Question

20 g silver nitrate solution is added to 20g of sodium chloride solution.What changes in mass do you expect after the reaction and why? In a given sample of ammonia,9g hydrogen and 42 g nitrogen are present.In another sample 5g hydrogen is present.Calculate the amount of nitrogen in second sample.

Answer 1

Dear User,
Silver nitrate reacts with sodium chloride to form silver chloride and sodium nitrate i.e.,
${\mathrm{AgNO}}_3+\mathrm{NaCl}\to \mathrm{AgCl}+{\mathrm{NaNO}}_3$
Total mass of the reactants = 20g + 20g =40 g
According to the Law of Conservation of Mass,
Total mass of reactants = Total mass of products
This is because mass can neither be created nor destroyed, it can only be transformed from one form to another. Therefore, total the mass of products will also be 40g, i.e. total mass will remain constant.

Now, In a given sample of NH_​3, 9g of Hydrogen and 42 g of Nitrogen are present. We aan use Law of constant proportion to calculate amount of nitrogen in second sample. Law of constant proportion states that "In a chemical substance the elements are always present in definite proportion by mass". Therefore,
$$\begin{gathered} \frac{\mathrm{Mass}\mathrm{of}\mathrm{Nitrogen}\mathrm{in}\mathrm{sample}1}{\mathrm{Mass}\mathrm{of}\mathrm{Hydrogen}\mathrm{in}\mathrm{sample}1}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{Nitrogen}\mathrm{in}\mathrm{sample}2}{\mathrm{Mass}\mathrm{of}\mathrm{Hydrogen}\mathrm{in}\mathrm{sample}2} \\ \mathrm{or},\frac{42}{9}=\frac{\mathrm{x}}{5} \\ \mathrm{or},\mathrm{x}=\frac{42\times 5}{9} \\ \mathrm{or},\mathrm{x}=23.33\mathrm{g} \end{gathered}$$