91Ó°ÊÓ

That are given sentences are :

According to the dilution expression:

According to the dilution expression:

Here.

The dilution expression to solve tor the unknown quantity $V_1$.

According to the problem,

$$\begin{gathered} C_2=3.0\%(\mathrm{m}/\mathrm{v}) \\ {\mathrm{V}}_2=250\mathrm{mL} \\ {\mathrm{C}}_1=10.0\%(\mathrm{m}/\mathrm{v}) \\ {\mathrm{V}}_1=? \end{gathered}$$

Rearrange the dilution expression to solve for the unknown quantity $V_1$.

$$\begin{gathered} V_1=\frac{{\mathrm{C}}_2×{\mathrm{V}}_2}{{\mathrm{C}}_1} \\ {\mathrm{V}}_1=\frac{3.0\%(\mathrm{m}/\mathrm{v})×250\mathrm{mL}}{10.0\%(\mathrm{m}/\mathrm{v})} \\ =75\mathrm{mL} \end{gathered}$$

The required initial volume of $\mathrm{HCl}$solution is $75\mathrm{mL}$.

Rearrange the dilution expression to solve for the unknown quantity $V_1$

According to the problem,

$$\begin{gathered} C_2=0.9\%(\mathrm{m}/\mathrm{v}) \\ {\mathrm{V}}_2=500\mathrm{mL} \\ {\mathrm{C}}_1=5.0\%(\mathrm{m}/\mathrm{v}) \\ {\mathrm{V}}_1=? \end{gathered}$$

Rearrange the dilution expression to solve for the unknown quantity $V_1$.

$$\begin{gathered} V_1=\frac{C_2×V_2}{C_1} \\ {V}_1=\frac{0.9\%(\mathrm{m}/\mathrm{v})×500\mathrm{mL}}{5.0\%(\mathrm{m}/\mathrm{v})} \\ =90\mathrm{mL} \end{gathered}$$

The required initial volume of $\mathrm{NaCl}$solution is $90\mathrm{mL}$.

Rearrange the dilution expression to solve for the unknown quantity $V_1$.

According to the problem,

$$\begin{gathered} C_2=2.0\mathrm{M} \\ {V}_2=350\mathrm{mL} \\ {C}_1=6.0\mathrm{M} \\ {V}_1=? \end{gathered}$$

Rearrange the dilution expression to solve for the unknown quantity $V_1$.

$$\begin{gathered} V_1=\frac{C_2×V_2}{C_1} \\ {V}_1=\frac{2.0\mathrm{M}×350\mathrm{mL}}{6.0\mathrm{M}} \\ =117\mathrm{mL} \end{gathered}$$

The required initial volume of $\mathrm{NaOH}$solution is $117\mathrm{mL}$.