112 ml of a gas is produced at S.T.P. by the action of 412 mg of alcohol ROH with CH3MgI. The molecular mass of alcohol is:
Correct answer: C. 82.4 g
- A. 32 g
- B. 41.2 g
- C. 82.4 g
- D. 156 g
Explanation
The correct answer is 82.4 g. The reaction between the alcohol ROH and CH3MgI produces CH4 as a gas. At STP, 22.4 liters of gas is equivalent to one mole of CH4. Given that 112 ml (0.112 liters) of CH4 is produced, this represents 0.112/22.4 moles of CH4. Since 412 mg (0.412 g) of alcohol produces this amount of CH4, the molar mass of alcohol is calculated as 0.412 g divided by 0.112/22.4, which equals 82.4 g. Other options are incorrect as they do not match this stoichiometric calculation.
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Mole calculations connect mass, number of particles and Avogadro's number, while balanced equations provide the mole ratios used in stoichiometry. Questions cover limiting and excess reactants, theoretical yield and percentage yield, including identifying which reactant is consumed first and comparing the actual product with the maximum possible product.
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