[JoeJoe]

Hi guys, from today in class I got an assignment which is due next week.

I don't really know where to begin, so if you could give me as much information I would appreciate it. I'll note this is my first chemistry class so go easy

I'm not specifically looking for direct answers, but rather the steps on how to complete the question.

Question 1:
Prepare 100ml of 0.166M CuSO4 5H2O

a) What is the mass calculated:
b) what is the molar concentration

Question 2:
Prepare 100ml of 4.12 x 10^-3 M CuSO4 5H2O
Volume of H2O:
Volume of CuSO4 .166M Required:

Question 3:
Initial Reading:
Final Reading:
Total Volume of Solution Dispensed:
Actual Concentration:

How would I calculate the actual concentration?



I'll check back for any responses when I can tomorrow, if anyone can help me with any steps (even if just one) I would appreciate it.

Thanks
Joe

[Borek]

What is the definition of molar concentration?

Please read forum rules.

[JoeJoe]

Question 1:

A) When it is asking for mass calculated, what does that refer to? The molar mass?
CuSO4 5H2O

Cu - 1
S - 1
O- 4
H - 10
O - 5

# of Atoms total
Cu (63.546) - 1 = 63.546
S (32.066) - 1 = 32.066
O (15.9994) - 9 = 143.9946
H (1.00794) - 10 = 10.0794
Total Mass = 249.689 M

Is this correct? I'm not sure if im missing something, does the 100ml or .166M have any effect on the mass? Sorry for the stupid question.

B) Molar Concentration

To calculate molar concentration I found this, C = V/N
Where:
N = Substance
V = Solution
C = Molarity

C = .166/100ml = .00166


If I am wrong, please inform me what I did wrong so I can try and fix it.

[Fizzy]

Hi Joe,

For question 1, the mass you have calculated is the relative molecular mass (RMM) of copper sulphate, but the units should be grams per mole (g.mol-1), not M.

Part a is asking for the mass of copper sulphate required to make 100ml of copper sulphate solution, of concentration 0.166 M.

First you need to calculate the number of moles of CuSO4.5H2O in the solution, I use the equation:

Number of moles (n) = concentration (c) x volume (v) - we'll call this equation 1. Since your concentration is in M your volume must be in dm3, unless you include a conversion factor (1 dm3 = 1000 cm3 = 1000 ml) i.e. divide your volume by 1000.

Once you have calculated the number of moles in the solution you can calculate the mass of CuSO4.5H2O required to make 100 ml of solution using the RMM you calculated earlier (249.681 g.mol-1) using the equation:

mass (m) = number of moles (n) x RMM - lets call this equation 2.

The molar concentration of part b may be referring to the number of moles of CuSO4.5H2O in 100 ml of 0.166 M solution, which you should have already calculated if you follow the method above.

For question 2, you are preparing a second solution of copper sulphate, of concentration 4.12 x 10-3 M. To do this you must find the number of moles in 100 ml of this solution - use equation 1 from above, don't forget to convert your volume!

When you have calculated the number of moles required you can use a rearranged form of equation 1 to calculate the volume of your 0.166 M CuSO4.5H2O solution required to prepare your second solution:

volume (v) = number of moles (n) / concentration (c) - again, don't forget to convert your volume! (The concentration value here refers to the concentration of the solution you are trying to prepare i.e. 4.12 x 10-3 M).

The answer to this calculation is the volume of 0.166 M solution required, to find the volume of water required to prepare 100 ml of solution, just subtract the volume of copper sulphate solution from 100 ml.

With regards to question 3, I am assuming it is a titration caluclation but you haven't given enough information for me to help you with the answers. Can you write the whole question out?

Anyway, hope that helped, if there's anything you don't understand give me a shout and I'll try to help more!

[Borek]

relative molecular mass (RMM) of copper sulphate

Why relative, and not just a molar mass?

Great post.

[JoeJoe]

Hey Fizzy, thanks for the informative response.

Question 1:
N=C*V
N= .166M * .1000L = .0166 moles

m = .0166 x 249.681g/mol = 4.1447046g

How's this? is there any easy way to know when to calculate g.mol-1, instead of M?

I'll update the rest of my answer when I get back, need to run out for a few minutes.

Really appreciate the help guys.