A weighed sample of crystalline sodium carbonate (Na2CO3.nH2O)was heated in a crucible until there was no further change in mass.The mass of the sample reduced by 14.5%.Calculate the number of moles (n) of the water of crystallization.

Answer 1

To calculate the number of moles of water of crystallization (n), we first need to calculate the change in mass.

Change in mass = Initial mass - Final mass
= 100% - 14.5%
= 85.5%

Next, we convert the percentage change in mass to a decimal:

Change in mass (decimal) = 85.5% / 100
= 0.855

Now, we can calculate the number of moles of water using the formula:

n = (Change in mass / Molar mass of water) / (Change in mass / Molar mass of water + Molar mass of anhydrous compound)

The molar mass of water (H2O) = 2 * (atomic mass of hydrogen) + atomic mass of oxygen
= 2 * 1 + 16
= 18 g/mol

The molar mass of anhydrous compound (Na2CO3) = 2 * (atomic mass of sodium) + atomic mass of carbon + 3 * (atomic mass of oxygen)
= 2 * 23 + 12 + 3 * 16
= 106 g/mol

Substituting the values into the formula:

n = (0.855 / 18) / (0.855 / 18 + 106)
= 0.0475 / (0.0475 + 106)
= 0.0475 / 106.0475
≈ 0.000448 mol

Therefore, the number of moles (n) of water of crystallization is approximately 0.000448 mol.