Chem qustion dealing with pH?

A pH meter is often used to measure the pH of an existing solution. An old bottle of hydrochloric acid was found in the stockroom with an unknown concentration (the label fell off) and it is desirable to dispose of the solution. A pH meter was used to determine that the pH of the hydrochloric acid solution is 1.80.
A) How many moles of hydronium ion are present in 25.0 mL of the sample?
B) How many milliliters of 0.0110 M NaOH would be required to neutralize a 50.0 mL sample of the hydrochlorie acid solution - increases its pH to 7.00 - so that it can be discarded?

Answer:
pH = - log [H+] = 1.80
[H+] = 10^-1.80 = 0.0158 M

Molarity = moles / L

moles = Molarity x L = 0.0158 x 0.0250 L = 0.000395 ( moles H+ in 25.0 mL= 0.0250 L)

Moles H+ in 50.0 mL = 0.0158 x 50 / 1000 = 0.000790

Moles OH- needed for titration = 0.000790

M = moles / L
L = moles / M = 0.000790 / 0.0110 = 0.0718 L = 71.8 mL

HCl is a strong acid and NaOH is a strong base : when moles OH- = moles H+ >> pH = 7

for part A you need to know how many moles of H+ are in one liter of solution, so you need to take ten to the negative pH. I'll leave it as 10^-1.80. to find how much is in 25.0 mL, you need to divide that number by 1000 and multiply it by 25 (or just divide it by 40, either way). this will give you your answer.

for part B, you need to realize that this is a one-to-one reaction, so the stoich is really easy. in 50 mL of the HCl solution, there will be twice the moles of H+ as in part A, so you can use that number. this will be the moles of NaOH you will have to use. to find the liters, divide the moles of H+ by the molarity of the NaOH, then multiply by 1000 to find the milliliters.

The answers post by the user, for information only, FunQA.com does not guarantee the right.

FunQA.com

Chem qustion dealing with pH?

Topic