Chemical Forums

Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: tm975 on February 28, 2012, 07:59:10 PM

Title: (Preparation of solutions and dilutions)
Post by: tm975 on February 28, 2012, 07:59:10 PM

Hi

This is my first post and Im struggling with these 2 questions (even though they are frustratingly simple) can someone help me out with working?

1) Calculate the number of grams of sucrose (MW 342) you would need in order to make 500ml of a 2.5mM solution.

2) Concentrated HCL (MW 36.5) is 11.6 M. Calculate the volume you would need to dilute to about 200ml to give a 10% (w/v) solution of HCL

Cheers

Title: Re: Ahhh, desperate help needed with 2 questions
Post by: tm975 on February 28, 2012, 08:05:44 PM

Do I use molarity for question 1? and do I convert from mM to M?

Title: Re: Ahhh, desperate help needed with 2 questions
Post by: Arkcon on February 28, 2012, 09:43:52 PM

Quote from: tm975 on February 28, 2012, 08:05:44 PM

Do I use molarity for question 1? and do I convert from mM to M?

Yes, you do use the molarity.  As for converting M to mM, you've used the 'm' before, as in mm or mL or mg, so you just divide.

Title: Re: (Preparation of solutions and dilutions)
Post by: tm975 on February 28, 2012, 10:11:23 PM

Would you be able to walk through the working with me? I got 0.00125 the first time and 0.4275 the second

Title: Re: (Preparation of solutions and dilutions)
Post by: Borek on February 29, 2012, 03:48:57 AM

Quote from: tm975 on February 28, 2012, 10:11:23 PM

I got 0.00125 the first time

0.00125 of what? Without units your answer doesn't say anything.

(That is, it tels a lot, but these are not answers you are looking for)

Quote

and 0.4275 the second

Of what, and how did get that number?