iGCSE Chemistry - Acids, Bases and Salt Preparations

Which 4 are always soluble?

• Potassium

• Sodium

• Ammonium

• Nitrates

Most Chlorides are --, except for -- and --

- soluble

• lead (II) chloride

• silver chloride

Most Sulphates are --, except for --, -- and --

• soluble

• barium sulphate

• calcium sulphate

• lead (II) sulphate

Most carbonates are --, except for --, -- and --

• insoluble

• potassium

• sodium

• ammonium

Most hydrocides are insoluble, except for the three constants and --, which is sparingly soluble

Calcium hydroxide

Acids are proton --, as they ionize in solutions producing protons, -- ions. Then, give an example using Hg

• donors

• H+

e.g: HCI (aq) --> H+ (aq) + CI- (aq)

Alkalis are proton --, as they ionize in solutions, producing -- ions. Use Sodium Hydroxide as an example

• acceptors

• OH-

e.g: NaOH (s) --> Na+ (aq) + OH- (aq)

Give the general word equation for metal and acid reaction and state why this is not a neutralisation reaction

Metal + Acid --> Salt + Hydrogen

This does not produce water, so it is not a neutralization reaction.

For the reaction of a metal + acid, give the 3 main acids and the salts they turn into

sulfuric acid ~ sulfate salt

hydrochloric acid ~ chloride salt

nitric acid ~ nitrate salts

Give the balanced general equation for Metal + Acid reaction, using Mg + HCl as your example

Mg + 2HCI --> MgCl2 + H2

Give the general word equation for the reaction of Acids + Bases

Base + Acid --> Water + Salt

Name the 2 main types of bases

• metal oxides

• Metal hydroxides

Give a balanced equation for the reaction of acids with bases, using calcium oxide + sulfuric acid as your example

CaO + H2S04 --> H20 + CaSO4

Give the general word equation for the reaction between Acids and Carbonates

Acid + Carbonte --> Salt + Water + Carbon Dioxide

Give the balanced equation for reaction between an acid and carbonate, using Zinc Carbonate + Nitric Acid as your example

ZnC03 + HNO3 --> Zn(NO3)2 + H20 + CO2

Briefly describe how you can test for the presence of a carbonate

React it with an acid, if CO2 is formed it is a carbonate

Define a base

Bases are substances which can neutralize an acid, forming a salt and water

All -- are --, but not all -- are --

Word Bank: Alkalis, Bases

Alkalis, bases, bases, alkalis

Bases are usually --, -- or -- of metals

• oxides

• hydroxides

• carbonates

What makes ammonia an unusual base?

It produces OH- ions in water despite not containing OH- ions itself.

What are the two things to consider about the suitability of the metal when making a soluble salt?

• It must be more reactive than hydrogen to react with acids

• It cannot be too reactive as it would be unsafe

How to know if a metal is too reactive and unsafe for making a soluble salt? also give 4

Any metal that reacts with cold water is too reactive, so this would be:

• Potassium

• Sodium

• Lithium

• Calcium

For Method A (metal/metal oxide/metal carbonate + acid --> salt + water), what are the first 3 steps?

1. heat acid until warm

2. add insoluble metal/base/carbonate in excess

3. stir until no more dissolves

For Method A, what are the next steps after 1-3?

4. filter mixture to remove excess base

5. transfer to evaporating basin

6. evaporate water using heat until crystals begin to form

7. allow crystals to form in a warm place

Why must you avoid overheating in method one of forming salt crystals?

This may lead to crystals decomposing

Briefly explain the second method of forming salt crystals, until the evaporating part.

1. add alkali and indicator to a conical flask using a pipette, note volume of alkali added

2. add acid to burette, note starting volume

3. add acid to alkali slowly until indicator changes colour

4. note final volume of acid

5. add same volume of acid into same volume of alkali without indicator

6. salt crystals form through heating (same as in method A)

Insoluble salts can be prepared using a — reaction

Precipitation

Give the general word equation for preparing an insoluble salt

Soluble salt 1 + Soluble Salt 2 —> Insoluble Salt + Soluble Salt 3

Describe the method for preparing an insoluble salt

1. Measure out a fixed volume of one salt solution

2. Then add the second salt solution until it is in slight excess

3. Recover the precipitate by filtration

4. Wash precipitate with distilled water to remove reactants that are contaminated with the residue

5. Leave to dry

When preparing an insoluble salt, why must the second salt solution be added in slight excess?

To ensure the maximum amount of precipitate is obtained

The method for preparing an insoluble salt is a good way to prepare — and — salts which are often insoluble.

Silver and Lead (II) salts