# EXAMPLE 14.2

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Solution : We must identify the acid and the base and know that they react to form water and a salt. Notice that Ca(OH) 2 contains 2 mol of OH – for every 1 mol of Ca(OH) 2 and will therefore require 2 mol of H + to neutralize it. We first write the skeletal reaction. - PowerPoint PPT Presentation

### Text of EXAMPLE 14.2

Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.2
Writing Equations for Neutralization Reactions
Write a molecular equation for the reaction between aqueous HCl and aqueous Ca(OH)2.
Write a molecular equation for the reaction that occurs between aqueous H3PO4 and aqueous NaOH. Hint: H3PO4 is a triprotic acid, meaning that 1 mol of H3PO4 requires 3 mol of OH- to completely react with it.
SKILLBUILDER 14.2
FOR MORE PRACTICE
Solution:
We must identify the acid and the base and know that they react to form water and a salt. Notice that Ca(OH)2 contains 2 mol of OH– for every 1 mol of Ca(OH)2 and will therefore require 2 mol of H+ to neutralize it. We first write the skeletal reaction.
We then balance the equation.
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
You are given the volume of an unknown HCl solution and the volume of a known NaOH solution required to titrate the unknown solution. You are asked to find the concentration of the unknown solution.
You will need two equations. The first is the equation for the neutralization reaction of HCl and NaOH (which you should write using your knowledge of acid–base reactions). The second is simply the definition of molarity
EXAMPLE 14.4
Acid–Base Titration
The titration of 10.00 mL of an HCl solution of unknown concentration requires 12.54 mL of a 0.100 M NaOH solution to reach the endpoint. What is the concentration of the unknown HCl solution?
Given:
Find: concentration of HCl solution (mol/L)
Equation:
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Introductory Chemistry, Third Edition By Nivaldo J. Tro
The solution map has two parts. In the first part, use the volume of NaOH required to reach the endpoint to calculate the number of moles of HCl in the solution. The final conversion factor comes from the balanced neutralization equation.
In the second part, use the number of moles of HCl and the volume
of HCl solution to determine the molarity of the HCl solution.
EXAMPLE 14.4
Continued
Calculate the moles of HCl in the unknown solution by following the first part of the solution map.
To get the concentration of the solution, divide the number of moles of HCl by the volume of the HCl solution in L. (Note that 10.00 mL is equivalent to 0.01000 L.)
The unknown HCl solution
0.125 M
Solution Map:
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.4
Continued
The titration of a 20.0-mL sample of an H2SO4 solution of unknown concentration requires 22.87 mL of a 0.158 M KOH solution to reach the endpoint. What is the concentration of the unknown H2SO4 solution?
SKILLBUILDER 14.4
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.5
Determining [H3O+] in Acid Solutions
What is the H3O+ concentration in each of the following solutions?
(a) 1.5 M HCl
(b) 3.0 M HC2H3O2
(c) 2.5 M HNO3
Solution:
(a) Since HCl is a strong acid, it completely ionizes. The concentration of H3O+ will be 1.5 M.
[H3O+] = 1.5 M
(b) Since HC2H3O2 is a weak acid, it partially ionizes. The calculation of the exact concentration of H3O+ is beyond the scope of this text, but we know that it will be less than 3.0 M.
[H3O+] < 3.0 M
(c) Since HNO3 is a strong acid, it completely ionizes. The concentration of H3O+ will be 2.5 M.
[H3O+] = 2.5 M
What is the H3O+ concentration in each of the following solutions?
(a) 0.50 M HCHO2
(b) 1.25 M HI
(c) 0.75 M HF
FOR MORE PRACTICE
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.6
Determining [OH–] in Base Solutions
What is the OH– concentration in each of the following solutions?
(a) 2.25 M KOH
(b) 0.35 M CH3NH2
(c) 0.025 M Sr(OH)2
Solution:
(a) Since KOH is a strong base, it completely dissociates into K+ and OH– in solution. The concentration of OH- will be 2.25 M.
[OH–] = 2.25 M
(b) Since CH3NH2 is a weak base, it only partially ionizes water. We cannot calculate the exact concentration of OH- but we know it will be less than 0.35 M.
[OH–] < 0.35 M
(c) Since Sr(OH)2 is a strong base, it completely dissociates into Sr2+(aq) and 2 OH-(aq). Sr(OH)2 forms 2 mol of OH- for every 1 mol of Sr(OH)2. Consequently, the concentration of OH- will be twice the concentration of Sr(OH)2. [OH–] = 2(0.025 M) = 0.050 M
What is the OH– concentration in each of the following solutions?
(a) 0.055 M Ba(OH)2
(b) 1.05 M C5H5N
(c) 0.45 M NaOH
FOR MORE PRACTICE
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.8
Calculating pH from [H3O+]
Calculate the pH of each of the following solutions and indicate whether the solution is acidic or basic.
(a) [H3O+] = 1.8 × 10–4 M
(b) [H3O+] = 7.2 × 10–9 M
Solution:
To calculate pH, simply substitute the given [H3O+] into the pH equation.
(a)
(b)
Since the pH > 7, this solution is basic.
Calculate the pH of each of the following solutions and indicate whether the solution is acidic or basic.
(a) [H3O+] = 9.5 × 10–9 M
(b) [H3O+] = 6.1 × 10–3 M
SKILLBUILDER 14.8
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.9
Calculating [H3O+] from pH
Calculate the H3O+ concentration for a solution with a pH of 4.80.
Solution:
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.12
Writing Equations for Neutralization Reactions
Write a molecular equation for the reaction between aqueous HBr and aqueous Ca(OH)2
Solution:
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.14
Acid–Base Titrations
A 15.00-mL sample of a NaOH solution of unknown concentration requires 17.88 mL of a 0.1053 M H2SO4 solution to reach the endpoint in a titration. What is the concentration of the NaOH solution?
Given: 15.00-mL NaOH
Find: concentration of NaOH solution (mol/L)
Equation:
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.14
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.15
Determining [H3O+] in Acid Solutions
What is the H3O+ concentration in a 0.25 M HCl solution and in a 0.25 M HF solution?
Solution:
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.16
Determining [OH–] in Base Solutions
What is the OH– concentration in a 0.25 M NaOH solution, in a 0.25 M Sr(OH)2 solution, and in a 0.25 M NH3 solution?
Solution:
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.17
Calculate [OH–] in a solution with
[H3O+] = 1.5 × 10–4 M.
Solution:
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.18
[H3O+] = 2.4 × 10–5 M.
Solution:
*
Introductory Chemistry, Third Edition By Nivaldo J. Tro
EXAMPLE 14.19
Calculating [H3O+] from pH
Calculate the [H3O+] concentration for a solution with a pH of 6.22.
Solution:
[H3O+] = invlog(– pH)

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