DR.BOB 22 PLS HELP
A chemist dissolves 0.099 g of CuSO4 · 5 H2O
in water and dilutes the solution to the mark
in a 500-mL volumetric flask. A 28.9-mL
sample of this solution is then transferred to a
second 500-mL volumetric flask and diluted.
What is the molarity of CuSO4 in the second
solution?
Answer in units of M.
**answer: .000046**
SECOND PART:
To prepare the second 500 mL of solution
directly, what mass of CuSO4 · 5 H2O would
need to be weighed out?
Answer in units of mg.
mols = grams/molar mass = 0.099 g/249.5 = 0.000397 in the first flask so
M = mols/L = 0.000397/0.500 = 0.000793 M.
You can use the dilution formula of
mL1 x M1 = mL2 x M2 but I prefer to to
0.000397 x (28.9/500) = 0.0000229 M CuSO4.5H2O. In reading the question, technically, you asked for molarity of CuSO4 (and not CuSO4.5H2O). I don't know if this was a typo or not; however, if you want M CuSO4, that is
0.0000229 x (159.5/249.5) = 0.0000146
part 2 new post.
Scratch that. I'm using a new calculator. Maybe punched the wrong buttons. Let me check those numbers.
Nope: not the calculator. I copied the wrong number. That line of
0.000397 x (28.9/500) = 0.0000229 M CuSO4.5H2O should be replaced with
0.000793 M x (28.9/500) = 4.59E-5 or 0.0000459 M
In case you wanted CuSO4 instead of CuSO4.5H2O that will be
4.59E-5 x (159.5/249.5) = ? M
I'll do part 2 new post.
i don't see the other new post, could you put the link
So you want to weigh out CuSO4.5H2O directly into a 500 mL volumetric flask to make 4.59E-5 M. You will want how many moles. That's
mols = M x L = 4.59E-5 M x 0.500 L = 2.29E-5 mols.
grams = mols x molar mass = 2.29E-5 mols x 249.5 g/mol = 5.73E-3 g = 0.00573 g = 5.73 mg CuSO4.5H2O
Check my numbers closely: I have poor eyesight and I make some typos>
To find the molarity of CuSO4 in the second solution, we need to use the given information about the initial solution and the dilution process. Let's break down the steps to solve this problem.
Step 1: Calculate the number of moles of CuSO4 in the initial solution.
We start by finding the molar mass of CuSO4 · 5 H2O:
Cu: 63.55 g/mol
S: 32.07 g/mol
O (from SO4): 4 * 16.00 g/mol = 64.00 g/mol
H2O: 5 * (2.02 g/mol + 16.00 g/mol) = 90.10 g/mol
The molar mass of CuSO4 · 5 H2O is:
63.55 + 32.07 + 64.00 + 90.10 = 249.72 g/mol
Next, we calculate the number of moles of CuSO4 · 5 H2O dissolved in water:
0.099 g / 249.72 g/mol = 0.000396 mol
Step 2: Calculate the concentration of CuSO4 in the initial solution.
The initial solution is in a 500 mL volumetric flask. Using the number of moles, we can calculate the molarity of CuSO4 in the initial solution:
Molarity (initial solution) = moles / volume (in liters)
Molarity (initial solution) = 0.000396 mol / 0.500 L = 0.000792 M
Step 3: Calculate the volume of the second solution.
A 28.9 mL sample of the initial solution is transferred to a second 500 mL volumetric flask and diluted. So the volume of the second solution is 500 mL.
Step 4: Calculate the moles of CuSO4 in the second solution.
Using the molarity and volume of the second solution:
Moles (second solution) = Molarity (initial solution) * Volume (second solution in liters)
Moles (second solution) = 0.000792 M * 0.0289 L = 0.0000229 mol
Step 5: Calculate the molarity of CuSO4 in the second solution.
Finally, we divide the moles of CuSO4 in the second solution by the volume of the second solution:
Molarity (second solution) = Moles (second solution) / Volume (second solution in liters)
Molarity (second solution) = 0.0000229 mol / 0.500 L = 0.0000458 M
Rounding to the appropriate number of significant figures, the molarity of CuSO4 in the second solution is approximately 0.000046 M.
Now let's move on to the second part of the question.
To prepare the second 500 mL of solution directly, we need to calculate the mass of CuSO4 · 5 H2O that needs to be weighed out.
Step 1: Determine the moles of CuSO4 needed.
Using the molarity and volume of the second solution:
Moles (second solution) = Molarity (second solution) * Volume (second solution in liters)
Moles (second solution) = 0.0000458 M * 0.500 L = 0.0000229 mol
Step 2: Calculate the mass of CuSO4 · 5 H2O.
Using the molar mass of CuSO4 · 5 H2O:
Molar mass = 249.72 g/mol
Mass of CuSO4 · 5 H2O = Moles of CuSO4 · 5 H2O * Molar mass of CuSO4 · 5 H2O
Mass of CuSO4 · 5 H2O = 0.0000229 mol * 249.72 g/mol = 0.00571 g
To convert the mass of CuSO4 · 5 H2O to milligrams (mg), we multiply by 1000:
Mass of CuSO4 · 5 H2O = 0.00571 g * 1000 mg/g = 5.71 mg
Therefore, to prepare the second 500 mL of solution directly, we would need to weigh out approximately 5.71 mg of CuSO4 · 5 H2O.
impatient much?
Give the guy a chance to see your post!