Question

A comic book villain is holding you at gun point and is making you drink a sample of acid he gives you a beaker with 100 ml of a strong acid with ph=5 he also gives you a beaker of a strong base with a ph=10 you can add as much of the strong base to the strong acid as you want, and you must then drink the solution. You'd be best off trying to make the solution neutral before drinking it. How much of the base should you add?

a. 1 ml
b. 10 ml
c. 100 ml
d. 1000 ml

Answer 1

We have to add 10 mL of base ( option B is correct)

Step-by-step explanation:

Step 1: Data given

Volume of the strong acid = 100 mL = 0.100 L

pH = 5

pH of the strong base = 10

Step 2: Calculate molarity of the strong acid

pH =[H+] = 5

[H+]= 10^-5 M

Step 3: Calculate moles of the strong acid

Moles = molarity * volume

Moles = 10^-5 M * 0.100 L

Moles = 10^-6 moles

Step 4: Calculate pOH

pOH = 14 - 10 = 4

Step 5: Calculate [OH-]

[OH-] = 10^-4 M

Step 6: Calculate volume need

We need 10^-6 moles of base

Volume = moles / molarity

Volume = 10^-6 moles / 10^-4 M

Volume = 0.01 L

Volume = 10 mL

We have to add 10 mL of base ( option B is correct)

Answer 2

b. 10 mL

Step-by-step explanation:

First we calculate the amount of H⁺ moles in the acid:

• pH = -log [H⁺]

• [H⁺] =
  `10^(-pH)`

• [H⁺] = 10⁻⁵ = 1x10⁻⁵M

100 mL ⇒ 100 / 1000 = 0.100 L

• 1x10⁻⁵M * 0.100 L = 1x10⁻⁶ mol H⁺

In order to have a neutral solution we would need the same amount of OH⁻ moles.

We can use the pOH value of the strong base:

• pOH = 14 - pH

• pOH = 14 - 10 = 4

Then we calculate the molar concentration of the OH⁻ species in the basic solution:

• pOH = -log [OH⁻]

• [OH⁻] =
  `10^(-pOH)` = 1x10⁻⁴ M

If we use 10 mL of the basic solution the number of OH⁻ would be:

10 mL ⇒ 10 / 1000 = 0.010 L

• 1x10⁻⁴ M * 0.010 L = 1x10⁻⁶ mol OH⁻

It would be equal to the moles of H⁺ so the answer is b.