Experimental techniques

1. Experimental techniques
Chapter 1
Chemistry0620
Coretier

2. Pure Substances Mixtures
Composition
A single substance
not mixed with
anything else
Contains two or
more substances
Melting and
boiling points
Fixed points
Over a range of
temperature
Chromatography
Produces a single
spot on the
chromatography
paper.
Contain two or more
spots.
Testing for Purity

3. 4.7 Purification of Substances
1. Pure substances are substances that
contain only one type of substance.
- do not have any impurities
- for example,
* pure sugar only contains sugar
molecules
* pure water only contains water
molecules
2. Pure substances have fixed boiling and
melting point.
- for example,
* pure water boils at 100°C

4. Effect of impurities on the boiling point
of a pure liquid
 The presence of impurities in a pure substance can
a) increase its boiling point
b) decrease its freezing point
• For example,
- when a salt is added to pure water, water will be
boil at a temperature higher than 100°C and will
melt at a temperature below 0°C

5. The Importance of Pure Substances
 Example #1:
Impurities in medicine may cause undesirable
side effects.

6.  Example #2:
Impurities in metals weaken its structure more
than it should be.

7.  Example #3:
◦ Chemicals are added to food and
beverages to make them last longer,
taste better or look more
attractive/appealing.
◦ Safe-for-consumption chemicals

13. Separation Techniques
methods of purification
 1) Filtration
◦ to separate insoluble
solid from liquid

14. 1. A mixture is poured into the filter funnel
lined with filter paper.
2. Liquid particles are small enough to go
through the pores of the filter paper but the
solid particles are too large to go through.
3. Collect the filtrate that passes through the
filter paper in a conical flask. The solid that
remains in the filter paper is called residue.

15.  2) Decanting
◦ just pouring the liquid away!
◦ to separate a dense insoluble solid from liquid

16.  3) Evaporation (to dryness)
◦ to separate soluble solid from liquid
evaporating dish

17. How can you separate a mixture
containing salt and sand?
THINK!
Add a suitable solvent, and
filter

18. Sand
Salt solution
1. Add some distilled water into the mixture
of salt and sand. Stir and make sure all
the salt has dissolved.
2. Filter the mixture.
Separating Salt and Sand

19. Sand
3. Wash the residue with a little distilled water to
remove all the salt solution from it.
4. Evaporate the filtrate to dryness.
Separating Salt and Sand
Salt solution

20. ◦ Limitations:
1. Some substances decompose strongly
when heated strongly.
2. Soluble impurities may be left behind
after all the water has been removed.

22.  4) Crystallization
◦ to separate soluble solid from liquid as crystals

23. Heating is stopped when a hot saturated solution is
formed.

24. How do we test for a saturated solution?
Procedure:
 A clean glass rod can be used to test whether a
solution is saturated.
 It is dipped into the solution and removed. There
will be a small amount of solution on the rod.
 If small crystals form on the rod as the solution
cools, the solution is saturated.

25. How would you purify solid sodium
nitrate contaminated with solid
lead(II) sulfate?
sodium nitrate is soluble in water, but lead sulfate` is not
THINK!

26.  5) Simple distillation
◦ to separate a pure
liquid from a solution
◦ the process of boiling
the liquid and
condensing the
vapour

27. Bunsen burner
What is
happening
here?
Mixture
(salt and
water)
Water
Vapour
Water

28.  Simple distillation
1. solution is heated until it boils
2. pure liquid turns into vapour and leaves the flask
3. vapour is then cooled by a condenser, which changes it
back into a liquid
4. the liquid is collected in the conical flask, and is called
the distillate

29. Distillation: separating a liquid from a
solution

30. Procedure:
1. Solution is heated in a flask until the
solution boils.
2. Pure liquid turns into a vapour and
leaves the flask
3. Vapour is then cooled by a
condenser, which changes it back
into a liquid
4. Liquid is called the distillate and is
collected in a conical flask.

31. 2. In the condenser, water
vapour condenses.
1. In the distillation flask,
water boils and enters
the condenser.
How does simple distillation work?
3. Pure
water is
collected as
distillate.

32. SAFETY MEASUREMENTS:
This ensures that the
thermometer measures the boiling
point of the substance that is
being distilled.
Thermometer
Boiling
Chips To ensure smooth boiling.

33. If the distillate is volatile, the
receiver can be put in a large
container filled with ice.
This helps to keep the
temperature of the distillate low
so that it remains in the liquid
state.

34. Where is the bulb of the thermometer placed?
It is placed beside the side arm
of the distillation flask, and
should not be dipped in solution.

35. Where does the water enter and leave the condenser?
Cold running water enters from
the bottom of the condenser
and leaves from the top.

36. Around 97% of the water on Earth is seawater.

37. Obtaining Pure Water from Seawater:
Desalination
 by distillation of seawater [one way]
 disadvantage: expensive method because
oil is the main fuel used to heat the water in the
distillation process, and a lot of oil is required, which
makes the process very costly

38.  6) Fractional distillation
◦ to separate mixtures of
miscible liquids with widely
differing boiling points

40. How does the temperature change as a solution of
ethanol and water undergoes fractional
distillation?
1. The temperature of
the mixture increases
as it is heated.
Temperature / oC
Time / s

41. How does the temperature change as a solution of ethanol
and water undergoes fractional distillation?
Temperature / oC
Time / s
2. At 78 °C, ethanol distils over.
The temperature remains constant
until all the ethanol has distilled out of
the round-bottomed flask.

42. How does the temperature change as a solution of ethanol
and water undergoes fractional distillation?
Temperature / oC
Time / s
3. The temperature then
increases until 100 °C.
At 100 °C, water distils
over.
The temperature remains
unchanged as water is being
distilled.

43.  Fractional distillation
the liquid with the lower boiling point will
be distilled first
Why is the fractionating column filled with
glass beads (or plates/spirals)?
Separation Techniques
methods of purification

44.  Use of separating
funnel
◦ to separate immiscible
liquids
Separation Techniques
methods of purification

45.  Use of separating funnel
1. pour the mixture into the
separating funnel, ensuring
the tap is closed
Separation Techniques
methods of purification

46.  Use of separating funnel
2. support the separating funnel
with a retort stand, placing a
clean beaker below it
Separation Techniques
methods of purification

47.  Use of separating funnel
3. allow some time for the
liquids to separate completely
4. open the tap to allow the
denser liquid at the bottom to
drain into the beaker
* close the tap before the liquid in
the top layer runs out!
Separation Techniques
methods of purification
the
denser
liquid

48.  Use of separating funnel
5. place another beaker below
the separating funnel and
allow a little of the liquid in
the top layer into it
* dispose this liquid collected
The mixture is separated!
Separation Techniques
methods of purification

49.  Sublimation
◦ to separate a mixture of solids, one of which sublimes

50. Some substances that sublime:
1. solid carbon dioxide
2. anhydrous iron (III) chloride
3. anhydrous aluminium chloride
4. iodine
5. ammonium chloride
6. naphthalene

51. QUIZ!
How would you separate…
(a) red dye from a mixture of red and blue dyes in
solution?
(b) oxygen from air?
(c) barium sulfate from a mixture of (insoluble) barium
sulfate and water?

52. QUIZ!
How would you separate…
d) water from oil and water?
e) petrol from crude oil?
f) iodine crystals from iodine and copper(II)
oxide?
g) salt from sea water?