Question

Calcium nitrate tetrahydrate dissolves in cold water to the extent of 266 g per 100 cm3. What is the concentration of nitrate ions in this solution? a. 32.4 M b. 22.5 M c. 11.3 M d. 16.2 M e. 8.10 M

Answer 1

Answer : The correct option is, (b) 22.5 M

Explanation : Given,

Mass of calcium nitrate tetrahydrate = 266 g

Molar mass of calcium nitrate tetrahydrate  = 236.15 g/mole

Volume of solution = $100cm^3=100mL$

Molarity : It is defined as the moles of solute present in one liter of solution.

Formula used :

$Molarity=\frac{\text{Mass of calcium nitrate tetrahydrate }\times 1000}{\text{Molar mass of calcium nitrate tetrahydrate }\times \text{volume of solution in ml}}$

Now put all the given values in this formula, we get:

$Molarity=\frac{266g\times 1000}{236.15g/mole\times 100ml}=11.26mole/L=11.26M$

As calcium nitrate tetrahydrate dissociate to give 1 mole of calcium ion, 2 moles of nitrate ion and 4 moles of water.

The concentration of nitrate ion = $2\times 11.26M=22.5M$

Thus, the concentration of nitrate ion is, 22.5 M