A 24.6\text{ g} sample of hydrated magnesium tetraoxosulfate(VI), \text{MgSO}_4 \cdot x\te… — JAMB UTME

A $24.6\text{ g}$ sample of hydrated magnesium tetraoxosulfate(VI), $\text{MgSO}_4 \cdot x\text{H}_2\text{O}$ , was heated strongly until all the water of crystallization was driven off, leaving behind $12.0\text{ g}$ of anhydrous $\text{MgSO}_4$ . What is the value of $x$ ? $[\text{Mg} = 24, \text{S} = 32, \text{O} = 16, \text{H} = 1]$

Cevap: 7

Cevap

The value of

x

is 7.

Heating the sample evaporates

12.6\text{ g}

of water of crystallization (

24.6\text{ g} - 12.0\text{ g}

). Converting the masses to moles gives

0.1\text{ mol}

of anhydrous

\text{MgSO}_4

(

12.0\text{ g} / 120\text{ g/mol}

) and

0.7\text{ mol}

\text{H}_2\text{O}

(

12.6\text{ g} / 18\text{ g/mol}

). The mole ratio of water to salt is

0.7 / 0.1 = 7

, which means

x = 7

Adım Adım Çözüm

Calculate the mass of water of crystallization lost during heating.

Mass of water =

24.6\text{ g} - 12.0\text{ g} = 12.6\text{ g}

The decrease in mass after heating represents the mass of water driven off from the hydrated salt.

Determine the molar masses of

\text{MgSO}_4

and

\text{H}_2\text{O}

Molar mass of

\text{MgSO}_4 = 24 + 32 + (4 \times 16) = 120\text{ g/mol}

; Molar mass of

\text{H}_2\text{O} = (2 \times 1) + 16 = 18\text{ g/mol}

Molar masses are required to convert the measured masses into chemical amounts (moles).

Calculate the number of moles of anhydrous salt and water.

Moles of

\text{MgSO}_4 = \frac{12.0\text{ g}}{120\text{ g/mol}} = 0.1\text{ mol}

; Moles of

\text{H}_2\text{O} = \frac{12.6\text{ g}}{18\text{ g/mol}} = 0.7\text{ mol}

The chemical formula stoichiometry is determined by the molar ratio of components.

Determine the mole ratio of water to anhydrous salt (

x

x = \frac{\text{Moles of } \text{H}_2\text{O}}{\text{Moles of } \text{MgSO}_4} = \frac{0.7\text{ mol}}{0.1\text{ mol}} = 7

The coefficient

x

is the integer ratio of moles of water of crystallization per mole of anhydrous salt.

Anahtar Kavram

Water of Crystallization Stoichiometry

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

Sık Yapılan Hatalar

Konular