Question

0.1 mole of compound S will weigh ....... g, 
(given the molar mass in g mol\(^{-1}\) \( {C} = 12, \, {H} = 1, \, {O} = 16 )\):

Hint:

When solving questions related to moles and molecular weight, always use the molar mass formula: \[ {Molar mass} = \frac{{Mass of substance}}{{Number of moles}} \]

Answer 1

- The compound \( S \) is formed by reducing a secondary alcohol (ethanol) to a hydrocarbon (alkane). 
- First, ethanol (\( {CH}_3{CH}_2{OH} \)) reacts with chromium trioxide (\( {CrO}_3 \)) to form acetaldehyde (\( {CH}_3{CHO} \)). 
- Then, acetaldehyde undergoes reduction by sodium borohydride (\( {NaBH}_4 \)) to form ethanol (\( {CH}_3{CH}_2{OH} \)) again. 
- Further, the reaction with Grignard reagent (\( {CH}_3{MgI} \)) and water (\( {H}_2{O} \)) forms a secondary alcohol. 
- Since \( S \) is an alcohol, it will have the same molecular weight as ethanol. The molar mass of ethanol (\( {CH}_3{CH}_2{OH} \)) is calculated as: \[ 12 \times 2 + 1 \times 6 + 16 = 46 \, {g/mol} \] For \( 0.1 \) mole of \( S \), the weight is: \[ {Weight of } S = 0.1 \times 46 = 4.6 \, {g} \] Thus, \( 0.1 \) mole of compound S weighs \( 4.6 \) grams.