2.1.4 Acids

Question 1

What are the formulae of common acids?

Answer 1

HCl = hydrochloric acid
H2SO4 = sulfuric acid
HNO3 = nitric acid
CH3COOH = ethanoic acid

Question 2

What are the formulae of common alkalis?

Answer 2

NaOH = sodium hydroxide
KOH = potassium hydroxide
NH3 = ammonia

Question 3

What is an acid? (Arrhenius theory)

Answer 3

A substance that releases H+ ions in aqueous solution

Question 4

What is an alkali? (Arrhenius theory)

Answer 4

A substance that releases OH- ions in aqueous solution
- A soluble base

Question 5

What is a strong acid?

Answer 5

A strong acid will fully dissociate in aqueous solution
e.g. HCl, H2SO4, HNO3

Question 6

What is a weak acid?

Answer 6

A weak acid will partially dissociate in aqueous solution
- Equilibrium lies to the right so backwards reaction is favoured
E.g. carboxylic acids

Question 7

What does monoprotic mean?

Answer 7

1mol of acid produces 1mol of H+ ions

Question 8

What are acids? (Bronsted-Lowry theory)

Answer 8

Proton donors

Question 9

What are alkalis? (Bronsted-Lowry theory)

Answer 9

Proton acceptors

Question 10

What are conjugate acid pairs?

Answer 10

They differ by one proton (H+)

Question 11

What is neutralisation?

Answer 11

• The reaction between the H+ ions from acids and the OH- ions from alkalis
• Forms water which is neutral
• H+ (aq) + OH- (aq) -> H2O (l)

Question 12

What are salts?

Answer 12

• Produced when acids and bases react
• Neutral
• Made from the metal from the base and the non-metal from the acid

Question 13

What does ammonia react with acids to form?

Answer 13

Ammonium salts

Question 14

What do metals react with acids to form?

Answer 14

Salt + hydrogen

Question 15

What do metal oxides react with acids to form?

Answer 15

Salt + water

Question 16

What do metal hydroxides react with acids to form?

Answer 16

Salt + water

Question 17

What do metal carbonates react with acids to form?

Answer 17

Salt + carbon dioxide + water

Question 18

What is a titration?

Answer 18

A technique used to accurately measure the volume of one solution that reacts exactly with another

Question 19

What is a standard solution?

Answer 19

A solution of a known concentration

Question 20

How do you prepare a standard solution?

Answer 20

1. Solid is weighed accurately using an electronic balance and weighing boat
2. Solid is transferred to a beaker and any solid left behind in the weighing boat is washed into the beaker using distilled water
3. Solid is dissolved fully in the beaker using less distilled water than will be needed to fill the volumetric flask and solution is stirred with a glass road
4. Solution is transferred to a volumetric flash using a funnel to avoid spillage and the beaker and glass road are rinsed with distilled water
5. Volumetric flask is filled to the graduation line with distilled water and a pipette is used at the end to ensure the bottom of the meniscus lines up exactly with the mark, whilst at eye level
6. Volumetric flash is slowly inverted several times to the mix the solution thoroughly

Question 21

How do you carry out an acid-base titration?

Answer 21

1. Add a measured volume of one solution to a conical flask using a pipette
2. Add other solution to a burette using a funnel and record initial burette reading to the nearest 0.05cm3
3. Add a few drops of indicator to the solution in the conical flask
4. Run the solution in the burette into the solution in the conical flask and swirl the conical flask throughout to mix the 2 solutions
5. Indicator will change colour at the end point of the titration
6. Record final burette reading and subtract the initial reading from the final reading to find the titre
7. A quick trial titration is carried out first to find the approximate titre
8. Titration is then repeated accurately, adding solution dropwise as the end-point is approached
9. Further titrations are carried out until at least two titres (excluding initial) are concordant

Question 22

What does concordant mean?

Answer 22

Agreeing to within 0.1cm3

Question 23

Why does adding water to the conical flask not have an effect?

Answer 23

It doesn’t change the number of moles added to the flask

Question 24

What calculation do you need to do in a titration?

Answer 24

1. Work out concentration of standard solution
2. Calculates moles in conical flask (using pipette volume and known concentration)
3. Use equation to calculate mols of other solution
4. Work out unknown information