Question

How many molecules approximately do you expect to be present in

(i) a small sugar crystal weighing 10 mg.

Answer 1

10mg=10^-3gm
mass of 1 mole of sugar=342g
if 342g sugar contain 6.023×10^23molecules of sugar
then 1g contain = 6.023×10^23/342=1.7×10^21(approx)
therefore 1mg contain = 1.7×10^18 molecules

Answer 2

Answer:

The number of molecules in 10mg of small sugar crystal will be equal to 1.76×10¹⁹ sugar molecules.

Explanation:

Given, the weight of sugar crystal = 10mg = 10×10⁻³g

Molecular formula of sugar = C₁₂H₂₂O₁₁

The molecular mass of sugar = 12 (12)+ 22 + 11(16)

                                                = 144 + 22 + 176

                                                = 342 gmol⁻¹

Number of moles of sugar $=\frac{10*10^{-3}}{342}$

                                           $=\frac{0.01}{342}=2.92*10^{-5}moles$

One mole of sugar crystal has sugar molecules = 6.023×10²³

2.92×10⁻⁵ moles sugar has molecules  $=(6.023*10^{23})*(2.92*10^{-5})$

                                                               $=1.76*10^{19}$ molecules

Therefore, 1.76×10¹⁹ sugar molecules present in 10mg of sugar crystal.