Question

Which of the following contains maximum number of molecules?
100 cc of CO2 at STP
150 cc of N2 at STP
50 cc of SO2 at STP
200 cc of NH3 a STP

Answer 1

22400 cc at STP has 6.022 x 1023 molecules of any gas. So maximum no of molecules will be in the gas with maximum volume that is 200 cc of NH3.
The correct answer is the fourth option.

Answer 2

Answer: The correct answer is 200 cc of $NH_3$ at STP

Explanation:

At STP conditions:

22.4 L of volume is occupied by 1 mole of a gas         .......(1)

According to mole concept:

1 mole of a compound contains $6.022\times 10^{23}$ number of molecules         .........(2)

For the given options:

• Option 1: 100 cc of $CO_2$ at STP

Volume given = $100cm^3=0.1L$       (Conversion factor: $1L=1000cm^3$ )

Using STP conditions:

0.1 L of volume will be occupied by = $\frac{1}{22.4}\times 0.1=0.0045mol$ of carbon dioxide gas

Using mole concept:

0.0045 moles of carbon dioxide gas will occupy = $0.0045\times 6.022\times 10^{23}=2.7099\times 10^{21}$

Number of molecules in given amount of carbon dioxide gas = $2.7099\times 10^{21}$

• Option 2: 150 cc of $N_2$ at STP

Volume given = $150cm^3=0.15L$

Using STP conditions:

0.15 L of volume will be occupied by = $\frac{1}{22.4}\times 0.15=0.0067mol$ of nitrogen gas

Using mole concept:

0.0067 moles of nitrogen gas will occupy = $0.0067\times 6.022\times 10^{23}=4.035\times 10^{21}$

Number of molecules in given amount of nitrogen gas = $4.035\times 10^{21}$

• Option 3: 50 cc of $SO_2$ at STP

Volume given = $50cm^3=0.05L$

Using STP conditions:

0.05 L of volume will be occupied by = $\frac{1}{22.4}\times 0.05=0.0022mol$ of sulfur dioxide gas

Using mole concept:

0.0022 moles of sulfur dioxide gas will occupy = $0.0022\times 6.022\times 10^{23}=1.325\times 10^{21}$

Number of molecules in given amount of sulfur dioxide gas = $1.325\times 10^{21}$

• Option 4: 200 cc of $NH_3$ at STP

Volume given = $200cm^3=0.2L$

Using STP conditions:

0.2 L of volume will be occupied by = $\frac{1}{22.4}\times 0.2=0.0090mol$ of ammonia gas

Using mole concept:

0.0090 moles of ammonia gas will occupy = $0.0090\times 6.022\times 10^{23}=5.42\times 10^{21}$

Number of molecules in given amount of ammonia gas = $5.42\times 10^{21}$

Hence, the correct answer is 200 cc of $NH_3$ at STP.