outermost particles react can the inner particles be available to react. So, basically, solid substances react from the outside in.

inner layers of atoms

outer layers of atoms

The surface layer reacts first

Changing the surface area can change the reaction rate.

By crushing up a solid, you end up with tiny grains or powder, with a much higher surface area than the original solid. By taking one large solid structure and breaking it down into tiny pieces, many of the particles that were once in the inner layers are now part of the surface of the smaller pieces. And remember, it’s the surface particles that collide and react first!

cube made of 8 small onestotal surface area = 6 x (2m x 2m) = 24 m2

8 smaller cubes total surface area = 8 x 6 x (1m x 1m) = 48 m2

2 m

2 m1m

1m

8 small cubes 6 faces on each cube

Increasing the surface area means no more hiding away for some reactants, and so the number of exposed particles increases. It’s a bit like increasing concentration at this point, because with more particles available to react, it’s a lot busier, and there’s more chances for reactants to collide and react. Therefore, the reaction rate increases.



More collisions can occur as more reactant is exposed

increase surface area

STOP AND CHECK:


How you can find out the surface area of something. How you can increase the surface area of a solid. What effect surface area has on the reaction rate.


Catalysts

Sometimes, by just adding one extra little ingredient, you can increase the reaction rate of certain reactions. These seemingly magical substances are called “catalysts”. Some common examples include platinum, nickel and vanadium oxide.

A catalyst is defined as a special molecule which speeds up a reaction when added to it - without being used up itself.

Catalysts do this by decreasing the activation energy. If the activation energy drops, we no longer need as much of a push to get cranking, and successful collisions and reactions can happen sooner - increasing the reaction rate.

Activation energywithout catalyst

Activation energywith catalystEnergy

Reaction Progress

28 Level 1 Science | Acids and Bases | © Inspiration Education Limited 2018. All rights reserved.


There are a few important things to remember about catalysts:

The catalyst is not a reactant or product of the reaction. This means it is not used up.Only a small amount of the catalyst substance is required to increase the reaction rate.

STOP AND CHECK:


The definition of a catalyst, and how it changes reaction rate.


Quick Questions:

What is the reaction rate and how can you measure it? What determines whether a reaction will occur or not?

Cheeky hint: think about Collision Theory. What is activation energy and why is it important in chemical reactions? Have a go at explaining how concentration, surface area, temperature and

catalysts change the reaction rate.

ACIDS AND BASESNow, for what you’ve all been waiting for, the section that’s the name of this external: acids and bases *roll credits*. So, what’s the plan?

Defining acids and basesThe pH scaleHow to tell whether compounds are acidic, basic or neutralReactions with acids and bases

Defining Acids and Bases

I’m sure you would have heard the term ‘acid’ before. If you haven’t heard it in a Chemistry context before, don’t fear.

?



The best way to describe an Acid is as a molecule that releases hydrogen ions (H+) when it reacts with water.

H+

H2O O2- H+

H+

O2-

H+

But how does this work? Essentially, you pour in the acid, the water causes the acid molecule to break apart, and the hydrogen ions are released. Knowing that hydrogen ions are released, we can deduce that acid molecules must contain a hydrogen somewhere. There are in fact 3 common acids that you should know:

1. Hydrochloric acid (HCl)2. Sulphuric acid (H2SO4) 3. Nitric acid (HNO3)

If a solution is acidic, it contains a lot of hydrogen ions swimming around.

H

H+

H+

H+

H+

Cl

HCl

H Cl

HCl

hydrogen ions are released into water

Acids containinga hydrogen atom water

Cl̄

Cl̄ Cl̄

Cl̄

But what about bases?

There are a few types of bases, but generally they are “acid-opposites”. Let’s focus on a specific type of base, called alkalis.

These are bases that contain a hydroxide ion, which is drawn as OH-. When alkalis react with water, they release these hydroxide ions. Simple as that!

Because of the hydroxide release, a basic solution is one that contains a lot of hydroxide ions.

Na OH

Na OH

OHˉ

OHˉ

OHˉ

Na

Na+

Na+

Na+

OH

OHˉ ions are released into the water / solution



STOP AND CHECK:


The definition of an acid and a base.


pH Scale

All you’ve learnt so far is that acidic solutions contain high concentrations of hydrogen ions, while basic solutions contain high concentrations of hydroxide ions (and really low concentration of hydrogen ions).

Unfortunately, to score top marks in Chemistry, we must move beyond saying ‘high concentrations’, and use a special measurement to describe how acidic or basic a compound really is. For this, we use something called the pH scale.

Acids

7 = neutral

0

Alkaline

1 2 3 4 5 6 7 8 9 10 11 12 13 14

The pH scale measures how acidic or basic a compound is.

There’s just a couple of things to remember about it:

The pH scale typically ranges from 0 to 14A pH of 7 defines a neutral solution – it’s a solution that isn’t acidic or basic (Put another way, the concentration of hydrogen ions equals the concentration of hydroxide ions.)Drop below 7 and the solution becomes acidic. The lower the pH, the more acidic it is.Rise above 7 and the solution becomes basic. The higher the pH, the more basic it becomes.

STOP AND CHECK:


What the pH scale tells us. What are the pH values of acidic, neutral and basic solutions?



Indicators

Now, here’s the thing: water, hydrochloric acid, and sodium hydroxide are all colourless solutions. One’s neutral, one’s acidic, one’s basic, and two of them will most probably kill you if you drink them – well, you would at least have a very painful time.

Although not knowing whether that refreshing cup of water is actually a corrosive acid isn’t really a common dilemma, it’s nice to have some reassurance. This is where indicators come in: they tell us whether solutions are acidic, basic or neutral, and sometimes even how acidic or basic they are.

The first indicator is Universal indicator. Many different colours can appear when you add a few drops of Universal indicator: it starts off at red for a strong acidic solution, and weakens to an orange or yellow as the solution becomes less acidic.

Once you hit green that solution is neutral. Keep going and you start to get a blue colour which indicates a basic solution, and the darker the blue the more basic it is.

NeutralAcidsincreasingly acidic

Alkalisincreasingly alkali

0 1 2 3 4 5 6 8 9 10 11 12 13 147

Unlike Universal indicator, litmus paper can only tell if something is acidic, basic or neutral; it can’t tell how acidic or basic it is. Litmus papers comes in two flavours: red and blue. Throw some blue litmus paper into a basic solution and nothing happens. But add it to an acidic solution and BAM! It goes through a transformation and comes out red. The opposite happens with red litmus paper. It stays true to itself in acidic solution, but goes blue when soaked in basic solution.

base

acid

neutral

base

acid

neutral

So, if you’re ever unsure about what’s in your cup, just add an indicator!



STOP AND CHECK:


The purpose of indicators.


Linking pH, indicators and acids and bases

Now that we’ve got a pretty good understanding of the pH scale and indicators - where do H+ and OH- ions fit into all of this?

Well, let’s start by imagining a glass of pure water, which has a pH of exactly 7 – making pure water perfectly neutral, and green when tested with Universal Indicator. Now, when a substance is perfectly neutral, this does not mean that it contains no H+ ions and no OH- ions. Instead, it means that a neutral substance like water contains equal quantities of these acidic and basic ions.

You can sort of imagine the pH scale as a kind of see-saw, where H+ ions sit on one end, and OH- ions sit on the other. As we start to pile on one kind of ion, then the see saw begins to tilt in that direction. The greater the imbalance, the more tilting is going to go on! For example, if you added an acid to a glass of pure water, which usually has a pH of 7, the see-saw would tip slightly towards the acidic end:

Acidic end

71 14The pH scale

Basic end

H+H+

H+OH¯OH¯

OH¯OH¯

H+

H+ H+

Aha! All that this result tells us is something we already knew really: that adding acid to a solution is going to make that solution more acidic. The most important thing you should be seeing here is the relationship between how many H+ and OH- ions there are in a solution, and how this affects the pH of that solution, which should be beginning to become more obvious to you.



Finally, we’re going to dump yet more HCl into our solution, which is fast becoming highly acidic. This means piling yet more H+ ions onto this hypothetical see-saw of ours, and it also, of course, means ending up with a solution that has an even lower pH:

Acidic end

71 14The pH scale

Basic end

H+H+

H+

OH¯ OH¯

OH¯ OH¯

H+

H+ H+

H+H+ H+H+

H+

H+H+

This idea of an ‘imbalance’ in the quantities of H+ and OH- ions is no doubt what your eventual exam in November is going to force you to write about, so it’s important that you have a clear understanding of what’s going on here.

In pure water, or any solution with a pH of 7, the number of H+ and OH- ions will be exactly the same. Then, by adding acid or base, we begin to create an imbalance. If that imbalance involves more H+ ions, we get a lower pH and a more acidic solution. On the other hand, if that imbalance involves more OH- ions, we get a higher pH and a more basic solution. As these changes happen, remember that the way they respond to indicators will also change! For example, as more H+ ions are added, and our solution becomes more acidic, we will start to see a red solution when tested with Universal indicator - and our litmus test results will get a little more interesting.

Neutralisation Reactions

So far, we’ve kept things nice and simple by letting you meet acids and bases as separate solutions.

However, we know that the fun in Chemistry really comes when we mix things together and create reactions. So, it’s time to see what happens when an acid meets a base!

A reaction between an acid and a base is known as a neutralisation reaction. It is called this because when an acid reacts with a base, the products we end up with are neither acidic nor basic: they are neutral!

We’ll cut straight to the chase, and give you an example using NCEA’s favourite acids and bases:



The acid in this reaction will be hydrochloric acid, HClThe base in this reaction will be sodium hydroxide, NaOH

Before we start, have a think about the fact that these are ionic substances.

Therefore, the HCl is not made up of atoms of hydrogen and chloride, but of the H+ and the Cl- ions. The same goes for NaOH, which is a compound containing one Na+ ion, and one OH- ion. You may be wondering where to begin when it comes to writing an equation for this neutralisation reaction. Well, in general, all neutralisation reactions follow this simple format:

Acid + base salt + water

A salt is simply some ionic compound - you’ll soon see that the idea of a ‘salt’ is really nothing special.

When writing a reaction, we can begin by filling in the left hand side, which is where the HCl and NaOH go, as well as part of the right hand side, where we know water will always end up:

HCl + NaOH salt + H2O

Excellent! Moving on, we can determine which salt we’re going to wind up with simply be eliminating the two H+ ions and one O2- ion from the left hand side:

HCl + NaOH salt + H2O

As you can see, we’re left with one Cl- ion, and one Na+ ion – therefore, by the simple process of elimination, it’s pretty clear that the ‘salt’ must be sodium chloride, or NaCl! So, all that’s left to do is fill in the final blank in the equation:

HCl + NaOH NaCl + H2O

Great – with that, we’re all finished up with this equation! When the left hand side of the equation contains the same number of the same ions as the right hand side, we can call the equation ‘balanced’. Every chemical equation you write in your exam must be balanced!



Other Reactions

Now we’ve covered a simple type of reaction, an acid-base neutralisation reaction, but this isn’t the only kind of reaction covered, you will also be tested on other types of reactions that don’t only make a salt and water. For example, if the base isn’t a hydroxide (contains an OH- ion) and is instead a carbonate (contains a CO3

2- ion) then the reaction will also produce carbon dioxide.

However, all of these reactions will produce a salt, so knowning how to predict the salt by using the table of ions provided is an essential skill. Here are the general word equations for both the basic acid-base reaction and acid-carbonate reaction:

On page 29 we mentioned the 3 acids that you have to know, HCl, H2SO4 and HNO3, however there are other acids that you can be tested on, you won’t have to know these by heart because they will tell you that it is an acid.

So far we have mentioned hydroxides, like NaOH which are also called alkalis because they are soluble in water, however there are other bases that you should be aware of, these are bicarbonates, carbonates and metal oxides.

A bicarbonate has an HCO3- (bicarbonate/hydrogen carbonate) ion, like NaHCO3

(also known as bakind soda) and will react with an acid to form a salt, water and carbon dioxide. If you remember making a volcano in school you would have added vinegar (acetic acid) to baking soda!

Similarly, a carbonate has a CO32- (carbonate) ion like CaCO3 , a major part of

seashells and limestone and will also react with acids to produce a salt, water and carbon dioxide.

The reaction between NaHCO3 and HCl would look like this:

Metal oxides are also bases, however they react with acid to form a salt and water too, an example of a metal oxide is Ag2O.

Acid + baseAcid + carbonate

salt + watersalt + water + carbon dioxide

Hydrochloric acid + sodium bicarbonate HCl + NaHCO3

sodium chloride + water + carbon dioxide

NaCl + H2O + CO2



Balancing equations

Let’s try out a neutralisation reaction that is slightly more complicated than the first one:

H2SO4 + NaOH salt + H2O

Unfortunately, this equation won’t ‘instantly’ balance.

To illustrate this point, let’s try and use the method that worked so well in the previous example: we’ll cross out one O and two H’s from the left side (to make up the water on the right hand side), and see what we end up with:

H2SO4 + NaOH salt + H2OAs you can see, we’re left with an Na+ ion, an SO4

2- ion, and a final H+.

That hydrogen ion on the left hand side won’t be included in the salt, and we’re not allowed to add another hydrogen to water, so, what do we do?

This is a situation that you’ll face time and time again during the next few years of chemistry – that is, if you choose to elevate your thrilling chemistry education to even wilder heights in Year 12 and 13.

One method that works quite well is to begin by writing the salt that’s getting produced on the right hand side. Using this method means that our very first mission is to establish what exactly this salt will be.

The ions that are available to us during this reaction are:

H+

OH-

SO42-

Na+

Hopefully it’s fairly obvious that, since the H+ and OH- ions will be used up in the production of water, it’s the Na+ and the SO4

2- that’ll produce the salt: so, our salt will be Na2SO4, which is called sodium sulfate.

From here, we just balance ions, check our equation, and then repeat this step as many times as we have to.



The first problem is this: our salt involves two Na+ ions, but on the left side right now, there is only one Na+ ion.

In order to fix this, we’ll stick a 2 in front of the NaOH. This doubles the amount of NaOH included in the reaction. We’ll also replace the ‘salt’ in the equation with an Na2SO4 , like so:

H2SO4 + 2NaOH Na2SO4 + H2O

Things are looking pretty good at the moment, but how can we be certain that we’ve not forgotten, in the daze and excitement of NCEA chemistry, to balance one of these things? We can make certain that we’re finished, simply by counting up each of the ions on each side, and checking that both sides contain equal numbers of these ions. This process doesn’t take long at all:

H2SO4 + 2NaOH4 x H1 x S6 x O2 x Na

2 x H1 x S5 x O2 x Na

Na2SO4 + H2O

Aha! As you can see, there is still an imbalance of ions lurking around in this equation: we need to somehow add in two more hydrogens and one more oxygen to the right hand side: this simply means adding in one more water on the right:

H2SO4 + 2NaOH4 x H1 x S6 x O2 x Na

4 x H1 x S6 x O2 x Na

Na2SO4 + 2H2O

Excellent, we’re all wrapped up with this messiness, then. The idea is that, by beginning with the salt formula on the right hand side, we’ve immediately got a fairly simple starting point for balancing the rest of the terms. After that, it’s all simple arithmetic, really – nothing remotely sinister!



?

How to physically make your desired salt in the lab

When you eventually get to the acid and base question in your dreaded science exam, you’ll quite possibly be asked not only to write down the equation for a neutralisation reaction, but also to describe how to physically make the salt you wish to end up with. The basic problem with neutralisation reactions is that you will always end up with some water at the end of it, and this water is frequently not wanted!

The best solution is this:

Carry out the neutralisation reaction so that both the salt and the water is produced.Place the resulting solution into an evaporating dish.Heat the dish over a Bunsen burner, until all of the water has disappeared, leaving behind only the neutral salt.

Another possibility is to simply leave the evaporating dish lying around somewhere inside, and within a few days, the water will have evaporated regardless of whether you physically heat the dish or not.

1 2

Quick Questions:


A student wishes to make a neutral salt from an acid, HNO3, and a base, KOH What is the name of this kind of reaction?

If the student begins with a beaker of the acid, briefly describe how he/she could use a bottle of base, and a few drops of Universal indicator, to determine when the acid has become completely neutralised.

Write down the balanced equation for this reaction. What is the name of the neutral salt that is produced.

What is one method that could be used to separate the salt from the water?



KEY TERMS Acid:

A molecule which releases hydrogen ions (H+) in water.

Activation Energy: The minimum energy barrier which must be overcome before particles which collide can react.

Atom: The small units of matter that make up everything!

Atomic number: The number of protons in an atom, which determines what element it is.

Base: A molecule which releases hydroxide ions (OH-) in water or reacts with water to form OH-

Catalyst: Any substance which increases the rate of reaction by lowering the activation energy.

Collision Theory: The set of rules that determine whether a successful collision between particles, and therefore a reaction, will occur: “particles must collide with enough energy and in the right orientation.”

Concentration: The amount of a substance (the number of particles) in a given volume. E.g. 100 particles per litre.

Electron Configuration: A way of showing how the electrons of an atom are allocated among each electron shell.

Electron shell: Regions around the nucleus in which electrons are found and orbit.

Electrons: The tiny negatively-charged particles which orbit the nucleus.

Indicators: Substances which change colour depending on the pH and are used to determine whether a solution is acidic, basic or neutral.



Ion: A charged atom formed after the loss or gain of electrons.

Ionic Bond: The electrostatic attraction which holds together a positively-charged ion (cation) and a negatively-charged ion (anion).

Ionic Compound: Where two or more ions are held together by ionic bonds.

Mass Number: The number of protons and neutrons inside the nucleus of an atom.

Neutralisation Reactions: Reactions between acids and bases which produce a salt and water.

Neutrons: The uncharged particles which make up the nucleus alongside protons.

Nucleus: The core of the atom composed of protons and neutrons.

pH Scale: A scale from 1 to 14 which measures the acidity, neutrality or basicity of a solution. (Note: numbers from 1-6 show an acid, 7 is neutral, and 8-14 show a base)

pH: A measure of the amount of hydrogen ions (H+) present in water.

Protons: The positively-charged particles which make up the nucleus alongside neutrons.

Reaction Rate: The number of reactions, or successful collisions, that occur in a given time. In other words, how quickly the reaction happens.

Valence Electrons: The electrons found in the valence shell (the outermost occupied electron shell of an atom).

Valence Shell: The outermost occupied electron shell of an atom.

ACIDS AND BASES - StudyTime NZ...Acids and Bases 27 Defining Acids and Bases 27 pH Scale 29...

Documents

Transcript of ACIDS AND BASES - StudyTime NZ...Acids and Bases 27 Defining Acids and Bases 27 pH Scale 29...