Question

40 cm3 of a solution of hydrated barium chloride , BaCl•xH2O, contain 1.952g of salt.
A) what is the mass concentration of the solution?
B) given that the concentration of the solution is 0.2 mol dm-3, find the value of x in the formula?

Answer 1

Question #83316

40 cm³ of a solution of hydrated barium chloride, BaCl·xH₂O, contain 1.952 g of salt.

A) what is the mass concentration of the solution?

B) given that the concentration of the solution is 0.2 mol dm⁻³, find the value of x in the formula?

Solution:

First of all, it is necessary to pay attention to the mistake in the formula of barium chloride – the correct chemical formula of barium chloride is BaCl₂.

A) According to the equation of the mass concentration [1], the mass concentration of the solution is:

$$\rho_{i} = \frac{m_{i}}{V} = \frac{1.952}{40} = 0.0488 \, \text{g/ml}$$

B) First of all, it is necessary to find out the molecular mass of BaCl₂·xH₂O:

$$\begin{array}{l} \vartheta (\mathrm{BaCl_2 \cdot xH_2O}) = 0.2 \, \frac{\text{mol}}{l} \cdot 0.04 \, l = 0.008 \, \text{mol} \\ M (\mathrm{BaCl_2 \cdot xH_2O}) = \frac{1.952 \, \text{g}}{0.008 \, \text{mol}} = 244 \, \text{g/mol} \\ \end{array}$$

As the molecular mass of BaCl₂ is equal to 208 g/mol, the difference between the hydrated barium chloride and pure barium chloride is equal to the contribution of water molecules in this salt:

$$244 - 208 = 36$$

As the molecular mass of water is equal to 18, the value of x is equal to:

$$x = \frac{36}{18} = 2$$

Answer:

A) The mass concentration of the solution is 0.0488 g/ml.

B) The value of x in the formula is 2.

Reference:

[1] https://en.wikipedia.org/wiki/Mass_concentration_(chemistry)

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