compounds

What is a pure substance?

A substance made up of only one kind of particles having fixed composition and fixed properties.

What is a compound?

A pure substance formed by chemical combination of two or more elements in a fixed ratio by mass.

What is a mixture?

A physical combination of two or more substances in any proportion.

Why cannot compounds be separated by physical methods?

Because the elements are chemically bonded together.

Why do compounds have different properties from constituent elements?

Because a new substance with completely new properties is formed after chemical combination.

What is the ratio of hydrogen and oxygen in water by mass?

1 : 8

Which type of reaction releases heat energy?

Exothermic reaction.

Which type of reaction absorbs heat energy?

Endothermic reaction.

Give one example of exothermic reaction.

Burning of candle.

Give one example of endothermic reaction.

Photosynthesis.

What is a homogeneous mixture?

A mixture having uniform composition throughout.

What is a heterogeneous mixture?

A mixture having non-uniform composition throughout.

What is a true solution?

A solution in which solute particles are extremely small and mix uniformly with solvent.

Why is salt solution a true solution?

Because salt particles are extremely small and mix completely with water.

What is a colloidal solution?

A solution having intermediate sized particles which do not settle down.

Why is milk a colloid?

Because tiny particles of fats and proteins remain dispersed in water and do not settle down.

Is milk homogeneous or heterogeneous?

Milk is actually a heterogeneous mixture but appears homogeneous.

What is a suspension?

A mixture in which particles are large and settle down on standing.

Give one example of suspension.

Chalk powder in water.

Which type of mixture is brass?

Homogeneous solid-solid mixture.

What are the components of brass?

Copper and zinc.

What are the components of smoke?

Carbon particles and air.

What are the components of gunpowder?

Nitre, sulphur and charcoal.

What are the components of air?

Nitrogen, oxygen, carbon dioxide and water vapour.

Why can iron be separated from sulphur by magnet?

Because iron is magnetic whereas sulphur is non-magnetic.

What happens when iron and sulphur mixture is heated strongly?

Iron sulphide (FeS) compound is formed.

Which compound is formed when iron and sulphur are heated strongly?

Iron sulphide.

What is the formula of iron sulphide?

FeS

FeS is the formula of which compound?

Iron sulphide.

Why can ammonium chloride be separated by sublimation?

Because ammonium chloride sublimes whereas common salt does not.

What is sublimation?

Process in which a solid changes directly into vapour without passing through liquid state.

Name four sublimable substances.

Camphor, iodine, naphthalene and ammonium chloride.

What is magnetic separation used for?

To separate mixtures in which one component is magnetic.

Give one example of magnetic separation.

Iron filings and sand.

Which method is used to separate a magnetic substance from a non-magnetic substance?

Magnetic separation.

What is gravity separation based on?

Difference in density.

What happens in gravity separation of sand and sawdust?

Sand settles down while sawdust floats.

What is solvent extraction?

Method in which one component dissolves in solvent while the other does not.

Which solvent is used to dissolve sulphur in solvent extraction?

Carbon disulphide.

Which solvent dissolves sulphur during solvent extraction?

Carbon disulphide.

What is sedimentation?

Process in which heavy insoluble particles settle down at the bottom.

What is decantation?

Process of carefully pouring out the clear liquid above sediments.

What is filtration?

Process of separating insoluble solid from liquid using filter paper.

Which method is used to separate insoluble solid from liquid using filter paper?

Filtration.

What is residue?

Solid left on the filter paper.

What is filtrate?

Clear liquid passing through the filter paper.

Why can chalk powder be separated by filtration?

Because chalk powder is insoluble and its particles are trapped by filter paper.

Why cannot salt solution be separated by filtration?

Because dissolved salt particles are extremely small and pass through filter paper.

What is distillation?

Process of converting liquid into vapour by heating and condensing vapour back into liquid.

Why is distillation used for salt and water mixture?

Because water is volatile whereas salt is non-volatile.

Which method is used to obtain pure water from salt solution?

Distillation.

What is evaporation?

Process of changing liquid into vapour below its boiling point.

Which method is used to obtain salt from sea water?

Evaporation.

Which method is used to obtain common salt from sea water?

Evaporation.

What is a separating funnel used for?

To separate immiscible liquids having different densities.

Why is separating funnel used for oil and water?

Because oil and water are immiscible liquids with different densities.

Which method is used to separate immiscible liquids having different densities?

Separating funnel.

Which liquid forms lower layer in oil and water mixture?

Water.

Which liquid forms upper layer in oil and water mixture?

Oil.

Which liquid forms the lower layer in oil and water mixture?

Water.

Which liquid forms the upper layer in oil and water mixture?

Oil.

Which liquid forms the lower layer in chloroform and water mixture?

Chloroform.

Which liquid forms the upper layer in benzene and water mixture?

Benzene.

What are miscible liquids?

Liquids which mix completely with each other.

What are immiscible liquids?

Liquids which do not mix with each other.

What is fractional distillation used for?

To separate miscible liquids having different boiling points.

Which method is used to separate miscible liquids having different boiling points?

Fractional distillation.

Which apparatus is used in fractional distillation?

Fractionating column.

Which liquid vaporises first in fractional distillation?

The liquid with lower boiling point.

What is the boiling point of ethyl alcohol?

78°C

Which liquid has boiling point 78°C?

Ethyl alcohol.

What is the boiling point of water?

100°C

Which liquid has boiling point 100°C?

Water.

What is the boiling point of methyl alcohol?

64.5°C

Which liquid has boiling point 64.5°C?

Methyl alcohol.

What is the boiling point of acetone?

56.5°C

Which liquid has boiling point 56.5°C?

Acetone.

Why are gases separated from liquids by heating?

Because solubility of gases decreases on heating.

Which compound is used to dry gases in drying chamber?

Anhydrous calcium chloride.

Which drying agent is used in the drying chamber?

Anhydrous calcium chloride.

Name the liquid metal.

Mercury.

Which metal remains liquid at room temperature?

Mercury.

Name the liquid non-metal.

Bromine.

Which non-metal remains liquid at room temperature?

Bromine.

Which non-metal conducts electricity?

Graphite.

What is the nature of true solution?

Homogeneous.

What is the nature of suspension?

Heterogeneous.

Can colloidal particles settle down?

No.

Can suspension particles settle down?

Yes.

Can suspension particles be filtered?

Yes.

Can colloidal particles be filtered easily?

No.

Which type of mixture is soil in water?

Heterogeneous mixture.

Which type of mixture is salt in water?

Homogeneous mixture.

Why does water extinguish fire?

Because it cools the burning substance below ignition temperature.

What gas with rotten egg smell is formed when iron sulphide reacts with hydrochloric acid?

Hydrogen sulphide gas.

Which gas with rotten egg smell is produced when iron sulphide reacts with hydrochloric acid?

Hydrogen sulphide gas.

What happens when carbon disulphide is added to iron and sulphur mixture?

Sulphur dissolves while iron remains behind.

Why is a compound considered a pure substance?

Because it has fixed composition and uniform properties throughout.

Which mixture is formed by nitrogen, oxygen, carbon dioxide and water vapour?

Air.

Which homogeneous solid-solid mixture is formed by copper and zinc?

Brass.