Question

A 50.6 grams sample of magnesium hydroxide (Mg(OH)2) is reacted with 45.0 grams of hydrochloric acid (HCl). What is the theoretical yield of magnesium chloride (MgCl2)? Mg(OH)2 + 2 HCl MgCl2 + 2 H2O 29.3 grams

Answer 1

The answer is C, 58.6

Answer 2

Answer: The theoretical yield of magnesium chloride is 58.6 g

Explanation:

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$      .....(1)

• For magnesium hydroxide:

Given mass of magnesium hydroxide = 50.6 g

Molar mass of magnesium hydroxide = 58.32 g/mol

Putting values in equation 1, we get:

$\text{Moles of magnesium hydroxide}=\frac{50.6g}{58.32g/mol}=0.87mol$

• For HCl:

Given mass of HCl = 45.0 g

Molar mass of HCl = 36.5 g/mol

Putting values in equation 1, we get:

$\text{Moles of HCl}=\frac{45.0g}{36.5g/mol}=1.23mol$

• The chemical equation for the reaction of magnesium hydroxide and HCl follows:

$Mg(OH)_2+2HCl\rightarrow MgCl_2+2H_2O$

By Stoichiometry of the reaction:

2 moles of HCl reacts with 1 mole of magnesium hydroxide

So, 1.23 moles of HCl will react with = $\frac{1}{2}\times 1.23=0.615mol$ of magnesium hydroxide

As, given amount of magnesium hydroxide is more than the required amount. So, it is considered as an excess reagent.

Thus, HCl is considered as a limiting reagent because it limits the formation of product.

By Stoichiometry of the reaction:

2 moles of HCl produces 1 mole of magnesium chloride

So, 1.23 moles of HCl will produce = $\frac{1}{2}\times 1.23=0.615mol$ of magnesium chloride

• To calculate the theoretical yield of magnesium chloride we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

Molar mass of magnesium chloride = 95.21 g/mol

Moles of magnesium chloride = 0.615 moles

Putting values in above equation, we get:

$0.615mol=\frac{\text{Mass of magnesium chloride}}{95.21g/mol}\\\\\text{Mass of magnesium chloride}=(0.615mol\times 95.21g/mol)=58.6g$

Hence, the theoretical yield of magnesium chloride is 58.6 g