Unit 1: Experimental Chemistry

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Measurement

Physical properties

SI Units

Other Common Units

Common measuring apparatus

Name

Symbol

time

second

s

  • hour (h)

  • minutes(min)

  • day

  • digital stopwatch

  • analogue stopwatch

mass

kilogram

kg

  • gram(g)

  • tonne(t)

  • milligram (mg)

  • electronic balance

  • beam balance

temperature

kelvin

K

  • degree Cesius(°C)

  • degree Fahrenheit (°F)

  • mercury-in-glass thermometer

  • alcohol-in-glass thermometer

volume

cubic metre

m3

  • litre( l )

  • millilitre ( ml )

  • cubic centrimetres(cm3)

  • cubic millimetres (mm3)

  • burettes

  • pipettes

  • measuring cylinders

  • gas syringe

Measuring volume

  • Many chemical reactions involve liquids, solutions or gases.

  • some common apparatus used to measure the volume of a gas, a solution or a liquid in a chemical reactions.

  • Gas: gas syringe, it is used to collect gases of any density.

  • Liquid:

    burette

    • it has an accuracy to 0.1 cm2

    • used to measure the volume of a solution accurately.

    pipette

    • used to deliver an accurate fixed volume of a solution.

    • There are different pipettes designed to deliver different fixed volumes of solutions, such as 20 cm3, 25 cm3 or 50cm3

    measuring cylinder

    it measures an approximate amount of volume of a solution.

    beaker

    it measures an approximate amount of a solution.

  • Meniscus is the surface of the liquid that curves at the side of the measuring intrument. To get an accurate volume reading, it must be read from the lowest or the highest level of the meniscus. The surface of the liquid may curve upwards or downwards depending on the type of liquids.

Collection of Gases

Methods for collecting gases

Gases can be collected by the following methods

  • Displacement of air

  • Displacement of water

  • Gas syringes

Displacement of air

  • Used to collect gases of densities higher or lower than air. it is not suitable for collecting a gas with a density same as air.

  • The air in a test tube will be displaced by the gas to be collected.

  • Two type of displacement of air

    • Downward delivery

    • Upward delivery

Downward delivery

  • used to collect a gas which is more dense than air

    Example Chemical formula

    Chlorine

    Cl2

    hydrogen chloride

    HCl

    sulfur dioxide

    SO2

    carbon dioxide

    CO2

    nitrogen dioxide

    NO2

  • The test tube or collecting apparatus is placed at the upright position. The gas produced sinks down into a test tube and displaces the air inside it.

Upward delivery

  • Used to collect a gas which is less dense than air.

    Example Chemical Formula

    hydrogen

    H2

    ammonia

    NH3

  • The test tube or collecting apparatus is placed at an inverted position. The gas produced rises up into a test tube and displaces the air inside it.

Displacement of water

Suitable for gases:

  • Insoluble or only slightly soluble in water

  • Has the density almost the same as air(displacement of air can’t take place)

    Example Chemical Formula Reason for collecting gas using displacement of air

    hydrogen

    H2

    slighted soluble in water only.

    oxygen

    O2

    has the same density of air, can’t displace air from a collecting tube.

    carbon dioxide

    CO2

    slightly soluble in water only

Drying Agents

Drying agent can be used to obtain a dry sample of gas by removing its moisture content.

The three common drying agents used in the laboratory to gases:

Chemical Name Chemical formula Examples of gases

anhydrous calcium chloride

CaCl2

all gases except ammonia(NH3)

concentrated sulfuric acid

H2SO4

all gases except alkaline gas such as ammonia ( NH2)

Calcium oxide

CaO

all gases except acidic gases such as sulfur dioxide ( SO2)

Elements, Compounds and Mixtures

Elements

  • All elements which are composed of only one type of atom are called an element.

  • Elements are the building blocks of matter because the elements alone or in combinations make up the entire universe such as the Sun, the Earth and all living and non-living things.

    Table 1. Elements in percent by mass in
    Earth’s crust Percentage Human body Percentage

    Oxygen

    49.5

    Oxygen

    65.0

    Silicon

    25.7

    Carbon

    18.5

    Aluminium

    7.5

    Hydrogen

    9.5

    Iron

    4.7

    Nitrogen

    3.3

    Calcium

    3.4

    Calcium

    1.5

    Others

    9.2

    Others

    2.2

  • 117 known elements. About 92 of them occur naturally on Earth.

  • Elements are pure substances that cann’t be broken down into any simpler substances by chemical methods.

  • In nature, elements can exist as

    • Single atoms called monatomic elements.

    • Moecules of elements which are pure substances made up of two or more atoms of the same type chemically joined together.

  • In chemistry, atoms in an element can be represented by colour or size. The diagramatic representation of elements.

    Substance Chemical Formula Diagrammatic representation Classification

    Helium

    He

    Monatomic

    Hydrogen

    H2

    Molecule of an element ( Diatomic)

    Ozone

    O3

    Molecule of an element

    Sulfur

    S8

    Molecule of an element

  • Each element has its own unique physical properties. Hence, we can use the following properties to identify an element:

    • Melting point

    • Boiling point

  • Element can be classified as metals and non-metals

    metals non-metals

    General properties

    • Shiny

    • Good conductors of electricity and heat

    • Malleable

    • Ductile

    • High density

    • High melting and boiling points

    • Dull

    • Poor conductors of electricity and heat

    • Not malleable

    • Brittle

    • Low density

    • Low melting and boiling points

    Examples

    Copper, zinc

    Iodine, sulfur

Compound

A compound is a substance that contains two or more elements that are chemically combined. The elements in a compound are present in fixed proportions.

A chemical formula can be used to represent a compound. The formula shows:

  • the symbols for each element in the compound

  • the number of atoms of each element in a unit of the compound

  • Examples of compounds and their formulae.

    Name of Compound Formual

    Sodium chloride

    NaCl

    Potassium bromide

    KBr

    Magnesium iodide

    MgI2

    Carbon dioxide

    CO2

    Carbon monoxide

    CO

    Sulfur trioxide

    SO3

    Water

    H2O

    Ammonia

    NH3

    Methane

    CH4
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