Preparing solutions
a. A solution was prepared by dissolving 5.65 g potassium bromide in 32.67 g water. What is the concentration of this solution in weight percent?
b. The solution was poured into a 100 mL volumetric flask and water was added to the mark on the flask. What is the concentration of the solution in moles per liter?
c. Using a pipet, 10 mL of the solution in part b was placed in a 25 mL volumetric flask and the flask filled to the mark with water. What is the concentration of the new solution?
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17.3
a. To determine the weight percent concentration of a solution, you need to divide the weight of the solute (in this case, potassium bromide) by the weight of the solution (which is the sum of the weights of the solute and solvent, water), and then multiply by 100.
Given:
Weight of potassium bromide (solute) = 5.65 g
Weight of water (solvent) = 32.67 g
Weight percent concentration = (Weight of solute / Weight of solution) x 100
Weight percent concentration = (5.65 g / (5.65 g + 32.67 g)) x 100
b. To determine the concentration of a solution in moles per liter, you need to convert the weight of the solute to moles using its molar mass, and then divide by the volume of the solution in liters.
Given:
Weight of potassium bromide = 5.65 g
Volume of solution = 100 mL = 0.1 L
First, calculate the number of moles of potassium bromide using its molar mass. The molar mass of potassium bromide (KBr) is 119 g/mol.
Number of moles of potassium bromide = (Weight of potassium bromide / Molar mass of potassium bromide)
Number of moles of potassium bromide = (5.65 g / 119 g/mol)
Then, divide the number of moles by the volume of the solution in liters to find the concentration:
Concentration (moles per liter) = (Number of moles of potassium bromide / Volume of solution)
c. To determine the concentration of the new solution in the 25 mL volumetric flask, you need to divide the number of moles of potassium bromide transferred into the flask by the volume of the new solution.
Given:
Volume of solution transferred = 10 mL = 0.01 L
Volume of new solution = 25 mL = 0.025 L
First, calculate the number of moles of potassium bromide transferred using the concentration in moles per liter calculated in part b:
Number of moles of potassium bromide transferred = (Concentration (moles per liter) x Volume of solution transferred)
Then, divide the number of moles by the volume of the new solution in liters to find the concentration:
Concentration of the new solution = (Number of moles of potassium bromide transferred / Volume of new solution)