This reference lists the quantities and units used in SPM Chemistry, from mass and moles to concentration and energy, with the metric prefixes and the key conversions such as 1 dm3 equals 1000 cm3. Correct units are needed for every calculation mark.
Many calculation marks are won or lost on units alone, because a right number with a wrong or missing unit does not score fully. This reference sets out the quantities and units used across SPM Chemistry, together with the metric prefixes and the conversions you use most, arranged the way the DSKP expects. Keep it beside your working so that every answer carries the correct unit and every conversion between cm3 and dm3, or grams and kilograms, is done cleanly.
Scope note
The tables below hold the standard KSSM units and prefixes for Form 4 and Form 5 calculations. They cover the quantities the syllabus tests and the conversions that appear in mole, concentration, gas-volume and thermochemistry questions. Learn the symbol as well as the name, because the exam writes units in symbol form.
Quantities and their units
| Quantity | Unit | Symbol |
|---|---|---|
| Mass | gram, kilogram | g, kg |
| Amount of substance | mole | mol |
| Molar mass | grams per mole | g mol-1 |
| Volume | cubic centimetre, cubic decimetre | cm3, dm3 |
| Concentration (by mass) | grams per cubic decimetre | g dm-3 |
| Concentration (molarity) | moles per cubic decimetre | mol dm-3 |
| Temperature | degree Celsius, kelvin | °C, K |
| Time | second, minute | s, min |
| Heat / energy | joule, kilojoule | J, kJ |
| Heat of reaction | kilojoules per mole | kJ mol-1 |
| Rate of reaction | per second (volume or concentration change) | cm3 s-1, mol dm-3 s-1 |
| Molar volume of gas | cubic decimetres per mole | dm3 mol-1 |
Metric prefixes
| Prefix | Symbol | Multiplying factor |
|---|---|---|
| mega | M | x 1 000 000 (10^6) |
| kilo | k | x 1000 (10^3) |
| deci | d | x 0.1 (10^-1) |
| centi | c | x 0.01 (10^-2) |
| milli | m | x 0.001 (10^-3) |
| micro | u | x 0.000001 (10^-6) |
| nano | n | x 10^-9 |
Key conversions
The conversions you use most are worth memorising exactly. One cubic decimetre equals one thousand cubic centimetres and is the same as one litre: 1 dm3 = 1000 cm3 = 1 litre. For mass, 1 kg = 1000 g. For temperature, a value in kelvin equals the Celsius value plus 273, so 25 °C is 298 K. In the mole chapter, the molar volume of a gas is 24 dm3 mol−1 at room conditions and 22.4 dm3 mol−1 at STP, and the Avogadro constant is 6.02 x 1023 mol−1. Using these standard values with the right units is what makes a calculation answer complete.
Worked conversion
Suppose a titration uses 25.0 cm3 of acid and you need the volume in dm3 for a concentration calculation. Divide by 1000: 25.0 cm3 becomes 0.025 dm3, and only then is it ready to multiply by a concentration in mol dm−3 to give moles. A common slip is to forget this step and work in cm3, which makes the final concentration a thousand times too large or too small. The same care applies to mass: if a sample is given as 0.5 kg, change it to 500 g before dividing by a molar mass in g mol−1. Doing the conversion first, and writing the unit at every line, keeps the whole calculation consistent and easy to check.
Common mistakes to avoid
- Leaving out the unit, or writing the wrong one, so a correct number does not score full marks.
- Forgetting to convert cm3 to dm3 in a concentration or gas-volume calculation.
- Mixing grams and kilograms in the same working.
- Writing molarity without dm−3, or heat of reaction without mol−1.
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Our online one-to-one teachers make unit checking part of every calculation, so you never lose a mark to a missing dm3 or a forgotten conversion. Lessons are in English, one to one, from RM50 per hour, with a paid one-hour trial. Because units run through every quantitative topic from the mole to thermochemistry, keeping them tidy is one of the simplest and most reliable ways to lift your Paper 2 marks.
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