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for this question A sample of air has a volume of 140.0 mL at 67 degrees celcius. At what temperature would its volume 50.0 mL at constant pressure
I did
140.0 ml... 67+273=340
T2... 50.0
140.0=50.0
340=T2
340*50.0/140.0=121.4

This question i don't get because of the scientific notation. A sample of oxygen that occupies 1.00 x 10^6 mL at 575 mm Hg is subjected to a pressure of 1.25 atm. What will the final volume of the sample be if the temp is held constant?

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asked by jerson
  1. The first one is ok EXCEPT that if your prof is a stickler for significant figures, you will get points counted off if not the entire question. The smallest number of significant figures is 3 (50.0, 340) so the most s.f. you are allowed in the answer is 3; therefore, you would round the answer to 121. ALSO, some profs will count off if you don't have units; therefore, the complete answer would be 121 Kelvin.
    For the second problem, 10^6 just means to add 6 zeros to 1 (which would be 1,000,000). Or you can key in the number with scientific notation to your calculator and let it keep track of the decimal. USUALLY, a number expressed as 1.00 x 10^6 mL means your prof looks at s.f.

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  2. ok i get that now.. but now im still confused with how to solve the problem because i don't see where it talks about temperature.

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    posted by jerson
  3. Sure. It says the temperature is held constant. This is a pressure/volume problem. Done the same way except
    P1V1 = P2V2.

    By the way, do you know how to keep all these formulas straight? Do it this way.
    The general formula is
    (P1V1)/T1 = (P2V2)/T2
    If T is constant, just cover up T1 and T2 with your fingers (or mentally) and you have P1V1 = P2V2 which is Boyle's Law.
    If P is held constant, cover up P1 and P2 with your fingers (or mentally), and you have V1/T1 = V2/T2 which is Charles' Law.
    If V is held constant, covert up V1 and V2 with yur fingers (or mentally) and you have P1/T1 = P2/V2. Easy, huh?
    You only need to memorize the general formula that contains all the variable and tailor it to fit the problem. And, of course, you must remember that T always goes in with Kelvin.

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  4. If V is held constant, covert up V1 and V2 with yur fingers (or mentally) and you have P1/T1 = P2/V2. Easy, huh?

    I made a goof here. This should read, if V is held constant, cover up V1 and V2 with your fingers (or mentally) and you have P1/T1 = P2/T2
    My fingers sometimes get ahead of my brain.

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  5. well im sure u can tell chemistry is my weakest subject because im still confused :/...

    so would it be 1000000= 575
    1.25= t2?

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    posted by jerson
  6. Why do you want to solve for t? It SAYS t is constant so we don't care what it is. And you haven't used the pressure at all.
    You didn't do what I said. Just follow the guide lines.
    P1V1/T1 = P2V2/T2.
    Now, since T is constant, cover T1 and T2 with your fingers, or mentally, and we are left with
    P1V1 = P2V2
    Now look at the problem.
    V1 = 1 x 10^6 mL
    P1 = 575 mm Hg
    V2 = ?? mL.
    P2 = 1.25 atm.
    Right away you see that the units on pressure don't match. You must change mm Hg to atmospheres OR change atmospheres to mm Hg. The conversion factor is 760 mm = 1 atm. The easy one to change is P1 so 575/760 = 0.756 atm.
    Then P1V1 = P2V2
    0.756*1x10^6 = 1.25*V2 and solve for V2.

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  7. ok thank you for all of your help tonight.. i really appreciate it!

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    posted by jerson
  8. You're welcome.

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  9. p1v1/t1=p2vp/t2;v2

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