Stoichiometry: Mole To Mass Problems 1. Mg + 2HCl → MgCl2 + H2 A. How Many Grams Of HCl Are Consumed By The Reaction Of 3 Moles Of Magnesium? B. What Is The Mass In Grams Of H, Gas When 5.0 Moles Of HCl Is Added To The Reaction?
The Correct Answer and Explanation is :
Stoichiometry: Mole to Mass Problems
Given Reaction:
[
\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2
]
A. How Many Grams of HCl Are Consumed by the Reaction of 3 Moles of Magnesium?
Step 1: Identify the Mole Ratio
From the balanced chemical equation, 1 mole of Mg reacts with 2 moles of HCl.
Step 2: Calculate Moles of HCl Needed
[
3 \text{ moles Mg} \times \frac{2 \text{ moles HCl}}{1 \text{ mole Mg}} = 6 \text{ moles HCl}
]
Step 3: Convert Moles of HCl to Mass
The molar mass of HCl is:
[
\text{HCl} = 1.01 + 35.45 = 36.46 \text{ g/mol}
]
[
6 \text{ moles HCl} \times 36.46 \text{ g/mol} = 218.76 \text{ g HCl}
]
Answer: 218.76 g of HCl
B. What Is the Mass in Grams of H₂ Gas When 5.0 Moles of HCl Is Added?
Step 1: Identify the Mole Ratio
From the balanced reaction:
[
2 \text{ moles HCl} \rightarrow 1 \text{ mole H}_2
]
Step 2: Calculate Moles of H₂ Formed
[
5.0 \text{ moles HCl} \times \frac{1 \text{ mole H}_2}{2 \text{ moles HCl}} = 2.5 \text{ moles H}_2
]
Step 3: Convert Moles of H₂ to Mass
Molar mass of H₂:
[
2.02 \text{ g/mol}
]
[
2.5 \text{ moles H}_2 \times 2.02 \text{ g/mol} = 5.05 \text{ g H}_2
]
Answer: 5.05 g of H₂
Explanation (300 Words)
Stoichiometry is the study of quantitative relationships in chemical reactions. It helps us determine how much reactant is needed or how much product is formed. In this case, we use stoichiometry to convert between moles and mass.
For the first problem, we start with 3 moles of Mg and use the balanced equation to find the amount of HCl required. The reaction shows that 1 mole of Mg reacts with 2 moles of HCl, so 3 moles of Mg will need 6 moles of HCl. Then, using the molar mass of HCl (36.46 g/mol), we convert the moles into grams, obtaining 218.76 g.
For the second problem, we determine how much hydrogen gas is produced when 5.0 moles of HCl reacts. According to the reaction, 2 moles of HCl produce 1 mole of H₂ gas. Using this mole ratio, 5.0 moles of HCl will produce 2.5 moles of H₂. Converting moles of H₂ to grams using its molar mass (2.02 g/mol), we get 5.05 g.
This method works for any stoichiometry problem by following these steps:
- Write a balanced equation.
- Use mole ratios to find the required reactant or product.
- Convert moles to grams using molar mass.
Stoichiometry is essential in chemistry as it helps predict reaction outcomes, ensuring the correct amount of reactants is used to avoid waste and optimize reactions.