Studied by 15 peopleLitmus in acid
Red
litmus in alkali
blue
Phenolphthalein in acid
Colourless
Phenolphthalein in alkali
Pink
Methyl Orange in acid
Red
Methyl Orange in alkali
Yellow
pH scale
0-14
pH scale Strongly acidic
0-4
pH scale Weakly acidic
4-6
pH scale neutral
7
pH scale weakly alkaline
8-10
pH scale strongly alkaline
10-14
What is universal indicator?
A mixture of different plant indicators which operate across a broad pH range and is useful for estimating the pH of an unknown solution
Describe the use of universal indicator to measure the approximate pH value of an aqueous solution
A few drops are added to the solution and the colour is matched with a colour chart which indicates the pH that matches with specific colours
When acids are added to water ...?
they form positively charged hydrogen ions (H+)
What makes a solution acidic?
the presence of H+ ions
When alkalis are added to water ...?
they form negative hydroxide ions (OH-)
What makes a solution alkali?
the presence of OH- ions
What is the pH scale?
a numerical scale which is used to show how acidic or alkaline a solution is. In other words, it is a measure of the amount of ions present in solution
When does a neutralisation reaction occur?
When an acid reacts with an alkali
What happens when an acid reacts in a neutralisation reaction with an alkali?
The H+ ions react with the OH- ions to produce water
Titrations
A method of analysing the concentration of solutions Can be used to prepare salts
How to perform a titration
(See method in booklet 2.6)
Soluble ionic compounds
Compounds of sodium, potassium and ammonium All nitrates Nearly all chlorides Nearly all sulphates Sodium, Potassium, and Ammonium carbonates Sodium Potassium, and calcium hydroxides
Insoluble Ionic compounds
Silver and lead (II) chlorides Barium, calcium, and lead (II) sulphates Nearly all carbonates Nearly all hydroxides
Salt
A salt is a substance formed from an acid where the H+ ions in the acid are replaced by either metal ions or ammonium ions Ionic compounds
Acids
Proton donors as they ionise in solution producing protons, H+ ions These H+ ions make the aqueous solution acidic Acids release H+ ions when dissolved in water
Alkalis are ________ bases
soluble
Bases (Alkalis)
Bases (alkalis) are proton acceptors as they ionise in solution producing OH- ions which can accept protons These OH- ions make the aqueous solution alkaline Alkalis dissolve in water to release OH- ions
A proton is the same as ...? And why?
a H+ ions because a hydrogen atoms only contains one proton and one electron. When a hydrogen ion is formed, the electron is lost and a proton is left behind
General equation for metals reacting with acid
metal + acid -> salt + hydrogen
Which metals will react with dilute acids?
only metals above hydrogen
Reaction of acids with bases makes ...?
Soluble salts
General equation in all acid-base neutralisation reactions
acid + base -> salt + water
Which substances act as bases?
Metal oxides, metal hydroxides and ammonium
Reactions of acids with metal carbonates make ...?
Soluble salts
General equation for the acids reacting with metal carbonates
metal carbonate + acid -> salt + carbon dioxide + water
Base
Substances which can neutralise an acid, forming a salt and water
Bases are usually ...?
Oxides, hydroxides or carbonates of metals
Describe an experiment to prepare a pure, dry sample of a soluble salt, starting from an insoluble reactant
(See method in booklet 2.7)
Solubility
The amount (mass) of solute needed for 100g of solvent to maintain a saturated solution at a certain temperature
Note
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