CSEC CHEMISTRY REVIEW2 - Separation of Mixtures and Compounds

OBJECTIVES• Distinguish between pure

substances, mixtures and compounds.

• Show examples common mixtures.

• Discuss the various separation techniques of mixtures based on the different properties of the components.

• Answer CSEC Chemistry Questions.

• A pure substance is defined as any substance that is made up of only one type of atom or molecule.

• When talking about pure substances consisting of single atoms, we often refer to the word “Element”.

• Any matter which cannot be split into a simpler form by a chemical process is known as an element.

• A list [118] of known and predicted elements can be found in the Periodic Table of Elements.

WHAT IS A PURE SUBSTANCE ?

TABLE SHOWING THE NAMES OF ELEMENTS

Common Elements in the Earth’s Crust Common Elements Found in Organisms Common Elements Found in the Universe

oxygen (O) carbon (C) hydrogen (H)

silicon (Si) hydrogen (H) helium (He)

aluminium (Al) oxygen (O) oxygen (O)

iron (Fe) nitrogen (N) carbon (C)

calcium (Ca) phosphorus (P)

sodium (Na) sulfur (S)

potassium (K)

magnesium (Mg)

hydrogen (H)

TABLE SHOWING A LIST OF COMMON ELEMENTS IN NATURE

• There are very few, pure elements, that exist naturally in our every day lives, what we usually interact with are compounds.

• A compound is formed when two or more elements are combined together chemically.

• For Example:

• Compounds can also be considered as pure substances, when they are made up of just one kind of molecule.

NB. Pure substances can be identified based on their well defined melting and boiling points. Impure substances that may be contaminated, typically have lower

M.p. and B.p. than their pure equivalent.

TABLE SHOWING A LIST OF COMMON COMPOUNDS

WHAT IS A MIXTURE ?• A mixture is a physical blend of two or more

substances (elements or compounds) in the same space.

• There is no chemical interactions taking place in a mixture and therefore the components of a mixture may retain their original properties.

• In a mixture only physical properties like: colour, size, density and state may be changed.

A mixture can be a combination of substances in any two phases of matter. What do I mean?

Mixture Example Made Of Image

Solid in Solid Brass Zinc + Copper (Metal Alloy)

liquid in Liquid Rum Ethanol in Water

Gas in Liquid Carbonated Beverages (Coke)

Carbon dioxide in Water

Gas is Gas Air Nitrogen (78%) and Oxygen (20%)

SUMMARY MIXTURES VS COMPOUNDS

No. Mixture Compound

1The composition (mass) can vary. It contains two or more

substances.

The composition (mass) is always the same. A single

substance is formed.

2 Retains the properties of the individual components.

The properties are very different from the original

components.

3 No chemical change occurs. Only physical changes.

A new substance is formed through a chemical change.

4 Mixtures can be separated quite easily by physical means.

Compounds are very hard to separate and this can only be done by chemical means.

• Mixtures can be separated in a number of ways and it is important to know the various separation techniques.

• You may be asked to identify industrial scale separations of mixtures. Like:

1. Separating the components of crude oil.

2. Separation of pure water from that stored in reservoirs or rain water collectors.

3. Separation of useful gases such as oxygen (O2) and Nitrogen (N2) from the atmosphere.

SEPARATION OF MIXTURES

Decantation is one process used for separating a liquid from an insoluble solid.

It is simple the pouring off of a liquid from a solid that has settled at the bottom of the container (Precipitate).

We use this method quite other in cooking. Lets say you are washing vegetables or rice in a bowl of water, when your finished you simple pour off the water.

1. DECANTATION

Filtration is used to separate a liquid from a suspended or settled solid e.g. soil or chalk from water.

2. FILTRATION

Used for obtaining a solid from a mixture of a solid dissolved in a liquid, e.g. the sodium chloride (salt) from its solution in sea water can be recovered by exporting all of the water from the solution leaving the less volatile sodium chloride behind. This process is limited to substances that do not decompose on heating, and those that do not retain water.

3. EVAPORATION

Crystallisation is used to separate and retain the solid solute from a solution especially if the solid contains water of crystallisation, e.g. copper sulphate from copper sulphate solution.

4. CRYSTALLISATION

To separate a pair of immiscible liquids (liquids that do not dissolve in each other), a separating funnel can be used. This is a funnel with a stop-cork at the end. E.g. An oil and water mixture, These two liquids occupy separate layers with the lighter oil on top. The water is allowed to run out completely and then the oil can then be removed.

5. SEPARATING FUNNEL

This is a widely used method of separation and it is used to separate several solutes present in a solution. E.g. dyes, inks, amino acids, sugars and pigments in chlorophyll There are a few different forms of chromatography but the one that we will focus on is paper chromatography.

6. CHROMATOGRAPHY

This is a process used to separate and retain a pure solvent from a solution. The solution is boil and the liquid with lower boiling point vaporises, and travels into the condenser. The vapour then cools and condenses back into a liquid where it is collected.

7. DISTILLATION

There are other separation techniques that have not been mentioned that you will need to know about such as:

1. Fractional Distillation (Industrial)

2. Solvent Extraction (Industrial)

3. Centrifuge Separation (Biological & Medical)

OTHER SEPARATION TECHNIQUES

REFERENCES• (Building Blocks of the World) https://

www.open2study.com/courses/chemistry

• Introduction to Solutions, Solute, and Solvent https://www.youtube.com/watch?v=SaNZAyqOeT0

• A Concise Revision Course For CXC - Anne Tindale

• CXC Revision for Chemistry - Comptom Mahase