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Standard XII

Chemistry

Molality

If the densit...

Question

If the density of some lake water is $1.25 g m L^{- 1}$ and contains $92 g$ of $N a^{+}$ ions per kg of water, calculate the molality of $N a^{+}$ ions in the lake.

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Solution

Mass of sodium ions $= 92$ g

Molar mass of sodium ions $= 23$ g/mol

Number of moles of sodium ions $= \frac{92 g}{23 g / m o l} = 4$

Mass of water $= 1$ kg

Molality $= \frac{number of moles of sodium ions}{Mass of water (in kg)} = \frac{4}{1} = 4$ m

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If the density of some lake water is $1.25 g m L^{- 1}$ and contains 92 g of $N a^{+}$ ions per kg of water, calculate the molarity of $N a^{+}$ ions in the lake.

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If the density of some lake water is 1.25g mL−1 and contains 92 g of Na+ ions per kg of water, calculate the molality of Na+ ions in the lake.

Mass of sodium ions =92 gMolar mass of sodium ions =23 g/molNumber of moles of sodium ions =92g23g/mol=4Mass of water =1 kgMolality =number of moles of sodium ionsMass of water (in kg)=41=4 m

If the density of some lake water is $1.25 g m L^{- 1}$ and contains $92 g$ of $N a^{+}$ ions per kg of water, calculate the molality of $N a^{+}$ ions in the lake.

Mass of sodium ions $= 92$ g

Molar mass of sodium ions $= 23$ g/mol

Number of moles of sodium ions $= \frac{92 g}{23 g / m o l} = 4$

Mass of water $= 1$ kg

Molality $= \frac{number of moles of sodium ions}{Mass of water (in kg)} = \frac{4}{1} = 4$ m