C2 - Acids, Bases & Salts Flashcards
What is a base?
A substance with a pH above 7
What is an acid?
A substance with a pH below 7 that forms H+ ions in water
What is an alkali?
A base that dissolves in water (forms OH- ions in water)
What is the reaction for neutralisation?
Acid + base –> salt + water
What are the 2 neutralisation reactions and the other similar reaction?
Acid + metal oxide –> salt + water
Acid + metal hydroxide –> salt + water
Similar reaction:
Acid + metal –> salt + hydrogen
What salts do hydrochloric, sulphuric and nitric acids produce?
Hydrochloric –> chloride
Sulphuric –> sulphate
Nitric –> nitrate
For the acid + metal reaction, what indicates the rate of reaction and what confirms the hydrogen?
Rate of reaction = rate at which bubbles of hydrogen are given off
Hydrogen confirmed by the burning splint test giving a squeaky pop
What happens when ammonia reacts with an acid?
Ammonia + hydrochloric acid –> ammonium chloride
Ammonia + sulphuric acid –> ammonium sulphate
Ammonia + nitric acid –> ammonium nitrate
What is ammonium nitrate used for and why?
Very good fertiliser
It has nitrogen from 2 sources (ammonia and nitric acid) and plants need nitrogen to make proteins
What are the 2 ways of making soluble salts?
Using metal or insoluble base
Using an alkali
Describe crystallisation
To get pure, solid crystals of the salt you use crystallisation
You evaporate some of the water to make the solution more concentrated and then leave the rest to evaporate very slowly
Describe how you make a soluble salt using a metal or insoluble base
Pick the correct acid and metal / insoluble base to make the salt you need
Add the insoluble base or metal to the acid and the solid will dissolve in the acid as it reacts
When all acid has been neutralised, the excess solid won’t dissolve
Then filter out the excess solid to get the salt solution
To get pure, solid crystals of the salt, use crystallisation
Describe how you make a soluble salt using an alkali
You can’t add an excess of alkali because you can’t tell whether the reaction has finished in this case
You add just the right amount of alkali to acid and order to neutralise the acid (you use an indicator to work out how much alkali is needed to neutralise the acid)
You repeat using exactly the same amounts of acid and alkali so that the salt isn’t contaminated by the indicator
Crystallise the salt
Describe how you would make insoluble salts
Use precipitation
Work out the positive and negative ion of the salt
Mix a nitrate of positive ion in solution with sodium and the negative ion in solution (this is because most nitrates and group 1 compounds are soluble)
You would then get a precipitate of the wanted salt (solid) and sodium nitrate solution in the flask
Then you filter the salt from the solution, wash it and dry it on filter paper
What are the 2 main uses of precipitation reactions?
To remove poisonous ions from drinking water
Treating sewage
