Making Salts and Electrolysis

Question 1

How do you make soluble salts using a metal or an insoluble base?

Answer 1

1/ Pick the right acid plus a metal or an insoluble base such as a metal oxide or metal hydroxide.
2/ Add the metal, metal oxide or hydroxide to the acid- the solid will dissolve in the acid as it reacts.
3/ Once all the acid has been neutralised the excess solid will sink to the bottom of the flask.
4/ filter out the excess metal to get the salt solution, in order to get pure solid crystals of the salt, evaporate some of the water and then leave it to evaporate slowly. This is called crystallisation.

Question 2

How would you make a soluble salt using an alkali?

Answer 2

Alkalis are soluble bases so you cannot tell when the reaction has finished. You have to add exactly the right amount of alkali to just neutralise the acid and use an indicator to show when the reactions finished. Repeat using the same volume of alkali and acid so the salt is not contaminated with indicator.
Evaporate off the water to crystallise the salt as normal.

Question 3

How do you make a insoluble salt?

Answer 3

by using a precipitation reaction, pick two solutions that contain the ions you need and mix them together.
Once the salt has precipitated out and is lying at the bottom of the flask, all you have to do is filter it from the solution, wash it and then dry it.

Question 4

What is electrolysis?

Answer 4

Electrolysis is the process by which you pass an electric current through an ionic substance thats molten or in solution and breaking it down into the elements it’s made of.

Question 5

What is the name given to the substance that you pass the current through to break it down during electrolysis?

Answer 5

electrolytes

Question 6

What allows electrolytes to pass a current through it and why can’t solids be used in electrolysis?

Answer 6

Electrolytes contain free ions which can move about and pass on a charge, however solids are in a fixed shape where ions cannot move.

Question 7

what is the name of the negative and positive electrode?

Answer 7

Cathode and anode

Question 8

What happens at the cathode?

Answer 8

positive ions are attracted to the negative charges of the cathode, and they form atoms again

Question 9

What reaction occurs at the cathode?

Answer 9

Reduction- ions gain electrons.

Question 10

What happens at the anode?

Answer 10

negative ions are attracted to the positive charges of the anode, and they form atoms again.

Question 11

What reaction occurs at the anode?

Answer 11

Oxidation- ions lose electrons

Question 12

How does the reactivity affect the products formed by electrolysis?

Answer 12

If the salt is dissolved in water then there will also be some H+ and OH- ions in the solution.
At the negative electrode if a metal and H+ ions are present, the metal will stay in the solution if it is more reactive than hydrogen in the reactivity series as the more reactive elements are keener to say in the solution. So the product formed at the negative electrode is hydrogen atoms and the metal remains in the solution as a hydroxide.

Question 13

Give the half equations for sodium chloride dissolved in water for electrolysis

Answer 13

positive electrode: 2Cl- –> Cl2 + 2e-

Negative electrode: 2H+ + 2e- —> H2

Question 14

What can the products from the electrolysis of sodium chloride solution be used for?

Answer 14

• Chlorine can be used for the production of bleach and plastics
• sodium hydroxide is a very strong alkali and is used widely in the chemical industry e.g to make soap.

Question 15

What is aluminium and where is it found?

Answer 15

Aluminium is an abundant mental and can be found naturally in compounds.

Question 16

Why can’t aluminium be electrolysed when it is molten?

Answer 16

Aluminium oxide has a very high melting point of over 2000 degrees so melting it would be very expensive and by the time you got it to 2000 degrees the equipment may have melted.

Question 17

What do we do instead with aluminium to separate it from its ore?

Answer 17

Aluminium oxide is dissolved in molten cryolite, which brings the temperature down to about 900 degrees making it much cheaper and easier.

Question 18

What are the electrodes made of in the extraction of aluminium?

Answer 18

graphite (contain carbon) which are a good conductor of electricity

Question 19

what atoms are formed at the negative and positive electrode?

Answer 19

aluminium forms at the negative electrode and oxygen forms at the positive, the oxygen then reacts with the carbon in the electrode to produce carbon dioxide which gradually eats away the positive electrode.