salts

Question 1

how do you make soluble salts

Answer 1

• neutralising the acid and crystallising the resulting solution
• acid + base -> salt + water

Question 2

explain the 2 stages of making pure, dry crystals of a soluble salt

Answer 2

1) the insoluble base method or the titration method
2) crystalise the salt

Question 3

what is the insoluble base method

Answer 3

• use this when making salts that do not contain na+, K+, NH4+ ions
• the acid is usually one of hydrochloric, sulphuric or nitric
• the base is usually a solid metal oxide
• in the method, the acid and base react to form salt + water

Question 4

describe the insoluble base method

Answer 4

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 guarantees the base is in excess so that we know all the acid has been used up
3) filter the excess base

Question 5

what is the titration method

Answer 5

• use this when making salts that do not contain na+, K+, NH4+ ions
• the acid is usually one of hydrochloric, sulphuric or nitric
• the alkali is usually on of sodium hydroxide, potassium hydroxide or ammonium hydroxide
• in the method the acid and alkali will react to form salt + water

Question 6

describe the titration method

Answer 6

1) perform a titration to measure the volumes of acid and alkali that neutralise each other
2) repeat the titration but this time don’t put the indicator in and use the burette to add exactly the right volume for neutralisation

Question 7

what is crystallisation

Answer 7

• once you’ve made a salt solution you perform crystallisation to get pure dry crystals

Question 8

describe crystallisation

Answer 8

1) heat the salt solution until crystals just start forming
- this causes the solution to become saturated
2) allow the solution to cool in an evaporating basin for a few days
- this lowers the solubility of the salt so that lots of crystals start to form
3) filter out the crystals
- this removes them from the excess salt solution in the basin
4) dry the crystals by dabbing them with filter paper
- this removes the last traces of water from the crystals

Question 9

what is the definition of a precipitate

Answer 9

an insoluble solid that forms inside of a solution
- the ions in the solution colide with each other and a precipitate forms and slowly sinks to the bottom

Question 10

when mixing two solutions, how can you tell if a precipitate has been formed

Answer 10

mixing the ions up and seeing if either of the resulting compounds is insoluble

Question 11

how can you make salts by precipitation

Answer 11

• make insoluble salts by mixing solutions to make precipitate
• each solution should contain one of the ions needed to make it
• when the ions collide they combine

Question 12

once the salt has been made by the precipitate we need to separate it from the solution, how do you do that

Answer 12

1) filter out the salt precipitate
- the residue is salt we want to keep
- the filtrate is the leftover solution
2) rinse the salt with water
- this washes of traces of the leftover solution
- it doesn’t dissolve our salt because its insoluble
3) dry the salt by dabbing it with filter paper
- this removes the ;ast few traces of water, leaving us with a pure dry salt

Question 13

what are spectator ions?

Answer 13

ions that are not involved in making the precipitate and the remain in the solution as leftovers