2.2 Acids, Bases and Salts

Question 1

What is the pH scale?

Answer 1

The pH (potential Hydrogen) is a non-linear scale that determines how acidic or alkaline a substance is. 
1 = Strongly acidic 
7 = Neutral (pure water) 
14 = Strongly Alkaline

Question 2

What are acids?

Answer 2

A substance that contains Hydrogen (H+) ions and has a pH lower than 7

Question 3

What are alkalis?

Answer 3

A substance that contains Hydroxide (OH-) ions and has a pH higher than 7

Question 4

What determines how strong or weak an acid/ alkali is on the pH scale?

Answer 4

The concentration of Hydrogen or Hydroxide ions in a substance when dissolved into water. The higher the concentration of Hydrogen/ Hydroxide ions, the stronger the Acid/ Alkali is.

Question 5

What is a solute?

Answer 5

a substance that can be dissolved by a solvent to create a solution (e.g. Salt is a solute to water)

Question 6

What is a solvent?

Answer 6

A substance that solutes dissolve into to form a solution (e.g water is a solvent to salt)

Question 7

What is concentration?

Answer 7

A measure of the amount of solute* particles in a solvent*. When there is a high number of solute particles, the solution is concentrated. When there is a low number of solute particles, the solution is dilute.

Question 8

How do we measure pH?

Answer 8

• Universal Indicator Paper
• Electronic pH meter
• Measuring the rate of reaction

Question 9

What is the reactivity series?

Answer 9

Potassium- Parry (Most reactive)
Sodium- Said
Calcium- Cancel
Magnesium- Mocks
Aluminium- And 
(Carbon- Car)-Gas
Zinc- Zoos
Iron- In
Tin- The
Lead- Lead.
(Hydrogen- Harrison)-Gas
Copper- Coppen
Silver- Sings 
Gold- Graham's 
Platinum- Pieces (Least Reactive)

Question 10

What are the 4 main neutralisation reactions?

Answer 10

• Acid + metal → Salt + Hydrogen
• Acid + Base → Salt + Water
• Acid + Alkali → Salt + Water
• Acid + metal Carbonate → Salt + Water + Carbon Dioxide

Question 11

What is titration?

Answer 11

Titration is a way of finding the concertation of an acidic (or alkaline) solution with a known volume by adding it to an alkaline (or acidic) solution with a known concentration and volume.

Question 12

What is the process of titration and the equipment needed?

Answer 12

1) You accurately measure the alkaline (or acidic) solution with a known concentration using a pipette (accuracy of ±0.1 cm³) and add it to a clean conical flask
2) Add a few drops of an indicator into this solution and mix
3) Clean the burette with distilled water and pour acid (or alkali) with unknown concentration into it with the tap closed
4) Record the reading on the burette and slowly add small amounts, mixing each time until the indicator changes colour
5) Record the amount of acid in the burette and work out the volume of the acid mixed in the solution (titre = original reading - reading after)
6) Repeat the entire process until you have two results within 0.1 cm³ of each other (discard anomalous results). The precise results are called concordant. Work out the mean.

Question 13

How do you test whether a solution is acidic without an indicator?

Answer 13

Add sodium carbonate to the solution and if CO2 is released then the solution is acidic- you can test if the gas is CO2 by passing it through lime water and it will turn milky white.

Because:
Acid + metal carbonate → salt + water + carbon dioxide

Question 14

What is a salt?

Answer 14

A compound founded by the neutralisation of an acid by a base.

Question 15

How do we find 1cm³ in dm³

Answer 15

÷1000 (10x10x10)
1cm³ = 0.001dm³
1dm³ = 1000cm³

Question 16

How do you find the amount of moles in a substance from grams?

Answer 16

m/Mr = mol

Mass(g)/ Molecular Mass =moles

Question 17

3 examples of a strong and and weak acids

Answer 17

Strong
- Hydrochloric acid (HCl)
- Sulfuric Acid (H₂SO₄)
- Nitric Acid (HNO₃) 
Weak 
- Ethanoic acid
- Citric acid
- Carbonic acids

Question 18

2 examples of a strong and weak acid

Answer 18

Strong 
- Sodium Hydroxide (NaOH)
- Potassium Hydroxide 
Weak
- Ammonium hydroxide (NH₄OH)
- Calcium hydroxide (Ca(OH)₂)

Question 19

How do you calculate concentration of a substance?

Answer 19

Concentration (mol/dm³) = Moles of substance (mol)/ Volume dm³

Question 20

How do we find out the concentration of a substance in grams?

Answer 20

We times the concentration in mol/dm³ by the molecular formula mass of the molecule.

Question 21

What is 1 gram of water equal to in volume?

Answer 21

1g = 1cm³ of water (and 1ml)

Question 22

What is the process of filtration and the equipment needed?

How are large and small crystals formed?

Answer 22

1) -Excess metal/base/carbonate is added to make sure all acid reacted and ‘used up’.
- Heating and stirring speeds up the reaction
- For metals and metal carbonates fizzing will stop once all acid has all reacted

2) The mixture is filtered using a filter funnel which removes excess solids (non-acid) but allows the salt solution to pass.

3) The water is evaporated from the salt solution in an evaporation basin (usually with the help of a Bunsen burner).
- Large crystals form when water evaporated slowly (window ledge/ radiator)
- Small crystals

Question 23

How are large and small crystals formed in filtration?

Answer 23

Large crystals- form when water evaporated slowly (window ledge/ radiator)
Small crystals- form when 2/3 is evaporated by a Bunsen burner and the rest naturally.

Question 24

How are insoluble salts made?

Answer 24

Mixing, filtration, washing and drying
1) Mix two solvable salts (aq) together and react in a precipitation reaction
2) The mixture is passed through a filter but the insoluble precipitate stays.
3) Water doesn’t dissolve the insoluble precipitate so impurities can be washed away while in the filter.
The filter paper is then opened out and put in an oven for the precipitate to dry.

Question 25

What is meant by (aq) in ionic bonding?

Answer 25

The substance is dissolved in water.

Question 26

What is the titre in titration?

Answer 26

Volume of unknown solution added to the solution with known volume and concentration

• Original volume of unknown in burette - volume of unknown after adding = titre.

Question 27

How do you create salts by titration?

Answer 27

1) Measure out exactly 25cm³ of alkali into a clean conical flask using a pipette
2) Add a few drops of indicator to the flask
3) Place the flask onto a white tile
4) Fill the burette with acid
5) Slowly add the acid from a burette to the alkali until the indicator changes- this is the endpoint of the reaction (neutral)
6) Record the volume of acid added to the flask (Titre)
7) Repeat steps 1-6 without using indicator and the same volume of acid from the burette.
8) Salt can be extracted from the solution by evaporation

Question 28

What is the equipment for titration?

Answer 28

Pipette 
Burette 
Stand + clamp 
White tile 
Evaporating Basin (not needed)

Question 29

What is the curved water line name and where do you measure water from on the line?

Answer 29

You measure water from the lowest point on the meniscus