S2 Chemistry – Acids and Alkalis

S2 Chemistry – Acids and Alkalis

🧪 S2 Chemistry — Acids & Alkalis

Safety: acids and alkalis can be irritant or corrosive. Wear eye protection in practical work, and wash hands after.

Practice papers

Use these like a real test: no notes, then mark, then fix mistakes using the Knowledge Organiser.

Open the papers

Open practice papers PDF Open Knowledge Organiser
How to use them (simple routine)do this
  1. Open the paper. Hide the answers page.
  2. Do it without notes.
  3. Mark it using the answers/marking.
  4. Write corrections using the Knowledge Organiser (not “I understand”).
  5. Redo the questions you got wrong 24 hours later.
Rule: If you didn’t write the unit / label / method, it’s not finished.

Key ideas

pH

  • Acid: pH below 7
  • Neutral: pH 7
  • Alkali: pH above 7
  • Dilution: pH moves towards 7.

Oxides in water

  • If the oxide is insoluble → no solution → pH stays 7.
  • Metal oxide that dissolves → alkaline (pH > 7).
  • Non-metal oxide that dissolves → acidic (pH < 7).

Neutralisation

  • acid + alkali → salt + water
  • acid + carbonate → salt + water + carbon dioxide
  • Salt name = metal (from base/carbonate) + ending (from acid)
⭐ One-sentence answers (tap to open)quick marks
  • Acid = pH below 7.
  • Alkali = pH above 7.
  • Neutralisation makes salt and water.
  • Insoluble oxide in water → pH stays 7 because no solution forms.
  • Dilution makes pH move towards 7.

Interactive pH scale

Slide the pH value. Watch the description update.

pH slider

pH 7 is neutral.
Dilution rule: Diluting an acid makes pH go up towards 7. Diluting an alkali makes pH go down towards 7.

Helpful examples

  • pH 1–3: strong acid
  • pH 4–6: weak acid
  • pH 7: neutral
  • pH 8–10: weak alkali
  • pH 11–14: strong alkali
Mini self-check (random)🎲

Tap 🎲 New numbers for a fresh set.

1) Classify by pH

A solution has pH ?. Is it an acid, neutral, or alkali?

2) More acidic

Which is more acidic: pH ? or pH ??

3) Universal indicator colour (approx)

Predict the universal indicator colour for pH ?.

Hint: pH below 7 = acid • pH 7 = neutral • pH above 7 = alkali.

Indicators

Choose an indicator and a pH. It will show the expected colour.

Indicator colour tool

Pick an indicator and pH, then press Show colour.

Quick reminder

  • Universal indicator shows a wide range of colours across the pH scale.
  • Methyl orange: red in acid, orange in neutral, yellow in alkali.

Neutralisation (and salt naming)

The papers test: identify the salt, name the acid from the salt, and use the patterns reliably.

Build a word equation

Press Build to generate the equation.
⭐ Patterns to remembereasy marks
acid + alkali → salt + water
acid + carbonate → salt + water + carbon dioxide

The salt name comes from: (acid gives the ending) + (metal from the base/carbonate).

  • Hydrochloric acid → chloride
  • Sulfuric acid → sulfate
  • Nitric acid → nitrate

Real-life neutralisation examples

  • Bee sting is acidic → can be neutralised by a weak alkali (e.g. baking soda).
  • Toothpaste can help neutralise acids in your mouth.
  • Soil that is too acidic can be treated with lime.

Oxides + solubility

The key exam idea: if the oxide is insoluble, there is no solution… so pH stays 7.

Oxide rule (3 lines)

  • Insoluble oxide → no solution → pH stays 7.
  • Metal oxide that dissolves → alkali (pH > 7).
  • Non-metal oxide that dissolves → acid (pH < 7).
Common trap (tap to open)don’t lose marks
Trap: “An oxide is added to water” does not automatically mean pH changes. If it’s insoluble, pH stays 7.

Oxide predictor (interactive)

Choose oxide type + solubility, then press Predict pH.

Acid rain + lime calculations

Key facts

  • Acid rain gases: sulphur dioxide and nitrogen dioxide.
  • Carbon dioxide makes rainwater slightly acidic, but does not cause acid rain.
  • Car engines (sparking air) can form nitrogen oxides (including nitrogen dioxide).

Graphs

Reminder: Use graph paper for bar charts.

Marking checklist (2 marks)

  • 1 mark: title + labelled axes + sensible scale
  • 1 mark: correct plotting (bars the right height)
Graph self-check (tap to open)before you hand in
  • I used graph paper.
  • I wrote a title.
  • I labelled x-axis (solution names) and y-axis (pH).
  • I used a sensible scale (even steps).
  • I plotted bars to the correct height.

Generate a bar-chart dataset

Press 🎲 Generate, then draw a bar chart on graph paper.

Tap 🎲 Generate to get a table.

Fertilisers

You need: the three elements, the reason farmers use fertilisers, a % mass calculation, and one environment issue.

Must-know facts

  • Essential elements: nitrogen, phosphorus, potassium.
  • Why fertilisers are used: replace nutrients removed when crops are harvested / help plants grow better.
  • Very soluble fertilisers can wash into rivers → algae blooms / eutrophication.
  • To reduce soil acidity: add lime (calcium compounds).
  • Calcium flame colour: orange-red / brick red.
  • Natural fertiliser example: manure / compost.

Quick check

Short questions. Instant feedback. Score saves on this device.

✅ Start the quick checktap to open

Questions (10)

🎲 Extra random questions (tap to open)new set

Tap 🎲 New extra questions for a fresh set.

Tip: If you miss a question, open the Knowledge Organiser and write the correct sentence, then re-try.

Links (use these to practise)

Use the Knowledge Organiser and practice papers as your main tools. These are extra.

Knowledge Organiser (KO) MAIN

Key definitions, pH, oxides, acid rain, neutralisation, fertilisers, graph skills.

Practice Papers PDF

Practice Test 1, Practice Test 2, and a Challenge Test (with answers/marking).

🔎 BBC Bitesize (search) read

Use for extra explanations and examples.

🧪 PhET simulations interactive

Explore pH / acids & bases simulations if available.

Readiness (G / A / R) — saved on this device

Tap each statement and choose G, A, or R.

Simple rule: if you have no Reds, you’re in a good place. If you have Reds, fix your top 2 first (using the Knowledge Organiser).
pH + dilutionG/A/R
Oxides + solubilityG/A/R
Acid rain + lime calculationsG/A/R
Graphs (bar charts)G/A/R
FertilisersG/A/R
Neutralisation + saltsG/A/R
Answering like a scientistG/A/R
    Revision tracker (ticks + progress)tap to open

    Ticks save on this device.