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WAEC Chemistry 2025 Paper

Question : 29

Total: 50

_2

_3

_2

_2

_3

_2

_2

O = 18 ]

Solution:

Concept:

The percentage by mass of water is found by dividing the mass of water in one mole of the hydrate by its total molar mass, then multiplying by

100

Explanation:

The hydrate is

\mathrm{Na_2CO_3 \cdot 10H_2O}

It contains

10

moles of water per mole of the hydrate.

Mass of water

= 10 \times 18 = 180

Total molar mass of the hydrate

= 286

Percentage of water

= \frac{180}{286} \times 100 = 62.9\%

Answer:

62.9\%

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