Acids, bases and salts Flashcards
What are acids?
Substances with a pH of less than 7
How can you detect an acid?
They turn litmus paper red or turn universal indicator orange or red.
What are bases?
Substances that can react with acids and neutralise them to make a salt and water
Give some examples of bases
Copper oxide,
Sodium hydroxide.
What are alkalis?
Bases that dissolve in water are called alkalis.
They have a pH of more than 7.
How can you detect alkalis?
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 are neutral solutions?
Neutral solutions have a pH of 7.
They do not change the colour of litmus paper, but they turn universal indicator paper green.
E.g. Water is neutral.
What ions are formed when acids dissolve in water?
When acids dissolve in water they produce aqueous hydrogen ions, H+(aq)
What does (aq) mean?
(aq) means aqueous (dissolved in water)
What happens when alkalis dissolve in water?
When alkalis dissolve in water they produce aqueous hydroxide ions, OH–(aq).
What happens when the H+(aq) ions from an acid react with the OH–(aq) ions from an alkali?
A neutralisation reaction occurs to form water:
H+(aq) + OH–(aq) → H2O(l)
What happens when acids react with bases?
A salt and water are made
Give two examples of an acid reacting with a base
acid + metal oxide → salt + water
acid + metal hydroxide → salt + water
Whats the equation for an acid reacting with a metal?
acid + metal → salt + hydrogen
What are the second part of the the salt called?
Chloride (if hydrochloric acid is used)
Nitrate (if nitric acid is used)
Sulfate (if sulfuric acid is used)
How do you crystallise a salt solution?
If the base dissolves in water, you need to add just enough acid to make a neutral solution.
Warm the salt solution to evaporate the water. You get larger crystals if you evaporate the water slowly.
How are insoluble salts made?
They can be made by mixing appropriate solutions of ions together.
Or by reacting together two soluble salts in a precipitation reaction.
What does it mean when a salt is insoluble?
The salt doesn’t dissolve in water.
What can you use a precipitation reaction for?
Precipitation reactions can be used to remove unwanted ions in solution.
This is useful for treating drinking water and waste water.
