Answer the following questions:-

(i) Calculate the total number of electrons present in one mole of methane.

(ii) Find

(a) the total number and

(b) the total mass of neutrons in 7 mg of 14C.

(Assume that mass of a neutron = 1.675 × 10–27 kg).

(iii) Find

(a) the total number and

(b) the total mass of protons in 34 mg of NHat STP.

Will the answer change if the temperature and pressure are changed?

Asked by Pragya Singh | 1 year ago |  82

#### 1 Answer

##### Solution :-

(i) 1 molecule of methane contains 10 electrons (6 from carbon, 4 from hydrogen)

Therefore, 1 mole of methane contains $$10\times N_A$$

= $$6.022\times 10^{24}$$ electrons.

(ii)

(a) Number of neutrons in 14g (1 mol) of 14

=$$8\times N_A$$

=$$4.817\times 10^{24}$$ neutrons.

Number of neutrons in 7 mg (0.007g)

= ($$\dfrac{0.007}{14}\times 4.817\times 10^{24}$$

= $$2.409\times 10^{21}$$ neutrons.

(b) Mass of neutrons in 7 mg of 14

$$(1.67493\times 10^{-27}kg)\times(2.409\times 10^{21})$$

$$4.03\times 10^ {-6}kg$$

(iii)

(a) Molar mass of NH3 = 17g

Number of protons in 1 molecule of NH3 = 7+3 = 10

Therefore, 1 mole (17 grams) of NH3 contains $$10\times N_A$$

=$$6.022\times 10^{24}$$ protons.

34 mg of NH3 contains

($$\dfrac{34}{1700})\times 6.022\times 10^{24}$$ protons

= $$1.204\times 10^{22}$$ protons.

(b) Total mass accounted for by protons in 34 mg of NH3

= $$(1.67493\times 10^{-27}kg)\times (1.204\times10^{22})$$

= $$2.017\times 10^{-5}kg$$.

These values remain constant regardless of any change in temperature and pressure (since these factors do not affect the number of protons in the atom and the mass of each proton).

Answered by Pragya Singh | 1 year ago

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