## anonymous one year ago Calculate the number of moles of helium that contains 3.25 x 10^21 atoms.

1. anonymous

Without numbers, can you figure this out. Always start with given value $\frac{ atoms}{ 1}\times \frac{ mol }{ atoms }$

2. anonymous

3.25 x 10^ 21 atom x (1mol/6.022 x 10 23 atom)

3. anonymous

Right?

4. anonymous

$3.25 x 10^{21} atom x \frac{ 1 mol }{ 6.022 x 10^{23} atom }$

5. anonymous

Yes, that is right. Sorry I was helping someone.

6. anonymous

And I get .539687811

7. anonymous

Units would be in moles of helium.

8. anonymous

So .539687811 mol He?

9. anonymous

It has to be 3 sf since the given value only has 3. Remember that your answer has a 0 in the front. It does not count as a sf.

10. anonymous

.540 mol He?

11. anonymous

Yes Nice rounding!

12. anonymous

Thanks

13. anonymous

No problem!

14. anonymous

It's saying the answer is wrong. I did it right...Right?

15. anonymous

I did not do the calculations since you got the right conversion. You did the calculation. Do the calculation again.

16. anonymous

I think you put 3.25*10^23 instead of 3.25*10^21

17. anonymous

I did it again and got the same answer.

18. anonymous

Write down what you calculate then.

19. anonymous

$3.25\times10^{21} atomtimes \frac{ 1mol }{ 6.022 \times10^{23 } }atom$

20. anonymous

3.25 x 10^21 atom x

21. anonymous

Dont forget parentheses. (3.25*10^21)/(6.022*10^23)

22. anonymous

Right

23. anonymous

Got .00540 mol He

24. anonymous

So what did you do wrong earlier?

25. anonymous

Forgot parentheses or wrong exponent?

26. anonymous

I put it in the calculator without parentheses

27. anonymous

Another way is multiply 3.25*10^21 and lets called that x then multiply 6.023*10^23 and call that y. Then just do x/y if you arent comfortable with parentheses.