GCSE Chemistry C4 - Chemical Changes

reactions of acids with metals

- they make salt and hydrogen

- redox reaction

neutralisation of acids

- neutralised by alkalis, bases and metal carbonates

what does an acid and a metal carbonate make

carbon dioxide, water, salt

hydrochloric acid creates what salt

chlorides (XCl)

nitric acid produces what salt

nitrates (XNO3)

sulfuric acid produces what salt

Sulfates (XSO4)

reactivity series

- potassium

- sodium

- lithium

- calcium

- magnesium

- alluminium

-carbon

- zinc

- iron

- hydrogen

- copper

- silver

- gold

soluble salts

- can be made from acids by reacting them with solid insoluble substances such as metals, metal oxides, hydroxides or carbonate

what ions do acids produce

H+ ions

what ions do alkalis produce

OH- ions

pH scale

smaller than 7 - acidic

7 - neutral

bigger than 7 - alkali

ionic equation for neutralisation

H+ (aq) + OH- (aq) --> H20 (l)

what can you measure pH with

- Universal Indicator

- pH probe

Titration experiment

- wash burette using dilute HCL and then water

- fill burette to 50cm^3 making sure the meniscus base is on the line

- use 25cm^3 pippette to add 25cm^3 of alkali into colonical flask using a pipette filler

- add a 2-3 drops of indicator (phenolphthalein which is pink when alkaline and colourless when acidic)

- add acid from burette to alkali until end point is reached

- the titre is the difference between the first and second reading of the burette

- repeat to gain more precise results so the results are concordinate

strong acids and weak acids

- strong = completely ionised in aqueous solution

- stronger the acid, the lower the pH

- weak = partially ionised in equeous solution

- as pH decreases by one unit, the H+ conc of solution increases by a factor of 10

- strong and weak acids is not the same as concentrated and dilute, the latter refers to the amount of substances in given volume, whereas the former refers to the H+ ion conc in aq solution.

example of weak acids

- citric

- ethanoic

- carbonic

examples of strong acids

- hydrochloric

- nitric

- sulfuric

process of electrolysis

- when ionic substance is melted or dissolved, ions are free to move about within the liquid or solution

- passing a current through substances that are molted or solution means that the solution can be broken down into elements.

- positively charged ions move to negative electrode (cathode), negative moves to anode

- ions are discharged at electrodes producing elements

using electrolysis to extract metals

- used if metal is above carbon in reacitivty series

- large amounts of energy are used in the extraction process to melt the compounds to produce the electrical current

- alluminium is manufactored by the electrolysis of molten mixture of alluminium oxide and cryolite using carbon as the anode

why does aluminium oxide need to be mixed with cryolite (why is a mixture used instead of pure aluminium oxide)

aluminium oxide has a very high melting point so it would be too expensive to melt it which is why it is mixed with cryolite

why does the anode need to be replaced often

- oxygen is formed which reacts with the carbon of the positive electrode, forming carbon dioxide and they gradually burn away.

electrolysis of aqueous solutions (at the anode)

- at the anode if OH- and halide ions (Cl-, Br-, I-) are present then one of the halide ions will be produced

-if no halide ions are present then oxygen is formed

electrolysis of aqueous solutions (at the cathode)

- at cathode hydrogen is produced unless the element is less reactive than hydrogen as the more reactive ions want to stay within the solution

electrolysis of aqueous solutions

This happens because in the aqueous solution water molecules break down producing hydrogen ions and hydroxide ions that are discharged.