Question

A container contains mixture of He and Ne gases at certain temperature. He is 20 % by mass of mixture. What is the ratio of partial pressure of Helium to Neon ?

• A. \(1:2\)
• B. \(2:1\)
• C. \(5:4\)
• D. \(3:2\)

Hint:

Partial pressure ratio equals the mole ratio, so convert 20 g He and 80 g Ne into moles.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
In an ideal gas mixture at one temperature and volume, the partial pressure of each gas is proportional to its number of moles. So the ratio of partial pressures equals the ratio of moles.

Step 2: Key Formula or Approach:
\[ p_i = x_i P_{\text{total}}, \qquad \frac{p_{He}}{p_{Ne}} = \frac{n_{He}}{n_{Ne}} \]
Molar masses: He = 4 g/mol, Ne = 20 g/mol.

Step 3: Detailed Explanation:
Take 100 g of the mixture. Then He is 20 g and Ne is 80 g.
\[ n_{He} = \frac{20}{4} = 5 \text{ mol} \]
\[ n_{Ne} = \frac{80}{20} = 4 \text{ mol} \]
Ratio of partial pressures:
\[ \frac{p_{He}}{p_{Ne}} = \frac{5}{4} \]
Using the mass ratio 20:80 = 1:4 directly would be a mistake, since pressure depends on moles and not on mass. Options (A) 1:2 and (B) 2:1 do not follow from these moles, and option (D) 3:2 would need 6 mol He for 4 mol Ne.

Final Answer:
The ratio of the partial pressure of helium to neon is 5:4, option (C). \[ \boxed{5:4 \text{ (C)}} \]