If 1.75kg of water is boiling at 100 C, what ass of NaCl (M=58.44 g/mole) would need to be added to the water to increase the boiling point by 2.5 C?

Question

A common practice in cooking is the addition of salt to boiling water (Kbp=0.52 C/m). One of the reasons for this might be to raise the temperature of the boiling water. If 1.75kg of water is boiling at 100 C, what ass of NaCl (M=58.44 g/mole) would need to be added to the water to increase the boiling point by 2.5 C?

Answer 1

T_b=ik_bm

T= change in boiling point: given as 2.5

i= vant hoff factor: 2 because NaCl breaks apart into 2 particles

k= constant: 0.512 for water

m=molality: we need to solve for this

2.5=(2)(.512)(m)

m=2.44

m=moles of solute/kg of solution

2.44=moles Nacl/1.75kg

moles Nacl=4.272

4.272 mol x (58.44g/mol)=249.68 g