CHAPTER 6 At the end of this chapter, the reader should be able to do the following: 1. Define the following abbreviations or terms: %w/v, %v/v, %w/w, anhydrous, hydrated, density. 2. Perform calculations to determine %w/v, %v/v, or %w/w concentrations of solutions. 3. Perform calculations to interchange between percentage concentrations and molarity or normality concentrations. 4. Calculate the concentrations of anhydrous solutions given the hydrated form and vice versa. 5. Determine the density of solutions based on the specific gravity (SG) of the solution. 6. Calculate the concentration of solutes and solvents by using ratio and proportion. How many grams of NaOH are needed to make a 30.0%w/w solution using deionized water as the solvent? To make this solution, 30.0 g of NaOH would be dissolved into 70.0 g of H2O in a beaker or flask. How many grams of HCl are necessary to make a 10% HClw/w solution using deionized water as the solvent? Using the formula for %w/w, 10 g of HCl would be dissolved in 90 g of H2O in a beaker or flask. How much solvent would be needed to make a 20%w/w solution of CuSO4? To make this solution, 80 g of solvent would be needed. This question asked for the amount of solvent, not the amount of solute (CuSO4). A percent weight/volume (%w/v) solution is calculated by the following formula: To solve this problem, use the formula for %w/v: How many grams of NaOH would be needed to make a 40%w/v solution using deionized water as the solvent? To make a 40%w/v solution, 40.0 g of NaOH would be dissolved into 100 mL of water. How many grams of CaCl2 would be needed to make a 10%w/v solution using deionized water as the solvent? To make a 10%w/v solution, 10 g of CaCl2 would be dissolved into 100 mL of water. A %v/v solution is calculated by the following formula: Percent v/v is similar to %w/w in that the total volume of the solution is 100 mL. Therefore, the amount of solvent is determined by the following formula: How many milliliters of water are necessary for this solution? The amount of water needed is determined by the following formula: How many milliliters of HCl are needed to make a 10%v/v solution using deionized water as the solvent? To make a 10%v/v solution, 10 mL of HCl are added to 90 mL of deionized water. How many milliliters of H2SO4 are needed to make a 2.5%v/v solution using deionized water as the solvent? To make a 2.5%v/v solution, 2.5 mL of H2SO4 are added to 97.5 mL of deionized water. Using algebra and crossmultiplying we derive the following: Therefore, an 0.85%w/v NaCl solution has a molarity of 0.14 mol/L. What is the molarity of a 40%w/v NaOH solution made with deionized water as the solvent? To solve, first determine how many grams of NaOH is in the 40%w/v solution. You know that a 40%w/v solution of NaOH contains 40 g of NaOH in 100 mL of water. In Example 6–4 the decimal point was moved one place to the right to convert 0.85 g/100 mL to 8.5 g/1000 mL. Therefore, by moving the decimal point one place to the right in this example, 40 g NaOH in 100 mL of water is the same as 400 g of NaOH in 1000 mL of water. Next, determine the gram molecular weight of NaOH by determining the sum of the gram atomic weights of Na, O, and H. The gram molecular weight of NaOH is 40.00. Next, substitute the values obtained so far in this problem into the molarity formula: Therefore, a 40.0%w/v NaOH solution has a molarity of 10.0 mol/L. What is the molarity of a 10.0%w/v CaCl2 solution? To solve, 10.0%w/v is equal to 10.0 g/100 mL or 100 g/1000 mL. The gram molecular weight of CaCl2 is 110.98. Therefore, Therefore, a 10%w/v CaCl2 solution has a molarity of 0.90 mol/L. What would be the normality of a solution of 15.0%w/v H2SO4? To solve this problem, remember that To determine the amount of g in 1.00 L: Crossmultiplying the equations results in the following: Next, use the normality formula to determine the normality of the solution. Therefore, a 10.0%w/v H2SO4 solution has a normality of 3.06 Eq/L. What is the normality of a 12.5%w/v NaOH solution? To solve, use the normality formula after determining the number of grams per liter and the gram equivalent weight of NaOH. Therefore, a 12.5%w/v solution of NaOH has a normality of 3.12 Eq/L. What is the normality of a 10%w/v H2CO3 solution? To solve, use the normality formula after determining the number of grams per liter and the gram equivalent weight of H2CO3. Therefore, a 10%w/v H2CO3 solution has a normality of 3.22 Eq/L. By crossmultiplying, the following equation is derived: Therefore, 13.4 g of CuSO4 · H2O qs to 100 mL of solvent will result in a 12.0 %w/v solution of You need to make a 5%w/v solution of CaCl2, but only CaCl2 · 2H2O is available. How do you make the 5%w/v solution? To make this solution, use the formula for interchanging between anhydrous and hydrated chemicals: You need to make a 25%w/v solution of CaSO4 but only To make this solution, use the formula for interchanging between anhydrous and hydrated chemicals: You need to make a 15%w/v solution of Na2CO3, but only To make this solution, use the formula for interchanging between anhydrous and hydrated chemicals: A buffer solution needs to be prepared. The directions call for 2.50 g of anhydrous The molecular weight of
Calculations Associated With Solutions
PERCENT SOLUTIONS
Example 6–1
Percent Weight/Volume
Example 6–2
Percent Volume/Volume
Example 6–3
Conversion of Percentage Calculations to Molarity
Example 6–4
Example 6–5
ANHYDROUS VERSUS HYDRATED SOLUTIONS
Example 6–6
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