Question

The formula for hydrated copper(ii) nitrate is Cu(NO3)2.xH2O. It contains 36.5% water crystallization by mass.

Answer 1

Answer:

6

Explanation:

The percent mass is equal to the ratio between the mass of the component of interest and the total mass of the compound, multiplied by 100 % in case we need to express it as a percentage.

We may apply this knowledge to write the formula for copper(II) nitrate x-hydrate. Let's assume that we take 1 mole of the compound. Then we will divide x molar masses of water by the molar mass of the overall compound and multiply by 100 % to get the mass percent of water:

$\omega = \frac{xM_{H_2O}}{M_{total}}\cdot 100\%$

Here:

$M_{H_2O} = 18.016 g/mol$

$M_{total} = M_{Cu(NO_3)_2} + xM_{H_2O} = (187.56 + 18.016x) g/mol$

Substitute into the formula:

$\frac{18.016x}{187.56 + 18.016x} = 0.365$

Solve for x:

$18.016x = 0.365(187.56 + 18.016x)$

$18.016x = 68.46 + 6.58x$

$11.44x = 68.46\therefore x = 6$