Question

find the weight of

2 g atoms of oxygen ,0.5g-molecules of ammonia,10g-moles of sulphuric acid

Answer 1

1) 2 g of oxygen atom
16 g of oxygen atom contains = 6.022 $\times$10²³ atoms of oxygen
2 g of oxygen atom contains = $\frac{6.022\times {10}^{23}\times 2}{16}$ = 0.75 $\times$10²³ atoms
2) 0.5 g molecules of ammonia (NH₃)
Molar mass of NH₃ = 14 + 3$\times$1 = 17 g mol^-1
17 g of NH₃ contains = 6.022$\times$10²³ molecules
0.5 g of NH₃ contains = $\frac{6.022\times {10}^{23}\times 0.5}{17}$ = 0.177 $\times$10²³ atoms
3) 10 g moles of sulphuric acid (H₂SO₄)
98 g of H₂SO₄ contains = 6.022$\times$10²³ moles
10 g of H₂SO₄ contains = $\frac{6.022\times {10}^{23}\times 10}{98}$ = 0.614$\times {10}^{23}$ moles of H₂SO₄