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  • Solve! 8 g of NaOH is dissolved in 18 g of H2O. Mole fraction of NaOH in solution and molality (in mol kg-1) of the solution respectively are :

8 g of NaOH is dissolved in 18 g of H2O. Mole fraction of NaOH in solution and molality (in mol kg-1) of the solution respectively are :

 

  • Option 1)

    0.2, 11.11

  • Option 2)

    0.167, 11.11

  • Option 3)

    0.2, 22.20

  • Option 4)

    0.167, 22.20

Answers (1)

best_answer

 

Molality -

Molality (m) = (number of moles of solute)/(mass of solvent in kg)

 

- wherein

It is defined as the number of moles of solute present in 1 kg of solvent. It is denoted by m.

 

 

Mole Fraction -

It is the ratio of moles of solute or moles of solvent to moles of the solution.

- wherein

If a substance ‘A’ dissolves in substance ‘B’ and their number of moles are n_{A} and n_{B} respectively; then the mole fractions of A and B are given as

Mole fraction of A = (number of moles of A)/(number of moles of solution ) = n_{A}/(n_{A}+ n_{B})

As we have learned in mole concept

8g NaOH, Mole \: of NaOH=  \frac{8}{40}=0.2mol

18g H_{2}O,mol\: \: of H_{2}O=\frac{18}{18}=1 mol

\therefore X_{NaOH}=\frac{0.2}{1.2}=0.167

molality =\frac{0.2\times 1000}{18}=11.11m

 


Option 1)

0.2, 11.11

Option 2)

0.167, 11.11

Option 3)

0.2, 22.20

Option 4)

0.167, 22.20

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