Concept explainers
Morphine, C17H19O3N, is a weak base
(a) Write a balanced net ionic equation for the reaction that takes place during titration.
(b) What are the species present at the equivalence point?
(c) What volume of hydrochloric acid is required to reach the equivalence point?
(d) What is the pH of the solution before any HCl is added?
(e) What is the pH of the solution halfway to the equivalence point?
(f) What is the pH of the solution at the equivalence point?
(a)
Interpretation:
The molarity of hydrochloric acid and morphine is 0.1045M and 0.1500M respectively. The titration of a solution of morphine which is a weak base of amount 50.00 mL is done with the hydrochloric acid. The value of the constant of equilibrium of base for morphine is
Concept introduction:
The titration is described as the process by which the concentration of the dissolved substance is to be determined in terms of the smallest amount of reagent of a given concentration.
Answer to Problem 50QAP
The balanced net ionic equation of reaction during titration is −
Explanation of Solution
From the question −
Morphine C17 H19 O3 N = base
Hydrochloric acid, HCl = acid which is represented as H+ ion
In this chemical reaction, one mole of acid is reacting with one mole of the base. The equation of this chemical reaction is represented as follows:
(b)
Interpretation:
The species present at equivalence point are to be determined.
Concept introduction:
The titration is described as the process by which the concentration of the dissolved substance is to be determined in terms of the smallest amount of reagent of a given concentration.
Answer to Problem 50QAP
The species present at equivalence point -
Explanation of Solution
The actual equation of the chemical reaction can be represented as
At equivalence point
The consumption of all reactants occurs and products will remain only.
Therefore at the equivalence point, species are-
(c)
Interpretation:
The volume of hydrochloric acid for equivalence point is to be determined.
Concept introduction:
The titration is described as the process by which the concentration of the dissolved substance is to be determined in terms of the smallest amount of reagent of a given concentration.
The Molarity equation-
Answer to Problem 50QAP
The volume of hydrochloric acid is 71.77 mL which is required to reach at equivalence point.
Explanation of Solution
At the equivalence point, the reaction is −
In the chemical reaction, one mole of acid is reacting with one mole of the base. Therefore ration between acid and base is 1:1.
Number of moles of Morphine is calculated by using the given formula:
Given that-
Molarity of morphine = 0.1500M
Volume = 0.050L
Put the above values in Equ (1)
Number of moles of morphine = 0.0075 mol
Now the volume of HCl is obtained by −
Given that-
Molarity of HCl is = 0.1045M
Number of moles of HCl = Number of moles of Morphine = 0.0075mol
Put the above values in Equ (2)
Volume of HCl = 0.07177 L or 71.77mL
(d)
Interpretation:
The pH value of the solution is to be determined before the addition of HCl.
Concept introduction:
The titration is described as the process by which the concentration of the dissolved substance is to be determined in terms of the smallest amount of reagent of a given concentration.
The equilibrium constant of acid-
The pH value can be calculated as follows:
Similarly, the pOH value can be calculated as follows:
And,
Answer to Problem 50QAP
The pH value of the solution is 10.52 before the addition of HCl.
Explanation of Solution
Before the addition of HCl −
The concentration of HCl or [OH-] = concentration of base, morphine = 0.1500 M
The chemical reaction is represented as-
Therefore,
At equilibrium,
Molar concentration of
Molar concentration of
Therefore,
Molar concentration of
Given that-
Kb = 7.4×10-7
Put the above values in Equ (1)
On solving −
The value of x = 3.33×10-4
So,
Molar concentration of
Molar concentration of
Now, the pH value can be calculated as follows:
And
pH +pOH =14
Then ,
pH = 14 − 3.48 = 10.52
The pH of the solution = 10.52
(e)
Interpretation:
The pH value of the solution at halfway of the equivalence point is to be determined.
Concept introduction:
The titration is described as the process by which the concentration of the dissolved substance is to be determined in terms of the smallest amount of reagent of a given concentration.
The pH value can be calculated as follows:
Similarly, the pOH value can be calculated as follows:
And,
Answer to Problem 50QAP
The pH value of the solution at halfway of the equivalence point is 7.87.
Explanation of Solution
At the halfway of the equivalence point is-
The concentration of OH or [OH-] = The value of pKb of the base
Now the pH of the solution is
Given that −
Kb = 7.4×10-7
Put the value of [OH-] in equation (1),
And
pH +pOH =14
Then ,
pH = 14 −6.13= 7.87
The pH of the solution = 7.87
(f)
Interpretation:
The pH value of the solution at the equivalence point is to be determined.
Concept introduction:
The titration is described as the process by which the concentration of the dissolved substance is to be determined in terms of the smallest amount of reagent of a given concentration.
The molarity equation −
The equilibrium constant of base and acid can be related as-
The pH value can be calculated as follows:
Answer to Problem 50QAP
The pH value of the solution at the equivalence point is 4.54.
Explanation of Solution
The actual reaction is −
In the chemical reaction, one mole of acid is reacting with one mole of the base. Therefore ration between acid and base is 1:1.
Number of moles of Morphine is calculated by using the given formula-
Given that-
Molarity of morphine = 0.1500M
Volume = 0.050L
Put the above values in Equ (1)
Number of moles of morphine = 0.0075 mol
Now, the volume of HCl is obtained by −
Given that-
Molarity of HCl is = 0.1045M
Number of moles of HCl = Number of moles of Morphine = 0.0075mol
Put the above values in equation (2)
Volume of HCl = 0.07177 mL or 71.77mL
Now
The concentration of [H+] is calculated by −
Also,
From above both equations −
Or,
On calculation,
Now the pH of the solution −
Thus, the pH of the solution is 4.54.
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Chapter 14 Solutions
Chemistry: Principles and Reactions
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