Grade 10 Physical Sciences · Chemical Change

Calculate molar mass

Add up the atomic masses in a formula to find molar mass in g/mol (H₂O is 2 × 1 + 16 = 18 g/mol).

past paper questions use it: 11 past paper questions use it
videos: 4 videos

Learn it: calculate molar mass

Pick one and watch it, then try the questions below. Videos load only when you tap play.

How To Calculate Molar MassMiss Martins Maths and Science

Calculating Mole Grade 10 | Part 1Kevinmathscience

How To Calculate The Molar Mass of a Compound - Quick & Easy!The Organic Chemistry Tutor

Water of Crystallization | Chemistry Grade 10-12Miss Martins Maths and Science

Now try it on a real exam question

No sign-up. Takes 3 minutes.

Question 7.6 · November 2024 · Paper 2 · National (DBE) · 5 marks

Hydrated potassium carbonate,

K_{2} CO_{3} \cdot x H_{2} O

, is a WEAK BASE. A solution is prepared by dissolving some of this solid in water.

The above

K_{2} CO_{3}

solution used in the titration, was prepared by completely dissolving

6, 525

g of the hydrated potassium carbonate,

K_{2} CO_{3} \cdot x H_{2} O

, in

600

^{3}

water.

7.6 Calculate the value of

x

in the formula

K_{2} CO_{3} \cdot x H_{2} O

.(5)

Work it out on paper first. Then mark yourself with the official memo, one tick at a time.

More past paper questions: calculate molar mass

Work each one out first, then open the memo and check every tick.

3. Question 8.3.1 · November 2024 · Paper 2 · Provincial · 2 marks
There are several steps in the production of fertelisers. In the third step, nitrogen dioxide is absorbed by water to produce nitric acid. Nitric acid and ammonia can react together in an acid-base process to form the salt, ammonium nitrate, which is soluble in water.

$3 NO_{2} (g) + H_{2} O(ℓ) \to 2 HNO_{3} (aq) + NO(g)$

$NH_{3} (ℓ) + HNO_{3} (ℓ) \to NH_{4} NO_{3} (s)$
8.3 Calculate the:
8.3.1 molecular mass of ammonium nitrate.(2)
Show the memo (2 ticks)Memo
1. ✓
  Sum of atomic masses $M (NH_{4} NO_{3}) = 14 + 4 (1) + 14 + 3 (16)$
  1 mark · Calculate molar mass
2. ✓
  Answer with unit $= 80$ g·mol $^{- 1}$
  1 mark · Calculate molar mass
4. Question 6.5 · November 2023 · Paper 2 · Provincial · 2 marks
In the reaction below, $3$ g of $Na_{2} CO_{3}$ were reacted with hydrochloric acid solution and an effervescence is observed.

$Na_{2} CO_{3} + HC ℓ \to NaC ℓ + CO_{2} + H_{2} O$
6.5 Calculate the molar mass of $Na_{2} CO_{3}$ .(2)
Show the memo (1 tick)Memo
1. ✓
  Molar mass $M (Na_{2} CO_{3}) = (2 \times 23) + 12 + (3 \times 16)$
  $= 106$ g·mol $^{- 1}$
  2 marks · Calculate molar mass
5. Question 6.3.2 · November 2025 · Paper 2 · Provincial · 5 marks
A certain organic compound ( $CxHyOz$ ) is composed of $54, 54$ g of carbon; $9, 1$ g of hydrogen and $36, 36$ g of oxygen and has a molecular mass of $88$ g·mol $^{- 1}$ .
6.3 A bottle in a laboratory contains an unknown metal hydroxide (MOH). A lab technician dissolves $1, 826$ g of the metal hydroxide to make a $100$ cm $^{3}$ solution.

Upon analysis it was found that the concentration of the metal hydroxide is $0, 326$ mol·dm $^{- 3}$ .

Answer the questions that follow.
6.3.2 Determine by calculation, the name of the metal hydroxide.(5)
Show the memo (5 ticks)Memo
1. ✓
  OPTION 1: Substitution into n = cV $n = c V$
  $n = (0, 326) (0, 1)$
  $n = 0, 0326$ mol
  1 mark · Calculate concentration of a solution
2. ✓
  OPTION 1: Formula M = m/n $M = \frac{m}{n}$
  1 mark · Calculate number of moles
3. ✓
  OPTION 1: Substitution $M = \frac{1 , 826}{0 , 0326}$
  $M = 56$ g·mol $^{- 1}$
  1 mark · Calculate number of moles
4. ✓
  OPTION 1: Subtract O and H $M + 16 + 1 = 56$
  1 mark · Calculate molar mass
5. ✓
  OPTION 1: Identify the metal hydroxide $M = K^{+}$
  MOH = Potassium hydroxide
  1 mark · Calculate molar mass
6. Question 5.3 · November 2023 · Paper 2 · Provincial · 3 marks
An unknown organic compound has a formula of $C_{x} H_{y} O_{z}$ . The molar mass of this compound is $88$ g·mol $^{- 1}$ .
5.3 Determine the molecular formula of this compound.(3)
Show the memo (3 ticks)Memo
1. ✓
  Molar mass of empirical formulaEmpirical formula molar mass $= 44$ g·mol $^{- 1}$
  1 mark · Calculate molar mass
2. ✓
  Ratioratio $= \frac{88}{44} = 2$
  1 mark · Determine empirical and molecular formulae
3. ✓
  Molecular formulaMolecular formula $= C_{4} H_{8} O_{2}$
  1 mark · Determine empirical and molecular formulae

Free on Android

Know exactly which skill is costing you marks.

Mark past papers tick by tick in the NavyBlue app. It remembers every mark you lose, shows you the skills to fix first, and picks your next questions.

The NavyBlue app showing a learner's weak skills