Question

A chemistry student must write down in her lab notebook the concentration of a solution of potassium chloride. The concentration of a solution equals the mass of what's dissolved divided by the total volume of the solution.Here's how the student prepared the solution:a. The label on the graduated cylinder says: empty weight: 8.550 g. She put some solid potassium chloride into the graduated cylinder and weighed it.

With the potassium chloride added, the cylinder weighed 84.02 g. She added water to the graduated cylinder and dissolved the potassium chloride completely. Then she read the total volume of the solution from the markings on the graduated cylinder. The total volume of the solution was 186.05 mL. What concentration should the student write down in her lab notebook? Be sure your answer has the correct number of significant digits.

Answer 1

The concentration of the potassium chloride solution should be written as approximately 0.405 g/mL in the student's lab notebook.

Step-by-step explanation:

To calculate the concentration of the solution, we need to determine the mass of potassium chloride dissolved and the total volume of the solution.

Mass of potassium chloride = Weight of graduated cylinder with potassium chloride - Empty weight of graduated cylinder

Mass of potassium chloride = 84.02 g - 8.550 g

Mass of potassium chloride = 75.47 g

Concentration = Mass of potassium chloride / Total volume of the solution

Concentration = 75.47 g / 186.05 mL

To ensure the correct number of significant digits, we need to use the same number of decimal places as the measurement with the fewest decimal places, which is the empty weight of the graduated cylinder (8.550 g) with three decimal places.

Concentration = 75.47 g / 186.05 mL ≈ 0.405 g/mL