Ch.4 - Reactions in Aqueous Solution

Brown - Chemistry: The Central Science 14th Edition

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Brown 14th Edition

Ch.4 - Reactions in Aqueous Solution

Problem 59b

Chapter 4, Problem 59b

(b) Can you identify which one between 0.10 mol ZnCl2 and 0.1M ZnCl2 contains more Zn2+ ion? Why?

Verified step by step guidance

First, understand the difference between moles and molarity. Moles (mol) is a measure of the amount of substance, while molarity (M) is the concentration of a solution expressed as moles of solute per liter of solution.

Next, identify the given quantities: 0.10 mol ZnCl2 is a measure of the amount of substance, and 0.1 M ZnCl2 is a measure of concentration.

For 0.10 mol ZnCl2, recognize that this is a pure amount of the compound, meaning it contains 0.10 moles of ZnCl2, which will fully dissociate in solution to give 0.10 moles of Zn2+ ions.

For 0.1 M ZnCl2, understand that this is a concentration, meaning there are 0.1 moles of ZnCl2 per liter of solution. To determine the amount of Zn2+ ions, you need to know the volume of the solution.

Compare the two scenarios: Without the volume of the 0.1 M solution, you cannot directly compare the number of Zn2+ ions. If the volume of the 0.1 M solution is 1 liter, then it contains 0.1 moles of Zn2+ ions, which is equal to the 0.10 mol ZnCl2. Otherwise, the comparison depends on the volume of the 0.1 M solution.

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Key Concepts

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

Molarity vs. Moles

Molarity (M) is a measure of concentration defined as the number of moles of solute per liter of solution. In this question, 0.1M ZnCl2 indicates a concentration of zinc chloride in a solution, while 0.10 mol ZnCl2 refers to a specific amount of zinc chloride without specifying the volume of the solution. Understanding the relationship between moles and molarity is crucial for determining the amount of Zn2+ ions present.

Dissociation of Ionic Compounds

Ionic compounds like ZnCl2 dissociate in solution into their constituent ions. For every mole of ZnCl2 that dissolves, it produces one mole of Zn2+ ions and two moles of Cl- ions. This dissociation is essential for calculating the total number of Zn2+ ions in a given solution, as it directly affects the concentration of the ions present.

Volume Consideration in Molarity

To compare the amount of Zn2+ ions in 0.10 mol ZnCl2 and 0.1M ZnCl2, one must consider the volume of the solution for the molarity case. If the volume of the 0.1M solution is not specified, it could be any volume, affecting the total moles of Zn2+. Thus, knowing the volume is critical to accurately assess which sample contains more Zn2+ ions.

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Textbook Question

You make 1.000 L of an aqueous solution that contains 35.0 g of sucrose (C12H22O11). (b) How many liters of water would you have to add to this solution to reduce the molarity you calculated in part (a) by a factor of two?

Textbook Question

(a) Calculate the molarity of a solution that contains 0.175 mol ZnCl₂ in exactly 150 mL of solution.

Textbook Question

(a) Is the number of moles of ions present in a solution an intensive or an extensive property?

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Textbook Question

The following reactions (note that the arrows are pointing only one direction) can be used to prepare an activity series for the halogens:

Br₂(aq) + 2 NaI(aq) → 2 NaBr(aq) + I₂(aq)

Cl₂(aq) + 2 NaBr(aq) → 2 NaCl(aq) + Br₂(aq)

(a) Which elemental halogen would you predict is the most stable, upon mixing with other halides?

Textbook Question

The following reactions (note that the arrows are pointing only one direction) can be used to prepare an activity series for the halogens:

Br₂(aq) + 2 NaI(aq) → 2 NaBr(aq) + I₂(aq)

Cl₂(aq) + 2 NaBr(aq) → 2 NaCl(aq) + Br₂(aq)

(b) Predict whether a reaction will occur when elemental chlorine and potassium iodide are mixed.