Textbook Question
Lead is a toxic metal that affects the central nervous system. A Pb-contaminated water sample contains 0.0011% Pb by mass. How much of the water (in mL) contains 150 mg of Pb? (Assume a density of 1.0 g/mL.)
Ch.14 - Solutions
Chapter 14, Problem 61
Describe how to prepare each solution from the dry solute and the solvent. a. 1.00×102 mL of 0.500 M KCl b. 1.00×102 g of 0.500 m KCl c. 1.00×102 g of 5.0% KCl solution by mass
Verified step by step guidance1
Step 1: For part (a), calculate the moles of KCl needed using the formula: \( \text{Moles of KCl} = \text{Molarity} \times \text{Volume in Liters} \). Convert 100 mL to liters by dividing by 1000.
Step 2: Convert the moles of KCl to grams using the molar mass of KCl. The molar mass of KCl is approximately 74.55 g/mol.
Step 3: Weigh the calculated mass of KCl using a balance.
Step 4: Dissolve the weighed KCl in a volume of water less than 100 mL, then transfer the solution to a 100 mL volumetric flask.
Step 5: Add more water to the volumetric flask until the bottom of the meniscus is at the 100 mL mark, ensuring the solution is well mixed.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Molarity (M)
Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in moles per liter (mol/L). To prepare a solution of a specific molarity, one must calculate the amount of solute needed based on the desired volume of the solution and the molarity formula: M = moles of solute / liters of solution.
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Mass Percent Concentration
Mass percent concentration is a way to express the concentration of a solution as the mass of solute divided by the total mass of the solution, multiplied by 100. For example, a 5.0% KCl solution means that there are 5.0 grams of KCl in every 100 grams of the solution. This concept is crucial for preparing solutions based on mass rather than volume.
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Dilution
Dilution is the process of reducing the concentration of a solute in a solution, typically by adding more solvent. The dilution equation, C1V1 = C2V2, relates the concentrations and volumes before and after dilution. Understanding dilution is essential for preparing solutions from concentrated stock solutions or adjusting concentrations to desired levels.
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