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Acids and bases — EST 2 Chemistry Revision Notes & Topical Questions

5 min read 8 parts Lesson 1 of 4 1 quiz

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Lesson summary

Acids and bases EST Chemistry notes: Compare acid–base definitions.Kw = [H+][OH−] = 1.0 × 10−14 at 25 °C.A change of 1 pH unit is a tenfold change in [H+].Strong vs weak describes ionisation; concentrated vs dilute describes amount.Water is amphotericit can act as acid or base.Ti…

  • Find the pH of 0.001 M HCl
  • 25.0 mL of NaOH is neutralised by 20.0 mL of 0.100 M HCl. Find [NaOH]
  • Acids and bases EST Chemistry: what to do next
  • Arrhenius acid
  • Arrhenius base
  • Brønsted–Lowry acid

Section 1 of 8Acids and bases

Litmus
Litmus red in acid, blue in base.
Phenolphthalein is colourless in acid, pink in base.
Polyprotic acids release H+ in steps.
Metal + acid gives salt + H2.
Carbonate + acid gives salt + water + CO2.

Section 2 of 8Process & sequence

1
Identify the species that gives or gains H+.
2
Write the conjugate base (acid minus H+) and conjugate acid (base plus H+).
3
For strong acids, [H+] = acid concentration.
4What the symbols mean:
pH = −log[H+]; pOH = −log[OH−].
What the symbols mean: pH has no unit · [H+] = concentration of hydrogen ions (mol dm−3); each 1 pH unit is a ten-fold change in [H+]
5
pH + pOH = 14 at 25 °C.

Solving a pH problemwrite these steps in this order; each step is a marking point.

  1. Strong or weak?
  2. Find [H+] or [OH−]
  3. Take −log
  4. Use pH + pOH = 14
  5. Classify solution

Section 3 of 8Compare

Three definitions
ModelAcidBaseExample
ArrheniusGives H+ in waterGives OH− in waterHCl, NaOH
Brønsted–LowryH+ donorH+ acceptorNH3 + H2O
Lewise−-pair acceptore−-pair donorBF3 + NH3
Common strong acids and bases
Strong acidsStrong bases
HCl, HBr, HILiOH, NaOH, KOH
HNO3, H2SO4, HClO4Ca(OH)2, Ba(OH)2
pH scale
pH[H+] (M)Nature
110−1Strongly acidic
710−7Neutral (25 °C)
1310−13Strongly basic

Section 4 of 8Worked examples

1Find the pH of 0.001 M HCl.
  • [H+] = 10−3; pH = 3.
225.0 mL of NaOH is neutralised by 20.0 mL of 0.100 M HCl. Find [NaOH].
  • Mb = 0.100 × 20.0 ÷ 25.0 = 0.0800 M.

Section 5 of 8Keep going

Acids and bases EST Chemistry: what to do next

These Acids and bases EST Chemistry notes covered the key ideas, worked examples and exam technique for this topic. Check your Acids and bases EST Chemistry understanding with the practice questions below, then reread any Acids and bases EST Chemistry point you were unsure about before moving on.

1
Practice: Acids and bases EST Chemistry practice questions
2
Previous lesson: 2.3 Solutions
3
Next lesson: 3.2 Oxidation and reduction
4
Course: EST 2 Chemistry — all units
5
Official syllabus: OpenStax free science textbooks

Acids and bases EST Chemistry revision notes

Section 6 of 8Key terms

Section 7 of 8Command terms

Command terms
Identify / Describe (FRQ)
A short, specific statement; describing requires relevant characteristics, not a single word.
Explain / Justify (FRQ)
Give the cause-and-effect reasoning or evidence; a restated fact does not score.
Calculate
Show setup, substitution and the answer with units.
Predict
State the expected outcome; add a reason only if asked to justify.
MCQ technique
Read every option; eliminate distractors that are true statements but do not answer the question; watch for NOT/EXCEPT.

Section 8 of 8Exam technique

Keywords the mark scheme looks for in this lesson

Keywords the mark scheme looks for in this lesson
Arrhenius acid · Arrhenius base · Brønsted–Lowry acid · Brønsted–Lowry base · Conjugate pair · Lewis acid · Strong acid · pH · Neutralization
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

1
Answer exactly what is asked; extra correct material does not earn credit, and contradictory statements can cancel credit (AP FRQ).
2
Use precise vocabulary (e.g. “active site”, “concentration gradient”, “allele”), never “it/stuff/things”.
3
Show units and working in calculations.
4
In MCQs, predict the answer before reading the options, then eliminate.

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