STANDARD SEPARATION TECHNIQUES -I

 

Week:                                                                                                      Date:                                                   

Period:                                     Duration:                                             Average age of learners: 15 YRS

Subject: CHEMISTRY                                                                           Class: SS ONE

Topic:             STANDARD SEPERATION TECHNIQUE

Sub topic:  separating techniques, pure and impure substances.

Reference materials:

(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA

(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO

(3) INTERNET

Instructional materials:

Entry behavior: The students have been taught filtration, distillation

Behavioural objective: At the end of the lesson the students should be able to:

1st PERIOD

i.                     write short note on sublimation

ii.                    explain magnetization

2nd PERIOD

i.                                       explain separating technique

ii.                                     Explain precipitation and centrifugation  

3rd PERIOD

i.                                 state the method involves in determining whether a substance is pure

ii.                               characteristics of a pure solid or liquids

iii.                              state how impurities affect a solid or liquid

1st PERIOD

 

STEP I: The teacher explains sublimation

8. Sublimation: To separate a mixture of solids containing one which sublimes and one (or more than one) which does not, by heating the mixture.

8. 9.

An cotton-stoppered inverted funnel is placed over the mixture. When the mixture is heated, the heat-liable solid sublime and turn into a gas, and travel to the top of the inverted funnel. Once the hot gas touches the cooler funnel, it solidifies back into a solid. The solid can then be scrapped off and collected in another container from the funnel.

STEP II: The teacher explains magnetization and paper chromatography

9. Magnetization or Magnetic Attraction: This method involves the separation of magnetic substances from non-magnetic substances by means of a magnet.

10.  Paper Chromatography: Used to separate a mixture of solutes (or liquid) with different solubility and degree of adsorption. This method uses a porous or absorbant medium (e.g. paper or jel) and a solvent which can move over the material. This method is commonly used for separating a mixture of dyes in ink or different types of sugars (e.g. glucose, fructose, sucrose).

EVALUATION: The teacher evaluates the students by asking the following questions.

i.                     Give two examples of compound that sublime

ii.                    Explain magnetization

iii.                  How can you explain chromatography in your own word.

2nd PERIOD

STEP I: The teacher explains separating technique

11. A separating funnel: This  is a glass funnel with a tap at the bottom. A separating funnel is a separation technique that is used for two liquids that do not dissolve in each other.
Liquids that do not dissolve in each other are called immiscible. The mixture of liquids is placed inside the separating funnel and a container is put beneath. The liquid with the lower density floats on top.

Applications:  

  • To separate a mixture of oil and water.
  • To separate a mixture of kerosene oil and water.

 

  When the tap is opened, the liquid with the higher density starts to flow through the separating funnel into the container. The tap is then closed just before the liquid with the lower density starts to flow through. The liquid with the lower density remaining in the separating funnel  can then be drained into a different container to separate the two liquids.

STEP II: The teacher explains precipitation

12. Precipitation:  Precipitation is a process in which a solid is separated from a suspension, sol, or solution. In a suspension such as sand in water the solid spontaneously precipitates (settles out) on standing. In a sol the particles are precipitated by coagulation. A solute (dissolved substance) may be precipitated from a solution by several means. A solution of salt may be concentrated by evaporation until the salt crystallizes. When a saturated solution of sugar is cooled, sugar crystals form. The addition of a solution of silver nitrate to a solution containing chloride ions results in the formation of insoluble silver chloride: AgNO3+Cl-→NO3-+AgCl↓. In each case the precipitate formed may settle out spontaneously or may be collected by filtration or centrifugation. It is often difficult to obtain a pure substance by a single precipitation, and a substance may be further purified by reprecipitation after it has been redissolved. The term precipitation is also applied to the separation of particles of a solid or liquid suspended in a gas.  

 

 

13. Centrifugation: Sometimes the solid particles in a liquid are very small and can pass through a filter paper. For such particles, the filtration technique cannot be used for separation. Such mixtures are separated by centrifugation. So, centrifugation is the process of separation of insoluble materials from a liquid where normal filtration does not work well. The centrifugation is based on the size, shape, and density of the particles, viscosity of the medium, and the speed of rotation. The principle is that the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly.

The apparatus used for centrifugation is called a centrifuge. The centrifuge consists of a centrifuge tube holder called rotor. The rotor holds balanced centrifugal tubes of equal amounts of the solid-liquid mixture. On rapid rotation of the rotor, the centrifuge tubes rotate horizontally and due to the centrifugal force, the denser insoluble particles separate from the liquid. When the rotation stops, the solid particles end up at the bottom of the centrifuge tube with liquid at the top.

Applications: 

  • Used in diagnostic laboratories for blood and urine tests.
  • Used in dairies and home to separate butter from cream.
  • Used in washing machines to squeeze water from wet clothes.

EVALUATION: The teacher evaluates the students by asking the following questions.

i.                     What method is used to separate two immiscible liquids

ii.                    What process does centrifugal is required

3rd PERIOD

STEP II: state the method involves in determining whether a substance is pure

three methods that can be used to determine whether a substance is pure.

•              Melting point comparison

•              Boiling point comparison

•              Chromatography

 

STEP II:  The teacher states the characteristics of a pure solid or liquids

characteristic of a pure solid and liquid: They are identify by a Fixed melting point

STEP II: :  The teacher states how impurities affect a solid or liquid

 How  impurities affect a solid’s melting point?

•              Impurities lower the melting point.

•              Impurities cause the solid to melt over a range of temperature.

. How impurities affect a liquid’s boiling point?

•              Impurities raise the boiling point.

•              Impurities cause the liquid to boil over a range of temperature.

Relationship between the amount of impurities in a substance and the substance’s melting / boiling point?

•              The greater the amount of impurities, the lower the melting point.

•              The greater the amount of impurities, the higher the boiling point.

Evaluation: The teacher evaluates the lessons by asking the following questions:-

(i)                   State two methods that can be used to determine whether a substance is pure

(ii)                  State one method each how impurities affect solid melting and liquid boiling

(iii)                 

 

 

 

 

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