Lab on Determination of copper in brass. I have mass of brass at .1011g. My concentration of diluted solution's unknown is .0037957, My concentration of mg/ml Cu^2+ unknown is 241.2. My professor is asking me to determine the percent of copper. I know that %Cu=mass of Cu/Mass of brass. I know the mass of the brass, I'm not sure how to figure the mass of copper though

To determine the mass of copper in the brass, you can use the concentration of the Cu^2+ unknown in mg/mL and the volume of the unknown solution.

1. First, calculate the volume of the unknown solution in milliliters (mL) using the equation:
Volume (mL) = Concentration (mg/mL) * Diluted Solution (unknown) concentration (mL)

In your case, the concentration of the diluted solution is 0.0037957 and the concentration of Cu^2+ unknown is 241.2 mg/mL. So,
Volume (mL) = 0.0037957 * 241.2 = 0.9146 mL (approximately)

2. Convert the volume of the unknown solution to grams (g) by multiplying it by the density of the unknown solution. Let's assume the density is 1 g/mL for simplicity:
Mass (g) = Volume (mL) * Density (g/mL)

Mass (g) = 0.9146 g (approximately)

3. Finally, use the percentage formula to calculate the percentage of copper in the brass. Remember that %Cu = (Mass of Cu / Mass of brass) * 100.
%Cu = (Mass of Cu / Mass of brass) * 100

%Cu = (0.9146 g / 0.1011 g) * 100
%Cu ≈ 905.5%

Therefore, the approximate percentage of copper in the brass is 905.5%.

To determine the mass of copper in the brass sample, you can use the equation:

Mass of Copper = Concentration of Cu^2+ (mg/mL) * Volume of Diluted Solution (mL)

First, let's calculate the volume of the diluted solution. Since you have the concentration of the diluted solution, you can rearrange the equation:

Concentration of Diluted Solution (mg/mL) = Mass of Brass (g) / Volume of Diluted Solution (mL)

Rearranging the equation gives us:

Volume of Diluted Solution (mL) = Mass of Brass (g) / Concentration of Diluted Solution (mg/mL)

Now, substitute the given values:

Volume of Diluted Solution (mL) = 0.1011 g / 0.0037957 mg/mL ≈ 26.67 mL

Next, substitute this volume into the formula to calculate the mass of copper:

Mass of Copper = Concentration of Cu^2+ (mg/mL) * Volume of Diluted Solution (mL)

Mass of Copper = 241.2 mg/mL * 26.67 mL ≈ 6429.2 mg

Finally, convert the mass to grams:

Mass of Copper = 6429.2 mg * (1 g / 1000 mg) ≈ 6.4292 g

Now that you have the mass of copper, you can calculate the percentage of copper in the brass sample using the equation you mentioned:

%Cu = Mass of Copper / Mass of Brass * 100

%Cu = 6.4292 g / 0.1011 g * 100 ≈ 63.60%

Therefore, the percent of copper in the brass sample is approximately 63.60%.

If the concn of the Cu^2+ is 241.2 mg/mL, my first question is mL of WHAT? If you know how many mL that is, then 241.2 x mL = total mg, convert that to grams and substitute into your % equation. That will do it.

The GENERAL method for any unknown, but specifically a Cu unknown is the following:
1. Write and balance the equation(s). You may have placed the unknown in solution, added iodate, and titrated the liberated iodine with thiosulfate using starch as the indicator.

2. millimoles standard soln = mL x M
3. Convert mmoles standard soln to mmoles of Cu in sample using the coefficients in the balanced equation(s).
4. Convert to moles Cu and moles Cu x atomic mass Cu = grams Cu
5. (g Cu/g sample)*100 = %Cu