I need some help w/ quantitative chemistry. if someone can walk me through the following problems that'd be great :-D

problem 1
The following questions deal with copper(II) sulfate.

a. In part B of this experiment, you will use copper(II) sulfate pentahydrate. What is the molar mass of this compound? Ans: 249.62 g/ mol

b. How much of this compound must be weighed to make 300.0 mL of a 0.15 M solution?
Ans: 11.23g

c. How many mL of the 0.15 M solution should be diluted to prepare 350.0 mL of a 0.05 M solution?
absolutely no idea how to do this part.

problem 2
b. Data has been collected to show that at a given wavelength in a 1 cm pathlength cell, Beer's Law for the absorbance of Co2+ is linear. If a 0.135 M solution of Co2+ has an absorbance of 0.350, what is the concentration of a solution with an absorbance of 0.450.

this problem uses Beer's law but i don't know which numbers to use b/c there are more numbers than needed for the equation.

1/22/2007 3:59:42 PM

c. try M*V=M*V
V*0.15=350*0.05

1/22/2007 6:43:49 PM

For question 2, you can set up a ratio and solve for your unknown. [x]/Ax=[y]/Ay where Ax and Ay are respective absorbance readings.

1/22/2007 7:12:02 PM

thanks for the help!

1/22/2007 7:26:43 PM

Oh God the memories.

1/22/2007 9:00:48 PM

^

1/22/2007 9:31:19 PM

I loved this class.

But at this point in my academic career, I have no clue what the hell is going on with these questions.

1/22/2007 10:16:03 PM

dont worry, its an easy A+

1/23/2007 11:53:32 AM

A solution is found to be 0.2170% by weight BaCl2. What is the concentration of the Cl1- ion expressed in ppm?

so here's what i did: I assumed there was 1 L of solution therefore 1 L=1000mL x (1 g/mL) = 1000 grams of solution. then that means there is 2.17 grams of BaCl2, or .01042 moles. setting up a ratio i get that there are .02084 moles Cl. so then the concentration would be .02084/1L =.02084M. i only have 1 more submission so could some one tell me if that is right, and if it is, how do i convert to ppm?

1/26/2007 6:12:24 PM