Ch.9 Solutions

McMurry - Fundamentals of General, Organic, and Biological Chemistry 8th Edition

McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook

McMurry 8th Edition

Ch.9 Solutions

Problem 11

Chapter 9, Problem 11

The maximum amounts of lead and copper allowed in drinking water are 0.015 mg/kg for lead and 1.3 mg/kg for copper. Express these values in parts per million, and tell the maximum amount of each (in grams) allowed in 100 g of water.

Verified step by step guidance

Step 1: Understand the relationship between parts per million (ppm) and mg/kg. Since 1 ppm is equivalent to 1 mg of solute per 1 kg of solution, the given values for lead (0.015 mg/kg) and copper (1.3 mg/kg) are already expressed in ppm. Therefore, lead is 0.015 ppm, and copper is 1.3 ppm.

Step 2: To find the maximum amount of lead allowed in 100 g of water, first convert the mass of water from grams to kilograms. Since 1 kg = 1000 g, 100 g of water is equivalent to 0.1 kg.

Step 3: Use the concentration of lead in ppm (0.015 ppm) to calculate the mass of lead in 0.1 kg of water. Multiply the concentration (in mg/kg) by the mass of water (in kg): \( \text{Mass of lead} = 0.015 \text{ mg/kg} \times 0.1 \text{ kg} \).

Step 4: Similarly, calculate the maximum amount of copper allowed in 100 g of water. Use the concentration of copper in ppm (1.3 ppm) and multiply it by the mass of water (in kg): \( \text{Mass of copper} = 1.3 \text{ mg/kg} \times 0.1 \text{ kg} \).

Step 5: Convert the calculated masses of lead and copper from milligrams to grams. Since 1 mg = 0.001 g, divide the results from Steps 3 and 4 by 1000 to express the masses in grams.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Parts Per Million (PPM)

Parts per million (PPM) is a unit of measurement used to describe the concentration of a substance in a solution. It indicates how many parts of a substance are present in one million parts of the total solution. For example, 1 PPM means 1 milligram of a substance in 1 liter of water, which is equivalent to 1 mg/kg in terms of concentration.

Conversion from mg/kg to PPM

The conversion from milligrams per kilogram (mg/kg) to parts per million (PPM) is straightforward, as 1 mg/kg is equal to 1 PPM. This equivalence arises because 1 kilogram of water is approximately equal to 1 liter, making the two units interchangeable in the context of water solutions.

Calculating Maximum Allowable Amounts

To find the maximum allowable amounts of lead and copper in grams for a specific volume of water, you can use the concentration values in PPM. For 100 g of water, you multiply the concentration (in PPM) by the mass of the water (in grams) and then convert from milligrams to grams, as there are 1000 mg in a gram.

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Which of the following pairs of substances would you expect to form solutions?

a. CCl₄ and water

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d. Ethyl alcohol (C₂H₅OH) and heptanol (C₇H₁₅OH)

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At a total atmospheric pressure of 1.00 atm, the partial pressure of CO₂ in air is approximately 4.0 × 10^-4atm. Using the data in Problem 9.4, what is the solubility of CO₂ in an open bottle of seltzer water at 20 °C?

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The typical concentration of Mg²⁺ in blood is 3 mEq/L. How many milligrams of Mg²⁺ are in 250 mL of blood?

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A solution is prepared by dissolving 12.5 g of KBr in 20 mL of water at 60 °C (see Figure 9.3). Is this solution saturated, unsaturated, or supersaturated? What will happen if the solution is cooled to 10 °C?

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