What mass of NaCl must be dissloved in 65.0g of water to lower the freezing point of water by `7.50^(@)` C? . The freezing point depression constant `(K_(f))` for water is `1.86^(@) C//m`. Assume Vant't Hoff factor for NaCl is 1.87.(Molar mass of NaCl = 58.5g)

Explanation

Here `M_(2) = 58.5 g mol^(-1), w_(1) = 65g, w_(2) = ?`
`DeltaT_(f) = 7.5^(@)C, i=1.87, K_(f) = 1.86 K kg mol^(-1)`
Using the formula, `DeltaT_(f) = iK_(f)m`
`DletaT_(f) = iK_(f) xx (w_(2) xx1000)/(M_(2)xxw_(1)) rArr 7.5 = 1.87 xx 1.86 xx (w_(2) xx 1000)/(58.5 xx 65)`
`:. w_(2) = (7.5 xx 58.5 xx 65)/(1.87 xx 1.86 xx 1000) = (28518.75)/(3478.2) = 8.188g`