EXERCISE 3C

A sample in vitamin C is known to contain $2.58\times {10}^{24}$ oxygen atoms. How many moles of oxygen atoms are present in the sample?

Calcium chloride, when dissolved in water, dissociates into its ions according to the following equation
${{\mathrm{CaCl}}_2}_{\left(\mathrm{aq}\right)}\to {\mathrm{Ca}}^{(2+)}{ }_{\left(\mathrm{aq}\right)}+2{\mathrm{Cl}}^{-}{ }_{\left(\mathrm{aq}\right)}$
 Calculate the number of ions obtained from ${\mathrm{CaCl}}_2$ when 222 g of it is dissolved in water.
 

Cinnabar ($\mathrm{HgS}$ ) is a prominent ore of mercury. How many grams of mercury are present in 225 g of pure $\mathrm{HgS}$? Molar mass of $\mathrm{Hg}$ and $\mathrm{S}$ are 200.6 $\mathrm{g} {\mathrm{mol}}^{-1}$ and 32 $\mathrm{g} {\mathrm{mol}}^{-1}$ respectively. 

Compute the difference in masses of ${10}^3$moles each of magnesium atoms and magnesium ions. 
(Mass of an electron =$9.1\times {10}^{-31}$ kg) 

The difference mass of $100$ moles each of sodium atoms and sodium ion is $5.48002 \mathrm{g}$. Compute the mass of an electron.

Compute the difference in masses of one mole each of aluminium atoms and one mole of its ions. (Mass of an electron is $9.1\times {10}^{-28}$ g). Which one is heavier?       

A silver ornament of mass 'm' gram is polished with gold equivalent to $1\%$ of the mass of silver. Compute the ratio of the number of atoms of gold and silver in the ornament.

A sample of ethane ${\mathrm{C}}_2{\mathrm{H}}_6$ gas has the same mass as $1.5\times {10}^{20}$molecules of methane (${\mathrm{CH}}_{4 }$). How many ${\mathrm{C}}_2{\mathrm{H}}_6$ molecules does the sample of gas contain?.