Answer to Question #163134 in General Chemistry for Jay

Question

What is the molar mass of glucose if a solution containing 18.00 g of glucose in 150 g of water boils at 100.34 degrees centigrade?

Answer 1

b = $\frac{\Delta T_b}{K_b}$

b= molarity of solution

$\Delta T_b$ = 100.34 - 100 = 0.34 ⁰C

K_b = ebullioscopic constant = 0.512 ⁰C Kg/mol

b = $\frac{0.34}{0.512}$ = 0.664 mol/Kg

This means that you have 0.664 moles of glucose for every 1 kg of water. The number of moles you'll have in 150 g of water will be

150 g × $\frac{0.664 mol}{1000g}$ = 0.0996 moles

0.0996 moles × $\frac{molar mass of glucose} {1 mole }$ = 18.9 g

molar mass of glucose = 189.75 g