assume an unknown sample to be 15% copper, weigh enough dried ore sample to use approximatele 35-45mL of .09M S2O3-. How many grams do I need to measure out to use 40.00mL of the thiosulfate solution?
Note: Your instructor may prefer the use of I3^- instead of I2. If so you may need to adjust the following.
2Cu^2+ + 4I^- ==> CuI2(s) + I2
I2 + S2O3^= ==> S4O6^= + 2I^-
From the above you can see that 1 mol Cu = 1 mol S2O3=.
If you want to use 45 mL, that is 0.045 L and M x L = 0.09 x 0.045 = 0.00405 mols.
g Cu = mols Cu x atomic mass = about 0.00405 x about 64 = about 0.257 g.
0.257/0.15 = about 1.71g. Check my thinking and my math. You need to redo this for 40 mL; I didn't see that until the 45 ml was done. I'm sure you have thought of this but you must NOT go over 50 mL; that means a refill on the buret. That won't ruin the titration but it increases the error.
To find out how many grams of the thiosulfate solution you need to measure out in order to use 40.00 mL, we can use the concept of stoichiometry and the concentration of the solution.
Let's start by setting up a proportion using the given concentrations:
(0.09 moles/Liter) / (1000 mL/Liter) = y moles / 40.00 mL
Simplifying this equation, we find:
0.09/1000 = y/40.00
Now, we can solve for y:
y = (0.09/1000) * 40.00
y = 0.0036 moles
Next, we need to calculate the molar mass of Na2S2O3 (sodium thiosulfate). The molar mass is the sum of the atomic masses of each element in the compound:
Na (sodium) = 22.99 g/mol
S (sulfur) = 32.07 g/mol
O (oxygen) = 16.00 g/mol
Molar mass of Na2S2O3 = 2 * (22.99) + 2 * (32.07) + 3 * (16.00) = 158.10 g/mol
Lastly, we can calculate the mass of the thiosulfate solution by multiplying the molar mass by the number of moles:
Mass = y * molar mass = 0.0036 * 158.10
Mass ≈ 0.571 g
Therefore, you would need to measure out approximately 0.571 grams of the thiosulfate solution to use 40.00 mL.