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Transcript of Science
Sciencesecondary 1
Nicco Alyssha Parikh
LABORATORY RULES - do not enter the science laboratory without the teacher’s permission .- No food or drinks are to be consumed in the laboratory.- Do not play/tamper with the equipment .- Keep your desk/working space clean .- Seek permission before carrying out an experiment . - Read all instructions carefully before any experiment - Prepare all apparatus and arrange them such that you will NOT knock them
over .- Wash all apparatus after the experiment and return them to their proper
places .- Dispose waste materials in proper waste bins .- Never throw solids or corrosive liquids in the sink .- Wash your hands thoroughly before leaving the science lab .- Do not remove chemicals and apparatus from the science laboratory .
What is science?
Science is the study of the world around us through observation , experimentation and analysis .
3 main areas of the study in science : Chemistry , Physics and Biology .
These different areas of science may link one another to form other branches of studies such as BIOCHEMISTRY , PHYSICAL CHEMISTRY AND BIOPHYSICS.
Life long skills and attitudes Besides a keen sense of curiosity , a good scientist should
also have the spirit of inquiry .Thus compromises qualities such as keen observation ,
open-mindedness , patience , objectivity , integrity , creativity and perseverance , scientists should be aware of what’s happening around the world . This leads to questioning about what they see and making sense of the data that they collect from their observations . They need to work well with their peers .
The skills of science inquiry – systematic observation , experimentation and analysis.
LABORATORY APPARATUSTEST TUBE
FILTER FUNNEL
BEAKER
CONICAL FLASK
FLAT-BOTTOMED FLASK
RETORT STAND
TRIPOD STAND
EVAPORATING DISH
MEASURING CYLINDER
Liquid holding and filtration
BUNSEN BURNERSource of heat / to raise a flame above the table , high enough for heating.
For supporting apparatus DURING heating
For containing small amounts of chemicals for heating/ for mixing solutions/liquids
For transferring liquid into containers with a small opening ./ For separating solids from liquids by the use of a FILTER PAPER
For containing and mixing chemicals and liquids to produce a gas when heating is NOT required
BELL JAR To separate the set-up of an experiment from the surroundings.
For mixing and heating the chemicals to produces gas when heating IS required .
For supporting apparatus during experiments
To evaporate the liquid IN a solution over a Bunsen burner
To measure volumes of objects
BUNSEN BURNER The yellow colour in a luminous flame is basically from hot particles of soot in the flame . In a blue flame , there are no particles of SOOT to give that incandescent radiation
The difference between a yellow and blue flame depend on the amount of oxygen that is mixed in with the fuel . More oxygen means that the combustion reaction is more efficient and more energy is released . Remember that the more blue the visible light appears , the more energy that light will have
BUNSEN BURNER
The non-luminous flame exists when there is a complete combustion or complete burning process . It happens when there is more than the enough oxygen in the surroundings or in the place where the process will happen.
The temperature of a non-luminous flame is hotter than the temperature of a luminous flame.
FLAMES
1- FUMING FLAME4- CALM FLAME
The scientific method The scientific method consists of main steps a person could take to solve a problem or find out new
things.
Step 1 Make observationsStep 2 Analyse ,infer, predict and hypothesiseStep 3 PLAN experiments to test your hypothesis - record - analyse - conclude Step 4 Record and analyse your results Step 5 DISCUSS with othersStep 6 Summarise your results and draw conclusionsStep 7 Communicate your findings to others
What is technology ?Technology is the application of scientific knowledge for practical
purposes . BENEFITS OF TECHNOLOGY Invention of medicines . Invention of the telephone ,computer, radio and television for
communication and dissemination of information . ABUSES OF TECHNOLOGY Sometimes technology can cause harm to the environment
and society , especially when misused. what do you mean by ‘when misused’? - should you blame the soldiers or the weapons for the lives
lost during battles ? - should you blame the car or the driver for road accidents?
Can technology solve ALL our problems ?
No , although technology has helped us in many ways, it cannot possibly solve all our problems such as natural disasters but however , we can use technology to predict the occurrence of natural disasters though they are not always accurate.
WHERE DO SCIENTISTS WORK?
- Laboratories - Rainforests - Space
Science is not confined to the laboratory but everywhere else too.
Doing field work is going outdoors , away from the laboratory to collect data .
Hazard symbols Explosive Toxic
Flammable Corrosive
Irritable Biohazardous
Radioactive
Substance will react violently when heated or struck
Substance catches fire easily
Substance produces vapours or fumes which irritates the eyes, nose and throat
Substance emits radiation
Substance is harmful in small doses
Substance will eat away other substances
Poisonous substance of a biological nature
Variables In the process of testing a hypothesis , the things that
have an effect on the experiment are called variables , THE INDEPENDENT VARIABLE is the variable you CHANGE.
The variables you DO NOT CHANGE are called CONTROLLED VARIABLES / THE CONTROL. The variable that we measure , which DEPENDS on
the independent variable is called the DEPENDENT VARIABLE .
TIME, RATE AND SPEED TIME is the DURATION OF AN EVENT.
S.I. unit (international system of units) of time is the SECOND and represented by the symbol ‘s’ . Other units of time : MINUTE (min) , HOUR (h) and millisecond (ms) .
Time can also be expressed in terms of days , weeks , months and years.
INSTRUMENTS TO MEASURE TIME
To measure a short period of time ACCURATELY , we use a STOPWATCHTHERE ARE TO TYPES : mechanical and electronic
MECHANICAL STOPWATCH - The mechanical stopwatch has a minute scale and a second scale - The smallest division on the mechanical stopwatch is 0.1 s . Thus the mechanical stopwatch is accurate to 0.1 s .
ELECTRONIC STOPWATCH - The electronic stopwatch/the digital stopwatch is MORE accurate than the mechanical stopwatch .- It can measure time intervals
accurate to 0.01 s ( 2 sig . Fig )
- It can also record time intervals in hours , unlike the mechanical stopwatch
CONVERSION OF UNITS
LENGTHS IN OTHER UNITS what to do? LENGTH IN METERS
30 dm divide 10 = 3 7km times 1000= 7000 2500cm divide 100= 25 32km times 100= 3200 600mm divide 1000= 0.6
74.5 cm divide 100= 0.745
S.I UNITS Prefix Value Symbol
Giga One billion G
Mega One million M
Kilo One thousand k
Deci One tenth d
Centi One hundredth C
Milli One thousandth m
Micro One millionth u
Nano One billionth n
Physical quantity Value Symbol
Length Metre m
Weight Mass Kilogram kg
Temperature Degree celcius Kelvin K
Time Second s
RATE IS AN EXPRESSION OF HOW ONE QUANTITY CHANGES WITH TIME . RATES ARE USEFUL FOR MAKING FAIR COMPRISONS
PHONE CHARGES , INTERNET ACCESS PLANS , BANK LOAN INTEREST RATES AND INFLATION RATES ARE SOME EXAMPLES OF RATES IN REAL LIFE
UNIT AND MEASUREMENTSMEASURING TAPE & METRE RULE
MEASURING TAPE / METRE RULE = measuring short lengths .
METRE RULE = measure to 100 cm (1m)
MEASURING TAPE = FLEXIBLE , SEVERAL METRES , ACCURATE TO 0.1 CM.
VERNIER CALIPERS
Vernier caliper = used to measure Internal and external diameters of cylinder or spherical objects. = have tails that are used to measure depth of narrow tubes = accurate to 0.01 cm
VERNIER CALIPERS
PARALLAX ERROR = Parallax error arises when the position of the eye is not at the same level as the markings to be read .
ZERO ERROR = Zero error in a vernier caliper arises when the zero marking on the main scale does not coincide with the zero marking on the scale , with the jaws if the vernier caliper closed.
VERNIER CALIPERS
Using the Vernier calipers
1) Close the jaws of the Vernier calipers . Ensure that the zero marking on the Vernier scale is in line with the zero marking on the main scale
2) Place the object within the jaws of the Vernier calipers and clamp it firmly in place .
3) Read the length
PARTS OF A VERNIER CALIPER
CHOOSING THE RIGHT INSTRUMENTS
Length to be measured Instruments to be used Accuracy of instrument
Between 0 and 10 cm Vernier calipers To the nearest 0.01 cm
10 cm to 100cm (1m) Meter rule To the nearest mm
5cm and above Measuring tape / contractor’s rule
To the nearest mm ( short lengths )To the nearest cm ( VERY long lengths )
SQUARE GRID Square grid – finding area
4km
4km
Count the ones more than half or half only, as 1 .
1
2
3 4
5
5 x 16= 80
(Not the most accurate way.)
FORMULAS FOR MEASURING AREA AND VOLUME
SQUARE = Length x Length RECTANGLE = Length x Breadth TRIANGLE = ½ x Base x Height CIRCLE = r (square)CUBE = Length x Length x Length CUBOID = Length x Breadth x Height PRISM = Base area x Height = 1/2 x Length x Breadth x HeightPARALLELOGRAM = Base x HeightCONE = 1/3 x x radius2 x heightSPHERE= 4/3 X x radius3
FORMULAS FOR MEASURING VOLUME
PYRAMID = Base area x Height = 1/3 x Length x Length x Height
CYLINDER = Base area x Height = x r(square) x Height
SPHERE = 4/3 r (cube)CONE = 1/3 r(square)Height
MEASURING VOLUME OF LIQUID
Volume of liquid – measured in cm(cube) or litres (1 litre is 1000cmc(cube))
Instruments = MEASURING CYLINDER , BURETTE , PIPETTER AND VOLUMETRIC FLASK
CURVE SEEN AT THE SURFACE OF A LIQUID IS KNOWN AS A MENISCUS . =* To prevent parallax error , the eye must be positioned at the same level as the meniscus
MEASURING MASS
• MASS IS THE AMOUNT OF SUBSTANCE THAT AN OBJECT HAS .
• SI UNIT : KG • MEASURED USING – DOUBLE BEAM BALANCE - ELECTRONIC BALANCE
MEASURING VOLUME OF IRREGULAR SOLIDS
VOLUME OF IRREGULAR SOLIDS CAN BE FOUND USING THE DISPLACEMENT METHOD
- Need a displacement can
VOLUME OF THE SOLID
ELEMENTS e.g) ; ELEMENTS : sucrose solution , ammonia , bromine and protein ;METALS: bronze , copper , mercury
- Oxygen makes up 21% of the atmosphere air .
- An element is a pure chemical substance consisting of one type of atom.
- Magnesium , iron and zinc are grey solids at room temperature .
- Nitrogen makes up 78% of the atmosphere air .
- Copper is a reddish-brown solid.
- Water is made up of the elements hydrogen and oxygen.
- Mercury is a silver-coloured liquid metal that expands evenly on heating.
- Iodine is used as an antiseptic in medicines to prevent infections from wounds (usually purple in colour then to brownish-yellow).
- Metals are usually present in the form of solids at room temperature.
- Hydrogen reacts violently with air and it is said to be explosive .
- Non-metals are usually dull in apprearance .
CLASSIFYING METALS AND NON-METALS
-Elements can be classified as metals and non-metals . (depending on their property)-Except for mercury , all metallic elements are solids at room temperature .-Non-metallic elements exist in solid , liquid and gas .
METALS NON-METALS
Shiny surface Dull surface
Ductile Non-ductile
Malleable Brittle
High melting point Low melting point
High density Low density
Good electrical conductor Poor electrical conductor
Good thermal conductor Poor thermal conductor
Properties
CLASSIFYING ELEMENTS BY STATE
Different elements exist in difference states at room temperature
In the periodic table , there are 11 elements that are in gaseous state , 2 in liquid state and the rest in solid state
PERIODIC TABLE
PERIODIC TABLE
Vertical groups ( SIMILAR chemical properties)Horizontal periods
Metalloids properties are metal + non-metal. They are solids that can be shiny or dull.They conduct heat and electricity better than non-metals but not as well as metals.They are ductile and malleable.
Metal alloy Mixture of 2 or more metals .
GROUPS AND PERIODS
Groups• Columns of elements are called
groups or families. • Elements in each group have
similar but not identical properties.
• For example, lithium (Li), sodium (Na), potassium (K), and other members of group IA are all soft, white, shiny metals.
• All elements in a group have the same number of valence electrons.
Periods• Each horizontal row of
elements is called a period.• The elements in a period are
not alike in properties.• In fact, the properties change
greatly across even given row.
• The first element in a period is always an extremely active solid. The last element in a period, is always an inactive gas.
FLOATING AND SINKING
When an object floats on a liquid , the object is less dense than the liquid .
When an object sinks in a liquid , the object is denser than the liquid .
The density of water is 1 g/cm(cube) . An object with a density LOWER than 1 g/cm(cube) will FLOAT on water . An object with a density HIGHER than 1 g/cm(cube) will sink in water
ELEMENTS,COMPOUNDS,MIIXTURES
Electrolysis – break down of substances using electricity
Nitrogen 78%
Oxygen 21%
Carbon dioxide 0.03%
Water Vapour 1%
IN THE EARTH’S CRUST THE 2 MOST ABUNDANT ELEMENTS ARE OXYGEN(47%) AND SILICON (28%)
Poor conductor insulator
PHYSICAL PROPERTIES Strength- is the ability to support a heavy load without breaking or tearing
Transparency – ability of a material to allow light to pass through.
Ductility-is the ability of a material to be drawn into wires without breaking
Hardness –is the ability to withstand scratching by another material
Electrical conductivity-is the ability to allow electricity pass through
Thermal conductivity-is the ability to allow heat to pass through
Malleability-is the ability of a material to be moulded into shapes
Flexibility –is the ability to bend or stretch without breaking
Melting point –is the temperature at which a solid changes into liquid
Boiling point-is the temperature in which liquid changes into gas
Density – refers to mass per unit volume (mass/volume)-mass over volume
PROPERTIES OF METAL ELEMENTSCOPPER - Reddish Brown - Good conductor of electricity - Ductile -Corrosion resistant -Strong
ZINC-Grey solid-Prevents rusting of iron -Good conductor of electricity-Strong -Corrosion resistant
ALUMINIUM-Silvery shiny solid-Low density -strong and light -malleable -corrosion resistant
MERCURY -Silvery liquid -does not react easily with other chemicals -Mercury vapour is fluorescent -Good conductor of heat - Expands evenly of heating
MAGNESIUM-Grey solid-Burns with dazzling light-forms alkali to neutralise excess acid in stomach
IRON-Grey solid-Good conductor of heat and electricity-Ductile-strong-Magnetic
PROPERTIES OF NON-METAL ELEMENTS
IODINE-Black crystals-poisonous-antiseptic-prevents wound infection
CHLORINE-greenish-yellow gas-bleaches dyes-poisonous
SULPHUR-yellow powdery solid-poisonous-soluble in organic solvent (alcohol) but not in water
DIAMOND(CARBON)-hardest substance known to man -can be polished to shiny , reflecting , transparent solid
HYDROGEN-colourless gas-gas with lowest density -explosive
CARBON (GRAPHITE)-black solid-smooth -lightweight -good conductor of electricity
PROPERTIES OF NON-METAL ELEMENTS
OXYGEN-colourless gas- Essential for life- Does not burn but
supports combustion (allows other things to burn)
NITROGEN-colourless gas-unreactive , does not burn or support combustion -low boiling point
WHAT ARE COMPOUNDS?
When different elements are chemically combined together , they form new substances known as compounds.
e.g: Hydrogen + Oxygen = water (compound ) Sodium + Chloride = table salt (compound) Carbon + Hydrogen + Oxygen = sugar (compound) Calcium + Carbon + Oxygen = chalk (compound)
CHARACTERISTICS OF COMPUNDS
To form water the ratio of hydrogen and oxygen that combine chemically is always 1:8 .
HOW ARE COMPOUNDS FORMED?Made of elements , other compounds , both elements and compounds – FORMED BY CHEMICAL REACTION
- 2 main methods of forming compounds : COMBINATION : DECOMPOSITION (heated to break down )
Combustion
BREAKING DOWN
CHEMICAL BREAKDOWNS heating electrolysis photolysis Involves breaking of chemical bonds
PHYSICAL BREAKDOWN physically breaking . (E.g.) tearing , chewing …) QUESTION
physical/chemical separation . ?
COMBINATION
One common example of combination is combustion . THIS HAPPENS WHEN ELEMENTS OR COMPOUNDS BURN AND COMBINE WITH OXYGEN TO FORM ONE OR MORE NEW COMPOUNDS .
Eg.) carbon + oxygen = carbon dioxide
DECOMPOSITION
Decomposition occurs when 2 or more complex compounds are heated to break them down into simpler compounds.It decomposes to form water vapour and carbon .
E.G ) sugar (compound) Water vapour ( compound) + Carbon ( element )
BREAKING DOWN
Some compounds can be broken down into simpler substances when EXPOSED TO LIGHT . For example CFC ( CHLOROFLUOROCARBON ) compound is Styrofoam is broken down by sunlight into a hazardous substance . THIS SUBSTANCE DEPLETES THE OZONE LAYER .
MIXTURES
Properties of Mixtures :When a mixture is formed , no chemical reaction occurs .A MIXTURE HAS THE PROPERTIES OF ITS CONSTITUENT SUBSTANCES .A mixture can be separated easily by physical methods (i.e. without involving chemical reaction).The components in mixtures are not mixed in any fixed proportion.Water bath is to ensure gentle and even heating .
DIFFERENT KINDS OF MIXTURES
Solid-solid ( Alloys )Liquid-Liquid ( Vinegar)Solid-Liquid ( Lotion )Liquid-Gas ( Foam )Gas-gas ( air )
MAGNETIC ATTRACTION
Used to separate magnetic materials from non-magnetic materials .
Separating iron from sulphur
USES OF MAGNETIC ATTRACTION- Food processing - To salvage scrap iron and steel
FILTRATIONBAKERS MUST USE A SIEVE TO REMOVE LUMPS FROM THE FLOUR MIXTURE.
Filtration works by allowing small liquid particles through , but not large solid particles.
The filter paper has tiny pores that allow the liquid component to pass through it . The insoluble liquid solid particles that are too large to pass through it . The insoluble liquid is called the residue and the liquid that passes through the filter paper is called the filtrate .
EVAPORATION
Evaporation(to dryness ) is used to separate a dissolved solid from a liquid . The dissolved solid must be stable to hear and NOT decomposes .
When the mixture has completely evaporated , no water is left behind . The solid salt left behind as the RESIDUE.
DISTILLATION
Distillation is used to separate a pure liquid from a solid-liquid or a liquid-liquid mixture . The pure liquid collected from distillation is called the distillate .
condensation
Vaporization
condenser
Ensure heating is gentle (water bath)
DESALINATION PLANTS
Desalination is a treatment process that removes dissolved salts from sea water to obtain pure water . Distillation is one of the traditional methods used to carry out desalination .
FRACTINAL DISTILLATIONGas – high temperature & HIGH KINETIC ENERGY .
Fractional distillation also depends on the difference in the boiling points of different liquids .
Crude oil is a mixture of liquids with different boiling points . Oil refineries use fractional distillation to separate crude oil into useful products such as petrol , diesel , kerosene
SEPARATE CREAM AND MILK AS MILK IS SOULUBLE IN CREAM.
PAPER CHROMATOGRAPHY
Separation methods like filtration and distillation require a large amount of the mixture to be separated .
This is usually used to separate mixtures of coloured substances such as ink and dyes.
Paper chromatography makes use of the fact that different paces . Similarly , different substance move through particular mediums at different rates.
Paper chromatography makes use of the fact that different substances dissolve to different extents in a mixture .
REVERSE OSMOSIS In reverse osmosis , sea water is pre-treated to remove debris and contaminants such as oil , grease and suspended solids . The pre-treated sea water is then pumped at high pressure through partially-permeable membrane to remove all traces if bacteria , viruses , chemicals and dissolve minerals .
WATER MOLECULES
What is reverse osmosis?
Reverse osmosis (RO) is a membrane-technology filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be "selective," this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely.
NEWaterTOWARDS A SUSTAINABLE WATER SUPPLY
• NEWater currently meets 30% of Singapore’s total water demand.
• NEWater is high-grade reclaimed water produced from treated used water that is purified further using advanced membrane technologies, making the water ultra-clean and safe to drink.
• The second stage of the NEWater production process is known as Reverse Osmosis (RO). In RO, a semi-permeable membrane is used.
• Consequently, undesirable contaminants such as bacteria, viruses, heavy metals etc., cannot pass through the membrane.
• Hence, NEWater is RO water and is free from viruses, bacteria and contains negligible amount of salts and organic matters.
GENERAL QUESTION
DESCRIBE and EXPLAIN how you would separate a mixture of sugar and chalk . (4 marks)
Add water to the mixture (1/2 mark) and stir well to mix (1/2 mark) . This dissolves the sugar (1/2 marks) to form a sugar solution (1/2 marks) . Carry out filtration(1 mark) . Separate sugar solution and chalk . The residue is the chalk and the filtrate is the sugar solution (1 mark).
SOLUTIONS AND SUSPENSIONSWhat are solutions ?Solutions are mixtures in which soluble particles are completely dissolved in a liquid or gas.
HOMOGENEOUS : same throughout BUBBLES : pocket of air
What are suspensions? Suspensions are mixtures in which insoluble particles are suspended in a liquid or gas .
What is solubility ?Solubility is the maximum amount of solute that can dissolve in 100grams of solvent at a given temperature .
SOLUTE , SOLVENT AND SOLUTION
The solute is the substance that dissolves in a solvent .
The solvent is the substance that dissolves in the solute .
The solution is the mixture of the solute and solvent .
CHARACTERISTICS OF A SOLUTION
Homogeneous
When left on it’s own , the solute does not separate from the solvent .
When filtered , no residual particles will remain on the filter paper . It will pass through completely .
SUSPENSION
It is the exact opposite of a solution .
A SUSPENSION IS A MIXTURE IN WHICH INSOLUBLE PARTICLES ARE SUSPENDED IN A LIQUID OR GAS .
SOLUBILITY
Factors that affect solubility _ nature of the solvent _nature of the solute _temperature
RATE OF DISSOLVING
• The rate of dissolving is how fast a substance dissolves in a fixed volume of solvent .
TEMPERATURE
RATE OF STIRRING
SIZE OF SOLUTE PARTICLES
ACIDS AND ALKALI
Adjectives : acids- acidic alkali-alkaline
Solutions can be sorted by whether they are: acid, alkali or neutral.
ACIDS
ALKALIS
SOUR BITTER
CORROSIVE CORROSIVE
TURNS BLUE LITMUS PAPER RED
TURNS RED LITMUS PAPER BLUE
NOT SLIPPERY SLIPPERY (SOAPY FEEL )
CONCENTRATED VS SATURATED
Concentrated acids / alkalis
Concentrated – amount of substance variable
Saturated – maximum amount of substance in the medium environment .
ACIDS• Acid are soluble in water produce hydroxide
ions – OH(when dissolved in water)When the oxide of some non-metals dissolve in water they make an acid. Acids have a sour taste.
They are corrosive
Hydrochloric acids Used to remove rust on iron and steel
Sulphuric acids Used in car batteries , Remove rust from steel objects , makes fertilisers .
Nitric acid used to manufacture fertilisers
REACTION OF ACIDS WITH METALS AND CARBONATES
Acid + carbonate salt + water+ carbon dioxide
Formed by chemical reaction
Metal + Acid Salt + Hydrogenmagnesium + magnesium chloride
hydrochloric acid hydrogen
ACIDS IN OUR DAILY LIVES
Acids are also present in everyday lives
Lemon juice contains citric acid, and vinegar contains ethanoic acid.
Some strong acids are hydrochloric acid, sulphuric acid and nitric acid.
Some weak acids are ethanoic acid, citric acid and carbonic acid.
NEUTRALISATION
Acids and alkalis react with each other. The alkali cancels out the acid in the reaction. This is called neutralisation.
SALT is made when from chemical reaction.
NEUTRALISATION IN EVERYDAY LIVES
Face tonersFace cleansersShampoosConditionersToothpasteInsect stings
CHEMICAL REACTIONS OF ACIDS1)Acid + Metal salt + hydrogen gas
2) Acid + Carbonate salt + carbon dioxide gas + H2O
3)Acid + Alkali salt + water
*** limewater(slake lime) will turn cloudy , white precipitate produced .
Not all metals react with acids (unreactive) Some are very reactive *Hazardous and explosive*
Hydrochloric – very strong acid ( CONCENTRATED )
*potassium + hydrochloric acid => vigorous
SALTS
The salts of sulphuric acid are known as sulphates. The salts of hydrochloric acid are known as chlorides. The salts of nitric acid are known as nitrates.
• The salt made depends on the acid and alkali used. • The salt contains the metal atom from the alkali,
and part of the acid molecule. • Reaction of salt with water is known as salt
hydrolysis
ALKALIS
Many everyday substances are alkalis. They have a soapy feel (slippery). They are corrosive.
When the oxides of some metals dissolve in water they make an alkali solution.
Alkalis react with acids and neutralise them.
ALKALIS IN OUR DAILY LIVESAlkalis are present in many cleaning substances in use in our
homes. Kitchen cleaners are alkaline because they contain ammonia
or sodium hydroxide, which attack grease.The PH of alkali is greater than 7.
Calcium hydroxide and sodium hydroxide are strong alkalis. The most recognisable and common weak alkali is ammonia.
Ammonia reacts with ammonium salt to produce ammonia gas
INDICATORS Indicators help you find out whether a solution is acidic or not.
They change colour in acid or alkaline solutions.
All indicator are weak alkaline or weak acid the colour of indicator is due to ionic part of indicator.
Different indicators change to
different colours.
LITMUS PAPER
• Litmus is an indicator. It changes colour in acid and alkaline solutions.
• Different indicator show different colour.• Litmus paper is red in an acid. (Acids turn blue
litmus paper red)• Litmus is blue in an alkali.(Alkalis turn red
litmus paper blue)
pH SCALE (INDICATORS)
Acids less than 7Alkalis more than 7 7 is neutral The lower the number for acids , the stronger the acid . The higher the number for alkalis , the stronger the alkali .
REVISION OF ACIDS AND ALKALIAcids : Corrosive Sour Reacts with blue litmus paper Turns blue litmus paper red Dilute sulphuric acid + magnesium = magnesium sulphate + hydrogen Dilute hydrochloric acid + magnesium = magnesium chloride + hydrogen Dilute acid + Metal = salt + hydrogen Effervescent => bubbly Citric : lemon Formic acid : Insect stings Lactic acid : milk Acid reacts with carbonates to give off carbon dioxide gas Calcium carbonate + dilute sulphuric acid = calcium sulphate + carbon dioxide + water Dilute acid + carbonate = salt + carbon dioxide + water( only with carbonates) Sulphuric acid = in car batteries Nitric acid = in fertilisers Hydrochloric acid = take out rust Dilute acid + carbonate salt + carbon dioxide + water
ALKALI
Bitter Corrosive Soapy feelTurn red litmus paper blue Ammonia : fertiliser maker Sodium hydroxide (caustic soda ) => detergents Calcium hydroxide ( slaked lime/limewater) =>
reduce acidity in soil in agriculture
Neutralisation
Sodium hydroxide + hydrochloric acid = sodium + water Acid + Alkali = Salt + Water Water : H2O
EVERYDAY LIVES NEUTRALISATION ( reduces acidity/alkaline)TonersShampoos , conditionersToothpaste
(mentos and coke )
Indicator
PH SCALE / RED OR BLUE LITMUS PAPERChanges colour depending on solution tested(acid
or alkali ) : definition 0-------------7-----------------14
Water = neutral ( PH 7 )
Acid neutral alkali
HEAT AND IT’S EFFECTS• EXPANSION (GAINS HEAT ENERGY )• CONTRACTION (LOOSES HEAT ENERGY )
Countering expansions LEAVING GAPSSolids Expands very little (particles are joined) Liquids Expands more than the solids but less than the gases (More particles than gases and a near each other)Gases Expands most ( Very little particles and are spread freelyBrass contracts/expands more than steel
EXPANSION AND CONTRACTIONSOLIDS Solids expand when heated and contract when cooled . However , some solids expand so little that we may not even notice the expansion .
Liquids If the kettle is filled to the brim with water , the water will spill out when it boils because water expands when heated and contracts when cooled.
Gases Before a loaf of bread is baked, thousands of tiny air bubbles are trapped inside the dough . As the dough is heated, these bubbles gain heat and expand, creating holes in the bread . This causes the bread to rise . Gases expand when heated and contract when cooled
ROADS AND PATHWAYS(-ve)
Excessive expansion on very hot days can cause roads or pavements to crack , or tiles pop-out . To get around with this problem , the tiles on pavements and walls are laid with EXPANSION GAPS
BRIDGES AND METAL GIRDERS
Long bridges sometimes expand up to a meter in hot weather . Without allowance for expansion , such structures are at risk of damage in very hot weather . Bridges and metal girders on buildings have EXPANSION GAPS or a free end resting on rollers to allow expansion .
* ROLLERS ALLOW BRIDGES AND GIRDERS TO EXPAND OR CONTRACT WITHOUT DAMAGE
WATER PIPES
Water pipes and oil pipelines can expand during hit weather , which might cause them to BURST . Hence , EXPANSION BENDS are made in these pipes to allow them to expand without any damage
* Expansion bends help prevent damage to pipes
TELEPHONE WIRES AND CABLES
Telephone wire and cables raised on poles contract in cold weather and become taut , and may even snap. So , they are STRUNG LOOSELY from pole to pole to allow contraction .
*Transmission wires must be strung loosely from pole to pole to allow contraction during hot weather.
LABORATORY GLASSWARE
If boiling water is poured into a thick glass , the glass is likely to crack due to the uneven expansion of the glass . ( THE CG(center of gravity)OF THE GLASS IS THE AREA WITH HIGHEST GRAVITY , with too much of it at the top , the glass will TOPPLE).
COUNTERING glassware expansion use of borosilicate / heat-resistant glass.
METAL TYRES(+ve)
A metal tyre can be heated up to fit over a wooden wheel . When the tyre cools , it clings on very tightly to the rim of the wheel .
heat
RIVETS
Rivets are used to join steel plates and girders.1) When red-hot , the rivet is put into position2) It is then hammered into a head and allowed
to cool.3) The contraction on cooling helps to pull the
steel together.
BIMETALLIC STRIP
rivets
brass
THE BRASS EXPANDS MORE (BECOMES BIGGER) than the steel when HEATED . SO , when heated , the strip bends with the brass on the outside of the curve.
WHEN COOLED , the brass contracts more ( BECOMES SMALLER ) than the steel . Hence , the strip bends with the steel on the outside if the curve .
BRASS AND STEEL
Steel = iron + carbon
Brass = zinc + copper
* THESE ARE BOTH METAL ALLOYS ( consists of two or more metals )
USES OF A BIMETALLIC STRIP
• THERMOSTAT keeps temperature constant : regulates the temperature (HOT/COLD)
*examples : used in refrigerators , ovens , air-conditioners.
Bimetallic strips are used in thermostats .
BIMETALLIC STRIPS
Cooling takes place when the temperature is too cold . The strip bends away to break the contact
Heating takes place when the current is on . When the temperature is too hot , the strip bends away to break the contact .
IN THE REFRIGERATORCOOLING hotter : connected colder : not connected
HEATING Cold air stops blowing , refrigerator heats up
CONTRACTION -Pulling (inwards)
CONDUCTION
• Heat moves from a hotter region to a cooler region .
• Conduction is the process of heat transfer through a medium or material without any movement of the medium or material
A material that conducts heat are called CONDUCTORS but those that do not conduct heat are called INSULATORS
GOOD CONDUCTORS OF HEAT
Most metals are good conductors of heat . However , some conduct better than others . The higher the THERMAL CONDUCTIVITY of a material , the better it conducts heat.
CONVECTION Convection is the transfer of heat from one place to another by the movement of fluids . A fluid with a given density rises within a fluid of greater density and sinks within a fluid of smaller density.
Convection takes place due to the expansion of fluid. When the fluid (i.e. a liquid or gas ) is hot , its volume increases . This means its density decreases . The less dense fluid then rises and floats while the denser fluid flows in to take its place.
USES AND EFFECTS OF CONVECTION
Household ventilation
Hot air rises and collects under the ceiling . A cool room has features that let hot air out and cool air in. HOT AIR RISES , COLD AIR SINKS . If there are no air vents , we can use an air conditioner to keep the room cool.
1) The hot air in the room rises to the ceiling 2) The air-conditioner cools the hot air , which then sinks to the
bottom of the room.3) More hot air rises and is cooled by the air-conditioner . The
cycle repeats itself until the room is cooled .
ELECTRIC KETTLE
What happens if the heating coil of an electric kettle is placed near the top of the kettle ?
If the heating coil is placed near the top of the kettle , the water near the top will start to boil while the other parts of the water will remain cool . There will be no circulation of heat .
LAND AND SEA BREEZESLand and sea breezes are caused by convection . (Water us a poor conductor of heat) . During the day , the land is hotter than the sea . Hot air rises from the land and cool sea breezes blow in to take its place . At night , the reverse takes place . The sea retains its heat and land cools faster.
Convection : Mode of heat transfer Convection current : Current flow of heat
RADIATIONRadiation is the method of heat transfer that
does not require the presence of matter .. Here from the sun radiates across millions of kilometers of empty space . The heat that comes by radiation is carried by light waves from the sun invisible infrared and visible light . This heat is sometimes called radiant heat.
RADIATION Radiation is the transfer of heat , in the form of waves (heat waves) , from one place to another without a medium .
HOW A BODY RADIATES HEAT
1) Nature of the surface of the body (whether it is black or white or coloured , rough or smooth or shiny )The darker and rougher the surface , the more heat it gives out per
second .2) Total surface area of a body The greater the area , the more heat per second is radiated. 3) Temperature of the body The hotter the body temperature , the more heart per second is radiated .
Why is it windy at the seaside?
Cold air sinks
Where is the freezer
compartment put in a fridge?
Freezer compartment
It is put at the top, because cool air sinks, so it cools the food on the
way down.
It is warmer at the bottom, so this warmer air
rises and a convection
current is set up.
Radiation
Radiation travels in straight lines
True/False
Radiation can travel through a vacuum
True/False
Radiation requires particles to travel
True/False
Radiation travels at the speed of light
True/False
Emission experiment
Four containers were filled with warm water. Which container would have the warmest water after ten minutes?
Shiny metal
Dull metal
Dull black
Shiny black
The __________ container would be the warmest after ten minutes because its shiny surface reflects heat _______ back into the container so less is lost. The ________ container would be the coolest because it is the best at _______ heat radiation.
shiny metal
radiation
dull black
emitting
Factors Affecting Radiation
1. Nature of surface of body2. Total surface area of body3. Temperature difference
between the body and its surrounding
113
Vacuum Flask
Radiation questions
Why are houses painted white in hot countries?
White reflects heat radiation and keeps the house cooler.
Why are shiny foil blankets wrapped around marathon runners at the end of a race?
The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold.
Convection questions
Why are boilers placed beneath hot water tanks in people’s homes?
Hot water rises.
So when the boiler heats the water, and the hot water rises, the water tank is filled with hot water.
Why does hot air rise and cold air sink?
Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.
1. How does heat energy reach the Earth from the Sun?
A. Radiation
B. Conduction
C. Convection
2. Which is the best surface for reflecting heat radiation?
A. Shiny white
B. Dull white
C. Shiny black
D. Dull black
3. Which is the best surface for absorbing heat radiation?
A. Shiny white
B. Dull white
C. Shiny black
D. Dull black
1201
Chemical Changes
GLOW STICK
Has a glass vial inside the plastic tubeBending the light stick causes the glass vial to
breakThe two solutions mix and undergo a reaction
called chemiluminiscene , light is emitted .
122
What are the changes that can take place?
Physical changes Chemical changes
123
Definition of chemical Reaction
• Chemical changes are permanent and irreversible
• Produced new substances• Reactants are changed into products
Example: reactant A + reactant B product C +
product B
124
Definition of physical reaction
• When a change is reversible, we call it a physical change
• No new substance is formed
PROCESSESBurning bottled gas for outdoor cooking Combustion Iron rusting in the presence of water and oxygen Combination Sugar being heated strongly Decomposition Water being broken down into its elements by electricity Electrolysis Water puddle slowly disappearing under sunlight Evaporation
126
Differences between physical and chemical changes
Physical Changes Chemical Changes
No new substances formed New substances are formed
No or little heat is taken in or given out
Heat and/or light energy may be taken in or given out
Properties of substance do not change
Properties of products different from starting reactants
127
between matter and different forms of energy:
1. Heat
2. Light
3. Electricity or by
4. Combination of 2 different matter
Physical & chemical changes are brought about by interactions
128
1. Changes in State of Matter
2. Combination
3. Thermal Decomposition
4. Combustion
Chemical Changes Caused by Heat
129
Heat Causes Changes in the State of Matter
• From Solid to liquid to gas or vice versa• Melting, freezing, boiling, evaporation• Sublimation: From solid change straight to gas
These are physical changes since changes are reversible and no new products are
formed
130
• Some substances undergo sublimation • Like dry ice (carbon dioxide) and iodine
SUBLIMATION
131
Combination
• Combination refers to a process in which two or more substances form a new substance
ExampleIron + Sulphur Iron Sulfide
Fe + S FeS
heatheat
132
Combination
2K + Cl2 2K2Cl
133
Combustion
• Refers to combination of a substance with oxygen in the presence of heat.
• One or more new substances may be produced
134
• Can combustion take place on the moon?• No, unless there is a supply of air or
oxygen present
CombustionCombustion
135
Combustion = BurningCombustion = Burning
136
• Processes such as rusting and combustion are oxidation reactions.
• Oxidation refers to a process in which a substance reacts with oxygen
Combustion is a type of oxidation reaction Combustion is a type of oxidation reaction
Oxidation
• Examples- Burning of magnesium in oxygen- Rusting of iron- Fireworks- Burning of paper or wood
Burning Mg
Rust
138
Thermal Decomposition
• A substance breaks down into 2 or more substances by effect of heatExample:
sugar carbon + water vapour
calcium carbonate calcium oxide + carbon dioxide
heatheat
heatheat
139
Decomposition
140
Chemical Changes Caused by Light
• Photosynthesis• Photography• Obtaining energy from solar cells
141
Chemical Changes Caused by Light• Photosynthesis:
Process in which green plants make food in the presence of light
carbon dioxide + water glucose + oxygensunlightsunlight
chlorophyllchlorophyll
Chemical Changes Caused by Light
143
Chemical Changes Caused By Light
Under the exposure of light, chemical reaction takes place with the formation of new productsUnder the exposure of light, chemical reaction takes place with the formation of new products
Fading of the colour of newspaper due to light
exposure
144
Chemical Changes Caused By Light
Example
photographic films : coating of silver bromide
silver bromide silver + bromine
Example
photographic films : coating of silver bromide
silver bromide silver + brominelight
145
Chemical Changes Caused By Light
• Does chemical changes take place if a digital camera is used?
• No, light is changed to electrical signals to form images in a digital camera.
146
• Solar cells are also called photovoltaic cells
• They convert light energy directly into electricity
Chemical Changes Caused by LightChemical Changes Caused by Light
Solar Cells
Solar Panels on House Roof
Solar cells are used in areas where electricity is not readily available.
Suggests some uses of this energy within the house.
148
Electricity
The changes that takes place include:• Heating• Light production• Magnetic effect• Chemical effect• Electrolysis
Heating a light bulb with electricity to produce light
• A physical process• The filament in the light bulb is heated up,
and electrical energy is converted to heat and light energy. No new substances are formed
149
Splitting water using electricity
• This process is called Electrolysis (breaking down of substance using electricity )
151
Chemical Changes Caused By Mixing
Sodium hypochlorite + water chlorine gas (bleaching)
Also used in swimming pools:
LIGHT CAN BE USEFUL TO US (3 WAYS)
Photosynthesis — plants use light to make food,
which in turn gives us food.
Photography — light causes chemical changes on photographic film, giving us photographs.
Obtaining energy from solar cells — light is
converted into electricity.
DIFFERENTIATING Process Change Cooking meat Chemical Extracting aluminum from aluminum ore Chemical Boiling water Physical Photosynthesis Chemical Exposing photographic film to light Chemical Iodine crystals turning into iodine gas Physical
USEFULNESSUSEFUL NOT USEFUL
Photosynthesis Rusting
Combustion of fuels in power stations Combustion of fuels producing air pollutants
Respiration Forest fires
Decay of dead organisms
Extracting iron from ore
Making electromagnets electroplating
digestion
IMPORTANCE OF CHEMICAL CHANGE
Why is the decay of dead organisms an important and useful chemical change? It returns nutrients back to soil to be recycled for use naturally by plants, otherwise dead organisms would be found everywhere and there would not be enough space on earth to bury them.
ENERGY CHANGES AND HOW THEY WORK
i) Furnace --Chemical energy in fuel is changed to heat by combustion.
ii) Boiler -- Heat causes the water particles to have more kinetic energy and turns into moving steam, which has kinetic energy.
iii) Turbine --The turbine transfers kinetic energy of the moving steam to the generator.
iv) Generator --Kinetic energy from the turbine turns the generator. Kinetic energy of the generator is changed to electricity.
DEFINITIONS
SUBLIMATION - Thermal exothermic (give out / release)- endothermic (take in ) OXIDATION- Refers to a process in which a substance reacts
with oxygen - Processes such as rusting and combustion are oxidation reactions .
SOLID
GAS LIQUIDM
ELTING
BOILING(1000C) / EVAPORATION
SOLI
DIFI
CATI
ON
/FR
OST
FORM
ATIO
N
FREEZING
CONDENSATIONSU
BLIM
ATIO
N
FILMS VS DIGITAL
Light rays that have bounced off the object and entered the lens of the camera . The source of light is the light shining on the films and images will be imprinted on the film due to light (reacting with silver bromide) .
FILMS VS DIGITAL
FILMS [CHEMICAL CHANGE] Light energy (from objects) converted into electrical energy.
DIGITAL [PHYSICAL CHANGE]Electrical signals
SOLAR CELLS
• In calculators • Use photovoltaic cells (in photography)
They convert light energy directly into electricity
LOMOGRAPHY Coloured films
GLOW STICK
Has a glass vial inside the plastic tubeBending the light stick causes the glass vial to
breakThe two solutions mix and undergo a reaction
called chemiluminiscene , light is emitted .
MATERIALS
• Grouping and sorting is called classification.• Grouping of objects always helps us to do our
work efficiently .• Classification of objects can be based on
similarities and differences . • NON-LIVING THINGS AND LIVING THINGS• MAN-MADE AND NATURAL• Metals, glass , ceramic , plastic , fibre
METALS
• Cobalt• Nickel • Iron
They have natural ores . Gold , silver … have ores too!
Loadstones
COPPER OREPlatinum ore
Lead ore