2.1.4 - Acids

Question 1

What is the general reaction of an acid and a base?

Answer 1

Acid + Base → Salt + Water

Question 2

What is formed when acids react with alkalis?

Answer 2

Acid + Alkali → Salt + Water

Question 3

What is the reaction between an acid and a carbonate?

Answer 3

Acid + Carbonate → Salt + Water + CO₂

Question 3

What is formed when acids react with metal oxide?

Answer 3

Acid + Metal Oxide → Salt + Water

Question 3

What is formed when acids react with metal?

Answer 3

Metal + Acid → Salt + Hydrogen

Question 3

Give an example reaction between sulfuric acid and sodium hydroxide.

Answer 3

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

Question 3

Give an example reaction between hydrochloric acid and sodium hydroxide.

Answer 3

HCl + NaOH → NaCl + H₂O

Question 4

Give an example reaction between hydrochloric acid and sodium carbonate.

Answer 4

2HCl + Na₂CO₃ → 2NaCl + CO₂ + H₂O

Question 4

Give an example reaction between hydrochloric acid and calcium carbonate.

Answer 4

2HCl + CaCO₃ → CaCl₂ + CO₂ + H₂O

Question 4

What ions do alkalis release in aqueous solution?

Answer 4

Hydroxide ions (OH⁻).

Question 4

Give examples of common alkalis.

Answer 4

Sodium hydroxide (NaOH), potassium hydroxide (KOH), aqueous ammonia (NH₃).

Question 4

What is an alkali?

Answer 4

A base that is soluble in water, to form aqueous hydroxide ions.

Question 4

What is meant by a proton in acid-base chemistry?

Answer 4

A hydrogen ion (H⁺), which is essentially a proton.

Question 5

What is an acid in terms of ions?

Answer 5

A substance that releases hydrogen ions (H⁺) in aqueous solution.

Question 5

What is the definition of an acid?

Answer 5

Proton Donor

Question 5

What are the 3 types of bases?

Answer 5

Metal oxides, metal hydroxides, and ammonia.

Question 5

What is the definition of a base?

Answer 5

A substance that neutralises an acid to form a salt.  Proton acceptor

Question 5

What is the reaction of HCl with ammonia?

Answer 5

HCl + NH₃ → NH₄Cl

Question 5

What is the reaction of HCl with ammonia?

Answer 5

HCl + NH₃ → NH₄Cl

Question 6

What base is used to treat acid ingestion?

Answer 6

Magnesium Hydroxide

Question 6

What is a salt?

Answer 6

A compound formed when the H⁺ of an acid is replaced by a metal ion or NH₄⁺.

Question 6

What are examples of acids?

Answer 6

HCl, H₂SO₄, CH₃COOH

Question 6

What is meant by complete dissociation of an acid?

Answer 6

All the acid molecules donate their protons (H⁺) in water – this is a strong acid.

Question 7

What is meant by partial dissociation of an acid?

Answer 7

Only some of the acid molecules donate protons – this is a weak acid.

Question 8

Which acids are strong acids?

Answer 8

Hydrochloric acid (HCl), sulfuric acid (H₂SO₄), nitric acid (HNO₃).

Question 9

Which acids are weak acids?

Answer 9

Ethanoic acid (CH₃COOH), carbonic acid (H₂CO₃).

Question 10

What is meant by “conjugate acid-base pairs”?

Answer 10

Two species that differ by a single proton (H⁺).

Question 11

Give an example of a conjugate acid-base pair.

Answer 11

HCl / Cl⁻ or NH₄⁺ / NH₃.

Question 12

What is the method for an acid-base titration?

Answer 12

1. Fill burette with acid, pipette alkali into conical flask. 2. Add indicator. 3. Titrate acid into alkali until endpoint is reached (colour change). 4. Repeat for concordant results.

Question 13

What indicators are used in titration?

Answer 13

Phenolphthalein and methyl orange.

Question 14

What colour change does phenolphthalein show?

Answer 14

Pink in alkali, colourless in acid.

Question 15

What colour change does methyl orange show?

Answer 15

Yellow in alkali, red in acid.

Question 16

Why is a white tile placed under the conical flask in titrations?

Answer 16

To help see the colour change more clearly.

Question 17

How should results from a titration be recorded?

Answer 17

In a results table with initial and final burette readings to two decimal places.

Question 18

What is a concordant result in titrations?

Answer 18

Two titres within 0.10 cm³ of each other.

Question 19

What is the purpose of a rough titration?

Answer 19

To estimate where the endpoint is so future titrations are more accurate.

Question 20

Why is only a single indicator used in titrations?

Answer 20

To produce a clear, sharp colour change at the endpoint.

Question 21

What are the safety considerations during titrations?

Answer 21

Wear goggles and gloves, treat unknown chemicals as toxic, rinse spills.

Question 22

What’s the correct way to calculate mean titre?

Answer 22

Only average concordant results (within 0.10 cm³ of each other).

Question 22

Why do we rinse the pipette and burette before use?

Answer 22

To prevent contamination or dilution affecting concentration.

Question 22

What is meant by ‘titre’?

Answer 22

The volume of acid required to neutralise the alkali.

Question 23

Does rinsing with water affect titration results?

Answer 23

No, water does not react or affect the number of moles.

Question 23

Why is distilled water used during titrations?

Answer 23

To rinse the sides of the flask, ensuring all acid and alkali react.

Question 24

What is percentage uncertainty?

Answer 24

% uncertainty = (uncertainty ÷ quantity measured) × 100.

Question 24

What is the difference between a reading and a measurement?

Answer 24

Reading = 1 judgement (e.g. thermometer) Measurement = 2 judgements (e.g. burette).

Question 24

Why is it important to remove air bubbles from the burette tap?

Answer 24

Air bubbles can cause inaccurate readings and affect titre.

Question 25

What are assumed uncertainties for instruments if not stated?

Answer 25

Analogue: ±0.5 of smallest division; Digital: ±1 in last digit.

Question 25

How do you reduce percentage uncertainty in weighing?

Answer 25

Weigh larger masses or use a more precise balance.

Question 26

How do you reduce uncertainty in titration?

Answer 26

Use more concentrated acid/base or larger volumes.

Question 27

What’s a common titration question for vinegar?

Answer 27

Find concentration of ethanoic acid in vinegar using NaOH and titration – answer = 64.8 g dm⁻³.

Question 28

How do you determine the % of CaCO₃ in a tablet?

Answer 28

React tablet with excess HCl, titrate leftover HCl with NaOH, calculate reacted acid → % CaCO₃ = 87.9%.

Question 29

How do you identify an unknown metal in M₂CO₃?

Answer 29

Use titration data to find Mr → determine metal identity (e.g., K⁺).

Question 30

How do you calculate % difference from actual value?

Answer 30

(Actual − Experimental) ÷ Actual × 100.

Question 31

How do you justify if a % error is acceptable?

Answer 31

Compare % difference with % uncertainty of apparatus used.

Question 32

What are amphoteric substances?

Answer 32

Substances that can act as acids and bases.

Question 33

How are ammonium salts formed?

Answer 33

When acid reacts with aqueous ammonia.

Question 34

What are hydrated crystals?

Answer 34

A crystalline structure containing water

Question 35

What are anhydrous crystals?

Answer 35

A crystalline structure that contains no water

Question 36

What does a dot formula indicate?

Answer 36

The amount of water present in a crystalline structure.