Question

1) Calculate mass of 1 molecule of O2...

2) How many molecules are in 17g of NH3??

Answer 1

1) Molar mass of O2 = 32

Now, 1 mole means 6.022×10²³ molecules.

Conversely,

6.022×10²³ molecules in 1 mole.

1 molecule in $\frac{1}{6.022 \times {10}^{23} } \: moles$

Now, n = Mass/Molar mass

Or, $\frac{1}{6.022 \times {10}^{23}} \: moles = \frac{mass}{32}$

Or, Mass = $\frac{32}{6.022 \times {10}^{23} }$

Or, Mass = $5.314 \times {10}^{ - 23}$

2) Molar mass of NH3 = 14+3 = 17

Now, Given mass = 17

Let Number of moles be "n".

Then,

n = Given mass ÷ Molar mass

Or, n = 17/17 = 1.

So, 1 mole means 6.022×10²³ molecules.

Hence, there are 6.022×10²³ molecules in 17g of NH3.