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Solutions question

2016 · Shift 0 · Q3
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Solutions question

2016 · Shift 0 · Q3

JEE MainChemistrySolutionsMCQ+4 / −1
18 g glucose (C6H12O6C_6H_{12}O_6C6​H12​O6​) is added to 178.2 g water. The vapor pressure of water (in torr) for this aqueous solution is :
  1. A
    76.0
  2. B
    752.4
  3. C
    759.0
  4. D
    7.6
View written solutionFree

Correct answer: B

  1. Use Raoult’s law for a non-volatile solute

Since glucose is a non-volatile solute, only water contributes to vapor pressure.

Psolution=Xwater⋅Pwater∘P_{\text{solution}} = X_{\text{water}} \cdot P^\circ_{\text{water}}Psolution​=Xwater​⋅Pwater∘​

Here, Pwater∘=760 torrP^\circ_{\text{water}} = 760\ \text{torr}Pwater∘​=760 torr.

  1. Calculate moles of glucose

Molar mass of glucose, C6H12O6C_6H_{12}O_6C6​H12​O6​:

6(12)+12(1)+6(16)=72+12+96=180 g mol−16(12) + 12(1) + 6(16) = 72 + 12 + 96 = 180\ \text{g mol}^{-1}6(12)+12(1)+6(16)=72+12+96=180 g mol−1

So,

nglucose=18180=0.1 moln_{\text{glucose}} = \frac{18}{180} = 0.1\ \text{mol}nglucose​=18018​=0.1 mol

  1. Calculate moles of water

Molar mass of water = 18 g mol−118\ \text{g mol}^{-1}18 g mol−1

nwater=178.218=9.9 moln_{\text{water}} = \frac{178.2}{18} = 9.9\ \text{mol}nwater​=18178.2​=9.9 mol

  1. Find mole fraction of water

Xwater=nwaternwater+nglucose=9.99.9+0.1=9.910.0=0.99X_{\text{water}} = \frac{n_{\text{water}}}{n_{\text{water}} + n_{\text{glucose}}} = \frac{9.9}{9.9 + 0.1} = \frac{9.9}{10.0} = 0.99Xwater​=nwater​+nglucose​nwater​​=9.9+0.19.9​=10.09.9​=0.99

  1. Calculate vapor pressure of the solution

Psolution=0.99×760=752.4 torrP_{\text{solution}} = 0.99 \times 760 = 752.4\ \text{torr}Psolution​=0.99×760=752.4 torr

  1. Match with the options

The correct option is:

B: 752.4 torr\boxed{\text{B: } 752.4\ \text{torr}}B: 752.4 torr​

  1. Comparison with stored answer

Stored correct answer: B

My derived answer: B

So, the derived answer agrees with the stored answer.

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