   Chapter 16, Problem 68PS

Chapter
Section
Textbook Problem

For each of the following cases, decide whether the pH is less than 7, equal to 7 or greater than 7.a) 25 mL of 0.45 M H 2 SO 4 is mixed with 25mL of 0.90 M NaOH.b) 15 mL of 0.050M formic acid, HCO 2 H is mixed with 15 mL of 0.50M NaOH.c) 25mL of 0.15M H 2 C 2 O 4 (oxalic acid) is mixed with 25mL of 0.30 M NaOH (Both H + ions of oxalic acid are removed with NaOH).

(a)

Interpretation Introduction

Interpretation:

The pH of the given 25 mL of 0.45 M H2SO4 is mixed with 25mL of 0.90 M NaOH has to be determined and the pH of the solution is whether less than 7, equal to 7, greater than 7 has to be determined.

Concept Introduction:

The pH of a solution is negative logarithm of the hydrogen ion concentration.

pH = -log[H+]

pH is a measure of the acidity or basicity of a solution. Pure water is said to be neutral with pH close to 7.0 at 250C.

Solution with a pH less than 7 is said to acidic and solution with a pH greater than 7 is basic.

Low pH indicates a high concentration of hydronium ions, while a high pH indicates low concentration of hydronium ions.

Explanation

Sodium hydroxide dissociates into Na+ and OH-.

Hydronium an ion from sulphuric acid reacts with hydroxide ions. The equilibrium chemical reaction is as follows.

H3O+(aq) + OH-(aq) H2O(l) + H2O(l)

Let’s calculate the consumed amount of H3O+ and OH-

H3O+:           = 0.025L × 0.45mol.L-1 = 0.01125molOH-:           = 0

(b)

Interpretation Introduction

Interpretation:

The pH of the given 15 mL of 0.050M formic acid, HCO2H is nixed with 15 mL of 0.50M NaOH has to be determined and the pH of the solution is whether less than 7, equal to 7, greater than 7 has to be determined.

Concept Introduction:

The pH of a solution is negative logarithm of the hydrogen ion concentration.

pH = -log[H+]

pH is a measure of the acidity or basicity of a solution. Pure water is said to be neutral with pH close to 7.0 at 250C.

Solution with a pH less than 7 is said to acidic and solution with a pH greater than 7 is basic.

Low pH indicates a high concentration of hydronium ions, while a high pH indicates low concentration of hydronium ions.

(c)

Interpretation Introduction

Interpretation:

The pH of the given 25mL of 0.15M H2C2O4(oxalic acid) is mixed with 25mL of 0.30 M NaOH (Both H+ ions of oxalic acid are removed with NaOH) has to be determined and the pH of the solution is whether less than 7, equal to 7, greater than 7 has to be determined.

Concept Introduction:

The pH of a solution is negative logarithm of the hydrogen ion concentration.

pH = -log[H+]

pH is a measure of the acidity or basicity of a solution. Pure water is said to be neutral with pH close to 7.0 at 250C.

Solution with a pH less than 7 is said to acidic and solution with a pH greater than 7 is basic. Low pH indicates a high concentration of hydronium ions, while a high pH indicates low concentration of hydronium ions.

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