Acid Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Acid.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A substance that donates $\text{H}^+$ ions (protons) when dissolved in water, increasing the hydrogen ion concentration and lowering the pH below 7.

Sour-tasting substances that can 'burn'—they give away hydrogen ions.

Read the full concept explanation →

How to Use These Examples

Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Acid starts by identifying the acid/base species, ions produced or transferred, and pH evidence.

Common stuck point: Students often know a formula related to acid but skip the recognition step: Am I tracking acid/base identity, pH, ions in solution, neutralization, buffer behavior, or salt formation? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I tracking acid/base identity, pH, ions in solution, neutralization, buffer behavior, or salt formation?

Common Mistakes to Watch For

Before you work through the examples, skim the mistake guide so you know which shortcuts and sign errors to avoid.

pH Mistakes

Worked Examples

Example 1

easy

According to the Arrhenius definition, what makes a substance an acid? Give two examples.

Answer

\text{Acids produce H}^+\text{ in water: HCl, H}_2\text{SO}_4

First step

An Arrhenius acid produces

\text{H}^+

ions (protons) when dissolved in water.

Full solution

2
Example 1: $\text{HCl} \rightarrow \text{H}^+ + \text{Cl}^-$ (hydrochloric acid).
3
Example 2: $\text{H}_2\text{SO}_4 \rightarrow 2\text{H}^+ + \text{SO}_4^{2-}$ (sulfuric acid).

The Arrhenius definition is the simplest model for acids. The Brønsted-Lowry definition extends this to any proton donor, even in non-aqueous solvents.

Example 2

medium

Distinguish between a strong acid and a weak acid. Give an example of each.

Example 3

easy

Classify each as a strong or weak acid:

\text{HF}

\text{HClO}_4

\text{HCN}

Example 4

medium

Write the dissociation equation for

\text{H}_2\text{SO}_4

in water, showing both ionization steps.

Example 5

medium

What volume of

0.50\,\text{M}

HCl contains

0.025\,\text{mol}

\text{H}^+

Example 6

medium

Write the net ionic equation when HCl reacts with NaOH in water.

Example 7

hard

25.0\,\text{mL}

sample of HCl is titrated to the endpoint with

32.0\,\text{mL}

0.150\,\text{M}

NaOH. Find the HCl molarity.

Example 8

challenge

Explain why pure water is not classified as an acid even though it contains

\text{H}^+

ions.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy

Name three common strong acids.

Example 2

easy

What particle does an acid donate in solution, and how does that affect the hydrogen-ion concentration of the solution?

Example 3

easy

By the Arrhenius definition, what ion does an acid produce in water?

Example 4

easy

By the Bronsted-Lowry definition, an acid is a proton ____.

Example 5

easy

Is the pH of an acidic solution above or below 7?

An acidic solution sits below pH 7 on the scale.

Example 6

easy

Classify

\text{HCl}

as a strong or weak acid.

Example 7

easy

Does 'strong acid' refer to the degree of ionization or the amount of acid per volume?

Example 8

easy

Name one common safe acid found in food.

Example 9

easy

\text{H}_2\text{SO}_4

can donate how many protons?

Example 10

easy

When

\text{HCl}

dissolves in water, write the ions produced.

Example 11

medium

0.01\,\text{M}

solution of the strong acid

\text{HCl}

has what

[\text{H}^+]

and pH?

0.01 M HCl is a strong acid: [H⁺] = 0.01 M, pH = 2.

Example 12

medium

Compare

1\,\text{M}

acetic acid (weak) and

1\,\text{M}

HCl (strong). Which has the lower pH and why?

Example 13

medium

\text{HNO}_3

ionizes completely. For a

0.001\,\text{M}

solution, find the pH.

HNO₃ is strong: [H⁺] = 10⁻³ M, so pH = 3.

Example 14

medium

Why does a concentrated weak acid not necessarily have a lower pH than a dilute strong acid?

Example 15

medium

Write the Bronsted-Lowry acid in the reaction

\text{HCl}+\text{H}_2\text{O}\rightarrow\text{H}_3\text{O}^++\text{Cl}^-

Example 16

medium

How many moles of

\text{H}^+

are available from

0.5\,\text{mol}

\text{H}_2\text{SO}_4

(fully ionized)?

Example 17

medium

A solution of pH 1 is diluted tenfold with water. Estimate the new pH (strong acid, ignoring water autoionization).

Tenfold dilution shifts [H⁺] from 10⁻¹ to 10⁻², raising pH by one unit.

Example 18

medium

Identify the conjugate base of the acid

\text{HNO}_3

Example 19

medium

0.10\,\text{M}

HCl solution: find

[\text{H}^+]

and pH (strong, fully ionized).

Complete ionization: [H⁺] = 10⁻¹ M, pH = 1.

Example 20

challenge

Equal volumes of

0.10\,\text{M}

HCl and

0.10\,\text{M}

acetic acid are titrated with NaOH. Which needs more NaOH to neutralize, and why?

Example 21

challenge

\text{H}_2\text{SO}_4

has two different

K_a

values for its two protons. Which proton is released more readily, and why?

Example 22

challenge

Why is

0.001\,\text{M}

HCl pH 3, but

0.001\,\text{M}

of a weak acid that is 10% ionized has a higher pH?

At 0.001 M, HCl (100% ionized) gives pH 3; the weak acid (10% ionized) gives pH 4.

Example 23

easy

What range of pH values are considered acidic?

Acidic solutions have pH < 7; basic solutions have pH > 7.

Example 24

easy

Which acid is found in the human stomach to aid digestion?

Example 25

easy

What color does blue litmus paper turn in an acidic solution?

Example 26

easy

Write the conjugate base of

\text{HBr}

Example 27

easy

True or false: a dilute strong acid solution can have a higher pH than a concentrated weak acid solution.

Example 28

medium

Calculate the pH of a

1.0\times 10^{-4}\,\text{M}

HCl solution.

Example 29

medium

What is

[\text{H}^+]

in a solution of pH 5?

Example 30

medium

How many moles of

\text{H}^+

are produced when

0.25\,\text{mol}

\text{H}_3\text{PO}_4

fully ionizes?

Example 31

medium

50.0\,\text{mL}

sample of

0.20\,\text{M}

HCl is mixed with

50.0\,\text{mL}

of water. What is the pH?

Example 32

medium

Identify the Bronsted-Lowry acid and its conjugate base in:

\text{NH}_4^+ + \text{H}_2\text{O} \rightleftharpoons \text{NH}_3 + \text{H}_3\text{O}^+

Example 33

medium

A weak acid HA has

K_a = 1.0\times 10^{-5}

. Estimate the pH of a

0.10\,\text{M}

solution.

Example 34

medium

Which has a lower pH:

0.10\,\text{M}

HCl or

0.10\,\text{M}

HF? Explain in one line.

Example 35

hard

0.0050\,\text{M}

solution of

\text{H}_2\text{SO}_4

(treat both ionizations as complete). Find the pH.

Example 36

hard

How many milliliters of

0.10\,\text{M}

NaOH are needed to neutralize

25.0\,\text{mL}

0.20\,\text{M}

HCl?

Example 37

hard

An acetic acid solution is 1.3% ionized at

0.10\,\text{M}

. Calculate

[\text{H}^+]

and pH.

Example 38

hard

Two solutions, A (pH 2) and B (pH 5), are compared. By what factor is

[\text{H}^+]

larger in A than in B?

A 3-unit pH difference means 10³ = 1000× more [H⁺] in solution A.

Example 39

challenge

0.20\,\text{M}

weak acid HA gives a pH of

2.85

. Determine

K_a

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Related Concepts

Ion Base pH Neutralization

Background Knowledge

These ideas may be useful before you work through the harder examples.

ion