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.
It seems like you made a minor rounding error in your calculations. When you divided 79 by 0.651, the result would be approximately 121.27 and should be rounded to the nearest whole number, which is 121, rather than 120. So, your calculation was correct, and the PT for this mixture is approximately 121 torr.
To find the partial pressure of a gas in a mixture, you need to know the mole fraction of that gas and the total pressure of the mixture.
In this case, you correctly calculated the mole fraction of C2H2 by dividing its moles (0.028 moles) by the total moles (0.043 moles), which gave you an answer of 0.651.
Next, you set up the equation: PC2H2 = mole fraction of C2H2 * PT, where PC2H2 is the partial pressure of C2H2 and PT is the total pressure. You substituted the given value of PC2H2 (79 torr) and the calculated mole fraction (0.651) into the equation and solved for PT.
You correctly divided 79 by 0.651, which gave you the value 121.437. However, you made a rounding error when you rounded 121.437 to the nearest whole number, resulting in 121 instead of the correct answer of 120.
To avoid this rounding error, you should have rounded 121.437 down to the nearest whole number, which is 121. Therefore, the correct answer for PT is 120 torr, not 121 torr.
It's important to be careful with rounding to ensure accurate calculations.
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).