Chemistry Q138 – AP-EAMCET 2025

Home Chemistry ElectrochemistryQuestion #388

Electrolysis of aqueous solution of potassium acetate gives an alkane (

x

) and

{CO}_{2} (y)

at anode. The volume ratio of these two gases

x

and

y

at STP is respectively

Clue 1 of 3: Kolbe's Electrolysis

Understand the products formed at the anode during the electrolysis of an aqueous solution of a carboxylic acid salt.

🧠 Full Solution Path

Step 1: Identifying the Electrolytic Reaction✦ Active

The question describes the electrolysis of an aqueous solution of potassium acetate. This is a classic example of Kolbe's electrolytic synthesis. Potassium acetate ( ${CH}_{3} COOK$ ) dissociates into ${CH}_{3} {COO}^{-}$ and $K^{+}$ ions in water. At the anode, oxidation of the acetate ion occurs.

💡 Teacher's Secret Hint

Remember that in Kolbe's electrolysis, the carboxylate ion loses electrons to form a free radical, which then dimerizes to form an alkane and releases carbon dioxide.

Step 2: Formulating the Anode Reaction○ Expand

At the anode, the acetate ions ( ${CH}_{3} {COO}^{-}$ ) are oxidized to produce an alkane (ethane, ${CH}_{3} {CH}_{3}$ ) and carbon dioxide ( ${CO}_{2}$ ). The balanced reaction is:

2 {CH}_{3} {COO}^{-} \overset{electrolysis}{\to} {CH}_{3} - {CH}_{3} (x) + 2 {CO}_{2} (y) + 2 e^{-}

💡 Teacher's Secret Hint

Don't forget to balance the equation for both atoms and charge. The number of electrons lost must correspond to the change in oxidation states.

Step 3: Calculating the Mole Ratio of Products○ Expand

From the balanced anode reaction, we can see the stoichiometric coefficients for the gaseous products:

- 1 mole of alkane ( $x$ , ethane, ${CH}_{3} {CH}_{3}$ )

- 2 moles of carbon dioxide ( $y$ , ${CO}_{2}$ )

Therefore, the mole ratio of $x$ to $y$ is $1 : 2$ .

Step 4: Determining the Volume Ratio at STP○ Expand

According to Avogadro's Law, at Standard Temperature and Pressure (STP), equal moles of any gas occupy equal volumes. This means the volume ratio of gases is directly proportional to their mole ratio.

\frac{Volume of x}{Volume of y} = \frac{Moles of x}{Moles of y} = \frac{1}{2}

Thus, the volume ratio of the alkane ( $x$ ) to ${CO}_{2}$ ( $y$ ) at STP is $1 : 2$ .

💡 Teacher's Secret Hint

This principle is crucial for gas stoichiometry problems. Always remember that for gases at the same temperature and pressure, volume ratios are equivalent to mole ratios.

✦ STEM Console utilizes AI models to generate step-by-step explanations and math clues. AI can make mistakes.

Chemistry Question 138 – AP-EAMCET 2025

Clue 1 of 3: Kolbe's Electrolysis

🧠 Full Solution Path