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Boiling point of water at 750 mm Hg is 99.63 degree C. How much sucrose is to be added to 500 g of water such that it boils at 100 degree C.

2.10    Boiling point of water at 750 \; mm \; Hg  is  99.63^{\circ}C. How much sucrose is to be added to 500 \; g of water such that it boils at 100^{\circ}C.

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Here we will use the formula :

                                                            \Delta T_b = \frac{K_b\times1000\times w_2}{M_2\times w_1}

Elevation in temperature =  100 -  99.63  =  0.37 

 Kb = 0.52 ;     Molar\ mass\ of\ sucrose = 11(12) + 22(1) + 11(16) = 342\ g\ mol^{-1}

Putting all values in above formula, we get :

                            w_2 = \frac{0.37\times342\times500}{0.52\times1000}= 121.67\ g

Thus 121.67 g of sucrose needs to be added.

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