Acid, Bases & Salts

​Acids, Bases & Salts

By Mischel Wink

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Identify basic examples of and compare and classify the properties of compounds, including acids, bases, and salts.

Key Vocabulary

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Acid

An acid is a solution with a pH lower than 7 and many hydronium ions.

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Base

A base is a solution with a pH higher than 7 and few hydronium ions.

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pH Scale

The pH scale measures how acidic or basic a solution is on a scale from 0-14.

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Neutralization

Neutralization is when an acid and a base react, forming a neutral solution of salt and water.

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Ion

An ion is an atom or molecule that has an electrical charge from gaining or losing electrons.

Acids are corrosive substances characterized by a strong smell, a sour taste, and a pH of less than 7. Acids produce hydronium ions when dissolved in water. Examples of acids include lemon juice, hydrochloric acid, vinegar, and sulfuric acid.

Bases are corrosive substances characterized by a bitter taste, slippery feel, and a pH greater than 7. Bases produce hydroxide ions when dissolved in water. Examples of bases include antacids, ammonia, soap, baking soda, and drain cleaner. A basic solution is also called alkaline.

Both acids and bases can be dangerous and can burn skin. They should only be worked with if an adult or trained individual is present.

​Acids and Bases

The pH of a solution is a chemical property that is related to the concentration of hydronium ions in a solution. The higher the concentration of hydronium ions in a solution, the lower its pH. The pH scale has a range of 0 to 14.

• Solutions with a pH less than 7 are acidic.

• Solutions with a pH greater than 7 are basic.

When equal amounts of an acid and base react chemically, they neutralize each other. The products of a neutralization reaction always include a salt and water.

• Solutions with a pH of 7 are neutral.

​pH and Acidity

Multiple Choice

Which statement best explains the difference between acids and bases in water?

• Acids and bases both release the same type of ion but in different amounts.

• Acids produce hydrogen ions (H⁺), while bases produce hydroxide ions (OH⁻).

• Acids and bases do not contain ions because they are neutral substances.

• Bases increase hydrogen ions (H⁺), while acids remove hydroxide ions (OH⁻).

Several kinds of indicators have been developed to measure whether a substance is acidic or basic. Litmus paper is a special type of paper that changes color when it comes in contact with an acid or base. It can be used to determine the relative pH of a substance.

Red litmus paper will remain red if it contacts an acidic liquid, but it will turn blue if it contacts a basic liquid. Blue litmus paper will remain blue if it contacts a basic liquid, but it will turn red if it contacts an acidic liquid. Both types of litmus paper will turn purple when contacting a neutral liquid.

​Measuring Acydity and pH

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Properties of Acids

• An acid is a solution with a pH value lower than 7.

• ​Acids are proton donors, releasing hydrogen ions (H⁺) in water.

• They have a sour taste and can conduct electricity in solution because they contain ions.

• Acids react with bases to form a salt and water (neutralization reaction).

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Multiple Choice

Why can acids conduct electricity in solution?

• Because acids contain metal atoms that allow electrons to flow easily.

• Because acids always have a high pH, which increases electric flow.

• Because acids release ions in water that can move and carry electric charge.

• Because acids are thick liquids that let current pass through easily.

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Properties of Bases

• A base is a solution that has a pH level higher than 7.

• When in water, bases produce negatively charged hydroxide ions (OH^-).

• Bases often have a bitter taste and can feel slippery to the touch.

• They react with acids to form a salt and water in neutralization.

• Many household cleaners, such as bleach and ammonia, are common bases.

• The strength of a base increases as its pH value gets higher.

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Multiple Choice

A student tests a clear liquid that feels slippery and has a pH of 11. How would this liquid be classified?

• A strong acid

• A base

• A neutral substance

• A weak acid

Salt solutions can have characteristic odors. Or, they can be odorless.

Solutions containing salts can possess a variety of tastes (e.g., salty, sweet, bitter, sour, savory). Sodium benzoate, for example—the sodium salt of benzoic acid—is used as a preservative in food. At low concentrations, it is not detectable, but in higher concentrations, it is perceived to be sweet or bitter.

Finally, many salts have colors that are characteristic of the metal they contain. Copper salts, for instance, often produce solutions that are blue or blue green. Iron salts can be yellow, orange, or red. Some mercury salts, such as mercury sulfide (HgS), appear reddish. Sodium chloride (NaCl) solutions are colorless.

Physical Characteristics

Salts are formed during neutralization reactions, which occur when acids react with bases. Neutralization reactions produce molecules of water in addition to molecules of salt. This type of reaction generally takes form: ACID + BASE --> SALT + WATER

For instance, hydrochloric acid (HCl) reacts with the base sodium hydroxide (NaOH) to produce water (H₂O) and the salt sodium chloride (NaCl).

HCl (aq) + NaOH (aq) -->NaCl (aq) + H₂O (l)

Salt Formation

Multiple Choice

What happens when blue litmus paper is placed in a solution with a pH of 3?

• It remains colorless.

• It turns blue.

• It turns pink.

• It turns red.

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Acids and Bases in the Body

The Stomach

• ​The stomach secretes a strong acid, creating an environment with a very low pH.

• ​​This acid allows the enzyme pepsin to start breaking down proteins from your food.

• ​Pepsin is an enzyme that can only do its important job in a strong acid.

The Small Intestine

• ​A strong base is released to neutralize the acid coming from the stomach.

• ​​This creates a basic environment, which means it has a high pH level.

• ​The enzymes here need a high pH to continue digesting your food properly.

Multiple Choice

Why must the acidic contents from the stomach be neutralized in the small intestine?

• To make the food taste better.

• To allow the enzyme pepsin to continue working.

• Because the small intestine needs an acidic environment.

• Because the enzymes in the small intestine require a basic environment to function.

Multiple Choice

An unknown substance is tested. It has a bitter taste and feels slippery. What can you infer about its pH level?

• The pH is likely higher than 7.

• The pH is likely lower than 7.

• The pH cannot be determined from these properties.

• The pH is likely equal to 7.

Multiple Choice

Why is maintaining a specific pH level crucial for enzymes in the human body?

• It helps dissolve food particles completely.

• It prevents the body from absorbing toxins.

• It changes the color of the food being digested.

• Enzymes can only perform their specific jobs within a narrow pH range.

Multiple Choice

A student adds red litmus paper to an antacid solution and it turns blue. What does this indicate about the solution's hydronium ion (H₃O⁺) concentration?

• The H₃O⁺ concentration is higher than in pure water.

• The H₃O⁺ concentration is the same as in pure water.

• The H₃O⁺ concentration is lower than in pure water.

• The litmus test gives no information about H₃O⁺ concentration.

Multiple Choice

If you have a solution of stomach acid (pH ~2) and you add a substance that causes the pH to rise to 7, what process has occurred and what type of substance was added?

• Dissociation; another acid was added.

• Corrosion; a metal was added.

• Neutralization; a base was added.

• Evaporation; water was removed.