Question

7.90g h₃po₄ →? mol
3.7 molecules →? mol

Explanation:

Step1: Calculate molar - mass of H₃PO₄

The molar - mass of H₃PO₄: $M = 3\times1+31 + 4\times16=98\ g/mol$.

Step2: Calculate moles of 7.90 g H₃PO₄

Using the formula $n=\frac{m}{M}$, where $m = 7.90\ g$ and $M = 98\ g/mol$. So $n=\frac{7.90}{98}\approx0.0806\ mol$.

Step3: Convert molecules to moles

We know that 1 mole of any substance contains $N_A = 6.022\times10^{23}$ molecules.
If there are $N = 3.7$ molecules, then the number of moles $n=\frac{N}{N_A}=\frac{3.7}{6.022\times10^{23}}\approx6.14\times10^{-24}\ mol$.

Answer:

The number of moles of 7.90 g H₃PO₄ is approximately 0.0806 mol, and the number of moles of 3.7 molecules is approximately $6.14\times10^{-24}$ mol.