CHEMISTRY TIPS FORM 4

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INTRODUCTION TO CHEMISTRY
COMMON CHEMICALS IN DAILY LIFE
Chemical
Uses
Sodium chloride
• Used in preserving food
• As table salt
Oxygen
For respiration and combustion
Carbon dioxide
Used in making carbonated drinks
Ethanoic acid
• Used in preserving food
• As vinegar
Calcium carbonate
Used in flooring in form of marble
Copper
• Made into wires
• Mixed with nickel to make coins
Sodium bicarbonate
Used in baking powder
Calcium oxide
Used in preparation of cement and mortar
VARIABLE
1.     A variable is a factor that affects the result of an experiment.
2.    For example, the mass of salt that can dissolve in water depends on the volume and the temperature of the water. Volume and temperature are called variables.
3.    There are three types of variables :
·         Manipulated variable – a variable that is changed during the experiment.
THE STRUCTURE OF ATOM
CONVERSION OF ENERGY
Change of state
Process
Change in energy
Solid to liquid
Melting
Heat energy is absorbed
Liquid to gas
Boiling / Evaporation
Heat energy is absorbed
Solid to gas
Sublimation
Heat energy is absorbed
Liquid to solid
Freezing
Heat energy is released
Gas to liquid
Condensation
Heat energy is released
Gas to solid
Sublimation
Heat energy is released
SUBATOMIC PARTICLE
1.     Proton number is the number of protons in the nucleus of an atom.
2.    Nucleon number is the total number of protons and neutrons in the nucleus of an atom.
 CHEMICAL FORMULAE AND EQUATIONS
RELATIVE MASS
1.     Relative atomic mass of an element is the number of times one atom of the element is heavier than one – twelfth the mass of one carbon-12 atom.
2.    Relative molecular mass of a compounds the number of times one molecule of the compound is heavier than one – twelfth the mass of one carbon-12 atom.
PERIODIC TABLE OF ELEMENTS
PERIODIC TABLE
1.     Elements with the same number of valence electron are arranged in the same group. Thus, they exhibit similar chemical properties.
2.    The period of an element is placed in is equal to the number of shells occupied with electrons in an atom of the elements.
GROUP AND PROPERTIES
1.     Group 1: Alkali Metals
·         Reaction with water produce metal hydroxide and hydrogen gas.
·         Reaction with oxygen produce metal oxide.
·         Reaction with halogen produce halide salts.
2.    Group 17 : Halogens
·         Reaction with water produce acid solution.
·         Reaction with alkali metals produce halide salts.
·         Reaction with hot iron wool produce brown iron(III) halide salts.
3.    Group 18: Noble Gases
·         Helium is used in filling hot air balloon.
·         Neon and argon are used in light bulbs.
·         Krypton is used in camera flashbulbs.
·         Radon is used to treat cancer patients
CHEMICAL BONDS
FORMATION OF IONIC BOND AND COVALENT BOND
Ionic Bond
Covalent Bond
Type of material
Between metals (Group 1,2 and 13) and non-metals (Group 15, 16 and 17)
Between non-metal and non-metals (Group 14, 15 and 16)
Electron
Electron is released by metal atoms and received by non-metal atoms
Electrons are shared between non-metal atoms
Type of particle produced
• Metal – positive ion
• Non-metal – negative ion
Neutral molecule
How to predict the formulae
Determine the charge of the ions and criss cross
Determine the number of electrons needed to achieve stable duplet / octet electron arrangement and criss cross
Formation of bonds
Strong electrostatic forces of attraction (ionic bond) between positively charged ion and negatively charged ion
·  Strong covalent bond held the atoms in the molecules
·  Weak Van der Waals forces held the molecules
Example
• Lead(ii) bromide, PbBr2
• Sodium chloride, NaCl
• Naphthalene, C8H10
• Acetamide, CH3CONH
PROPERTIES OF IONIC COMPOUND AND COVALENT COMPOUND
Ionic Bond
Covalent Bond
Melting and boiling point
High melting and boiling point
Low melting and boiling point
Electrical conductivity
Conduct electricity in molten or aqueous state
Cannot conduct electricity at all state
Solubility
Soluble in polar solvents
Insoluble in organic solvents
Soluble in organic solvents
Insoluble in polar solvents
Volatility
Non-volatile
Very volatile
ELECTROCHEMISTRY
1.     Electrochemical Series
i.        Electrochemical series is an arrangement of metals based on the tendency of each metal atom to release electrons to form positive ions.
ii.        It can be constructed based on :
·         Potential difference between two metals
·         Ability of a metal to displace another metal from its salt solution
iii.        Importance of the series :
·         To determine the terminals of voltaic cells
·         To determine the standard cell voltage
·         To determine the ability of a metal to displace another metal from its salt solution
2.    Electrolysis in Industry
a.    Electroplating
·         The electroplating metal is made the anode.
·         The object to be electroplated is made the cathode.
·         The electrolyte consists of the electroplating metal
b.    Purifying metal
·         The impure metal is made the anode.
·         The piece of pure metal is made the cathode.
·         The electrolyte consists of the metal to be purified.
c.    Extraction of reactive metal
·         Metals which are above carbon in the reactivity series are extracted using electrolysis of the molten metal oxide or salt.
·         The metal ions move to the cathode and discharge by receiving electrons.
ACIDS AND BASES
ACIDS
1.     Acid is a chemical substance which ionizes in water to produce hydrogen ions, H+ or hydroxonium ions, H3O+.
2.    Properties of acid:
·         React with bases to form salts and water
·         React with reactive metals to form salts and hydrogen gas
·         React with carbonates to form salts, water and carbon dioxide gas
·         Turn moist blue litmus paper red
·         Have pH values less than 7
3.    Basicity of an acid is the number of ionisable of hydrogen atom per molecule of an acid molecule in an aqueous solution.
a.    Monoprotic
b.    Diprotic
c.    Triprotic
BASES
1.     Base is a substance which can react with an acid to form salt and water only.
2.    Base that can dissolve in water is known as alkali.
3.    An alkali is a substance which ionizes in water to produce free moving hydroxide ions, OH.
4.    Alkaline properties:
·         React with acids to form salts and water
·         Produce ammonia gas when heated with ammonium salts
·         Turn moist red litmus paper blue
·         Have pH values more than 7
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