## anonymous one year ago A sample of gas with a mass of 8.40 g occupies a volume of 4.50 L at 298 K and 1.10 atm. What is the molar mass of the gas? Show all work used to find your answer. *Best answer gets medal, fan and testimony*

1. aaronq

Use the ideal gas law, substitute in the definition of moles, solve for M, molar mass. Ideal gas law: $$\sf PV=nRT$$ moles: $$\sf n=\dfrac{m}{M}$$ $$\sf \huge PV=\dfrac{m}{M}RT\rightarrow M=\dfrac{mRT}{PV}$$

2. anonymous

May you help me plug in the variables?

3. aaronq

I can check it for you if you give it a try

4. anonymous

Ok. Give me a second.

5. anonymous

I have: 1.10*4.50 L = n(0.08206atm)(298K) And that's all I can do. Unfortunately.

6. aaronq

that's right! you can now solve for n, then divide the mass 8.4 g by the moles.

7. aaronq

the mass is given in the question, it's 8.4 grams

8. anonymous

So it would be: 1.10 atm * 298 K = 24.45388 8.4 g / 24.45388 = 0.3435

9. aaronq

not quite, first solve this equation: 1.10*4.50 L = n(0.08206atm)(298K) divide the mass by the answer (moles)

10. anonymous

4.95 = n(0.08206*298) 4.95 = n(24.45388) 4.95/24.45388 = 0.202421... n = 0.202421

11. aaronq

okay, looks good! now divide the mass by n

12. anonymous

244.5398

13. aaronq

There you go

14. anonymous

WOOHOO! How would I properly write with sig figs?

15. aaronq

all the numbers used have 3 sig figs, so make the answer have 3 figures.

16. anonymous

244. Thank you so much! You're a life saver :D

17. aaronq

that's not quite right. look at the fourth digit, you have to round up

18. anonymous

Oh... 245, correct?

19. aaronq

yeah. you should give this a look https://www.physics.uoguelph.ca/tutorials/sig_fig/SIG_dig.htm

20. anonymous

Will do.

21. anonymous

Got it. Thanks :)

22. aaronq

no problem!

23. anonymous

@aaronq there is problem in this question

24. aaronq

whats the problem?

25. anonymous

should the answer be around 41 to 42 because we are dividing 8.4 by n

26. anonymous

@aaronq

27. aaronq

you're right, the answer is 41.4974933333333333 I guess this person plugged the numbers into the calc wrong

28. anonymous

oh thank so much

29. aaronq

np!

30. aaronq

thanks for double checking lol

31. anonymous

np!