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Chemistry Paper 2, test for calcium - add NaOH -> white precipitate, or…
Chemistry Paper 2
Rates of Reaction
- 3 ways of measuring the rate of reaction
- Mean rate = quantity of reactant used / time
- Mean rate = quantity of product formed / time
- Observe a precipitate being formed. This will mean there is an insoluble solid
- Rates of reaction can be determined from graphs.
- The gradient will tell you how fast or slow the reaction is.
- The steeper the gradient, the faster the reaction.
Collision Theory
Surface area:
- Smaller particle size means higher surface area to volume ratio, means more successful collisions can take place, means greater rate of reaction
Temperature:
- Increasing temperature, increases the rate of reaction because particles are moving faster and will collide more often.
- Also, particles have more energy, so more successful collisions will result in a reaction
Pressure
- At a higher pressure, the gas particles are closer together, so there is a greater chance of successful collisions, resulting in higher rate of reaction.
Reversible
- In some reactions, the products of the reaction can react to produce the original reactants.
- These reactions are called reversible reactions
- Eg
- Heating ammonium chloride:
- Ammonium chloride -> Ammonia + Hydrogen Chloride (endothermic)
- Ammonia + Hydrogen Chloride -> Ammonia (exothermic)
- Heating hydrated copper (II) sulphate:
- Hydrated Copper sulphate -> anhydrous copper sulphate + water (endothermic) (add heat)
- Anhydrous copper sulphate + water -> hydrated copper sulphate (exothermic) (add water)
- If the forward reaction is endothermic (absorbs heat) then the reverse reaction must be exothermic (releases heat
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Polymerisation
- Addition polymerisation - process of joining lots of small molecules (monomers) together to form large molecules (polymer) The monomers must be alkenes as the carbon-carbon double bond must break to form the polymer.
- Uses:
- Polyethene – plastic shopping bags and water bottles Strong and light
- Polychloroethene (PVC) – water pipes and electrical cable Water proof, flexible and inslator
- Polypropene – crates and ropes Strong and rigid
- Polytetrafluoroethene (PTFE) – lining non-stick saucepans Slippery, chemically inert
- Condensation polymerisation – takes place when the monomers have two functional groups in the molecule such as ethane diol, which contains the OH group at each end of the molecule
- You could also produce Hexanedioic acid which has the carboxylic acid functional group at both ends
- Seeing as alcohols react with carboxylic acids to form esters, these two molecules polymerise
- Amino acids have two different functional groups – NH2 and COOH and also undergo condensation polymerisation.
- DNA is made of two polymer chains made from 4 monomers called nucleotides, arranged in a double helix
- Other naturally occurring polymers include proteins, starch and cellulose and fats.
Testing for common gases
- Hydrogen: - Burning splint (squeaky pop). Hydrogen burns rapidly with a squeaky pop sound.
- Oxygen: - Glowing splint. The splint relights in oxygen.
- Carbon dioxide: - Lime water (Aqueous calcium hydroxide). Turns milky when CO2 is bubbled through or shaken with.
- Chlorine: - Damp litmus paper. The litmus paper is bleached and turns white.
- Purity – single element or compound – pure water only contains water and nothing else.
- Formulation – a mixture designed as a useful product eg fuels, cleaning materials, paints, medicines, foods, fertilisers.
Chromatography
- Used to separate mixtures of dyes and to help to identify substances.
- A solvent – mobile phase, Moves up the paper (stationary phase) carrying different components different distances depending on the their attraction for the paper and the solvent.
- This is called a chromatogram.
- In this one you can see that the bottom dots in A and C are the same substance as they have travelled the same distance (measured in cm with a ruler)
- Some musts – Baseline drawn in pencil or the line will move up the paper with the dots
- Baseline above the line of the solvent or it will be dissolved in solvent
- The ratio of distance moved by compound to solvent is known as the Rf value.
- Rf = distance moved by substance / distance moved by solvent
- Gas chromatogram – mobile phase an inert gas.
- The stationary phase is a thin layer of liquid on a solid support.
- It is much more sensitive and allows you to determine the amount of each chemical.
Flame tests
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test for calcium - add NaOH -> white precipitate, or flame test -> orange flame
test for sulphate - barium chloride -> white precipitate
reason why bromine water turns colourless: double bond gets broken and bromine adds to either side of that double bond