Is matter around us pure Worksheet-2

Is matter around us pure Worksheet-2

1. The most abundant element in earth's crust is:

A. carbon           B. silicon            C. nitrogen        D. oxygen

2. Which of the following is a semi-metal?

A. phosphorus                               B. nitrogen

C. bismuth                                     D. lead

3. Presence of impurities :

A. lowers the melting point of solid

B. increases the freezing point of liquid

C. increases the boiling point of liquid

D. lowers the boiling point of liquid.

4. The element which is a liquid slightly above 30° C is:

A. cesium                                       B. lithium

C. magnesium                               D. sodium

5. Which of the following is a heterogeneous mixture ?

A. air                                               B. brass   

C. Iodised table salt.                    D. steel

6. Which of the following is not a compound ?

A. marble                                       B. washing soda

C. quick lime                                 D. brass

7. Carbon burns in oxygen to form carbon dioxide. The properties of carbon dioxide are :

A. similar to carbon

B. similar to oxygen

C. totally different from both carbon and oxygen

D. much similar to both carbon and oxygen.

8. Size of colloidal particles in a solution is :

A. more than 100 nm                  B. less than 1 nm

C. between 100 to 1000 nm       D. between 1 to 100 nm.

9. When a beam of light is passed through a colloidal solution, it gets :

A. reflected        B. absorbed       C. scattered       D. refracted

10. Cloud is an example of:

A. solid dispersed in a gas

B. liquid dispersed in a gas

C. liquid dispersed in a solid

D. solid dispersed in a liquid

Answer Key:

1. D

Explanation: Oxygen (46.1%), Silicon (28.2 %),

2. C

Explanation: Bismuth is a semi-metal also called metalloid.

Phosphorous and Nitrogen are non metals, lead is a soft and malleable metal which is regarded as heavy metal or poor metal.

3. C

Explanation: Due to the presence of impurities the boiling point of liquid increases.

4. A

Explanation: Cesium is the most reactive metal in the periodic table and will catch fire when exposed to air. It melts at temperatures just above room temperature and is sometimes referred to as the third liquid element in the periodic table. The metal shows a unique golden color to its shiny metallic appearance. Melting point of Cesium is 29⁰ C.

5. C

Explanation: Iodised table salt is a heterogenous mixture. Air is a homogeneous mixture of gases. Steel, Brass, Bronze are alloys they are homogenous mixtures.

6. D

Explanation: Brass is a mixture of copper and zinc (alloy).

Marble is composed of mineral calcite its chemical formula is CaCO₃.

Washing soda is a chemical compound Na₂CO₃.10H₂O.

Quick lime is a compound CaO

7. C

Explanation: The property of a compound is different from constituent elements.

Carbon is a solid whereas carbon dioxide is a gas. Oxygen supports combustion whereas carbon dioxide is fire extinguisher.

8. D

Explanation: Size of particles in suspension is > 100 nm, Colloidal solution is 1 to 100 nm, and true solution is < 1 nm

9. C

Explanation: Beam of light is scattered and the phenomenon is called Tyndall effect.

Particles present in colloidal have size big enough to scatter or disperse the light rays present in the beam as they fall on them.

10. B

Explanation: Cloud is aerosol. Dispersed phase is liquid and Dispersion medium is Gas.