Answer
a. Initial volume = 75 mL of the original 10.0 % (m/v) $HCl$ solution.
b. Initial volume = 90. mL of the original 5.0 % (m/v) $NaCl$ solution.
c. Initial volume = 117 mL of the original 6.00 M $NaOH$ solution.
Work Step by Step
1. Write the dilution expression, and solve for the initial volume $(V_1)$
$C_1V_1 = C_2V_2$
$$V_1 = \frac{C_2V_2}{C_1} $$
a.
2. Substitute the values and calculate the initial volume:
$$V_1 = \frac{(250 \space mL)(3.0 \space \% (m/v))}{10.0 \space \% (m/v)}$$
$$V_1 = 75 \space mL$$
b.
2. Substitute the values and calculate the initial volume:
$$V_1 = \frac{(500. \space mL)(0.90 \space \% (m/v))}{5.0 \space \% (m/v)}$$
$$V_1 = 90. \space mL$$
c.
2. Substitute the values and calculate the initial volume:
$$V_1 = \frac{(350. \space mL)(2.00 \space M)}{6.00 \space M}$$
$$V_1 = 117 \space mL$$