Calculate the molecular masses of H2, O2, Cl2, CO2, CH4, C2H6, C2H4, NH3, CH3OH.
Atomic mass includes the masses of three subatomic particles which make up an atom i.e. proton, neutron and electron.
Unit of atomic mass is 'u'
‘u’ = unified atomic mass unit & 1/12 th mass of single carbon-12 atom
‘u’ = 1.66 x 10-24 g
(Just for understanding - Atomic mass approximately equal to twice of atomic no.)
Molecular mass of a substance is the sum of atomic masses of all the atoms in a molecule of a subitance.
Unit of molecular mass = 'u’
Molecular mass of H2 = 2 x 1 = 2u (Atomic mass of H=1)
Molecular mass of O2 = 16 x 2 = 32 u (Atomic mass of O=16)
Molecular Mass of Cl2 = 35.2 x 2 = 71 u (Atomic mass of Cl = 35.5)
Molecular Mass of CO2 = 12 x 1 + 16 x 2
= 12 + 32 = 44 u ( Atomic Mass of C = 12)
Molecular Mass of CH4 = 12 x 1 + 4 x 1
= 12 + 4 = 16 u
Molecular Mass of C2H6 = 12 x 2 + 6 x 1
= 24 + 6 = 30 u
Molecular Mass of C2H4 = 12 x 2 + 4 x 1
= 24 + 4 = 28 u
Molecular Mass of NH3 = 14 X 1 + 3 x 1
= 14 x 3 = 17 u (Atomic Mass of N = 14)
Molecular Mass of CH3OH = 12 x 1 + 4 x 1 + 16 x 1
= 12 + 4 + 16 = 32 u
Popular Questions of Class 9 Science
- Q:-
Abdul, while driving to school, computes the average speed for his trip to be 20 km h-1. On his return trip along the same route, there is less traffic and the average speed is 40 km h-1. What is the average speed for Abdul’s trip?
- Q:-
Fig 8.11 shows the distance-time graph of three objects A,B and C. Study the graph and answer the following questions:
Fig. 8.11
(a) Which of the three is travelling the fastest?
(b) Are all three ever at the same point on the road?
(c) How far has C travelled when B passes A?
(d) How far has B travelled by the time it passes C? - Q:-
Two objects of masses 100 g and 200 g are moving along the same line and direction with velocities of 2 m s-1 and 1 m s-1, respectively. They collide and after the collision, the first object moves at a velocity of 1.67 m s-1. Determine the velocity of the second object.
- Q:-
The speed-time graph for a car is shown is Fig. 8.12.
Fig. 8.12
(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.
(b) Which part of the graph represents uniform motion of the car? - Q:-
Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
- Q:-
How do poriferan animals differ from coelenterate animals?
- Q:-
Why is the weight of an object on the moon 1/6th its weight on the earth?
- Q:-
Convert into mole.
(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide. - Q:-
From a rifle of mass 4 kg, a bullet of mass 50 g is fired with an initial velocity of 35 m s-1. Calculate the initial recoil velocity of the rifle.
- Q:-
Name the technique to separate
(i) butter from curd,
(ii) salt from sea-water,
(iii) camphor from salt.
Recently Viewed Questions of Class 9 Science
- Q:-
How much momentum will a dumb-bell of mass 10 kg transfer to the floor if it falls from a height of 80 cm? Take its downward acceleration to be 10 m s-2.
- Q:-
Explain the basis for grouping organisms into five kingdoms.
- Q:-
How do poriferan animals differ from coelenterate animals?
- Q:-
A hammer of mass 500 g, moving at 50 m s-1, strikes a nail. The nail stops the hammer in a very short time of 0.01 s. What is the force of the nail on the hammer?
- Q:-
A motorboat starting from rest on a lake accelerates in a straight line at a constant rate of 3.0 m s-2 for 8.0 s. How far does the boat travel during this time?
- Q:-
Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
- Q:-
Two objects of masses 100 g and 200 g are moving along the same line and direction with velocities of 2 m s-1 and 1 m s-1, respectively. They collide and after the collision, the first object moves at a velocity of 1.67 m s-1. Determine the velocity of the second object.
- Q:-
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
- Q:-
An automobile vehicle has a mass of 1500 kg. What must be the force between the vehicle and road if the vehicle is to be stopped with a negative acceleration of 1.7 m s-2?
- Q:-
When a carpet is beaten with a stick, dust comes out of it. Explain.
- NCERT Chapter