science
posted by Tiffany .
A mixture of two gases, C2H2 and H2, has the properties listed below.
nC2H2=0.028moles
nH2=0.015moles
PC2H2=79torr
What is the PT for this mixture?
I first found out the mole fraction by first adding H2 and C2H2 and got 0.043, then did 0.028/0.043. I rounded it to 0.651. I then set up my equation like this:
79 = (0.651)*Pt
i divided 79 by 0.651 (so the equation was like this: 76/0.651) and got 121 (rounded to nearest whole number). However, the answer was 120. What did I do wrong?
PS: My teacher never taught me this.

All numbers in the original data were given to two significant figures, so your answer cannot be expected to be more accurate. Rounding it to two significant figures (i.e. 120) would be appropriate.
Check that the answer is 120 and not 120. 120 means two significant figures, while 120. means 3 (wrong).