Frequently Asked Question

Equation of reaction

Na2CO3.xH2O(aq) + 2HCl(aq) ---→ 2NaCl(aq) + H2O(l) + CO2(g)

Concentration of base

Using the formula:
Moles of HCl = Concentration of HCl * Volume of HCl

Moles of HCl = 0.16 mol/dm3 * 13.20 cm3 / 1000 cm3/dm3

Moles of HCl = 2.112 * 10^-3 mol

Since the mole ratio of HCl to Na2CO3.xH2O is 2:1, the moles of Na2CO3.xH2O is half the moles of HCl:

Moles of Na2CO3.xH2O = 2.112 * 10^-3 mol / 2

Moles of Na2CO3.xH2O = 1.056 * 10^-3 mol

Concentration of base = Moles of base / Volume of base

Concentration of base = 1.056 * 10^-3 mol / 25 cm3 * 10^-3 dm3/cm3

Concentration of base = 0.04224 mol/dm3

Molar mass of the base

Using the formula:
Molar mass = Mass of base / Moles of base

Moles of base = 1.056 * 10^-3 mol

Mass of base = 3 g

Molar mass = 3 g / 1.056 * 10^-3 mol

Molar mass = 284.2 g/mol

Value of x

The molar mass of anhydrous sodium trioxocarbonate(iv) (Na2CO3) is 106 g/mol. Therefore, the molar mass of the water of crystallization is:

Molar mass of water of crystallization = Molar mass of base - Molar mass of Na2CO3

Molar mass of water of crystallization = 284.2 g/mol - 106 g/mol

Molar mass of water of crystallization = 178.2 g/mol

The empirical formula of the water of crystallization is H2O, which has a molar mass of 18 g/mol. Therefore, the value of x is:

x = Molar mass of water of crystallization / Molar mass of H2O

x = 178.2 g/mol / 18 g/mol

x = 9.9

Percentage by mass of water of crystallization

Using the formula:
Percentage by mass of water of crystallization = (Mass of water of crystallization / Molar mass of base) * 100%

Mass of water of crystallization = (Value of x * Molar mass of H2O) = 9.9 * 18 g/mol = 178.2 g

Percentage by mass of water of crystallization = (178.2 g / 284.2 g) * 100%

Percentage by mass of water of crystallization = 62.7%