i really need help with this chem. problem please?

Question

Thermochem. Problem?
im working on a series of problems that are based off each other, ive got the first 2 correct but i cant seem to solve the third.

When 3.5g of sodium hydroxide (NaOH) was dissolved in 100g of water a value of 10.5oC was obtained for ΔT.

1. [1pt]
Calculate the molarity of the sodium hydroxide solution.
Correct: 0.875

2. [1pt]
Calculate the heat (calories) produced by the solution of 3.5 g of NaOH.

Correct: -1032.4125



3. [1pt]
Calculate the number of calories that would be produced if one mole of sodium hydroxide was dissolved. (ΔHsolnNaOH)


#3 is the one i cant solve, i think i have to do a ratio but it doesnt take my answer i seem to get or -1179.9 as answers but it doesnt take it.

Answer 1

You have the heat produced from disolving 3.5 g of NaOH: To get the delta H for a whole mole of NaOH you need to divide by moles of NaOH: (the part in parentheses is moles of NaOH).

-1032.4 cal/(3.5g/40g/mol) = -1032.4/0.0875 = -11798.8

cal/mol, or -11.8Kcal/mol

I think you had the right idea, but you divided by molarity of the solution (instead of moles NaOH) which threw the answer off by a factor of 10.