Janelle needs to make 150.0 mL of a 0.250 M HCl solution. How much concentrated HCl (12.0 M) will she need

3.125 mL

Explanation:

The following data were obtained from the question:

Molarity of stock solution (M1) = 12 M

Molarity of diluted solution (M2) = 0.250 M

Volume of diluted solution (V2) = 150 mL

Volume of stock solution needed (V1) =.?

The volume of stock solution needed can be obtained by using the dilution formula as shown below:

M1V1 = M2V2

12 × V1 = 0.250 × 150

12 × V1 = 37.5

Divide both side by 12

V2 = 37.5/12

V2 = 3.125 mL

Therefore, the volume of the stock solution needed is 3.125 mL

pH = 5.056

Explanation:

Acetic acid (CH₃COOH), is in equilibrium with water, thus:

CH₃COOH + H₂O ⇄ CH₃COO⁻ + H₃O⁺

From here, it is possible to obtain H-H equation to find pH of a solution:

pH = pka + log₁₀ [CH₃COO⁻] / [CH₃COOH]

Where molarity of acetic acid, [CH₃COOH], is 0.150mol / 1.00L = 0.150M and molarity of acetate ion, [CH₃COO⁻], is 0.300mol / 1.00L = 0.300M. pKa of the buffer is -log Ka: 4.754

Replacing:

pH = 4.754 + log₁₀ [0.300M] / [0.150M]

pH = 5.056