Answer to Question #140948 in Chemistry for Hanna Faith Dagar

Question

What is the molality of 25.0 grams of KBr dissolved in 750.0 mL pure water?

Answer 1

Molality is calculated using thee following formula:

molality = moles of solute / mass of solvent (in kg)

The number of moles of KBr can be determined as following:

n = m / Mr

where n - number of moles, m - mass, Mr - molecular weight.

n (KBr) = 25.0 g / 119 g/mol = 0.21 mol

From here, as 750.0 mL of pure water weight 750.0 g:

molality (KBr) = 0.21 mol / 750.0 g = 0.21 mol / 0.75 kg = 0.28 mol/kg

Answer: 0.28 mol/kg