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Melvin Plant

What is the molarity of a sugar solution where 25g of sugar is dissolved in 500g of water? What is its molar fraction?

Cherie Valeithian  Follow

There are many different types of sugars so assuming you meant glucose whose chemical formula is C6H12O6

molarity= moles of solute/volume of solution

moles= mass/molar mass

mass of C6H12O6=25g

molar mass of C6H12O6=180g/mol

so

moles of C6H12O6=25/180=0.13888mol

H2O is the solvent whose volume is found by using the formula

density= mass/volume

so

volume= mass/density

knowing that the density of H2O= 1g/ml

while the given mass of H2O= 500g

plugging these values into the formula

volume of H2O=500/1=500ml

converting ml to liters

(1000ml=1L)

(500ml)*(1L)/(1000ml)=500/1000 =0.5L

the molarity of the sugar solution=0.13888/0.5=0.28M

the mole fraction of C6H12O6 in the solution is found by using the formula

X(C6H12O6)= moles of C6H12O6/moles of C6H12O6 + moles of H2O

where

X represents the mole fraction of a substance,

X(C6H12O6)= unknown

moles of C6H12O6=0.28mol

the moles of H2O= given mass of H2O/molar mass of H2O

moles of H2O=500/18=28moles

so

X(C6H12O6)=0.28/0.28+28

X(C6H12O6)=0.01

the mole fraction of H2O is found by knowing that the sum of all the mole fractions in a solution must =1

so

the mole fraction of H2O is

X(H2O)= 1–0.01=0.99

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Dennis Leppin  Follow

It is impossible to calculate the molarity of a solution prepared by dissolving 25 g sugar in 500 g of water . These figures are normally used when dealing with molaLity of solutions . Not molarity.

I will calculate molality :

Molality = moles of solute dissolved in 1.0 kg water .

You have 25 g sugar dissolved in 500 g water

This is the same as 50 g sugar dissolved in 1000 g water or 1.0 kg water .

Molar mass sugar = 342 g/mol

Mol sugar in 50 g = 50 g / 342 g/mol = 0.146 mol dissolved in 1.0 kg water

Molality = 0.146 m .

Mole fraction

Moles of sugar = 0.146 mol

Moles of water = 1000 g / 18 g/mol = 55.5 mol H2O

Total moles = 55.646

Mol fraction sugar = 0.146 /55.646= 0.0026

Mol fraction H2O = 55.5 / 55.646 = 0.9974

Mol fraction has no units

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