Homework Help: Chemistry

Posted by Susie on Tuesday, February 10, 2009 at 8:13pm.

The molecular weight of glucose is 180.2 and the molecular weight of lactose is 342.3. What is the molarity of a 25% glucose solution? What is the molarity of a 25% lactose solution?

I know that molarity = mol/L or mol/1000 mL and that molecular weight is g/mol. But I'm not sure where to go from there.

Chemistry - bobpursley, Tuesday, February 10, 2009 at 8:20pm
If the solution is 25 percent glucose, then

.25(mass glucose+masswater)=mass glucose
So you assume the mass of the water is 1kg. Without density, you really dont know that, so you have to just assume adding glucose doesnt change the volume of the water.
.25massglucose-massglucose=-250kg
massglucose=you do it.
then calc the moles glucose, and you have an approximation for molarity, assuming the volume is still 1liter.

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