Problem based on Atoms and Molecules

1. a). Calculate the relative mass of water
b). Calculate the molecular of NaCl
Sol. a). Atomic mass of hydrogen = 1 u
Atomic mass of oxygen = 16 u
So molecular mass of water = 2 * 1 + 1 * 16
= 18 u
b). Atomic mass of sodium = 23 u
Atomic mass of chlorine = 35.453 u
So molecular mass of water = 23 + 35.453
= 58.453 u

2. a). Calculate the relative mass of HCl
b). Calculate the molecular of calcium oxide
Sol. a). Atomic mass of hydrogen = 1 u
Atomic mass of chlorine = 35.453 u
So molecular mass of HCl = 1 + 35.453
= 36.453 u
b). Atomic mass of calcium = 40 u
Atomic mass of oxygen = 16 u
So molecular mass of calcium oxide = 40 + 16
= 56 u

science ncert solutions

3. Calculate the number of moles for the following
a) 26 g of H
b). 6.022 * 10^23 number of H atoms
Sol. a). Atomic mass of H = 1 u
Molar mass of H = 1 g
The number of moles = Given mass / Molar mass
n = m / M
= 26 / 1 = 26 u
b). 1 mole = 6.022 * 10^23
The number of moles = Given number of particles / Avogadro Number
n = (6.022 * 10^23) / (6.022 * 10^23)
n = 1

4). Calculate the mass of following
a). 0.1 mole of hydrogen gas
b). 0.1 mole of H atom
c). 3.011 * 10^23 number of H atom
d). 6.022 * 10^23 number of hydrogen gas
Sol. a). Mass = Molar Mass * Number of moles
m = M * n
m = 2 * 0.1
m = 0.2 g
b). Mass = Molar Mass * Number of moles
m = M * n
m = 1 * 0.1
m = 0.1 g
c). The number of moles = Given number of particles / Avogadro number
m = M * n
= 1 * (3.011 * 10^23) / (6.022 * 10^23)
= 0.5 g
d). n = Given number of particles / Avogadro number
m = M * (Given number of particles / Avogadro number)
= 2 * (6.022 * 10^23 / 6.022 * 10^23)
= 2 * 1
= 2 g

5). Calculate the mass of following
a). 32 g of oxygen gas
b). 0.4 mole of carbon atom
c). 23 g of sodium atom
d). 0.4 mole of oxygen atom
Sol. a). The number of atoms = (Given mass / Molar mass) * Avogadro number
N = (m / M) * Avogadro number
= (32 / 32) * 6.022 * 10^23
= 6.022 * 10^23
b). The number of particles = Number of moles of particles * Avogadro number
= 0.4 * 6.022 * 10^23
= 2.4088 * 10^23
c). The number of atoms = (Given mass / Molar mass) * Avogadro number
N = (m / M) * Avogadro number
= (23 / 23) * 6.022 * 10^23
= 6.022 * 10^23
d). The number of particles = Number of moles of particles * Avogadro number
= 0.4 * 6.022 * 10^23
= 2.4088 * 10^23

Milan Tomic

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