can someone please help!!
A zero-order reaction has a constant rate of 4.90×10−4 M/s M/\rm s. If after 70.0 seconds the concentration has dropped to 4.00×10−2 M M, what was the initial concentration?

-I continue to get -1.17M but the program tells me its wrong I don't know what to do know?

Question

can someone please help!!
A zero-order reaction has a constant rate of 4.90×10−4 M/s M/\rm s. If after 70.0 seconds the concentration has dropped to 4.00×10−2 M M, what was the initial concentration?

-I continue to get -1.17M but the program tells me its wrong I don't know what to do know?

anonymous · Answer

So your method should have been to calculate the drop over those 70 seconds and then adding that value to the final concentration after the 70 seconds.  Is that what you did?

anonymous · Answer

the program gave me this equation to use [A]=[A] 0 −rate×time

anonymous · Answer

Oops, concentrations.  Okay, so that's a negative or..?  Haha, I want to try and see what my answer comes out to be.

anonymous · Answer

I plugged in positive 1.17 and it wouldn't take it either. Any advise? I only have one attempt left......

anonymous · Answer

Is your unit chemical kinetics?

anonymous · Answer

What you're studying, I mean.

anonymous · Answer

This looks like a good resource. http://www.elcamino.edu/faculty/pdoucette/All-1B-CSM.pdf

anonymous · Answer

I believe it is M isn't it? It uses M/s units, and the seconds would cancel out leaving M.

anonymous · Answer

The unit of your study I mean, as in is this question a chemical kinetics question? :p

anonymous · Answer

Yes! sorry

anonymous · Answer

So then the equation says the final concentration equals the initial concentration minus rate times time elapsed, I think.

anonymous · Answer

And you're solving for [A]0 or initial concentration.

anonymous · Answer

[A]0 would be the initial concentration

anonymous · Answer

$$[A] = [A]o - (rate \times time)$$
$$[A] + (rate \times time) = [A]o$$

and I feel like that should work...but maybe I'm thinking too simply.

anonymous · Answer

that's what I used, and I continue getting 1.17 M

anonymous · Answer

Haha, can I see the calculation?  If that's what you used, it must be right.

anonymous · Answer

the program says its incorrect for some reason what do you end up getting?

anonymous · Answer

I must be doing it completely wrong, that's why I want to see your calculation lol

anonymous · Answer

And it's not multiple choice, right?

anonymous · Answer

yes!!

anonymous · Answer

oh wait, I got it right!!!

anonymous · Answer

thanks!!!!! I understand what you did with the formula!!!

anonymous · Answer

I really appreciate your help, I spend an hour on this problem!!
Thank a million!!!

anonymous · Answer

LOL, you're welcome. :'D  Got the right answer?

anonymous · Answer

yes I got the right answer!!!! thank you so much

anonymous · Answer

:3 you're welcome