Question

Part A:

0.65 g of hydrogen chloride (HCl) is dissolved in water to make 8.0 L  of solution. What is the pH of the resulting hydrochloric acid solution?

Part B:

0.20 g of sodium hydroxide (NaOH) pellets are dissolved in water to make 3.0 L of solution. What is the pH of this solution?​

Answer 1

Part A :

Given data,

Mass of HCl = 0.65 g

Volume = 8.0 L

Molar mass of HCl = 36.5 g per mol

Moles of HCl = mass / Molar mass

= 0.65 g / 36.5 g per mol

Moles of HCl = 0.0178 mol

Molarity = moles / volume in liter

= 0.0178 / 8.0 L

= 0.00222 M

Now calculate the pH,

pH = - log [H⁺]

= - log [0.00222]

= - ( -2.65 )

pH = 2.65

PartB:

Given data, mass = 0.20 g

molar mass of NaOH = 40 g/mole

Moles of NaOH = mass / molar mass of NaOH

= 0.20 / 40

= 0.005 mol

[OH^-] = [NaOH] = moles of NaOH / volume

= 0.005 / 3

= 0.00166 M

p^OH = -log[OH^-]

= -log[0.00166]

= 2.77

p^H = 14 - p^OH

= 14 - 2.77

p^H = 11.23