Some Basic Concepts in Chemistry: Chemistry | JEE Main
Zinc reacts with hydrochloric acid to give hydrogen and zinc chloride. The volume of hydrogen gas produced at STP from the reaction of 11.5 g of zinc with excess HCl is L (Nearest integer)
(Given : Molar mass of Zn is 65.4 g mol−1 and Molar volume of H2 at STP=22.7 L )
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Hint 1 of 3
What is the stoichiometric ratio between Zn and H₂ in the reaction between zinc and hydrochloric acid?
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Correct answer
The volume of hydrogen gas produced at STP is approximately 4 L.
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Solution
StepWorking
01given
Mass of Zn=11.5 g, molar mass of Zn=65.4 g mol−1, molar volume of gas at STP=22.7 L mol−1.
02find
Volume of H2 gas produced at STP in liters (rounded to the nearest integer).
03visualise
Balanced reaction equation: Zn+2HCl→ZnCl2+H2(g). One mole of Zn produces one mole of H2.
04strategise
Calculate the moles of Zn consumed, relate to moles of H2 produced by stoichiometry (1:1), and multiply by molar volume (22.7 L mol−1).
05execute
nH2=nZn=65.411.5≈0.17584 molVH2=0.17584×22.7=3.9916 L≈4 L
✓verify
11.5/65.4≈1/5.7≈0.175. 0.175×22.7≈3.99, which rounds to 4. The unit is liters and magnitude is physically expected.
Hints that build this answer step by step
What is the stoichiometric ratio between Zn and H₂ in the reaction between zinc and hydrochloric acid?
1 mol Zn produces 1 mol H₂
How many moles of Zn are present in 11.5 g of Zn (molar mass = 65.4 g mol⁻¹)?
n = 11.5 / 65.4 ≈ 0.176 mol
What is the volume of hydrogen gas produced at STP using the given molar volume of 22.7 L mol⁻¹, rounded to the nearest integer?
Under the current IUPAC definition of STP (1 bar and 273.15 K), the molar volume of an ideal gas is 22.7 L/mol, whereas 22.4 L/mol was for 1 atm. Follow the value given explicitly in the question.