C8. Acids, bases and salts Flashcards
What is the pH scale range for acids?
1 - 6
What is the pH scale for neutral?
7
What is the pH scale for bases?
8 - 14
What are ‘acids’?
A compound which produces hydrogen ions when dissolved in water.
Name the reactions of dilute acids.
- Metal + acid -> salt + hydrogen
- Metal pxides + acid -> salt + water
- Carbonates + acid -> salt + water + carbon dioxide
What is a ‘base’?
A substance that can neutralise an acid.
What is an ‘alkali’?
A soluble base.
Name the reactions of bases with acids.
- Base + acid -> salt + water
What are ‘oxides’?
Compounds of metals or non-metals with oxygen.
How are acidic oxides formed?
Non-metals reacting with oxygen.
How are basic oxides formed?
Metals reacting with oxygen.
How do we make salts?
- Reacting a metal with an acid
- Reacting an insoluble base with an acid
- Neutralising an alkali with an acid by the titration method
- By precipitation
What are the conditions for making salts from metals?
Only for metals above hydrogen in the reactivity series.
How do we make salts from metals?
- Add the metal to the acid in a flask so that the metal is in excess.
- Warm the flask gently to complete the reaction.
- Filter off the excess metal.
- Put the filtrate into an evaporating basin and evaporate the water until the crystallisation point is reached; allow salt to crystallise at room temp.
- Filter off the crystals and wash them with a tiny amount of solvent so they don’t dissolve.
- Dry the crystals between sheets of filter paper.
How to make salts from insoluble bases?
By reacting an insoluble base with an acid.
Only for metals that are low in the reactivity series.
How to test for hydrogen?
Lighted splint at the mouth of the test tube -> squeaky pop
How to test for oxygen?
Glowing splint into the test tube -> splint relights
How to test for ammonia?
Holds a damp red litmus paper at the mouth of the test tube -> turns red litmus blue
How to test for carbon dioxide?
Limewater -> turns cloudy/milky
How to test for chlorine?
Damp litmus paper at the mouth of the test tube -> paper turns white - bleached
How to test for sulfur dioxide?
Potassium mangante(VII), which is purple -> turns the liquid colourless
Tests for cations by means for aqueous sodium hydroxide:
- ammonium
- copper(II)
- iron(II)
- iron(III)
- zinc
Ammonium: white precipitate Copper: light blue precipitate Iron(II): grey-green precipitate Iron(III): reddish-brown precipitate Zinc: white precipitate
Tests for cations by means for aqueous ammonia:
- ammonium
- copper(II)
- iron(II)
- iron(III)
- zinc
Ammonium: white precipitate Copper: light blue precipitate Iron(II): grey-green precipitate Iron(III): reddish-brown precipitate Zinc: white precipitate
How to identify carbonates?
Adding a dilute acid to an unknown compound then testing the gas produced with limewater.
