Question

16. (TW) A very large volume of perchloric acid having a concentration of 2.0% by mass was prepared. The 16. (SYW) A very large volume volume, temperature, and density of the solution are as follows: Vol = 9.75 x 1022 L Temp. -22°C density = 1.0109 g/ml What is the pH of the solution? A) 0.2 B) 9.6 C) 0.7 D) 2.7 E) 0.02 un matol ir hanted to a temperature of 100.0°C and placed in 100.0 ml of

Answer 1

Perchloric acid (HClO4) is strong acid therefore it will almost dissociates into H+ and ClO4-.

Concentration of Perchloric acid = 2% by mass which means there is 2g of perchloric acid for every 100g of solution or we can say that for every 1g of solution we have (2/100)g of perchloric acid. We need the concentration to convert this into Molarity(mol/Litre).

Conversion of concentration by mass into Molarity :-

We have Volume = 9.75*1022 L = 9.75*1025 mL

So Mass of solution = density of solution * volume of solution = 1.0109*9.75*1025 = 9.8562*1025 g

Mass of perchloric acid = 9.8562*1025 * (2/100) = 1.9712*1024 g

Moles of Perchloric acid = Mass of perchloric acid / Molar mass of perchloric acid = 1.9712*1024/100.46 =1.9622*1022 moles

Molarity of HClO4 = Moles of perchloric acid / Volume of solution (in L) = 1.9622*1022 / 9.75*1022 = 0.2012M

Since HClO4 is a strong acid, Molarity of H+  = Molartity of HClO4 ⇒ [H+] = 0.2012M

Calculation of pH of solution :-

pH = -log10[H+] = -log10[0.2012] = 0.696 ≈ 0.7

pH of solution is 0.7.