Chemistry · Unit 7

Acids, Bases and pH

Acids, alkalis and neutralisation

Acids and bases are defined by what they do with hydrogen ions, and once that definition is in place the rest of the unit follows from it.

It covers acids, bases and alkalis, the pH scale, neutralisation and the salts it produces, and the distinction between a strong acid and a concentrated one.

This unit breaks down into 20 short steps and 120 questions, starting at difficulty 1 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps: 20
Questions: 120
Difficulty: 1-3

What this unit covers

Acids
Bases and Alkalis
The pH Scale
Neutralisation and Salts
Strong and Weak Acids

Where this fits

Needs Chemical Reactions and ideally Moles and Calculations.

Where people slip

Strong and concentrated are unrelated. Strong means fully dissociated; concentrated means a lot of it per litre. A dilute strong acid and a concentrated weak one are entirely different things.

How the unit is structured

Acids, Bases and pH runs as 20 short steps that unlock in order. 15 are practice rounds and 5 are challenge rounds that pull together everything before them. Questions start at difficulty 1 and climb to 3 as you progress.

Step 1 · easierStep 20 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 120 in the unit altogether.

Acids

Fill the blankLevel 1
1. The acid found in vinegar is ____ acid.
- ethanoiccorrect
- citric
- sulfuric
- carbonic
Vinegar is a dilute solution of ethanoic acid (also called acetic acid).
Multiple choiceLevel 1
2. H2SO4 is the chemical formula for which acid?
- Sulfuric acidcorrect
- Hydrochloric acid
- Nitric acid
- Carbonic acid
H2SO4 is sulfuric acid, a strong acid used in car batteries and industry.
Build the sentenceLevel 2
3. Build the general word equation for the reaction of an acid with a reactive metal.
Answer: acid + metal -> salt + hydrogen
A reactive metal reacts with an acid to give a salt plus hydrogen gas, e.g. Mg + 2HCl -> MgCl2 + H2.
Odd one outLevel 2
4. Which is the odd one out?
- Sodium hydroxidecorrect
- Sulfuric acid
- Nitric acid
- Citric acid
Sodium hydroxide is a base (alkali); the others are all acids.
Guess the numberLevel 3
5. How many equivalence points appear on the titration curve of a diprotic acid, such as ethanedioic (oxalic) acid H2C2O4, being neutralised by a strong base?
Answer: 2 equivalence points
A diprotic acid has two removable protons, so its titration curve shows two separate equivalence points.
Match the pairsLevel 3
6. Match each acid to its conjugate base (the species left after it donates one proton).
Answer: HCl = Cl-; HNO3 = NO3-; H2SO4 = HSO4-; HF = F-
A conjugate base forms by removing one H+ from the acid, so H2SO4 gives HSO4- rather than SO4^2-.

Bases and Alkalis

Fact or fibLevel 1
7. An alkali is a base that dissolves in water.
Answer: True
An alkali is simply a soluble base; all alkalis are bases, but not all bases dissolve in water.
Fill the blankLevel 1
8. The alkaline gas with a sharp smell, used in some cleaning products, is ____.
- ammoniacorrect
- oxygen
- nitrogen
- methane
Ammonia (NH3) is a weakly alkaline gas that dissolves in water and smells sharp.
Multiple choiceLevel 1
9. What is the chemical name for NaOH?
- Sodium hydroxidecorrect
- Sodium chloride
- Sodium carbonate
- Sodium oxide
NaOH is sodium hydroxide, a common strong alkali used in soap making and drain cleaner.
Match the pairsLevel 2
10. Match each base to its chemical formula.
Answer: Sodium hydroxide = NaOH; Potassium hydroxide = KOH; Calcium hydroxide = Ca(OH)2; Ammonia = NH3
Sodium hydroxide is NaOH, potassium hydroxide is KOH, calcium hydroxide is Ca(OH)2 and ammonia is NH3.
Picture questionLevel 2
11. 🧼 Which of these substances is alkaline and turns red litmus paper blue?
- Soap solutioncorrect
- Lemon juice
- Vinegar
- Fizzy cola
Soap solution is mildly alkaline, so it turns red litmus blue, whereas lemon juice, vinegar and cola are acidic.
Guess the numberLevel 3
12. Calculate the pH of a 0.1 mol/dm3 solution of the strong base NaOH at 25 C. (Since [OH-] = 0.1, pOH = 1.)
Answer: 13 pH
NaOH fully dissociates so [OH-] = 0.1, giving pOH = 1; then pH = 14 - pOH = 13.

Neutralisation and Salts

Multiple choiceLevel 1
13. An acid reacting with a base always produces a salt and what else?
- Watercorrect
- Hydrogen
- Oxygen
- Carbon dioxide
Neutralisation follows the pattern acid + base -> salt + water.
Build the sentenceLevel 2
14. Build the products of a neutralisation reaction: an acid and an alkali make a...
Answer: salt and water
An acid neutralised by an alkali produces a salt and water.
Choose all that applyLevel 2
15. When a dilute acid reacts with a metal carbonate, which products are formed? (Select all that apply.)
- A saltcorrect
- Watercorrect
- Carbon dioxidecorrect
- Hydrogen gas
Acid + metal carbonate -> salt + water + carbon dioxide; no hydrogen gas is released.
Guess the numberLevel 2
16. In a titration of a strong acid with a strong alkali, what is the pH at the equivalence point?
Answer: 7 pH
When a strong acid exactly neutralises a strong base, the salt solution formed is neutral, so the pH is 7.
Match the pairsLevel 2
17. Match each acid to the family of salt it forms.
Answer: Hydrochloric acid = Chloride; Sulfuric acid = Sulfate; Nitric acid = Nitrate; Phosphoric acid = Phosphate
Hydrochloric acid makes chlorides, sulfuric acid makes sulfates, nitric acid makes nitrates and phosphoric acid makes phosphates.
Odd one outLevel 3
18. Three of these salts give an alkaline solution in water. Which is the odd one out (it gives an acidic solution)?
- NH4Clcorrect
- Na2CO3
- CH3COONa
- KF
Na2CO3, CH3COONa and KF are all salts of weak acids and give alkaline solutions; NH4Cl is the salt of a weak base and is acidic.

Strong and Weak Acids

Multiple choiceLevel 1
19. Which ion is responsible for making a solution acidic?
- Hydrogen ion (H+)correct
- Hydroxide ion (OH-)
- Sodium ion (Na+)
- Chloride ion (Cl-)
The hydrogen ion (H+) is what makes a solution acidic.
Choose all that applyLevel 2
20. Select the strong acids.
- Hydrochloric acidcorrect
- Nitric acidcorrect
- Citric acid
- Ethanoic acid
Hydrochloric and nitric acids are strong acids; citric and ethanoic acids are weak acids.
Fact or fibLevel 2
21. The words 'strong' and 'concentrated' mean exactly the same thing for acids.
Answer: False
They are different: strength is how much an acid ionises, while concentration is how much acid is dissolved in the water.
Fill the blankLevel 2
22. A weak acid only ____ ionises when dissolved in water.
- partiallycorrect
- fully
- never
- instantly
Weak acids such as ethanoic acid only partially ionise, so fewer H+ ions are released.
Odd one outLevel 2
23. Which is the odd one out?
- Ethanoic acidcorrect
- Hydrochloric acid
- Sulfuric acid
- Nitric acid
Ethanoic acid is a weak acid; hydrochloric, sulfuric and nitric acids are all strong acids.
Put in orderLevel 3
24. Order these acids from weakest to strongest using their pKa values.
Answer: Phenol (pKa 10.0) -> Ethanoic acid (pKa 4.8) -> Methanoic acid (pKa 3.8) -> Chloroethanoic acid (pKa 2.9)
A higher pKa means a weaker acid, so weakest-to-strongest runs from phenol down to chloroethanoic acid.

The pH Scale

Fact or fibLevel 1
25. A solution with a pH greater than 7 is alkaline.
Answer: True
Values above 7 on the pH scale are alkaline, while values below 7 are acidic.
Fill the blankLevel 1
26. Universal indicator turns ____ in a neutral solution.
- greencorrect
- red
- purple
- orange
Universal indicator is green at pH 7, showing the solution is neutral.
Guess the numberLevel 1
27. On the pH scale, what is the pH of a neutral solution such as pure water?
Answer: 7 pH
Pure water is neutral with a pH of 7, exactly in the middle of the 0-14 pH scale.
Multiple choiceLevel 1
28. What colour does blue litmus paper turn in an acid?
- Redcorrect
- Blue
- Green
- Purple
Acids turn blue litmus paper red; alkalis turn red litmus blue.
Match the pairsLevel 3
29. Match each acid-base indicator to its approximate pKin value.
Answer: Methyl orange = pKin about 3.7; Methyl red = pKin about 5.1; Bromothymol blue = pKin about 7.0; Phenolphthalein = pKin about 9.3
Common indicators have different pKin values, so each is chosen for titrations whose equivalence point lies near that pH: methyl orange ~3.7, methyl red ~5.1, bromothymol blue ~7.0, phenolphthalein ~9.3.
Picture questionLevel 3
30. 📈 This titration curve has a buffer region on the way up and a single steep vertical jump centred above pH 7. Which titration produced it?
- A weak acid titrated with a strong basecorrect
- A strong acid titrated with a strong base
- A strong acid titrated with a weak base
- A weak base titrated with a weak acid
A weak acid titrated with a strong base has a buffer region early on and an equivalence point above pH 7, because the salt formed is slightly alkaline.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 17 different question formats, so you are recalling and applying rather than recognising the same layout every time.

Build the sentence
Choose all that apply
Fact or fib
Fill the blank
Guess the number
Listen and choose
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sequence recall
Sort into groups
Spell it
Tap the pairs
True or false
Type the answer

Practise Acids, Bases and pH

120 questions across 20 steps. Start with step one and crawl at your own pace.

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Read about Acids, Bases and pH

Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.

Acids, Bases, and the pH Scale in Everyday LifeAcids and bases appear in food, cleaning, digestion, soil, and water. The pH scale helps you compare them without turning chemistry into a swamp of mysterious numbers.July 24, 2026 · 6 min read

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