Please explain how to solve these problems I have posted the answers below but I

Question

Please explain how to solve these problems I have posted the answers below but I would like to see how they are done.

You dissolve 0.250 g of your compound (AwBxCyDz) in exactly 10.00 mL of water

producing 10.00 mL of solution. Using colorimetry, you find that the concentration of A is 2.00

x 10-2 M. The molar mass of A is 750.0 g/mol.

Calculate the following values:

1. Moles of A in the solution

2. Mass of A in the solution

3. Mass % of A in the compound

4. Moles of A in 100 g of the compound

Answers: (1) 2.00 x 10-4 mol A; (2) 0.150 g A; (3) 60.0% A; (4) 0.0800 mol A

Explanation / Answer

(1) Moles of A = volume x concentration of A

= 10.00/1000 x 2.00 x 10^(-2)

= 2.00 x 10^(-4) mol


(2) Mass of A = moles x molar mass of A

= 2.00 x 10^(-4) x 750.0

= 0.150 g


(3) Mass% of A = mass of A/mass of compound x 100%

= 0.150/0.250 x 100%

= 60.0%


(4) Mass of A in 100 g of compound = 60.0/100 x 100 = 60.0 g

Moles of A in 100 g of compound = mass/molar mass of A

= 60.0/750.0

= 0.0800 mol

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