This document discusses various laboratory equipment and techniques used to measure elements, compounds, and mixtures. It describes apparatuses for measuring volume, time, mass, and temperature. Specific tools covered include beakers, measuring cylinders, burettes, pipettes, and gas syringes. It also discusses hazards in the laboratory and rules for working safely. Key concepts explained are the differences between elements, compounds, and mixtures, and techniques for checking purity and separating mixtures like chromatography, distillation, filtration, crystallization, and decantation.
2. Learning objectives:
Apparatus used in taking measurements
Hazards labels and Laboratory rules for working in a laboratory
What are elements, mixtures and compounds and mixtures
Check purity
Separation of mixtures
4. Beaker
Beakers are often graduated,
that is, marked on the side
with lines indicating the
volume contained. For
instance, a 250 mL beaker
might be marked with lines to
indicate 50, 100, 150, 200 and
250 mL of volume
5. Measuring cylinder
A graduated cylinder is
meant to be read with the
surface of the liquid at
eye level, where the
bottom of the meniscus
shows the measurement
line. A measuring cylinder
is accurate to nearest
cm3.
6. Burette
A burette is a volumetric measuring
glassware which is used in analytical
chemistry for the accurate dispensing of a
liquid, especially of one of the reagents in
a titration. The burette tube carries
graduated marks from which the
dispensed volume of the liquid can be
determined. Burettes are available in a
limited range of sizes; the most common
size is 50-mL. The scale of a 50-mL
burette is divided into 0.1mL increments.
Therefore, when the liquid level in a
burette is read, it is read and recorded to
the nearest 0.1 mL .
7. Pipette
Graduated pipettes made of
glass or plastic and are used
to accurately measure the
liquid volumes. Use them for
measuring volumes between 1
ml and 10 ml: For larger
volumes, you would use a
graduated cylinder, and for
smaller volumes.
8. Gas syringe
To measure the volume of a
gas, we use a gas syringe.
The plunger is pressed fully
into the barrel to expel any gas
present in the syringe. As gas
is produced during a reaction
and enters the syringe, the
plunger is pushed outwards
and the volume of the gas
produced can be measured.
9. Mass
The units for measuring mass are grams and kilograms.
1kg= 1000 g
• Electronic balance can be
used to measure the mass.
• They measure mass to an
accuracy of one hundredth of
grams.
• When taking measurements
using electronic balance, you
should wait until the reading is
steady before taking it in order
to reduce the errors.
10. Temperature
A laboratory thermometer, is used for measuring temperatures other than the
human body temperature. It ranges from -10˚C to 110˚C. Laboratory
thermometers are designed for lab purposes such as checking boiling point,
freezing point, or temperature of other substances.
11. Time
Experiments involving rates of
reaction will require the use of an
accurate stop watch – one that
measures time to a hundredth of a
second.
The units of measuring time are
hours, minutes and seconds.
12. Hazard symbols in lab
Hazard symbols are always shown in all
chemistry laboratory to precaution a person
from dangerous and toxic materials. These
signs are present on all chemical labels to
make the use and handling of chemicals
safer.
16. What is an Element?
Substances that cannot be chemically broken down into simpler substances.
They are primary constituents of matter.
Each element is distinguished by its atomic number, i.e. the number of protons in the nuclei of its
atoms.
17. What is a Compound?
A compound is a material formed by chemically bonding two or more chemical
elements.
The type of bond keeping elements in a compound together may vary. Covalent
bonds and ionic bonds are two common types.
The elements are always present in fixed ratios in any compound.
18. What is a Mixture?
A mixture is a material made up of two or more different substances which are
physically combined.
A mixture is the physical combination of two or more substances in which the
identities are retained and are mixed in the form of solutions
Mixtures are not chemically united and the substances in it exist in no fixed
proportion to each other.
19. Difference between Elements,
Compound and Mixtures
Elements Compounds Mixtures
Made up of only one
kind of atom
Made up of more than
one atom
Made up of more than
one kind of molecule
Cannot be broken down
by chemical means
Can be broken down by
chemical means
Can be separated by
physical means
Has the same properties
as the atoms making it
up
Has different properties
from the elements
making it up
Has same properties as
the substances making it
up
Has the same properties
throughout
Has the same properties
throughout
Has different properties
throughout
20. Examples of Elements, Compounds
and Mixture
Elements
Sodium(Na)
Calcium(Ca)
Magnesium(Mg)
Hydrogen(H)
Compounds
Water(H22O)
Magnesium Oxide(MgO)
Hydrogen Chloride(HCl)
Mixture
Sugar Solution
Milk and Water
Salt Solution
Coffee and Milk
21. Checking Purity
Why do we check purity of a substance?
-Because pure substances form predictable products whereas impure substances
might give unexpected results
There are three ways you can check if the substance is pure or not:
-Measuring it’s melting point
-Measuring it’s boiling point
-Chromatography
22. Measuring its melting point
In this process the substance’s melting point will be checked multiple times and
if it has a sharp melting point it is considered to be a pure substance whereas if
the substance melts over a range of temperatures it is considered to be non-pure
substance. Pure substances will have lower melting point then the impure
substance.
For example, pure ice melts completely at zero degree Celsius but the impure
ice will start to melt before zero degree Celsius. The more impurities a substance
contains, the lower its melting point will be.
23. Measuring its boiling point
In this process the substance’s boiling point will be checked multiple times and if
it has a sharp boiling point it is considered to be a pure substance whereas if the
substance boils over a range of temperatures it is considered to be non-pure
substance. Impure substances will have higher boiling point then the pure
substance.
For example, pure water boils completely at 100 degree Celsius but the impure
water will start to boil after 100 degree Celsius. The more impurities a substance
contains, the higher its boiling point will be.
24. Chromatography
A chromatogram produced by paper chromatography can be used to distinguish
between pure and impure substances. A pure substance would produce one
spot on the chromatogram whereas an impure substance would produce
multiple spots on the chromatogram.
For example water from lakes and rivers will produce 2 marks and water from
drinking water will produce 1 mark
25. Miscible and immiscible liquids
Miscible liquids
Miscibility is the property of two
substances to mix in all proportions.
The term is most often applied to
liquids but also applies to solids and
gases. For example, water and ethanol
are miscible because they mix in all
proportions.
Immiscible liquids
Immiscible liquids are those which
won't mix to give a single phase. Oil
and water are examples of immiscible
liquids
26. Miscible liquids Immiscible liquids
Water and ethanol Water and oil
Milk and water Water and cyclohexane
Rubbing alcohol and water Gasoline and water
Petrol and kerosene Pentane and acetic acid
Water and vinegar Molten silver and lead
29. Fractional Distillation
To separate two or more liquids that are miscible with one another and have
different boiling point.(e.g. ethanol and water from a mixture of the two).
30. Important applications of fractional distillation
Separation of ethanol and water
Separate of liquid air into oxygen and nitrogen.
Separation of crude oil into useful fractions
32. Decantation
Decantation is a process to separate mixtures by removing a liquid layer
that is free of a precipitate or the insoluble solid.
The solution is kept undisturbed for sometime and just pouring the liquid
of from the sediments.
33. Filtration
• To separate an insoluble solid from a mixture.
• E.g. sand from seawater.
• Upon filtration the mixture is separated into residue and filtrate.
• Residue – the insoluble solid that remains on the filter paper.
• Filtrate – the liquid that passes through the filter paper.
34. Evaporation to dryness
To evaporate solvent from the solution, obtaining the soluble salt from the
mixture. • E.g. to obtain salt from seawater.
Procedure of Evaporating a Solution
1. Pour the solution into an evaporating dish.
2. Heat the solution to dryness to evaporate away the
solvent, leaving behind the solute.
3.Wash with distilled water
4.Dry in oven
35. Crystallization
When a solid dissolves in a liquid solvent, a solution is produced. If this
solution is heated, some of the solvent evaporates. When the hot solution is
allowed to cool, some of the dissolved solid reappear as pure crystals. This
process is called crystallisation.
Example: Sugar crystals can be obtained from sugar solution
36. Procedure of Crystallisation
1. Pour the solution, into an evaporating dish.
2. Heat the solution till the crystallization point.
3. Leave the solution to cool for the crystals to form.
4 Filter the mixture to collect the crystals which will be the
residue.
5. Dry between filter paper.
37. Simple distillation
To separate a liquid and soluble solid from a solution
When a solution is boiled , the solvent changes to vapour, the vapour passes
down a condenser where it is converted back to liquid and collected as
distillate.
Example: water can be separated from salt solution by simple distillation.
41. Things to remember
The number of spots indicates the number of substances present in the
mixture.
A pure substance gives only one spot.
If a spot remains on the starting line then it means that the substance is
insoluble in the solvent used.
42. Using Rf values to identify
components of a mixture
Rf value = distance moved by compound ÷ distance moved by
solvent
The Rf value of a particular substance is always the same.
Rf value is always less than 1.
43. Applications of chromatography
1. Separate dyes in ink
2. Pigments in plants
3. Amino acids obtained from proteins
4. To identify poisons (e.g. pesticides)
5. To detect traces of banned substances in food
