Making salts Flashcards
Most [ ] are soluble in water. What is the main exception?
Chlorides, sulphates and nitrates
Lead chloride, lead sulphate, and silver chloride
Most [ ] are insoluble in water
Oxides and hydroxides
How do you make salts using metal or an insoluble base?
1) Pick the right acid, metal/insoluble base (metal oxide/hydroxide)
2) Add the metal/insoluble base to the acid - the solid will dissolve in the acid as it reacts. When the acid has been neutralised the excess solid will sink to the bottom of the flask
3) Then filter out the excess metal/insoluble base to get the salt solution. To get pure, solid crystals of the salt, evaporate some water and then leave the rest to evaporate very slowly (Crystallisation)
Why can’t you use the metal/insoluble base method with alkalis?
You can’t tell whether the reaction has finished - you can’t just add an excess to the acid and filter out hat’s left
How do you make soluble salts using an alkali?
Add exactly the right amount of alkali to naturalise the acids - you need to use an indicator to show whether the reaction’s finished. Then repeat using using exactly he same volumes of alkali and acid so the salt isn’t contaminated with indicator
Then just evaporate off the water to crystallise the slat as normal
What reaction do you use if you want to make a insoluble salt?
Precipitation reaction
Describe the Precipitation reaction
Pick 2 solutions that contain the right ions that you need
Once the slat has precipitated out all you have to do is filter it from the solution, wash it, then dry it on filter paper
What are the uses of precipitation reactions?
1) Remove poisonous ions (lead) fro drinking water
2) Calcium + magnesium ions can also be removed from water - they make water ‘hard’, which stops soap lathering properly
3) Treating effluent (sewage) - unwanted ions an be removed
