Chapter 15: Problem 32

For each of the given pairs, determine which solution is more acidic. All are water solutions. Explain your answer. (a) \(1 \mathrm{M} \mathrm{HCl}\) or \(2 \mathrm{M} \mathrm{HCl}\) ? (b) \(1 M \mathrm{HNO}_{3}\) or \(1 M \mathrm{H}_{2} \mathrm{SO}_{4}\) ?

Short Answer

Expert verified

(a) 2 M HCl is more acidic. (b) 1 M H2SO4 is more acidic.

Step by step solution

Identify the concentration of the acids

Higher concentration of an acid will result in a more acidic solution if comparing the same acid.(a) Compare 1 M HCl and 2 M HCl.(b) Both are 1 M solutions (1 M HNO3 and 1 M H2SO4).

Compare the same acid with different concentrations

For part (a), both solutions are of the same acid (HCl). Higher concentration means more H+ ions in solution.Since 2 M HCl has more H+ ions than 1 M HCl, 2 M HCl is more acidic.

Compare different acids with the same concentration

For part (b), compare the dissociation of HNO3 and H2SO4.HNO3 is a strong acid that dissociates completely to produce H+ ions.H2SO4 is a diprotic acid, meaning it can donate two H+ ions. Even though it dissociates completely in the first step and partially in the second step, it still results in more H+ ions than HNO3 at the same concentration.Therefore, 1 M H2SO4 is more acidic than 1 M HNO3.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

'acid concentration'

When discussing acid concentration, we're essentially talking about the amount of acid molecules present in a given volume of solution. If you have a higher concentration, there are more acid molecules available to donate protons (H⁺ ions). For example, in the exercise, we compared 1 M HCl and 2 M HCl. Here, 'M' stands for molarity, which measures concentration.

Because 2 M HCl has twice as many H⁺ ions per unit volume as 1 M HCl, it is more acidic. Higher molarity directly impacts the acidity by increasing the number of free hydrogen ions in the solution.

To sum up, higher acid concentration means:

More available protons
Higher acidity
Lower pH

'acid strength'

Acid strength refers to how completely an acid dissociates in water to produce H⁺ ions. A strong acid fully dissociates, releasing more protons into the solution, while a weak acid only partially dissociates.

In the exercise, we compared HNO₃ (a strong acid) and H₂SO₄ (a diprotic strong acid). Although both are strong acids, H₂SO₄ can dissociate twice, releasing two protons compared to one from HNO₃. This means that, at the same concentration, H₂SO₄ will result in more available H⁺ ions.

Strong acids like HNO₃ and H₂SO₄ have:

Complete dissociation in water
High H⁺ ion concentration
Significantly lower pH

'pH level'

The pH level is a scale used to measure the acidity or basicity of a solution. It is inversely related to the concentration of H⁺ ions. The formula to calculate pH is:

\[ \text{pH} = -\text{log}[\text{H}^+] \]

Lower pH values indicate higher acidity. A strong acidic solution with a high concentration of H⁺ ions will have a low pH. The pH scale ranges from 0 to 14, with 7 being neutral. Values lower than 7 are acidic, and those above are basic.

In the provided exercise, solutions with higher concentrations of strong acids, like 2 M HCl or 1 M H₂SO₄, will have very low pH values compared to their less concentrated counterparts.

Key points about pH levels:

Lower pH means higher acidity
pH is determined by H⁺ ion concentration
Strong acids significantly lower pH

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For each of the given pairs, determine which solution is more acidic. All are water solutions. Explain your answer. (a) \(1 \mathrm{M} \mathrm{HCl}\) or \(2 \mathrm{M} \mathrm{HCl}\) ? (b) \(1 M \mathrm{HNO}_{3}\) or \(1 M \mathrm{H}_{2} \mathrm{SO}_{4}\) ?

Short Answer

Step by step solution

Identify the concentration of the acids

Compare the same acid with different concentrations

Compare different acids with the same concentration

Key Concepts

'acid concentration'

'acid strength'

'pH level'

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