Ch.4 - Reactions in Aqueous Solution

Problem 59b

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Chapter 4, Problem 59b

b. What is the difference between 0.50 mol HCl and 0.50 M HCl?

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Step 1: Understand the concept of 'mole' in chemistry. A mole is a unit that measures the amount of substance. 0.50 mol HCl means you have 0.50 moles of hydrogen chloride, which is a specific number of molecules (Avogadro's number: \(6.022 \times 10^{23}\) molecules per mole).

Step 2: Understand the concept of 'molarity'. Molarity (\(M\)) is a measure of concentration, defined as the number of moles of solute (in this case, HCl) per liter of solution. 0.50 \(M\) HCl means you have 0.50 moles of HCl dissolved in 1 liter of solution.

Step 3: Compare the two terms. 0.50 mol HCl refers to the quantity of HCl, while 0.50 \(M\) HCl refers to the concentration of HCl in a solution.

Step 4: Consider the implications of each term. 0.50 mol HCl could be in any volume of solution, whereas 0.50 \(M\) HCl specifically indicates the concentration in a 1-liter solution.

Step 5: Reflect on practical applications. Knowing the difference helps in preparing solutions and understanding chemical reactions, as the concentration affects reaction rates and equilibrium.

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Key Concepts

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

Moles (mol)

A mole is a unit in chemistry that represents a specific quantity of particles, typically atoms or molecules. One mole is equivalent to approximately 6.022 x 10^23 particles, known as Avogadro's number. In the context of the question, 0.50 mol HCl indicates a quantity of hydrochloric acid that contains 0.50 moles of HCl molecules.

Molarity (M)

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in units of moles per liter (mol/L). The notation 0.50 M HCl means that there are 0.50 moles of HCl dissolved in one liter of solution, which provides information about the concentration of the acid in a solution.

Concentration vs. Amount

The difference between 0.50 mol HCl and 0.50 M HCl lies in the distinction between the total amount of substance and its concentration in a solution. While 0.50 mol refers to a specific quantity of HCl, 0.50 M indicates how concentrated that amount is in a given volume of solution. Understanding this difference is crucial for calculations involving reactions and solutions in chemistry.

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Textbook Question

The metal cadmium tends to form Cd²⁺ ions. The following observations are made: (i) When a strip of zinc metal is placed in CdCl₂(aq), cadmium metal is deposited on the strip. (ii) When a strip of cadmium metal is placed in Ni(NO₃)(aq), nickel metal is deposited on the strip. b. Is cadmium above or below zinc in the activity series?

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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?

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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

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?

(b) How many moles of KBr are present in 150 mL of a 0.112 M solution?

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