Question

how many molecules of so₂ are present in 79g so₂? {____ x 10²³ molecules so₂}. report your answer with the proper number of significant figures.

Explanation:

Step1: Calculate molar mass of SO₂

The molar mass of S is approximately 32 g/mol and of O is approximately 16 g/mol. For SO₂, molar mass $M=(32 + 2\times16)$ g/mol = 64 g/mol.

Step2: Calculate number of moles

Number of moles $n=\frac{m}{M}$, where $m = 79$ g and $M = 64$ g/mol. So $n=\frac{79}{64}$ mol $\approx1.234$ mol.

Step3: Calculate number of molecules

We know that 1 mole of any substance contains $N_A = 6.022\times 10^{23}$ molecules. So number of molecules of SO₂ $N=n\times N_A=1.234\times6.022\times 10^{23}$ molecules $\approx7.43\times 10^{23}$ molecules.

Answer:

$7.43$