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Chapter 15: Problem 51

Determine whether each of the following describes a substance that is acidic, basic, or neutral: (a) Red litmus paper turns blue (b) \(\mathrm{pH}=6\) (c) \(\left[\mathrm{H}^{+}\right]=1 \times 10^{-7}\) (d) \(\left[\mathrm{OH}^{-}\right]=1 \times 10^{-8}\) (e) Blue litmus paper turns red (f) \(\mathrm{pH}=12\)

Short Answer

Expert verified
(a) Basic, (b) Acidic, (c) Neutral, (d) Acidic, (e) Acidic, (f) Basic

Step by step solution

01

Determine the Nature of Substance (a)

Red litmus paper turning blue indicates that the substance is a base.
02

Determine the Nature of Substance (b)

A solution with \(\text{pH}=6\) is slightly acidic since the pH value is less than 7.
03

Determine the Nature of Substance (c)

For \(\text{[H}^{+}] = 1 \times 10^{-7}\), we calculate the pH as follows: \[ \text{pH} = -\text{log}(\text{[H}^{+}]) \] Plugging in the given concentration: \[ \text{pH} = -\text{log}(1 \times 10^{-7}) = 7 \] A pH of 7 is neutral.
04

Determine the Nature of Substance (d)

For \(\text{[OH}^{-}] = 1 \times 10^{-8}\), we first need to find the pOH and then calculate the pH. First, calculate pOH: \[ \text{pOH} = -\text{log}(\text{[OH}^{-}]) \] \[ \text{pOH} = -\text{log}(1 \times 10^{-8}) = 8 \] Now, use the relationship between pH and pOH: \[ \text{pH} + \text{pOH} = 14 \] So, \[ \text{pH} = 14 - 8 = 6 \] A pH of 6 indicates that the solution is slightly acidic.
05

Determine the Nature of Substance (e)

Blue litmus paper turning red indicates that the substance is an acid.
06

Determine the Nature of Substance (f)

A solution with \(\text{pH} = 12\) is basic since the pH value is greater than 7.

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Key Concepts

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

Acid-Base Identification
Acids and bases are classified based on their chemical properties and behavior in different conditions. Acids usually taste sour, can conduct electricity, and react with metals to form hydrogen gas. Bases, on the other hand, taste bitter, feel slippery, and can also conduct electricity. An important tool for identifying acids and bases is the litmus test.

In a litmus test:
  • Red litmus paper turns blue when exposed to a base.
  • Blue litmus paper turns red when exposed to an acid.
This simple test helps quickly determine if a solution is acidic or basic. If there is no reaction with litmus paper, the substance is likely neutral.
pH Calculations
The pH scale measures how acidic or basic a solution is. It ranges from 0 to 14, with 7 being neutral. Solutions with a pH less than 7 are acidic, while those with a pH greater than 7 are basic. The pH of a solution is calculated using the formula:

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

For example, if the concentration of hydrogen ions, \text{[H}^{+}]\, is \(1 \times 10^{-7}\), the pH is:

\[ \text{pH} = -\text{log}(1 \times 10^{-7}) = 7 \]

This indicates a neutral solution. For hydroxide ions, \text{[OH}^{-}]\, the pOH is calculated first:

\[ \text{pOH} = -\text{log} (\text{[OH}^{-}]) \]

Then, use the relationship \text{pH} + \text{pOH} = 14\ to find the pH.
Litmus Test
The litmus test is a common and quick method to identify whether a substance is acidic or basic. This test uses colored papers: red and blue litmus papers. Here's how to interpret the results:

  • Red litmus paper turns blue – the substance is a base.
  • Blue litmus paper turns red – the substance is an acid.
When performing the test, dip the litmus paper into the solution. Observe the color change to determine the acidity or basicity of the solution. If no color change occurs, the substance is likely neutral.
Concentration of Ions
The concentration of ions in a solution determines its pH level. Hydrogen ions ( \text{[H}^{+}]\ ) make a solution acidic, while hydroxide ions ( \text{[OH}^{-}]\ ) make it basic. To find the pH with \text{[H}^{+}]\ concentration, use:

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

To find pH with \text{[OH}^{-}]\ concentration, first calculate the pOH:

\[ \text{pOH} = -\text{log} (\text{[OH}^{-}]) \]

Then use:

\[ \text{pH} + \text{pOH} = 14 \]

This relationship helps to determine whether the solution is acidic, basic, or neutral based on the ion concentrations.

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Most popular questions from this chapter

Identify the conjugate acid-base pairs in each of the following equations: (a) \(\mathrm{H}_{2} \mathrm{~S}+\mathrm{NH}_{3} \rightleftharpoons \mathrm{NH}_{4}^{+}+\mathrm{HS}^{-}\) (b) \(\mathrm{HSO}_{4}^{-}+\mathrm{NH}_{3} \rightleftharpoons \mathrm{SO}_{4}^{2-}+\mathrm{NH}_{4}^{+}\) (c) \(\mathrm{HBr}+\mathrm{CH}_{3} \mathrm{O}^{-} \rightleftharpoons \mathrm{Br}^{-}+\mathrm{CH}_{3} \mathrm{OH}\) (d) \(\mathrm{HNO}_{3}+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{NO}_{3}^{-}+\mathrm{H}_{3} \mathrm{O}^{+}\)

Determine whether each of the following substances is an electrolyte or a nonelectrolyte. All are mixed with water. (a) \(\mathrm{SO}_{3}\) (d) \(\mathrm{O}_{2}\) (insoluble) (b) \(\mathrm{K}_{2} \mathrm{CO}_{3}\) (e) \(\mathrm{CuBr}_{2}\) (c) \(\mathrm{CH}_{3} \mathrm{OH}\) (methyl alcohol) (f) \(\mathrm{HI}\)

Two drops \((0.1 \mathrm{~mL})\) of \(1.0 \mathrm{M} \mathrm{HCl}\) are added to water to make \(1.0 \mathrm{~L}\) of solution. What is the \(\mathrm{pH}\) of this solution if the \(\mathrm{HCl}\) is \(100 \%\) ionized?

Calculate the \(\left[\mathrm{H}^{+}\right]\)for (a) black coffee, with a \(\mathrm{pH}\) of \(5.0\) (b) black tea with a pH of \(6.8\) (c) green tea with a pH of \(7.9\) (d) laundry detergent with a pH of \(9.7\)

Identify the conjugate acid-base pairs in each of the following equations: (a) \(\mathrm{NH}_{3}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{NH}_{4}^{+}+\mathrm{OH}^{-}\) (b) \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}+\mathrm{H}_{3} \mathrm{O}^{+}\) (c) \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}+\mathrm{OH}^{-} \rightleftharpoons \mathrm{HPO}_{4}^{2-}+\mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{HCl}+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{Cl}^{-}+\mathrm{H}_{3} \mathrm{O}^{+}\)
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