Question

1. calculate the number of neutrons in a 10g sample of ar atoms (40g/mol)

Explanation:

Step1: Calculate moles of Ar

Moles = mass / molar mass. Mass is 10g, molar mass is 40g/mol. So moles = $\frac{10\mathrm{g}}{40\mathrm{g/mol}}$ = 0.25 mol.

Step2: Find number of Ar atoms

Using Avogadro's number ($N_A = 6.022\times10^{23}$ atoms/mol), number of atoms = moles × $N_A$ = 0.25 mol × $6.022\times10^{23}$ atoms/mol = $1.5055\times10^{23}$ atoms.

Step3: Determine neutrons per Ar atom

Ar has atomic number (Z) 18, mass number (A) 40. Neutrons = A - Z = 40 - 18 = 22 per atom.

Step4: Calculate total neutrons

Total neutrons = number of atoms × neutrons per atom = $1.5055\times10^{23}$ × 22 = $3.3121\times10^{24}$ (approx $3.31\times10^{24}$ or $3.3\times10^{24}$ depending on precision).

Answer:

Approximately $\boldsymbol{3.31\times10^{24}}$ (or $3.3\times10^{24}$) neutrons.