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
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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?
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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?
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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?
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