Acids, Alkalis and Salts

Question 1

What does concentration mean?

Answer 1

How much solid is dissolved in a certain volume of solution

Question 2

What does dilute mean?

Answer 2

Relatively few particles in a given volume

Question 3

What does concentrated mean?

Answer 3

Relatively many particles in a given volume i.e. particles much closer together

Question 4

How do you convert cm^3 to dm^3?

Answer 4

1 dm^3 = 1000 cm^3

To convert cm^3 into dm^3, divide by 1000

Question 5

What is the formula for mass concentration?

Answer 5

Mass concentration (g/dm^3) = Mass (g) / Volume (dm^3)

Question 6

What is the formula for mole concentration?

Answer 6

Mole concentration (mol/dm^3) = Number of moles / Volume (dm^3)

Question 7

What is the formula for the number of moles?

Answer 7

Number of moles = Mole concentration x Volume (dm^3)

Question 8

What is the formula for mass concentration with moles?

Answer 8

Mass concentration = Mole concentration x Mass of one mole

Question 9

What are formula for some common acids?

Answer 9

Nitric acid - HNO3
Hydrochloric acid - HCl
Sulphuric acid - H2SO4
Phosphoric acid - H3PO4
Ethanoic acid - CH3CO2H

Question 10

What is an acid?

Answer 10

A substance that releases H+ (aq) ions when added to water

Question 11

What is a base?

Answer 11

A substance that reacts with acids

Question 12

What are the three types of base?

Answer 12

Metal oxide e.g. CaO
Metal hydroxide e.g. Ca(OH)2
Metal carbonates e.g. CaCO3

Question 13

What are alkalis?

Answer 13

Substances that release OH- (aq) ions when added to water

Question 14

What is the difference between a strong and a weak acid?

Answer 14

In strong acids all molecules ionise and release H+ ions in water in an irreversible reaction e.g. Hydrochloric
In weak acids only a small fraction of the molecules ionise and release H+ ions in water in a reversible reaction e.g. Ethanoic

Question 15

How does concentration of H+ ions affect pH?

Answer 15

Each time the concentration of H+ ions increases by 10 the pH decreases by 1

Question 16

What is the pH at H+ concentration of 0.1 mol/dm^3?

Answer 16

1

Question 17

What is the reaction of an acid and a metal?

Answer 17

Acid + metal –> Salt + hydrogen (not a neutralisation reaction)

Question 18

What is the reaction of an acid and a metal oxide (base)?

Answer 18

Acid + metal oxide –> Salt + water

Question 19

What is the reaction of an acid and a metal hydroxide (base)?

Answer 19

Acid + metal hydroxide –> Salt + water

Question 20

What is the reaction of an acid and a metal carbonate (base)?

Answer 20

Acid + metal carbonate –> Salt + water + carbon dioxide

Question 21

What is a titration?

Answer 21

An experiment that is used to find out the concentration of an unknown solution
E.g. You have a solution of unknown concentration of an alkali and an acid of known concentration. You add the acid until an indicator shows it is exactly neutralised. By using the volume of acid, concentration of acid, and volume of alkali you can calculate the concentration of alkali

Question 22

How would you carry out a titration?

Answer 22

Wash the burette with acid and the pipette with alkali
Place a white tile under a conical flask
Fill the burette with acid. Use the pipette to fill a conical flask with a
certain volume of alkali
Add a few drops of indicator to the conical flask
Using the burette add acid to the conical flask drop by drop. Swirl the conical flask
The indicator changes colour when all the acid has been neutralised
Repeat the process to get similar results

Question 23

What colour does phenolphthalein turn in acids and alkalis?

Answer 23

Acids - Colourless

Alkalis - Pink

Question 24

What colour does methyl orange turn in acids and alkalis?

Answer 24

Acids - Red

Alkalis - Yellow

Question 25

How would you carry out a titration calculation?

Answer 25

Find the number of moles of the solution you know about
Write out the equation
Work out the number of moles of the unknown substance (same if it is 1:1)
Work out the concentration of the unknown substance

Question 26

How can you make soluble salts?

Answer 26

You can make soluble salts from:
An acid and an insoluble base (e.g. hydrochloric acid and zinc oxide make zinc chloride)
An acid and a soluble base (e.g. hydrochloric acid and sodium hydroxide make sodium chloride)

Question 27

How could you prepare a soluble salt from an acid and an insoluble base?

Answer 27

Add the acid to a beaker
Add the solid base to the acid and stir
Warm the acid gently to allow a faster rate of reaction
Add the base until no more dissolves, ensuring all the acid has reacted
Filter to remove excess base and leave behind pure salt solution
Use crystallisation to get pure, dry crystals

Question 28

How could you prepare a soluble salt from an acid and a soluble base?

Answer 28

Add some of the base in solution to a beaker
Add drops of indicator (not universal indicator)
Add the acid carefully using a burette
Stir
Add acid until the indicator just changes colour. Record the amount
Repeat without any indicator now you know the exact volume of acid required
Use crystallisation to get pure, dry crystals