Answer to Question #66670 in General Chemistry for emily

Question

A stock solution of lead was produced by weighing 5 mg lead into a 50.0-mL volumetric flask and the flask was filled into the mark with water. 3 mL of this stock solution was pipetted into another 25-mL volumetric flask and filled to the mark with water.

Note: the answer is a mass NOT a concentration.

Calculate the mass of lead in mg which was added to the 25-mL volumetric flask.

Answer 1

In the first part of experiment we finally get 5 mg of lead in 50.0 mL of stock solution. Therefore 1 mL of this solution contains 5 mg / 50.0 mL = 0.1 mg/mL of lead.
In the second part we take 3 mL of the stock solution and therefore it contains 3 mL * 0.1 mg/mL = 0.3 mg of lead.
Answer:
0.3 mg of lead.