Salt Formation - TN

Question 1

how do we make soluble salts (simply)

Answer 1

by neutralising acids and crystallising the resulting solution

Question 2

what is the general equation for making soluble salts

Answer 2

acid(aq) + base(s)/alkali(aq) -> salt(aq) + water(l)

Question 3

what are the two stages of making pure, dry crystals of soluble salt

Answer 3

1: make the salt solution
->using either the insoluble base method or the titration method
2: crystallise the salt (done in the same way no matter what method you used before

Question 4

when would you use the insoluble base method for making soluble salts

Answer 4

when making salts that do not contain Na, K, or NH4 ions

Question 5

in the insoluble base method of creating soluble salts: how do you choose what acid or base to use

Answer 5

depends on which salt you want to make

Question 6

in the insoluble base method of creating soluble salts: what are usually the options of acid and bas to use

Answer 6

acid: usually hydrochloric, sulfuric, or nitric
base: usually a solid metal oxide

(you can also use a solid metal carbonate as a base. the only difference is that it creates CO2 so there will be fizzing)

Question 7

what are the three stages of the insoluble base method of making the salt solution and why do we do them

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 (to ensure the base is in excess so that all the acid is used up)
3. filter out the excess base (because you don’t need it)

Question 8

when would you use the titration method for making soluble salts and why

Answer 8

when making salts that contain Na, K, or NH4 ions because their bases are all soluble so you wouldn’t be able to filter out the excess if you used the soluble base method

Question 9

in the titration method of making soluble salts, what acids and alkali would you normally use

Answer 9

acid: hydrochloric, sulfuric, nitric
alkali: sodium hydroxide, potassium hydroxide, or ammonium hyrdoxide

Question 10

what are the steps of the titration method of creating soluble salts

Answer 10

1. perform a titration (to measure the volumes of acid and alkali that neutralise each other
2. repeat the titration without the indicator but instead using the burette to measure out the exact volume calculated previously (so that the crystals aren’t stained by the indicator)

Question 11

what are the steps of crystallisation when making soluble salts

Answer 11

1. heat the salt solution until crystals start to form (this causes the solution to become saturated
2. allow the solution to cool in an evaporating basin for a few days (lowers the solubility of the salt so that solids form)
3. filter out the crystals (removes them from the excess salt solution)
4. dry the crystals using filter paper (remove last traces of water)

Question 12

what is a precipitate

Answer 12

an insoluble solid that forms inside a solution

Question 13

how can we tell if a precipitate will form when mixing two solutions

Answer 13

by finding out what ions will form and seeing if any are insoluble

Question 14

method for making insoluble salts

Answer 14

by mixing solutions to make a precipitate

Question 15

how to choose which solutions to use when making insoluble salts through precipitation

Answer 15

each solution should contain one of the ions needed to make the precipitate

Question 16

what are spectator ions

Answer 16

the leftover ions that aren’t used to make the precipitate

Question 17

once the salt has been made by precipitation, how do we get the final crystals

Answer 17

• filter out the precipitate (the residue is the salt we want to keep, the filtrate is the leftover solution
• rinse the salt with water (washes off traces of leftover solution and the salt is fine because it is INSOLUBLE)
• dry the salt by dabbing with filter paper

Question 18

Why do we add the base in excess in making soluble salt

Answer 18

To make sure all the acid has been used up because otherwise any unreacted acid would become dangerously concentrated during evaporation and crystallisation