Acids are compounds which ionise/dissociate in water to produce hydrogen ions (H+).
Bases are compounds that are metal oxides or hydroxides that react with an acid to give a salt and water only.
Alkalis are bases that ionise/dissociate in water to produce hydroxide ions (OH-).
Examples of Acids & Bases
Copper (II) Oxide
Acids 1 to 3 are known as mineral / inorganic acids while Acids 4 to 6 are known as organic acids.
Bases 1 & 2 are insoluble bases while Bases 3 to 6 are soluble bases / alkalis.
Types of Reactions
Metal + Acid Salt + Hydrogen Gas
Metal Carbonate + Acid Salt + Water + Carbon Dioxide
Metal Oxide + Acid Salt + Water
Metal Hydroxide + Acid Salt + Water
Base + Acid Salt + Water (Neutralisation)
Alkali + Acid Salt + Water (Neutralisation)
Alkali + Ammonium Salt Salt + Water + Ammonia Gas
Alkali + Salt Metal Hydroxide + Salt
Tests for Gases:
Hydrogen Gas - Extinguishes a lighted splinter with a 'pop' sound.
Carbon Dioxide Gas - Released as effervescence. Reacts with limewater to form a white precipitate.
Ammonia Gas - Pungent odour. Turns red litmus paper blue.
Base / Alkali + Acid is an exothermic reaction.
Pb (s) + H2SO4 / HCl PbSO4 / PbCl2 + H2
Lead reacts slowly then stops. Salt forms on the surface of the lead. The salt formed is insoluble.
Acidic solutions have pH values < 7.
They contain more H+ ions and fewer OH- ions.
Neutral solutions have pH values = 7.
They contain equal amounts of H+ ions and OH- ions.
Alkaline solutions have pH values > 7.
They contain more OH- ions and fewer H+ ions.
1. Write a balanced chemical equation with state symbols.
2. Check which reactants and products can form ions in water. (Aqueous)
3. Split up these reactants and products into their respective ions.
4. Check for ions that appear in both LHS & RHS of the equation, these are spectator ions that can be removed from the equation.
5. For those reactants and products which are unable to form ions, do not split the compounds.
6. What is left will be the net ionic equation. The coefficients must be in the lowest ratio.
Silver ion: Ag+
Zinc ion: Zn2+
Properties of Acids
1. Acids are corrosive.
2. Acids have a sour taste.
3. Acidic solutions conduct electricity. (Electrolytes)
4. Acids change the colour of indicators.
Litmus Paper: Blue to Red
Methyl Orange Solution: Orange to Red
Universal Indicator Paper: Orange to Red
Universal Indicator Solution: Green to Red
Properties of Alkalis
1. Alkalis have a soapy feeling and a bitter taste.
2. Alkaline solutions conduct electricity. (Electrolytes)
3. Alkalis change the colour of indicators.
Litmus Paper: Red to Blue
Methyl Orange Solution: Orange to Yellow
Universal Indicator Paper: Orange to Violet
Universal Indicator Solution: Green to Violet
Balancing Chemical Equations
Step 1: Write down the chemical equation.
Step 2: List down the atoms (or polyatomic ions) involved in both sides.
Step 3: Count the number of atoms on both sides.
Step 4: Compare both sides and change the coefficients (not subscripts) so that the atoms on the left side are equal to the atoms on the right side.
(Tip: Balance the Metals first, then the Non-Metals, and then the Oxygen atoms and Hydrogen atoms.)
Step 5: Double check both sides to make sure the atoms on both sides are equal.
Lead sulfate, barium sulfate and calcium sulfate
Most chlorides, bromides and iodides
Silver chloride, silver bromide, silver iodide, lead chloride, lead bromide, lead iodide
Sodium carbonate, potassium carbonate, ammonium carbonate
Most other carbonates
Sodium hydroxide, potassium hydroxide, ammonium hydroxide
Most other hydroxides
Uses of Acids
Used as a sour flavouring agent in food
Used as a rust remover
Used in car batteries
Used in fertilisers
Used as a food preservative
Used in making soft drinks
Uses of Alkalis
Used in making soap
Used in making toothpaste and to reduce acidity in soil
Used in making fertilisers and as a bleaching agent
Used in making fertilisers and as a bleaching agent
Used in electroplating and in making cement and plaster
Used as a detergent
Strength of Acids
React very fast & vigorously
Ionise completely to produce large amounts of H+ ions
React slowly & less vigorously
Ionise partially to produce small amounts of H+ ions
Do not confuse the strength of an acid with the concentration of an acid. The strength tells you how many H+ ions are produced while the concentration tells you how much of an acid is dissolved in water.
Strength of Alkalis
Strong Alkalis ionise completely to produce large amounts of OH- ions.
Weak Alkalis ionise partially to produce small amounts of OH- ions.
How to Carry Out Titration
1. For solid samples, weigh the solid and dissolve in a known volume of solution (usually 100cm3).
2. Use a pipette to measure a known volume of the solution (e.g 10cm3) and empty into an Erlenmeyer flask.
3. Add a few drops of indicator into the solution.
4. Put the second chemical into a burette. This other solution will react with the synthesised chemical sample in the flask. Often the solution in the burette is an acid or alkali, and it must be of a precise, known concentration.
5. Drop by drop, mix the chemical in the burette into the Erlenmeyer flask until the end point is reached. A colour change indicates the correct amount has been added to react completely with the chemical in the sample.
6. Take note of the volume of the solution added from the burette.