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Stoichiometry - Engineering

Q1:

In the reaction, Ca + 2H2O = Ca(OH)2 + H2 ; what volume (c.c.) of hydrogen at STP would be liberated, when 8 gm of calcium reacts with excess water ? (atomic weight of calcium = 40)

A 4480

B 2240

C 1120

D 0.4

ANS:A - 4480

To solve this problem, we need to follow these steps:

  1. Determine the moles of calcium (Ca) reacting.
  2. Use the stoichiometry of the reaction to find the moles of hydrogen (H2) produced.
  3. Apply the ideal gas law to calculate the volume of hydrogen at STP.
Given:
  • Mass of calcium (Ca) = 8 g
  • Atomic weight of calcium (Ca) = 40 g/mol
  • Reaction: Ca + 2H2O → Ca(OH)2 + H2
  1. Moles of calcium: Moles of Ca=MassMolar mass=8 g40 g/mol=0.2 molMoles of Ca=Molar massMass​=40g/mol8g​=0.2mol
  2. According to the balanced chemical equation, 1 mole of calcium reacts to produce 1 mole of hydrogen gas: So, moles of hydrogen produced = 0.2 mol.
  3. At STP (Standard Temperature and Pressure), 1 mole of any gas occupies 22.4 liters or 22.4 * 1000 c.c. Volume of hydrogen at STP=moles of hydrogen×22.4 liters/mol×1000 c.c./literVolume of hydrogen at STP=moles of hydrogen×22.4liters/mol×1000c.c./liter Volume of hydrogen=0.2 mol×22.4 liters/mol×1000 c.c./liter=4480 c.c.Volume of hydrogen=0.2mol×22.4liters/mol×1000c.c./liter=4480c.c.
So, the volume of hydrogen gas liberated at STP when 8 g of calcium reacts with excess water is 4480 c.c. Therefore, the correct answer is 4480.