Question 2 of 36intermediate🔧 ApplyNumerical3 marks

Calculate the mass per cent of different elements present in sodium sulphate (Na₂SO₄).

Correct Answer

The mass per cent of Sodium (Na) is 32.39%, Sulphur (S) is 22.54%, and Oxygen (O) is 45.07%.

Exercise: EXERCISES | Q: 1.2 | (Page 25)
For More Understanding

Explanation

To find the mass per cent of elements in a compound, we first determine the molar mass of the compound by summing the atomic masses of its constituent elements. Then, we use the mass per cent formula: (Mass of the element in one mole of the compound / Molar mass of the compound) × 100. Using atomic masses from the context (Na = 23.0 u, O = 16.00 u) and standard atomic mass for S (32.0 u), the molar mass of Na₂SO₄ is calculated as 142.0 g/mol.

Solution Steps

  1. Step 1: Calculate the molar mass of sodium sulphate (Na2SO4Na_2SO_4) Molar mass of Na2SO4Na_2SO_4 = 2×23.0+32.0+4×16.002 \times 23.0 + 32.0 + 4 \times 16.00 = 46.0+32.0+64.0=142.0 g mol−146.0 + 32.0 + 64.0 = 142.0 \text{ g mol}^{-1}

  2. Step 2: Calculate the mass per cent of Sodium (Na) Mass per cent of Na = Mass of NaMolar mass of Na2SO4×100\frac{\text{Mass of Na}}{\text{Molar mass of } Na_2SO_4} \times 100 = 2×23.0142.0×100=46.0142.0×100=32.39%\frac{2 \times 23.0}{142.0} \times 100 = \frac{46.0}{142.0} \times 100 = 32.39\%

  3. Step 3: Calculate the mass per cent of Sulphur (S) Mass per cent of S = Mass of SMolar mass of Na2SO4×100\frac{\text{Mass of S}}{\text{Molar mass of } Na_2SO_4} \times 100 = 32.0142.0×100=22.54%\frac{32.0}{142.0} \times 100 = 22.54\%

  4. Step 4: Calculate the mass per cent of Oxygen (O) Mass per cent of O = Mass of OMolar mass of Na2SO4×100\frac{\text{Mass of O}}{\text{Molar mass of } Na_2SO_4} \times 100 = 4×16.00142.0×100=64.0142.0×100=45.07%\frac{4 \times 16.00}{142.0} \times 100 = \frac{64.0}{142.0} \times 100 = 45.07\%

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