Skip to main content
Next exam on November 14 – 15, 2026:
All concepts

Solution Composition and Concentration

溶液组成与浓度计算

What a solution is made of, saturation and solubility, calculating molar concentration and mass fraction, and the conservation of solute on dilution.

12 real-exam questions · 4 sittings14 in mock papers17 practice

Formulas

  • Molar concentration

    Definition
    c=nVc=\frac{n}{V}

    Applies when：V is the volume of the solution, not of the solvent; units mol/L

  • Dilution law

    Law
    c1V1=c2V2c_1V_1=c_2V_2

    Applies when：The amount of solute is unchanged by dilution; valid only when diluting, not reacting

  • Mass fraction of solute

    Definition
    w=msolutemsolution×100%w=\frac{m_{\text{solute}}}{m_{\text{solution}}}\times 100\%

    Applies when：The denominator is the mass of the solution (solute plus solvent), not of the solvent

How the real exam tests it

Questions from real CSCA papers that test this concept. Work each one out before you open the answer.

  1. CSCA Chemistry December 2025 Past Paper
    Which of the following is a solution? ( )
    • A. Distilled water
    • B. Normal saline (physiological saline)
    • C. Peanut oil
    • D. Cement slurry
    Show answer & solution

    Answer: B

    Answer: B A solution is a homogeneous, stable mixture. Normal saline is an aqueous solution of NaCl. Distilled water is a pure substance, peanut oil is not a solution of a solute in a solvent, and cement slurry is a suspension, not homogeneous.
    See it in the full CSCA Chemistry December 2025 Past Paper
  2. CSCA Chemistry April 2026 Past Paper
    The method to change a saturated NaCl solution into an unsaturated solution is ( ).
    • A. Evaporating the solvent
    • B. Adding solid NaCl
    • C. Lowering the temperature
    • D. Adding water
    Show answer & solution

    Answer: D

    Answer: D Adding water turns a saturated NaCl solution into an unsaturated one.
    Take the full CSCA Chemistry April 2026 Past Paper — timed & graded
  3. CSCA Chemistry March 2026 Past Paper
    Which liquid is an emulsion?
    • A．Milk
    • B．Sugar water
    • C．Muddy water
    • D．Iodine tincture
    Show answer & solution

    Answer: A

    Milk = fat droplets in water = emulsion. B: solution. C: suspension. D: solution. Answer: A.
    Take the full CSCA Chemistry March 2026 Past Paper — timed & graded

Real-exam evidence

Recorded past-paper appearances are listed below; online verification is labelled separately.

12 questions across 4 sittings1 of 4 sittings available to verify free online

14 questions across 5 mock papers — our own papers, so a coverage signal rather than real-exam evidence

17 related practice questions availablePractise free: Mole CalculationsPractise free: Electrolyte Solution Theory

Sitting evidence comes from the CSCA past papers on record; questions whose original paper is missing are excluded, and sprint papers are deliberately not counted.

Glossary

mole

Related concepts

Classification of MatterAmount of Substance