Homework Help: ap chem

Posted by just on Tuesday, February 20, 2007 at 6:16pm.

a solution is prepared by dissolving 4.87 g of sodium dichromate in 25.0 ml of water. (d=1.00g/mL).calculate
a. the mass percent of sodium dichromate in the solution.
b. the mass percent o water in the solution.
c the mole fraction of sodium dichromate in the solution.

How much of this do you know how to do?
Show as much as you can do and I can help from there.

well mass percent is mass solute divided by total mass solution times 100..so would it be..25.0/4.87 x 100?

Your formula is ok. Your use of it is not.
[mass solute/total mass]x100=
4.87 g Na2Cr2O7 is the solute.
Total mass = 4.87 + 25 = ??
You do the math.

b) Solvent is water so mass percent H2O = mass H2O (25 g)/total mass
total mass still 4.87 + 25 = ??
You do the math.

c) mol fraction Na2Cr2O7 =
mols Na2Cr2O7/total mols.

mol Na2Cr2O7 = 4.87/molar mass = ??
mol H2O = 25 g/molar mass H2O = ??

You do the math.
Post your work if you get stuck.

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