Railway Science (Chemistry-Structure of Atom) (Part-III)

Total Questions: 41

31. In 144 grams of magnesium, ______ grams of atoms are present. [RRB Group D 06/12/2018 (Evening)]

Correct Answer: (b) 6
Solution:

Atomic weight of Magnesium = 24 gmol⁻¹
Number of gram atoms = Number of moles
= 𝑚𝑎𝑠𝑠 𝑖𝑛 𝑔𝑟𝑎𝑚𝑠/𝐴𝑡𝑜𝑚𝑖𝑐 𝑤𝑒𝑖𝑔ℎ𝑡 = 144/24 = 6.

32. The atomic mass of Nitrogen is 14, that of Hydrogen is 1 and that of Chlorine is 35.5. What will be the molecules mass of Ammonium Chloride [RRB Group D 11/12/2018 (Morning)]

Correct Answer: (d) 53.5
Solution:

The atomic mass of nitrogen (N) = 14 u,
the atomic mass of hydrogen (H) = 1 u
and the atomic mass of chlorine (Cl) = 35.5 u
Molecular mass of ammonium chloride (NH₄Cl) = (1 × atomic mass of N) + (4 × atomic mass of H) + (atomic mass of Cl) = (1 × 14) + (4 × 1) + 35.5 = 53.5 u.

33. The total number of neutrons in positive zinc ion with mass number 70 is _______. [RRB Group D 13/12/2018 (Morning)]

Correct Answer: (a) 40
Solution:

Mass number of Zinc = 70 which is also same in Zn²⁺ since the number of protons are not affected.
Atomic number = Number of protons = 30 Number of neutrons = Mass number - Number of protons = 70 - 30 = 40
We know that in Zn²⁺ , the number of protons and the number of neutrons will be the same as that of Zn.

34. Atomic mass of Nitrogen is 14 and that of Hydrogen is 1. What will be the molecular mass of Ammonia ? [RRB ALP Tier - I (17/08/2018) Afternoon]

Correct Answer: (a) 17
Solution:

The atomic mass of Nitrogen is 14 and that of Hydrogen is 1
Hence, The molecular mass of NH₃
= ( 1 × 14 ) + ( 3 × 1 )
Molecular mass of NH₃ = 17 g/mole.

35. The mass of one molecule of oxygen is_________. [RRB ALP Tier - I (20/08/2018) Evening]

Correct Answer: (d) 5.3 × 10⁻²³g
Solution:

36. Atomic mass of Sulphur is 32 u. The number of moles in 16 grams of Sulphur is: [RRB ALP Tier - I (21/08/2018) Afternoon]

Correct Answer: (d) 0.5 moles of Sulphur
Solution:

1 gram is equal to 6.022 × 10²³ u or 1 mole.
The atomic mass of Sulphur = 32u = 32 grams.
1 mole sulphur = 32u = 32 grams.
So, 16 gram sulphur = 16/32 = 0.5
Moles in 16 g of sulphur is 0.5.

37. How many moles are present in 60 g of He ? [RRB ALP Tier - I (29/08/2018) Evening]

Correct Answer: (d) 15 moles
Solution:

Given, mass of He (m) = 60 g .
Molecular mass is the sum of total protons and neutrons.
The molecular mass (M) of Helium = 2 × 2 = 4.
Molar mass of He (M) = 4 g .
So number of moles in 60 g of helium,
n = 𝑚/m = 60/4 .  n = 15 moles .

38. In 540 gram of glucose, the number of moles present are: [RRB ALP Tier - I ( 29/08/2018) Evening]

Correct Answer: (b) 3
Solution:

39. The percentage of water of crystallisation in washing soda is ______. [RRB ALP Tier - I (30/08/2018) Morning]

Correct Answer: (a) 62.9
Solution:

40. The mass number of an isotope of an element is 298. If its nucleus has 196 neutrons, what is its atomic number? [RRB ALP Tier - I (30/08/2018) Evening]

Correct Answer: (c) 102.0
Solution:

Atomic Number = Number of Protons Atomic Mass Number = Number of Protons + Number of Neutrons
Here, Atomic Mass Number = 298 Number of Protons + Number of Neutrons = 298 Number of Protons = 298 - 196 = 102
Isotopes are defined as elements with the same number of protons but a different number of neutrons present in their nucleus.