unit 5 lesson 2 acids, bases, and salts copyright © houghton mifflin harcourt publishing company

Unit 5 Lesson 2 Acids, Bases, and Salts

Copyright © Houghton Mifflin Harcourt Publishing Company

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What are acids and bases?• Acids and bases are chemicals that increase the

number of ions present in a water solution when they dissolve.

• Lemon juice and vinegar both contain acid.

• Shampoo and window cleaner both contain bases.


How do acids and bases interact with water?

• Water is made up of molecules of H2O. In any given sample of water, a small number of these molecules break apart to form hydronium ions (H3O+) and hydroxide ions (OH–).

• An acid increases the number of positively charged H3O+ ions when it dissolves in water.

• A base increases the number of negatively charged OH– ions when it dissolves in water.




• A water sample contains mostly whole H2O molecules, with only a few H3O+ ions and OH–.

• The molecules of all acids contain at least one atom of hydrogen that can be pulled off by a water molecule to form H3O+ ions.

• The molecules of many bases contain at least one hydroxide ion. When these bases dissolve in water, they break apart to release the OH– ions. Other bases do not contain OH– ions. When they dissolve in water, they take hydrogens from water molecules and form OH– ions.




• Locate the hydronium ions in the acidic solution. Locate the hydroxide ions in the basic solution.



What is the difference between strong and weak acids and bases?

• The strength of an acid or a base depends upon how many ions it releases into solution.

• The strength of an acid or a base is not the same as its concentration. Dilute hydrochloric acid is still strong and can damage your skin, but concentrated citric acid does not harm your skin.




• In water, all of the molecules of a strong acid break apart completely, forming many H3O+ ions. All of the molecules of a strong base also break apart completely in water to form OH– ions.

• Weak acids and bases do not break apart completely into ions. Only a few molecules form ions in water. Therefore, few hydronium ions or hydroxide ions are produced.




• How do strong acids and bases behave differently than weak acids and bases?



No-Nonsense Self Defense


• Many insects and sea animals use acids or bases to protect themselves from predators. Some animals spray the acids or bases at their enemies. Other animals can secrete acids from their skin.

• Fire ants use a structure on their abdomen to inject a toxic base into their victim. They hold on to its skin with their pincers and sting again and again.


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What are the physical properties of acids?

• Acids taste sour. However, you should never use taste, touch, or smell to identify an unknown chemical. Some acids can damage body tissue. Most strong acids are poisonous.

• When a strong acid is dissolved in water, it breaks apart and forms ions in solution. The ions make it possible for the solution to conduct an electric current.


What are some chemical properties of acids?

• Acids are corrosive. They can react with and destroy body tissue, clothing, and other things. Acids react violently with many metals.

• Acids react with certain compounds called acid-base indicators. They cause the indicators to change color.

• For example, litmus paper is a type of indicator. Blue litmus paper turns red in the presence of an acid.



What are the physical properties of bases?

• Bases taste bitter. However, you should never use taste, touch, or smell to identify a base because many bases can cause burns.

• Bases feel slippery. If your hands feel slippery while working with a base during a lab activity, immediately rinse your hands with water and tell an adult.

• Like acids, solutions of bases conduct an electric current.



What are some chemical properties of bases?

• Bases are caustic. This property means that they can burn or corrode other substances.

• Bases also change the color of acid-base indicators. Most indicators turn a different color in the presence of a base than they do in the presence of an acid.

• For example, a base causes red litmus paper to turn blue.



Shift into Neutral


What is a neutralization reaction?• A neutralization reaction is the reaction

between an acid and a base in a water solution.

• Two products of a neutralization reaction are water and a salt. Water molecules form when the hydrogen ions from the acid combine with the hydroxide ions from the base to make H2O.

• A salt is an ionic compound that forms from the negative ion of the acid and the positive ion of the base.


What are some examples of salts?• The identity of the salt that forms in a

neutralization reaction depends on the identities of the acid and base.

• Salts have many uses in industry and in homes.

• Sodium chloride is used to make baking soda as well as to season your food.

• Sodium nitrate is a salt that preserves food.



What are some examples of salts?• Calcium sulfate is used to make plasterboard,

which is an important component in the construction of homes and buildings.

• Calcium chloride is used to help keep ice from forming on roads and sidewalks in winter.

• Calcium sulfate can be compressed into colored sticks of chalk used by artists.



unit 5 lesson 2 acids, bases, and salts copyright © houghton mifflin harcourt publishing company

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