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Ch.9 Solutions
Timberlake - Chemistry: An Introduction to General, Organic, and Biological Chemistry 14th Edition
Timberlake14thChemistry: An Introduction to General, Organic, and Biological ChemistryISBN: 9781292472249Not the one you use?Change textbook
Chapter 9, Problem 27a

A solution containing 80. g of KCl in 200. g of H2O at 50 °C is cooled to 20 °C. a. How many grams of KCl remain in solution at 20 °C?

Verified step by step guidance
1
Step 1: Understand the solubility concept. Solubility refers to the maximum amount of solute (in this case, KCl) that can dissolve in a given amount of solvent (H₂O) at a specific temperature. Look up the solubility of KCl at 20 °C in a solubility table.
Step 2: Compare the solubility of KCl at 20 °C with the amount of KCl initially dissolved (80 g). If the solubility at 20 °C is less than 80 g, the excess KCl will precipitate out of the solution.
Step 3: Calculate the amount of KCl that remains dissolved in the solution at 20 °C. Use the solubility value from the table to determine how many grams of KCl can stay dissolved in 200 g of water at this temperature.
Step 4: Subtract the solubility value (grams of KCl that can dissolve at 20 °C) from the initial amount of KCl (80 g) to find the amount of KCl that precipitates out. The remaining amount in solution will be equal to the solubility value.
Step 5: Ensure the units are consistent throughout the calculation. Verify that the solubility value corresponds to the same amount of water (200 g) as given in the problem. If necessary, adjust the solubility value proportionally to match the 200 g of water.

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Key Concepts

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

Solubility

Solubility refers to the maximum amount of a solute that can dissolve in a solvent at a given temperature and pressure. For KCl in water, solubility changes with temperature; typically, as temperature decreases, solubility also decreases, meaning less solute can remain dissolved.
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Temperature Effects on Solubility

The solubility of ionic compounds like KCl is significantly affected by temperature. Generally, higher temperatures increase solubility, allowing more solute to dissolve, while lower temperatures can lead to precipitation of the solute as it exceeds the solubility limit.
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Saturation Point

The saturation point is the concentration of a solute in a solution at which no more solute can dissolve at a specific temperature. When a solution is cooled, if the concentration exceeds this saturation point, the excess solute will precipitate out of the solution.
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