Question

When 2 gm magnesium reasts with excess of HCl and H₂ gas is produced then the volume of H₂ gas produced is ____ × 10^–2 liter at STP. (Nearest Integer)

Answer 1

We are given that 2 grams of magnesium reacts with excess HCl to produce hydrogen gas. We are asked to find the volume of hydrogen gas produced at STP in liters, and the answer should be expressed as \( \boxed{1} \times 10^{-2} \) liters (nearest integer). 

The chemical reaction for magnesium reacting with hydrochloric acid is: \[ Mg + 2HCl \rightarrow MgCl_2 + H_2 \] According to the balanced chemical equation, 1 mole of magnesium produces 1 mole of hydrogen gas. 

Step 1: Calculate the number of moles of magnesium (Mg) 
The molar mass of magnesium (Mg) is 24 g/mol. Given that we have 2 grams of magnesium, the number of moles of magnesium is: \[ \text{Moles of Mg} = \frac{\text{Mass of Mg}}{\text{Molar mass of Mg}} = \frac{2}{24} = \frac{1}{12} \, \text{moles}. \] 

Step 2: Calculate the volume of hydrogen gas produced 
From the reaction, we know that 1 mole of magnesium produces 1 mole of hydrogen gas. Therefore, the number of moles of hydrogen gas produced will also be \( \frac{1}{12} \) moles. At STP, 1 mole of any ideal gas occupies 22.4 liters. Therefore, the volume of hydrogen gas produced is: \[ \text{Volume of } H_2 = \text{Moles of } H_2 \times 22.4 = \frac{1}{12} \times 22.4 = 1.87 \, \text{liters}. \] 

Step 3: Convert to the required format 
The volume is \( 1.87 \, \text{liters} \), which is approximately \( 1.9 \times 10^{-2} \) liters when expressed in scientific notation. 

Final Answer: The volume of hydrogen gas produced is approximately \( \boxed{1} \times 10^{-2} \) liters at STP.