Chemistry Notes- Metals.docx

8/14/2019 Chemistry Notes- Metals.docx

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Metals

Outline and examine some uses of different metals through history, including

contemporary uses, as uncombined metals or as alloys An alloy is a mixture of two or more metal elements or non-metal and metal elements

fused together through dissolving each other in molten state

Metal Historic Uses Contemporary uses

Copper metal (around 6000years ago)

Ornaments, tools, weaponsand cooking

Electrical cables and wiring,radiators, refrigeration

systems, water pipes

Iron metal (3000 BC) Tools and weapons found at3000BC

Usually converted into steeldue to its corrosion to makebuildings, bridges,automobiles

Gold uncombined metal Oldest native metal.Egyptians used gold in theirornaments

Jewellery, dentistry, electricalconnections

Bronze alloy

3000-1000BC

Used for cutting tools andarmour

Church bells, statues


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Metal Properties Common Uses How it relates to its propertiesSteel Usually is

susceptible tocorrosion butwhen alloyed withother metals, it willbecome corrosionresistant. Steel isalso strong

Sinks, cutlery,buildings

Steel is a ferrous metal, meaning it containsiron. The iron in the metallic matrix willcombine with oxygen creation iron oxide(rust). Therefore, to counter rust, othermetals are alloyed with steel to createdifferent types of alloy steels. For example,stainless steel, which is used in cutlery andutensils that handle food, must be resistantto corrosion to ensure that foodcontamination does not occur. This ismainly due to the 10% chromium that isadded to the steel, by mass.

Brass Resists corrosionand ductile

Doorknobs,screws

Solder Low melting point Joining wires

Explain why energy input is necessary to extract a metal from its ore Process of extraction

1. Mining To extract the ore, energy for heavy machinery is needed to break and obtainthe desired ores from the earth (Physical separation method/process)

2. Milling Processes such as froth floatation are needed which requires a lot of waterand energy to agitate the bubbles to separate the gangue. Also transportation of theores/minerals is needed in this process. (Physical separation method/process)

3. Smeltin g Ores are blasted at high temperature to extract the metal. Energy isrequired to maintain the high temperatures in a furnace. (Chemical separationmethod/process)

4. Refining High amounts of heat and electricity is needed and is to be maintainedthroughout the process to purify the metal, depending on the type of refining process.In electrolytic refining (electrolysis), electricity/energy is needed to separate thechemical bonds. (Chemical separation method/process)


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Identify why there are more metals available for people to use now than there were 200 yearsago

More advanced technology and extraction processes to extract ores that were unable tobe used 200 years ago. In previous centuries, there was limited knowledge on theextraction processes that offered pure extracts. As the rate of technology and knowledgeincreased, mankind began to apply more advanced machinery and derive better extractionmethods and thus extract and use more metals. Some technology/extraction methods weuse today to obtain metals were unavailable centuries ago due to the slow rate oftechnology advance.

More discoveries of metal and locations allows more extraction


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Identify the reaction of metals with acids as requiring the transfer of electrons Oxidation is losing electrons O.I.L (Electrons on the right) [Reductant] Reduction is gaining electrons R.I.G (Electrons on the left) [Oxidant]

Reactions with dilute acid Most metals react with dilute hydrochloric acid and sulphuric acid to form hydrogen. We can write these

equation as:

Describe observable changes when metals react with dilute acid, water and oxygen.

When a very reactive metal reacts with water, a metal hydroxide and hydrogen gas isproduced.

o metal + water metal hydroxide + hydrogen gasEg.2Na (s) + 2H O(l) 2NaOH (aq) + H (g)

When a less reactive metal reacts with water, a metal oxide is produced.o metal + oxygen metal oxide

Eg. 2Mg (s) + O (g) 2MgO (s)

When a metal reacts with an acid, a metal salt and hydrogen gas is formedo metal + acid metal salt + hydrogen gas

Eg.Zn (s) + 2HCL (aq) ZnCl (aq) + H (g)

describe and justify the criteria used to place metals into an order of activity based on their ease of reaction with oxygen, waterand dilute acids

the most active metals are at the top , the least reactive areat the bottom

the more reactive, the harder it is to extract It can be established by observation of the reaction of the

metals with water, oxygen or acids. The lower the metal, the earlier it was found/discovered.,

The order of reactivity with oxygen is {Li, Na, K, Ca, Ba} > {Mg, Al, Fe,Zn} > {Sn, Pb, Cu}, {Ag, Au, Pt}

The order of reactivity with water is { Na, K } > {Li, Ca, Ba} > {Mg, AL,Fe, Zn}, {Sn, Pb, Cu, Ag, Au, Pt}

construct half-equations to represent the electron transfer reactions occurring when metals react with dilute hydrochloric anddilute sulfuric acids.

Half-equations help us understand the electron transfer process between metals and non-metals. Generally: metals lose electrons to form metal ions (cations)

non -metals gain electrons to form non-metal ions (anions) hydrogen ions gain electrons to form hydrogen gas.Using these generalisations, we can write half-equations for the reactions between metals and dilute acids. Half-equations must bebalanced in terms of atoms and charges.

Example: Reaction of aluminium with hot sulfuric acidAluminium atoms will lose three electrons and the hydrogen ions will gain two electrons.Electron loss: Al(s) > Al 3+(aq) + 3e Electron gain: 2H+(aq) + 2e > H2(g)

To balance the electrons, multiply half-equation (1) by 2 and halfequation (2) by 3, and then add the two half-equations. Check thatthe atoms and charges balance.Electron loss: 2Al(s) > 2Al3+(aq) + 6e

Electron gain: 6H +(aq) + 6e > 3H2(g)Ionic equation: 2Al(s) + 6H+(aq) > 2Al3+(aq) + 3H2(g)


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o Balanced formulae equations- shows the whole balanced equationo Net ionic equations- shows only the ionic species that undergo changeo Complete ionic equations- shows all the ions involved in the solutions used for the reaction.

For example when aluminium reacts with Hydrochloric acid we get: o 2AI2+ + 6HCI > 2AlCI3+ + 3H2 o 2AI + 6H + 6CI- > 2AI3+ + 6CI- + 3H2 o 2AI + 6H+ > 2AI 3++ 3H2

Outline examples of the selection of metals for different purposes based on their reactivity,with a particular emphasis on current developments in the use of metals

1. Magnesium: Used as a sacrificial layer. The magnesium is galvanised, over the layerof steel on the underside of ships. Because of the reactivity, magnesium will corrodebefore the steel.

2. Calcium: In vacuum tubes, calcium is used, where air must not be present. Thecalcium will react the oxygen forming calcium oxygen which will no longer affectthe vacuum tubes application.

3. Tin and chromium: Both metals are used to coat another metal to create a shinyappearance.

Identif ytheimportanceoffirstionisationenergyindeterminingtherelativereac

Outline the relationship between the relative activities of metals and their positions on thePeriodic Table

For alkali and alkaline earth metals:1. Left is more reactive than right2. Down is more reactive than up3. Left-right is more dominant than down-up4. Therefore, potassium is the most reactive most down and most left) and

magnesium is the least reactive most top and most right)

5.

Trends are non-existent for transitional metals


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tivity ofmetals


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Outline the history of the developments of the Periodic Table including its origins, the original data used to construct it andthe predictions made after its construction

In 1789, Antoine La voisier published a table of 33 elements.1. Contained some compounds which at that time could not be broken down into simpler substances2. Divided his table into metals and non-metals

In 1817 and 1829, Johann Dobereiner observed the chemical similarities between certain groups of 3 elementscalled triads.

In 1864, Meyer arranged that elements in order of increasing atomic mass and placed them in groups based ontheir valency.

In 1869, Dmitri Mendeleev arranged the elements in horizontal rows in order of increasing atomic mass.Elements with similar properties were arranged in vertical columns in the table. Mendeleev was also able tomake accurate predictions about elements that bad not been discovered by leaving gaps.

In 1913, Henry Moseley proposed the concept of atomic number to fix the irregularities in Mendeleevs table. Itwas eventually determined that atomic number determines the chemical properties rather thanatomic mass.

Explain the relationship between the position of elements in the Periodic Table, and their properties.

- electrical conductivity

Trend

Identify an appropriate model that has been developed todescribe the atomic structure

The modern atomic model At the centre of the atom is a positively charged

nucleus consisting of neutral charged neutrons andpositively charged protons

Around the nucleus are negatively charged electrons


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Physical Property Definition Across a Period Down A group

Electrical Conductivity A materials ability toconduct electriccurrents

Generally decreases aselements become lessmetallic. Non-metals haveno free mobile electrons

Generally increases as elements becomemore metallic (except group III)

Ionisation Energy The energy requiredto remove an electronfrom an gaseousatom. Inner electron

shells also reducesthe energy neededfor ionisation.

Increases because theatomic radius decreasesacross the period so thevalence electrons are closer

to the nucleus

Decreases because the atomic radiusincreases hence meaning there are moreelectron shells. The outer shell electronsare weaker attracted to the nucleus.

Atomic Radius The radius of anatom. It depends onthe number ofelectron shells andthe size of the nucleuscharge

Decreases as the valenceshell moves closer towardsthe increasingly positivenucleus

Increases as the number of electron shellincreases

Meting Point andBoiling Point

Melting point is whenthe element turns

into an liquid. Boilingpoint is when anelement turns into anliquid. The metallicbond is strongest inthe transition metals.

increases in groups I to IV

decreases as the latticechanges from metallic tocovalent network and thencovalent molecular

decreases in groups I to IV increases in groups V to VIII

generally increases for transition metals

Combining Power(Valency)

the combining powerof an element that itwill combine with

Maximum valency increasesfrom groups I to VII, inwhich group number equalsmaximum valency.

Maximum valency is constant and equal tthe group number (except for group VIIIwith a valency of 0).

Electronegativity A measure of theelectron-attractingability of an element.

increases as the metalliccharacter decreases

decreases as the metallic characterdecreases

Reactivity The rate at which achemical substancetends to undergo achemical reaction intime.

Each period starts with areactive metal and endswith an unreactive noblegas.

increases down groups I and II. decreases down the group of transition

metals. decreases down groups III and IV for soft

metals. generally decreases down groups V to VII

for non-metals. increases down the group of noble gases.


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Hence, most reactive elements at bottom left and least reactive elements at top right

Moles The unit of measurement for the amount of substance or chemical amount.

12g of the carbon-12 isotope contains 6.0221023

atoms which is 1 mole The moles of an substance = mass/molar mass

isotopeso Each of 2 or more forms of the same element contain equal numbers of protons but different amount of

neutrons.Molar mass

o The mass of an element per mole of its atom. E.g. the molar mass of water, (H 20 ) is 1.008+1.008 +16) =18.061g/mol

compare mass changes in samples of metals when they combine with oxygen Law of conservation of mass: matter can neither be created nor destroyed in a

chemical reaction 2Mg s) + O 2 g) 2MgO s) using the periodic table to find the elements masses)

1. 224.305 + 2x15.999 2 24.305 + 15.999)2. 80.608 80.6083. LHS = RHS, therefore it obeys the law of conservation

Describe the contribution of Gay-Lussac to the understanding of gaseous reactions andapply this to an understanding of the mole concept

Gases combine in simple whole number ratios; Stoichiometric Ratio


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Derives chemical equations and finds moles

Recount Avogadros law and describe its importance in developing the mole concept Avogadros law states that equal volumes of gases, at the same temperature and pressure,

contain equal number of molecules1. The number of molecules in equal volume of gases is independent of size or mass.2. If each gas has the same volume and under the same conditions, they will contain the

same amount of molecules

3. E.g. hydrogen + chlorine > hydrogen chloride. 1 litre + 1 litre > 2 litres 4. 1 mole of any gas is 24.79L at SLC or 25 degrees5. 1 mole of any gas is 22.71L at 0 degrees

Distinguish between empirical formulae and molecular formulae An empirical formula shows the ratio in which atoms are present in a compound A molecular formula shows how many of each type of atom are present To change between molecular and empirical,

Determine the molecular formula

If it is written structurally, convert it to standard Write the new equation

E.g. hydrogen peroxide1. Molecular formula = H 2O2 2. All subscripts divided by 2 or lowest common factor3. Empirical = HO

How to create an empirical formula from mass or percentage composition1. Create a chart with six columns, and the number of rows should be equal to the number of element in the compound.2. In the first column write the elements.3. In the second column write the percent composition of each element.4. Using the percent composition as the mass, divide each by the molecular mass of the respective element.5. Divide each of those numbers by the smallest of the numbers in that column to reduce the ratio.

Example: Determine the empirical formula for a compound containing 74.0% carbon (C), 8.65% hydrogen (H), and 17.3%nitrogen (N) by mass.

element percentage % / molar mass Divide by largestdenominator

Round up

C= 74% 74/12 6.16/1.24 4.96 5H= 8.65% 8.65/1.01 8.56/1.24 6.9 7N= 17.3% 17.3/14.01 1.24/1.24 1 1

Therefore the formula is C 5H7N

Examples:A 9.2 gram sample of a compound is 2.8 grams nitrogen and 6.4 grams oxygen. Find the empirical formula of the compound.

Therefore the empirical formula is NO 2

element Mass over total percentage Percentage/mmN= 2.8/9.2 30% 30/14.0 2.143/2.143 1 1O= 6.4/9.2 70% 70/16 4.375/2.143 2.04 2

Define the terms mineral and ore with reference to economic and non-economic deposits of


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natural resources An ore is a deposit of minerals that contains metal s) that are considered

valuableenough to be mined Minerals are naturally occurring solid homogeneous inorganic that contain a

metal s) that are deemed valuable

Describe the relationship between the commercial prices of common metals, their actualabundances and relative costs of production

Abundance:1. A mineral must be sufficiently concentrated in the ore body to make it

economically viable to extract. If the concentration is low, it is usually noteconomical, as the costs of extraction and production are greater thanthe value of the mineral obtained.

Cost of production:1. Companies need to determine the cost of mining, milling and extracting

a metal from its ore. This would impact upon the final price;transportation costs may also vary due to the remoteness of some orebodies. The location can also affect the price as there may be a lot of

energy/water or the site may be environmentally protected. Common metals:

Some metals are more expensive to extract than others due to higher energy costs involved.For example, aluminium is more expensive to extract than copper due to the high cost of theelectrolytic process used to make aluminium.

Explain why ores are non-renewable resources Ores are non-renewable resources as they were formed when the earth was

formed and there is no way of forming more ores. Also, the rates at which humans are using these ores are much faster than the

rate that these ores are formed in the earth. Therefore our consumption ofthese ores is much greater than their production, resulting in the classification ofores as non-renewable resources.

Describe the separation processes, chemical reactions and energy considerations involved in the extractionof copper from one of its ores

Extraction of copper from copper sulphide ores Mining and Milling: Ores are mined from the earth and crushed, which are both physical

methods of separation. The ores are merely reduced in particle size.

Froth Floatation: With the ore in smaller particle size, froth floatation can be used to removeimpurities called gangue. In this physical separation technique, bubble are agitated in asolution of water and detergent. The copper particles cling onto these bubbles and areskimmed off.

Roasting: The copper is then roasted with sand and air. It is subjected to high temperatures. Achemical separation technique involves the chemical reaction of sand (SiO 2) combining withiron oxide (FeO) impurities to form a compound called a silicate (SiO 3).

o 2CuFeS 2(s) + 4O2(g) > Cu 2S(l) + 2FeO(s) + 3SO 2(g) Smelting: Like roasting, smelting is a chemical separation technique that subjects the copper to

high temperatures with carbon and air. The copper concentrate reacts with oxygen in the hotair to remove the sulphur as sulphur dioxide (SO 2). This leaves copper of 98% purity which iscalled blister copper.


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o FeO(s) + SiO2(s) FeSiO3(l) Electrolytic Refining: The copper is transported to a facility that refines copper using

electricity, which is a chemical separation technique. The blister copper anode graduallydissolves and pure copper deposits on the cathode. Impurities that give up electrons lessreadily than copper fall to the bottom. This leaves the copper 99.99% pure.

o Anode: Cu(s) Cu 2+ > (aq) + 2e o Cathode: Cu2+(aq) + 2e > Cu(s)

Energy considerations:1. Froth floatation requires very little energy2. Roasting requires little fuel since the reaction is strongly exothermic (gives out heat).

It releases energy that can be useful in returning some energy.3. Electrolysis process requires a high amount of energy since it is using electricity4. Since copper is so reactive with other elements, it requires more energy to separate

them. Elements such as gold require very little energy since no other elements arecombined with gold.

Recounts the steps taken to recycle aluminium1. Aluminium is collected from recycling bins2. The aluminium is transported to a recycling plant/facility3. Differ the aluminium from its alloys and aluminium metal4. Aluminium products are deposited in a furnace where they are subjected to very high

temperatures. This process purifies the metal, as it removes the impurities based onmelting points.

5. Analyse the purity of the aluminium and adjust it composition before casting it intoingots.

6. The solution, pure aluminium, is remoulded into the desired product and sold tocompanies that need it.

Chemistry Notes- Metals.docx

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