Acid Reactions & Salts
Describe word equations for suitable metals reacting with dilute hydrochloric acid, and for acids reacting with alkalis and basic metal oxides or hydroxides. Name salts, describe the supervised hydrogen test, and explain practical neutralisation.
What a learner can do afterwards
- Writes word equations for suitable metals with dilute hydrochloric acid producing salt and hydrogen, and for acids with alkalis or basic metal oxides or hydroxides producing salt and water
- Names the salt formed from a given acid and base (e.g. hydrochloric acid + sodium hydroxide → sodium chloride)
- Describes the squeaky-pop test for a small collected hydrogen sample in a teacher-supervised laboratory with eye protection
- Explains what neutralisation means and gives a practical example (indigestion tablets, treating acidic soil)
1 · Read
You have learned about acids and alkalis. Their reactions can produce salts. A salt is an ionic compound containing positive and negative ions. The salts here contain a metal ion and an ion from the acid, though some other salts contain no metal. A word equation lists reactants before an arrow and products after it. The arrow means 'produces'.
Magnesium and zinc react with dilute hydrochloric acid. For zinc: hydrochloric acid + zinc → zinc chloride + hydrogen. The bubbles are hydrogen gas. Magnesium follows the same pattern and forms magnesium chloride. Copper does not react this way with dilute hydrochloric acid. Check the stated reactants before choosing a product pattern.
In a teacher-supervised laboratory, a small hydrogen sample is collected in a test tube. A lighted splint held at the tube's mouth gives a squeaky pop. Wear eye protection and follow the teacher's method. Do not try this with household chemicals. Carbon dioxide turns limewater cloudy; that is a different gas test.
A base reacts with acid to reduce its acidity. An alkali is a base that dissolves in water. Common basic metal oxides and metal hydroxides react with acids to make salt and water. This is neutralisation. With hydrochloric acid, they form a metal chloride and water, not hydrogen. Sodium hydroxide solution is an alkali. Copper oxide is a base but not an alkali. Excess acid or base can leave the mixture non-neutral.
To name these salts, take the metal name from the metal or base. Hydrochloric acid gives chloride salts; sulfuric acid gives sulfate salts; nitric acid gives nitrate salts. For example: sulfuric acid + lithium hydroxide → lithium sulfate + water. You can also work backwards: a nitrate salt points to nitric acid in these reactions.
Some antacids contain magnesium hydroxide, a base that reacts with stomach acid to make salt and water. Agricultural lime often contains calcium carbonate, a base used to reduce soil acidity. Carbonates react with acids to make salt, water and carbon dioxide. These bases need not be alkalis. Follow medical directions for antacids; this lesson is not advice to treat stomach pain.
Suitable metals with dilute hydrochloric acid make salt and hydrogen. Basic oxides and hydroxides make salt and water. Carbonates also make carbon dioxide. Gas tests need teacher supervision.
Lesson, questions and flashcards written for this dataset.
Check the reactants first and Bases used to reduce acidity were written for this dataset. Flashcards were written for this dataset.
More to read
Check the reactants first
A product prediction starts with both reactants. A metal and a compound containing that metal need not react with acid in the same way.
Magnesium reacts with dilute hydrochloric acid to make magnesium chloride and hydrogen. Copper does not react this way with that acid. The pattern is useful only when the metal and acid are suitable.
A basic metal oxide reacts with acid to make salt and water. Common metal hydroxides follow that product pattern too. An alkali is a base that dissolves in water, but a base does not have to be an alkali to neutralise acid.
Salt names provide another check. Hydrochloric acid gives chloride salts, sulfuric acid gives sulfate salts, and nitric acid gives nitrate salts. Use the metal name from the other reactant. You can reverse this reasoning to identify the acid from a salt name.
Gas identification belongs in a supervised laboratory. A small collected hydrogen sample gives a squeaky pop with a lighted splint. Wear eye protection and follow the teacher's method. Do not try gas tests with household chemicals.
Bases used to reduce acidity
Different bases can reduce acidity through chemical reactions.
Some antacids contain magnesium hydroxide. It reacts with hydrochloric acid in the stomach to form magnesium chloride and water. This explains a reaction, not how to choose or take medicine. Follow medical directions.
Agricultural lime often contains calcium carbonate. When it reacts with acid in soil, it reduces acidity. Carbonates produce carbon dioxide as well as salt and water when they react with acids. That extra gas distinguishes their product pattern from the oxide and hydroxide patterns.
Neutralisation does not mean any mixture automatically finishes at pH 7. If acid remains in excess, the mixture can remain acidic. If a soluble base remains in excess, it can be alkaline. The amounts of the reactants matter.
2 · Watch
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