Question

What will be the freezing point of an aqueous solution containing 80 g of NaCl? 

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Answer 1

Assuming the 80.0g are dissolved in 3.4L of water.

$\Delta\>T_f=K_f×m.i$

Molar mass of NaCl $=58.44g/mol$

Moles of NaCl $=1.3689$ moles

Density of water $=1kg/L$

Mass of 3.4L of water $=3.4kg$

Concentration of NaCl $=\frac{1.3689}{3.4}=0.4026m/kg$

$K_f$ of water $=-1.86°c/M$

$i=2$

$\Delta\>T_f=-1.86×0.4026×2$

$=-1.4977°c$

Freezing point $=0+-1.4977$

$=-1.5°c$