Molecules

Q.

What is the difference between precipitation and condensation?

Q.

What kind of change is shown by tearing of paper?

Q.

What is uniform composition?

Q.

Which amongst the following molecules contains the maximum number of hydrogen atoms in it?

1. $HCl$
2. $HN{O}_3$
3. $N{H}_3$
4. $N{H}_{4}Cl$

Q. State the information obtained from the chemical formula of a compound.

Q.

‘The reddish-brown substance deposited over iron objects in the presence of moist air.

Q.

The stretching of rubber band is a/an ___________ (irreversible/reversible) change.

Q.

Formation of clouds is a ____________ change. (reversible/irreversible)

Q.

A type of change in which the chemical composition does not change.

Q. State four important characteristics of compounds. ​

Q.

Give reasons for the following.

Evaporation can be desirable or undesirable.

Q.

The rotting of fruits is a desirable change.

1. True
2. False

Q. In one molecule of water, how many hydrogen atoms combine with one atom of oxygen?

Q.

The property which forms the basis of winnowing is difference in

1. weight

2. size

3. colour

4. shape

Q. Which of the following is correct with respect to the chemical formula of $H_{2}O$?

1. A molecule contains two atoms of H and one atom of O.
2. The ratio of the mass of H to the mass of O in the molecule is 2:1.
3. There are twice as many O atoms in the molecule as there are H atoms.
4. The ratio of the mass of H to the mass of O in the molecule is 1:2.

Q.

Give two differences between a physical change and a chemical change.

Q.

When a chemical change takes place with the evolution of heat energy, the change is said to be_________.

Q. State the information obtained from the chemical formula of a compound.

Q.

Which of the following is a chemical change?

1. Shredding of paper to very small particles

2. Burning of paper

3. Breaking a water bottle

4. Grinding charcoal to powder form

Q. Which of the following substances, when mixed with water, do not leave a residue when passed through a filter paper?

1. Salt
2. Sand
3. Corn
4. Brown sugar

Q.

Which among the following are physical or chemical changes?

(d) Curdling of milk

Q.

Oil can be separated from water by:

1. decantation

2. sedimentation

3. filtration

4. threshing

Q.

A. Fill in the blank spaces by choosing the correct words from the words given in list.
List: composition, heat, chemical, photosynthesis, physical

5 ………………. energy is generally given out or absorbed during a chemical change.

Q.

Define the following term:

• Homogeneous mixture

Q.

Burning of paper is not a chemical change.

1. True
2. False

Q. Riya observed two scenes around her. Choose the correct classification of changes for the observations.
1. A few children were inflating balloons.
2. Farmers were harvesting crops in their fields.

Q. Pair the given compounds with their correct chemical formulas.

1. Gypsum
2. ${\mathrm{MgSO}}_4.7H_{2}O$
3. $C_6{H}_5\mathrm{OH}$
4. Epsom
5. ${\mathrm{CaSO}}_4{.}_2^1{H}_{2}O$
6. Plaster of Paris
7. Phenol
8. ${\mathrm{CaSO}}_4.2H_{2}O$

Q. Answer the following questions:
(A) Mention any two important properties of mixtures. [1 Marks]
(B) Water in a container is mixed with dust, sand, and oil. How can we get the water back? [4 Marks]