Elements, Compounds and Mixtures

Helium (He)

Silver (Ag)

Krypton (Kr)

Antimony (Sb)

Barium (Ba)

Na — Sodium

C — Carbon

Kr — Krypton

U — Uranium

Ra — Radium

Fe — Iron

Co — Cobalt

(a) An element is a pure substance that cannot be converted further into anything simpler than itself by any physical or chemical process. It is made up of only one kind of atoms.

(b) A compound is a pure substance formed by the chemical combination of two or more elements in a fixed ratio by mass.

(a) Iron

(b) Calcium

(c) Magnesium

(d) Aluminium

Hydrogen(H), Chlorine(Cl), Sulphur(S), Phosphorus(P)

(a) Metalloids are those elements that show some properties of metals and some properties of non-metals. They are hard solids. Examples — Boron(B), Silicon(Si).

(b) Noble gases or inert gases are those elements that do not react chemically with other elements or compounds and they are found in air in traces. Examples — Helium(He), Neon(Ne).

The characteristic properties of a pure substance are:

1. They have a definite composition and a definite set of properties like boiling point, melting point, density etc.
2. They are all homogeneous i.e. their composition is uniform throughout the bulk.

We need pure substances to:

1. Prepare medicines.
2. Maintain good health of human beings.
3. Prepare chemicals in laboratories.

(a) Sand and sugar, Brass

(b) Sand and water, salt in water

(c) Oil in water, Alcohol and water

(a) Evaporation is the process of converting a liquid into its vapour state either by exposing it to air or by heating.

(b) The process of separating insoluble solid particles from a liquid by allowing it to pass through a filter is called filtration.

(c) The process in which a solid substance directly changes into its vapour state on heating without passing through its liquid state is called sublimation.

(d) Distillation is the method of getting a pure liquid from a solution by evaporating and then condensing the vapours.

(e) Liquids which dissolve in each other completely in all proportions are called miscible liquids.

(f) Liquids which do not dissolve in each other are called immiscible liquids.

(a) Magnetic separation

(b) Sublimation

(c) Evaporation

(d) Winnowing

(e) Separating funnel

(f) Crystallization

(g) Centrifugation

On heating the mixture, camphor will evaporates as it is a sublime substance. Its vapours can be collected which will solidify on cooling. Common salt and chalk powder mixture is then mixed in water. Common salt gets dissolved in water while chalk powder does not. Then by filtration, chalk powder is removed from the solution as it gets deposited in filter paper. The filtrate contains water and common salt. Common salt can be separated from water by evaporation process.

Distillation is more advantageous than evaporation because both the components of the solid-liquid mixtures are obtained in distillation process but in evaporation process only solid is obtained.

(a) The process of separating different dissolved constituents of a mixture by their adsorption(particles getting adhered to a surface) on an appropriate material is called chromatography.

(b) The word chromatography means colour writing. It is named so because earlier it was used to separate mixtures containing coloured components only.

(c) The advantages of chromatography are:

1. A very small quantity of the substance can be separated.
2. Components with very similar physical and chemical properties can be separated.
3. It identifies the different constituents of a mixture.

(d) Paper chromatography.

(e) Chromatography separates the components of a mixture on the basis of differences between two phases, one of which is stationary while the other is mobile.

(f) The stationary phase is made up of common adsorbents like filter paper, silica gel as they are stationary and the mobile phase is made up of common solvents like water, ethyl alcohol, acetic acid etc. which moves or spreads on the stationary phase.

(a) This method is used for solid mixtures in which one of the components can sublime on heating. It is used to separate a mixture of common salt and ammonium chloride.

(b) This method is used for separating the components of a heterogeneous solid-liquid mixture in which solids are insoluble in liquids. A mixture of chalk and water can be separated by this method.

(c) This method is used when the solid component is insoluble and heavier than the liquid component. A mixture of sand and water can be separated by this method.

(d) This method is used when one component is soluble in a particular liquid while the other component is insoluble. A mixture of sand and salt can be separated by this method.

(e) This method is used when one of the components of the mixture is magnetic in nature. A mixture of iron and sulphur can be separated by this method.

(f) It is used to separate components of liquid-liquid heterogeneous mixture when one of the liquid components is heavier than the other. Kerosene oil and water can be separated by this method.

(g) It is used to separate components of homogeneous liquid-liquid mixture on the basis of their difference in boiling points. A mixture of water and alcohol can be separated by this method.

(a) Elements

(b) Elements, compounds

(c) mixture

(d) filtration

(e) Crystallization

(f) sublime

(a) residue

(b) distillate

(c) decantation

(d) fractional distillation

distillation

Reason — Distillation is the method of getting a pure liquid from a solution by evaporating and then condensing the vapours.

fractional distillation

Reason — Petrol, kerosene, diesel etc. are obtained from crude petroleum by fractional distillation as they have different boiling points.

tap water

Reason — Tap water is a homogeneous mixture because it contains small amounts of dissolved salts and air in it that we cannot see.

stationary phase

Reason — The stationary phase in the process of chromatography is made of common adsorbents like filter paper.

ink, honey, ice cream, milk

Reason — They are homogeneous mixtures where constituents are uniformly distributed throughout its volume and cannot be recognized separately.