Acids, bases and salts Flashcards
What is the pH of an acid?
Under 7.
What is the pH of a base?
Over 7.
What are bases known as when they dissolve in water?
Alkalis.
When are salts made?
When an acid reacts with a base, carbonate or metal.
What does the name of a salt depend on?
The metal in the base and the acid used.
What happens if a substance has a low pH?
It is highly acidic. Acidic solutions turn blue litmus paper red. They turn universal indicator paper red if they are strongly acidic, and orange or yellow if they are weakly acidic.
What is a base?
Substances that can react with acids and neutralise them to make a salt and water.
What if a substance has a high pH?
It has a strong alkali. Alkalis turn red litmus paper blue. They turn universal indicator paper dark blue or purple if they are strongly alkaline, and blue-green if they are weakly alkaline.
What happens if a substance has pH of 7?
It is neutral. They do not change the colour of litmus paper, but they turn universal indicator paper green. Water is neutral.
What are ions and when do they form?
Ions are charged particles which are formed when atoms, or groups of atoms, lose or gain electrons.
What happens when acids dissolve in water?
When acids dissolve in water they produce aqueous hydrogen ions.
What happens when alkalis dissolve in water?
When alkalis dissolve in water they produce aqueous hydroxide ions.
What happens when acids react with bases?
A salt and water are made.
What happens when an acids reacts with a reactive metal?
A salt and hydrogen are produced.
How is a soluble salt made?
If the base dissolves in water, you need to add just enough acid to make a neutral solution. Check a small sample with universal indicator paper. If ammonia solution is used, you can add a little more than needed to get a neutral solution.
Warm the salt solution to evaporate the water. You get larger crystals if you evaporate the water slowly.
Copper oxide, and other transition metal oxides or hydroxides, do not dissolve in water. If the base does not dissolve in water, you need an extra step. You add the base to the acid until no more will dissolve and you have some base left over (called an excess). You filter the mixture to remove the excess base, then evaporate the water in the filtrate to leave the salt behind.
