All materials may be divided according to the three headings given here.
 But what is a material?. | 
A material (or a substance or a chemical )
is anything that has a mass . |
Then, are there any non materials? | Yes. Heat, Light and Electricity are a few forms of non- materials |
I know what mixtures are. If you mix two or more pure substances you get a mixture . | You may be right; but do you know what a pure substance is? |
Yes. The water we drink, the air we breathe, the food we eat are always pure?
| For ordinary conversation it may be correct but for science it’s absolutely wrong. Let us take a few examples and analyse the problem. |
Here are some common pure substances and mixtures.
Pure Substances | Mixtures | Main constituents in the mixture |
Common salt | Sea water. (Saline) | Water, many solids including salts and gases are dissolved,(Read the label in a drinking water bottle) |
Sand | Soil | Soil contains sand, clay, water, salts, air and many materials from decaying organic substances. |
Oxygen | Air | Air has 4 parts of nitrogen to 1 part of oxygen and in addition to this there’ll be water and dust particles. |
Flour | Cake | Sugar, eggs, nuts and food colours are mixed in making a cake. |
Carbon | Gun powder | Potassium nitrate, sulphur are mixed with carbon. |
Here are the main differences between Pure substances and Mixtures
Mixtures | Pure substances. |
In mixtures of solids the different substances can be seen | Separate substances cannot be seen even through a microscope. |
Substances in a mixture will undergo changes of state at different temperatures. | There will be a definite boiling point and a freezing point. |
Constituents 1 can be separated considering their physical properties such as density and solubility. | Even if they are made up of different substances such as Hydrogen and Oxygen in water, they behave as one substance and cannot be separated by physical methods. |
1 Different substances in it. | |
There are actually two kinds of Pure substances they are ELEMENTS and COMPOUNDS.
An assignment :-
Divide the following as above prior to proceeding with lesson. Results can be checked with the table given below.
Sugar, Carbon, Common salt, Chlorine, water, Oxygen, Iron, rust, sulphur dioxide , sulphur, Aluminium , Alum
Compound | Elements present | Formula |
Water | Hydrogen , Oxygen. | H2O. |
Common salt | Sodium , Chlorine. | NaCl |
Sugar | Carbon, Hydrogen, Oxygen, | C6H12 O6 |
Rust | Iron, Oxygen, Hydrogen | Fe2O3.xH2O |
Lime stone (Calcium carbonate) | Calcium, Carbon and Oxygen. | CaCO3 |
Baking powder. (Sodium hydrogen carbonate) | Sodium, Hydrogen. Carbon and Oxygen. | NaHCO3 |
Silica (Sand) | Silicon and Oxygen | SiO2 |
| Carbon dioxide | Carbon and Oxygen | CO2 |
There are only a limited number of elements in the entire universe . They are all listed in the Periodic Table given below.
Atoms of an element has a definite number of protons.
Protons are the positively charged particles present in the nucleus of atoms. The number in each cell gives the number of protons present in an atom of that element.
The nucleus will also contain some neutral particles called neutrons. Every atom will have an equal number of electrons orbiting to neutralize the charge in protons.
Compounds are formed by joining atoms.
This is something more than mixing of substances. Combinations can take place either by sharing electrons or by donating electrons and get affiliated due to unequal charges.
Please click chemical bonds..to learn about these methods.
There is an unlimited number of mixtures as you can mix any number of pure substances in any proportion you like. Chemical combinations take place according to definite proportions.
MIXTURES | COMPOUNDS |
In a mixture the properties of its constituents are not destroyed. ( If you mix sugar and water the sweetness will remain) | The properties of a compound will be quite different from the properties of the elements in it. ( Sodium is a highly reactive silvery metal . Chlorine is a greenish coloured suffocating gas. Sodium chloride is quite a harmless white crystalline substance) |
Mixing does not involve chemical changes. (Usually no energy is absorbed or released) | Quite a lot of energy is either absorbed or released during chemical combinations that form compounds.( Forming oxides of Carbon, Hydrogen or Sulphur releases a lot of heat, These reactions are called burning) |
Constituents can be separated by physical methods such as filtering or dissolving. | Constituents can only be separated by chemical methods. |
A mixture cannot have a definite boiling point and a freezing point. (In crude petroleum different fractions evaporate at different temperatures.) | There will be a definite boiling point and a freezing point. (Pure water boils at 100˚C and freezes at 0˚C.) |
Compounds
Compounds may be again divided as Acjds, Bases and salts.
Acids
These are compounds that can form Hydrogen ions. (H+) more than hydroxide (OH-) ions..
Bases
These are oxides and hydroxides of metals.
Q, 1.0
A | B |
1. A pure substance with a definite composition. 2..A pure substance used in chemistry. 3. A gaseous element 4. A method of separating miscible solutions. 5 Separating suspended particles in a liquid. 6 There is no fixed value in a mixture for this. 7. Atoms of these have a definite number of protons. 8. Smallest particles of a compound. 9. A subatomic particle with no electric charge. 10. A pure substance that freezes at 0 C. 11. A good example of a gaseous mixture. 12. Listed second in the Periodic table. 13. The properties of this can be expected from the properties of its constituents. 14.A compound containing Hydrogen, Sulphur and Oxygen. 15.Use this to separate iron in some cereals. | A Distillation. B Filtering. C Molecule. D Element. E Neutron F Compound. G Water H Chemical. I Air J Helium K Boiling point. L Nitrogen. M Mixture N Sulphuric acid. O Magnet. |
(2 x15 = 30)
Q. 2.0
Name at least two constituents in the following mixtures.
1 Salad 2 Water in a pond 3 A cup of tea. 4 Concrete mixture
5 Gun powder 6. Soil 7 Blood , . 8. Ice cream
9. Paint
(2x 9 = 18 Marks)
Q.3.0
Name the elements in these compounds.
1. Potassium chlorate 2 Nitric acid 3 Starch 4 Sugar
5 Sodium carbonate 6 Soda (Carbonic acid) 7. Rust 8. Sea shells
9 Glass 10 Calcium hydroxide
(3 x10= 30 Marks)
Q.4.0
State whether the following are True or False.
1. In a mixture there are many kinds of molecules.
2. A pure compound should have only one kind of molecules.
3. An atom is the indivisible smallest part of a compound.
4. A mixture can never have any compounds.
5. Energy is absorbed or released when atoms combine to make compounds.
( 10 marks)
Q.50
Fredie after after investigating 3 substances recorded the observations.
Name | Appearance | On mixing with water. | On filtering | On evaporating the filtrate. |
a. X | Course cream coloured grains. | Hardly any change. | Remained on filter paper. | Hardly any residue. |
b. Y | Fine powder. White. | Turned to a milky liquid. | Some residue on filter paper. | Some residue left. |
C. Z | White crystalline. | Solid disappeared. | No residue on filter paper. | Light brownish liquid. |
State whether the substances are soluble, slightly soluble or insoluble.
X ……………. b. Y...................c. Z-.............
2. Mixing with water had been a physical reaction or a chemical reaction?
A, ………………………b…………………...c…………………
3. Evaporation of filtrate had been a physical or a chemical reaction?
a.………………………..b…………………..c………………….
4. Name a common substance that will behave as each of these.
X………………………Y………………….Z…………...
12 marks
For Answers click Answer page science.
