C6 - Revision Summary

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chemicals that you might come across in everyday life are food additives,

cleaning and decorating products.

Small

scale – pharmaceuticals (drugs). Large scale – sulfuric

acid

a)Acid b)alkali c)acid d) neutral

An

example of a pure acidic compound that is a liquid is ethanoic acid.

2

ways of measuring the pH of a substance is by using Indicators

(litmus paper or universal indicator) or pH meters.

a) Hydrogen

ions (H+) are always present in acids dissolved in water. b) Hydroxide

ions (OH-) are always present in alkali dissolved in water.

H+ (aq) +

OH- (aq)

→ H2O (l)

ai) Mg + 2HCl → MgCl2 + H2 magnesium chloride aii) 2Al + 6HCl → 2AlCl3 + 3H2

aluminium chloride aiii) Zn + 2HCl → ZnCl2 + H2 zinc chloride bi) Mg + H2SO4

→ MgSO4 + H2 magnesium sulfate bii) 2Al + 3H2SO4

→ Al2(SO4)3 + 6H2

aluminium sulfate biii) Zn + H2SO4

→ ZnSO4 + H2 zinc sulfate

a) copper chloride, CuO + 2HCl → CuCl2 + H2O b) calcium chloride, Ca(OH)2 + 2HCl → CaCl2 + 2H2O

A risk assessment involves identifying hazards, assessing who might be harmed & deciding what action can be taken to reduce the risk.

The

apparatus needs to be the correct size (for the amount of product and

reactants) and strength (for the type of reaction being carried out e.g. if it

is explosive or gives out a lot of heat).

The

yield tells you about the overall success of the process. It compares what you

think you should get with what you actually get in practice.

Answers on page 108

You would separate an insoluble product from a liquid reaction mixture by filtration

Evaporation

can be useful when Isolating

the product – evaporating the solvent to leave behind solid crystals of the

product and purifying

the product – products are dissolved and the solvent evaporated. This is

repeated several times to improve the purity and is called recrystallisation.

You can dry a product by using

a drying oven or a desiccator. Desiccators contain chemicals like silica gel

which remove water from their surroundings.

percentage yield= actual yield/ theorteical yield x 100 The percentage yield

is the actual yield (mass of pure, dry product) as a percentage of the

theoretical yield (maximum possible mass of product that could have been made).

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Purification of a product is important Pharmaceuticals

– it is important to make sure drugs intended for human consumption have no

impurities as these could cause harm. Petrochemicals

– if there are impurities or contaminants in petrol products, they could cause

damage to the car’s engine.

0.479

/ 0.5 x 100 = 95.8%

The term

is used to describe a reaction where energy is given out is exothermic.

The term

is used to describe a reaction where energy is taken in is endothermic.

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It

is important to control the rate of a chemical reaction in industry for safety – if the

reaction is too fast it could cause an explosion and economic reasons –

changing the conditions can be expensive (e.g. higher temperature means burning

more fuel so means higher fuel bills) but a faster rate means more product will

be produced in less time. Companies need to find a balance between low production

cost and the rate of production of product (yield of product).

4 things that affect the rate of reaction are temperature, concentration, catalyst & surface area.

The reaction would be faster because the acid is more concentrated.

Precipitation and

colour change Advantage – the

product does not have to be a gas Disadvantage

– it is not very accurate and very subjective as to when the reaction is

complete. Change in mass Advantage – most

accurate method Disadvantage –

releases gas into the room – dangerous for some gases. Volume of gas Advantage

– quite precise (to the nearest cm3) Disadvantage

– only works for gases.