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A solution containing 30 g of non-volati...

A solution containing 30 g of non-volatile solute exactly in 90 g of water has a vapour pressure of 2.8 kPa at 298 K. Further 18 g of water is then added to this solution, the new vapour pressure becomes 2.9 kPa at 298 K. Calculate (i) the molar mass of solute, (ii) vapour pressure of water at 298 K.

Text Solution

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Case I `(p_A^0 -p_A)/(p_A^0) = (w_B //M_B)/(w_A // M_A)`
Substituting the values, we have
`(p_A^0 - 2.8)/(p_A^0) = (30 // M_B)/(90 //18) = (6)/(M_B) " or " (p_A^0 - 2.8)/(p_A^0) = (6)/(M_B)` ....(i)
Case II `(p_A^0 -2.9)/(p_A^0) = (30//M_B)/(108//18) = (5)/(M_B) " or " (p_A^0 - 2.9)/(p_A^0) = (5)/(M_B)` ...(ii)
Dividing equation (i) by (ii), we get
`(p_A^0 - 2.8)/(p_A^0 - 2.9) = 6/5`
On solving we get `p_A^0 = 3.4 kPa`
ubstituting the value of `p_A^0` in equation (i), we get
`(3.4-2.8)/(3.4) = ( 6)/(M_B) " or " M_B = 34` g/mol
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A solution containing 30 g of a non-volatile solute exactly in 90 g water has a vapour pressure of 2.8 kPa at 298 K. Further 18 g of water is then added to the solution, the new vapour pressure becomes 2.9 kPa at 298 K. Calculate (i) molar mass of the solute. (ii) vapour pressure of water at 298 K.

A solution containing 30 g of non-volatile solute exactly in 90 g of water has a vapour pressure of 2.8 kPa at 298 K. Further, 18 g of water is then added to the solution and the new vapour pressure becomes 2.9 kPa at 298 K. Calculate : (i) molar mass of the solute (ii) vapour pressure of water at 298 K.

Knowledge Check

  • A solution containing 30g of a non-volatile non-electrolyte solute exactly in 90g water has a vapour pressure of 2.8 kPa at 298K. Further, 18g of water is then added to solution, the new vapour pressure becomes 2.9kPa at 298K. The solutions obey Raoult's law and are not dilute, molar mass of solute is

    A
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    B
    `34 g mol^(-1)`
    C
    `43g mol^(-1)`
    D
    `32 g mol^(-1)`

  • In a solution of 90 g water, 30 g of non-volatile solute is present which has exactly a vapor pressure of 2.8kPa at 298 K. On further addition of 18 g water to the solution, the new vapour pressure of the solution becomes 2.9 kPa at 298 K. Determine (i) the molecular weight of the solute (ii) vapor pressure of water at 298 K

    A
    `23"g mol"^(-1), 3.53`
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    `26"g mol"^(-1), 3.53`
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  • A solution containing 0.5g of a non-volatile solute in 0.2dm^(3) of the solution exerts an osmotic pressure of 44.44 kPa at 300K . Thus, molar mass of the solute is

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