4.4 Making salts
Summary: Here are the formulae of three acids. What do they have in common? Tags: science oxford-science student-book-7 chemistry Created: 2026-05-19 Last Updated: 2026-05-19
After this topic, you will be able to:
- explain what a salt is in science
- predict the salt that forms when an acid reacts with a metal or base
- describe how to make a given salt from an acid and a metal or insoluble base.
Think back
- What is the chemical symbol of hydrogen?
- Is the pH of an acid below or above 7?
- Give the names of two Acids.
Key idea The reaction of an acid with a metal or a base makes a salt solution. You can evaporate the water from the salt solution to make salt crystals.
Key word salt
Here are the formulae of three acids. What do they have in common?
HCl – hydrochloric acid
HNO3 – nitric acid
H2SO4 – sulfuric acid
The formulae show that the acids are Compounds. They all include hydrogen Atoms.
What are salts?
A salt is a compound that forms when an acid reacts with a metal element or compound. The hydrogen atoms of the acid are replaced by atoms of the metal element. Figures 1 and 2 show two salts.
Figure 1Sodium chloride.
Figure 2Copper sulfate.
Sodium chloride is the salt you may add to food. Its formula is NaCl. A sodium atom (chemical symbol Na) has replaced the hydrogen of hydrochloric acid.
Farmers use copper sulfate to kill fungus. Its formula is CuSO4. Copper atoms (chemical symbol Cu) have replaced the hydrogen atoms of sulfuric acid.
A Write the definition of a salt.
Which reactions make salts?
Many salts exist naturally. Sodium chloride makes the sea salty. It also exists underground. Figure 3 shows the salt flats of Bolivia. These contain huge amounts of salts.
Figure 3Bolivian salt flats.
You can also make salts in Chemical Reactions.
The chemical reaction of an acid with a metal makes two Products: a salt and hydrogen. For example:
- Magnesium reacts with hydrochloric acid to make magnesium chloride (a salt) and hydrogen:
- Zinc reacts with sulfuric acid to make zinc sulfate (a salt) and hydrogen:
B Predict the name of the salt made when zinc reacts with hydrochloric acid.
Reacting an acid with a base also makes a salt. The products are a salt and water. For example:
Full text alternative to the content
C Predict the name of the salt made when sodium hydroxide reacts with nitric acid.
How can you make salt crystals?
The reactions of acids with metals or bases make salt solutions. Removing water makes salt crystals. Figure 4 shows how to make copper sulfate crystals.
Figure 4Steps for making copper sulfate crystals. Full text alternative to the content
Stretch zone
- Copy and complete the sentences. A salt is an element/a compound. In a salt, the hydrogen/oxygen atoms of an acid are replaced by metal atoms.
- Predict the name of the salt made when magnesium reacts with sulfuric acid.
- Predict the name of the salt made when potassium hydroxide reacts with hydrochloric acid.
Stretch zone
- Describe the steps in making copper chloride crystals from a base and an acid. Include the names of the base and the acid.