How much sinnapinic acid (Mr of 224) would you weight out to make 400 ml of a 10mM solution? I got an answer 0,896g , but it is not correct, because I need to choose between
a) 0,90g
b)8,96g
c089,6g
d) 90g
Can anyone check
How I do:
10mM is 0,01M, 400ml is 0,4l so n=cV=0,01M*0,4L=0,004mol

m=n*Mr=0,004*224=0,896g

Any help?

Question

How much sinnapinic acid (Mr of 224) would you weight out to make 400 ml of a 10mM solution? I got an answer 0,896g , but it is not correct, because I need to choose between 
a) 0,90g
b)8,96g
c089,6g
d) 90g
Can anyone check
How I do:
10mM is 0,01M, 400ml is 0,4l so n=cV=0,01M*0,4L=0,004mol

m=n*Mr=0,004*224=0,896g

Any help?

kamille · Answer

or, or maybe I should round up to 0,9g?

kamille · Answer

@yrelhan4

kamille · Answer

I bet you can help me with this;)

yrelhan4 · Answer

Rounding up should do. That gives you the correct answer?

kamille · Answer

I don't know, I don't have answers. Do you know when I should round up and when not?

yrelhan4 · Answer

Well there is no rule when to round up and when not. Depends on the options. The only option thats the closest to the answer is 0.9. 
If there was 0.896 and 0.9, you would go in for 0.896.

kamille · Answer

I see,thanks;)!!!!

yrelhan4 · Answer

Cheers. :)