Multiple Choice Questions
Chemistry: Chemical Reactions and Stoichiometry
Topic: Chemical Reactions and Stoichiometry
Grade: 11
Question 1:
What is the balanced equation for the reaction between magnesium (Mg) and hydrochloric acid (HCl)?
a) Mg + HCl → MgCl2 + H2
b) Mg + 2HCl → MgCl2 + H2
c) Mg + HCl → MgCl + H2
d) 2Mg + HCl → MgCl2 + H2
Answer: b) Mg + 2HCl → MgCl2 + H2
Explanation: The balanced equation for the reaction between magnesium and hydrochloric acid is 2Mg + 2HCl → 2MgCl2 + H2. This is because the reaction requires two moles of hydrochloric acid to react with one mole of magnesium, resulting in the formation of two moles of magnesium chloride and one mole of hydrogen gas. The balanced equation reflects the conservation of mass, as the number of atoms of each element is the same on both sides of the equation.
Example 1: When 0.5 moles of magnesium reacts with excess hydrochloric acid, how many moles of hydrogen gas will be produced?
Solution: According to the balanced equation, 2 moles of magnesium react with 2 moles of hydrochloric acid to produce 1 mole of hydrogen gas. Therefore, if 0.5 moles of magnesium is used, the amount of hydrogen gas produced would be 0.25 moles.
Example 2: If 10 grams of magnesium reacts with 100 mL of 2M hydrochloric acid, what is the limiting reactant and how many grams of magnesium chloride will be formed?
Solution: To determine the limiting reactant, we need to compare the number of moles of each reactant. First, calculate the number of moles of magnesium by dividing the mass by its molar mass. Then, determine the number of moles of hydrochloric acid by multiplying the concentration (2M) by the volume in liters. The balanced equation tells us that 2 moles of magnesium react with 2 moles of hydrochloric acid to produce 2 moles of magnesium chloride. Therefore, whichever reactant has the smaller number of moles is the limiting reactant. Once the limiting reactant is identified, you can use stoichiometry to calculate the amount of magnesium chloride formed.