5.3 SALTS

Question 1

how do you make soluble salts?

Answer 1

• by neutralising acids and crystallising the resulting solution
• acid + base/ alkali —-> salt + water

Question 2

stage 1 of making a soluble salt:

Answer 2

first you make the salt solution, this is one using one of two methods, depending which salt you’re making:
a. the insoluble base method
b. the titration method

Question 3

stage 2 of making a soluble salt:

Answer 3

crystallise the salt

Question 4

when do we use the insoluble base method?

Answer 4

when making salts which don’t contain Na+, K+ or NH4+ ions

Question 5

what are the acids usually in an insoluble base method?

Answer 5

• hydrochloric
• sulfuric
• nitric

Question 6

what are the bases usually in an insoluble base method?

Answer 6

• solid metal oxide
• solid metal carbonate

Question 7

steps of the insoluble base method:

Answer 7

1. heat the acid (hot acid has more energy so it reacts faster with the base)
2. while stirring, add base until no more will dissolve (this guaruntees the base is in excess so that we know all the acid has been used up)
3. filter out the excess base
4. gently heat to evaporate water
5. leave to dry

Question 8

when do we use the titration method?

Answer 8

when we are making salts including Na+, K+ or NH4+ ions because their bases are all soluble

Question 9

what acid do we use in titration?

Answer 9

• hydrochloric
• sulfuric
• nitric

Question 10

what alkali do we use in titration?

Answer 10

• sodium hydroxide
• potassium hydroxide
• ammonium hydroxide

Question 11

what do acid and alkali react to form in a titration?

Answer 11

salt and water

Question 12

method of titration:

Answer 12

1. use a pipette to measure the alkali into a conical flask and add a few drops of phenolphthalein or methyl orange
2. add the acid into the burette and note the starting volume
3. add the acid very slowly from the burette into the conical flask until the indicator turns the appropriate colour
4. note and record the final volume of acid in the burette
5. add this same volume of acid into the same volume of alkali without the indicator
6. heat partially, leaving saturated solution
7. leave to crystallise

Question 13

what do you do once you’ve made the salt solution?

Answer 13

you perform crystallisation

Question 13

method of crystallisation:

Answer 13

1. heat the salt solution until crystals just start forming
2. allow the solution to cool in an evaporating basin for a few days
3. filter out crystals
4. dry the crystals by dabbing them with filter paper

Question 14

what is a precipitate?

Answer 14

an insoluble solid that forms inside a solution

Question 15

how do we make insoluble salts?

Answer 15

by mixing solutions to make a precipitate, each of the solutions should contain one of the ions needed to make it

Question 16

precipitation method:

Answer 16

1. mix two solutions to form precipitate
2. filter out the salt precipitate- the residue is the salt we want to keep
3. rinse the left over salt to remove any leftover solution
4. dry the salt by dabbing it with filter paper- this removes the last few drops of water