Question

For 480. 0 mL m L of pure water, calculate the initial pH p H and the final pH p H after adding 2. 0×10−2 mol m o l of HCl H C l

Answer 1

Given that the volume of the pure water is 480 mL and the mole of HCl added to the water is 2×10¯² mole. Therefore, the Initial and final pH of the water are:

1. The initial pH of the pure water is 7

2. The final pH of the water is 1.38

What is pH ?

This is simply a measure of the acidity / alkalinity of a solution.

The pH measures the hydrogen ion concentration while the pOH measures the hydroxide ion concentration

pH scale

The pH scale is a scale that gives an understanding of the variation of the acidity / alkalinity of a solution.

The scale ranges from 0 to 14 indicating:

• 0 to 6 indicates acid
• 7 indicates neutral (pure water)
• 8 to 14 indicate basic

How to determine the molarity

• Volume = 480 mL = 480 / 1000 = 0.48 L
• Mole of HCl = 2×10¯² mole

• Molarity =?

Molarity = mole / Volume

Molarity = 2×10¯² / 0.48

Molarity = 4.17×10¯² M

Dissociation equation

HCl(aq) —> H⁺(aq) + Cl¯(aq)

From the balanced equation above,

1 mole of HCl contains 1 mole of H⁺

Therefore,

4.17×10¯² M HCl will also contain 4.17×10¯² M H⁺

How to determine the pH

• Hydrogen ion concentration [H⁺] = 4.17×10¯² M
• pH =?

pH = –Log H⁺

pH = –Log 4.17×10¯²

pH = 1.38

Learn more about pH:

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