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The Particulate Nature of Matter
2. Experimental Techniques
Measurement & Criteria of Purity
Methods of Purification
3. Atoms, Elements and Compounds
Atomic Structure and the Periodic Table
Bonding : the structure of matter
Ions and ionic bonds
Molecules and covalent bonds
Symbols, Formulae & Equations
Mole Part 1
Mole Part 2
Mole Part 3
Mole Part 4
Mole Part 5
Electricity and Chemistry
7. Chemical Reactions
Speed of Reaction
Ways of Determining Rates of Reaction
Factors Affecting Rates of Reaction
Acids, Bases and Salts
Characteristic properties of acids & bases
Types of oxides
Preparation of Salts
8.4 Identification of ions & gases
The Periodic Table
9.2 Group properties
Group I Elements
Group VII Elements
Group 0 Elements - Noble gases
Air and Water
14.1 Names of compounds
14.8(a) Synthetic polymers
14.8(b) Natural macromolecules
Properties of acids and bases
Properties of Acids
Physical Properties of Acids
1. Acids have a
2. Acids dissolve in water to form solutions which
3. Acids such as sulfuric acid dissociates in water to produce hydrogen ions and sulfate ions.
are responsible for the electrical conductivity of acids.
turn blue litmus paper red
6. Acids have pH values of
Properties of Acids
Reaction of Acids with Metals (Displacement Reaction)
Acids react with
and a salt.
The reactivity of the metals depend on its position in the reactivity series.
Group I elements are very reactive. They react explosively with acids. See the video clip below.
Hydrogen gas was given off during the reaction.
Test for Hydrogen Gas
Magnesium ribbon reacts wtih hydrochloric acid
Effervescence of colourless and odourless gas, which extinguished burning splint with a "pop" sound, was produced.
Reaction of Acids with Carbonate
Acids react with
carbonates to form
a salt, carbon dioxide and water
Calcium carbonate (marble) reacts with hydrochloric acid to produce calcium chloride, water and carbon dioxide.
A colourless and odourless gas, which form a white precipitate in limewater is produced
**Calcium carbonate is also known as marble or limestone.
Limewater is calcium hydroxide.
Calcium hydroxide (limewater) reacts with carbon dioxide to form calcium carbonate (white precipitate).
Test for carbon dioxide
(Note the source of carbon dioxide in this link come from the heating of copper(II) carbonate)
Carbon dioxide test
3.Reaction of Acids with Bases (Neutralisation Reaction)
This is a neutralisation reaction.
Bases are metal oxides and metal hydroxides.
Examples of bases are aluminium oxide, copper(II) oxide, sodium hydroxide, magnesium oxide, magnesium hydroxide etc.
Acids react with metal oxides or metal hydroxides to form salt and water.
Properties of Alkalis
Physical Properties of Alkalis
1. Alkalis have a
2. Alkalis turn
red litmus paper blue
Alkalis such as sodium hydroxide dissociates in water to produce hydroxide ions and sodium ions.
are responsible for the electrical conductivity of alkalis.
4. pH above 7.
Chemical Properties of Alkalis
All alkalis can react with acids to form a salt and water only.
Alkali + Acids --> Salt + Water
NaOH + HCl --> NaCl + H2O
2. Reaction of Alkalis and Ammonium Salts
Alkalis react with ammonium salts, with heating, will produce ammonia gas.
The general equation for this reaction is shown below:
alkali + ammonium salt --> ammonia + water + salt
Sodium hydroxide + ammonium chloride
sodium chloride + water + ammonia
Test for ammonia gas
colourless, pungent gas
red litmus paper blue
is produced, gas is ammonia.
Alkalis can react with a solution of one metal salt to give metal hydroxide (which is insoluble) and another metal salt (which is soluble).
Alkali (hydroxide of metal A) + salt (of metal B) --> hydroxide metal B + salt (of metal A)
The metal hydroxide will appear as a precipitate if it is insoluble in water.
Sodium hydroxide reacts with copper(II) sulfate solution to give a blue precipitate of copper(II) hydroxide.
Sodium hydroxide + copper(II) sulfate
sodium sulfate + copper(II) hydroxide
The reaction only work if the metal hydroxide produced is insoluble in water.
All Metal hydroxides are
except LiOH, NaOH, KOH, and Ba(OH)2
pH and Indicators
The pH Scale
The pH scale is a set of numbers from 1 – 14 used to indicate whether a solution is acidic, neutral or alkaline.
Acids have pH values less than 7.
Alkalis have pH values more than 7.
A neutral solution (eg. salt solution or water) has a pH value of exactly 7.
The pH of some common substances are shown in the pH comparison table below:
The pH and Concentration of hydrogen ions
The pH of a solution is calculated mathematically based on the number of hydrogen ions or hydroxide ions present in a solution.
Acids with a
smaller pH value
higher concentration of hydrogen ions
Alkaline solutions with
a larger pH value
higher concentration of hydroxide ions.
Neutral solutions have
equal number of hydrogen ions and hydroxide ions
, i.e. neutralization giving predominantly water molecules.
Thus pH is used to compare the strength of acids and alkalis. (Refer to 1.4 for strength of acid and 2.4 for strength of alkali).
Indicators are substances that change colour when an acidic or alkaline solution is added to them.
The pH value of a solution can be determined by using Universal Indicator. It contains a mixture of dyes and gives different colours in solutions of different pH.
Colours of the Universal Indicator in substances of varying acidity and alkalinity:
Very acidic - Red
Acidic - Orange/Yellow
Neutral - Green
Basic/base/alkali - Blue
Very basic/base/alkali – Purple
Table below shows the colour changes of other common indicators.
Colour in acidic solution
Colour in alkaline solution
pH range at which indicator change colour
1. Animation on pH
2.Animation on titration
1. Acids and Bases
3. Virtual Chemistry Lab – The pH Factor
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