Preparing soluble salts
| English | Chinese | Pinyin |
|---|---|---|
| salt | 盐 | yán |
| filter | 过滤 | guò lǜ |
| evaporate | 蒸发 | zhēng fā |
| crystallise | 结晶 | jié jīng |
Making salts 盐 you can dissolve
- A salt forms when the hydrogen of an acid is replaced by a metal.
- For soluble salts, there's a reliable way to make and collect them.
Why is an excess of the base added to the acid?
Excess base ensures complete reaction of the acid.
A salt forms when the hydrogen of an acid is replaced by a ______.
A metal (or ammonium) ion replaces the acid's hydrogen.
The method
- React an acid with an excess of an insoluble base, metal or carbonate.
- The excess ensures all the acid is used up; then filter 过滤 off the leftover solid.
Making a soluble salt: react with excess solid, filter, evaporate 蒸发, then crystallise 结晶
Preparing a soluble salt
Step through the method. React an acid with excess insoluble base, filter off what's left over, then evaporate and crystallise to get pure salt crystals.
After the reaction, the leftover excess solid is removed by:
Filtration removes the undissolved excess.
Pure salt crystals are obtained by:
Slow crystallisation gives pure crystals.
Getting the crystals
- The filtered solution contains the dissolved salt.
- Evaporate some water, then leave it to crystallise — the salt forms pure crystals.
Put the soluble-salt preparation steps in order.
React → filter → evaporate → crystallise.
The full sequence
-
- Add excess base to warm acid. 2. Filter off the excess.
-
- Evaporate to concentrate. 4. Crystallise and dry the crystals.
Worked example. To make copper sulfate: warm sulfuric acid, add excess copper oxide until no more dissolves, filter off the leftover oxide, then evaporate and crystallise the blue solution.
You've got it
- a soluble salt is made by reacting acid with excess base/metal/carbonate
- filter off the excess solid, then evaporate and crystallise
- using an excess ensures all the acid reacts