<< Chapter < Page Chapter >> Page >

Ph changes in buffered and unbuffered solutions

Acetate buffers are used in biochemical studies of enzymes and other chemical components of cells to prevent pH changes that might change the biochemical activity of these compounds.

(a) Calculate the pH of an acetate buffer that is a mixture with 0.10 M acetic acid and 0.10 M sodium acetate.


To determine the pH of the buffer solution we use a typical equilibrium calculation (as illustrated in earlier Examples):

Four tan rectangles are shown that are connected with right pointing arrows. The first is labeled “Determine the direction of change.” The second is labeled “Determine x and the equilibrium concentrations.” The third is labeled “Solve for x and the equilibrium concentrations.” The fourth is labeled “Check the math.”
  1. Determine the direction of change. The equilibrium in a mixture of H 3 O + , CH 3 CO 2 , and CH 3 CO 2 H is:
    CH 3 CO 2 H ( a q ) + H 2 O ( l ) H 3 O + ( a q ) + CH 3 CO 2 ( a q )

    The equilibrium constant for CH 3 CO 2 H is not given, so we look it up in Appendix H : K a = 1.8 × 10 −5 . With [CH 3 CO 2 H] = [ CH 3 CO 2 ] = 0.10 M and [H 3 O + ] = ~0 M , the reaction shifts to the right to form H 3 O + .
  2. Determine x and equilibrium concentrations . A table of changes and concentrations follows:
    This table has two main columns and four rows. The first row for the first column does not have a heading and then has the following in the first column: Initial concentration ( M ), Change ( M ), Equilibrium ( M ). The second column has the header of “[ C H subscript 3 C O subscript 2 H ] [ H subscript 2 O ] equilibrium arrow H subscript 3 O superscript plus sign [ C H subscript 3 C O subscript 2 superscript negative sign ].” Under the second column is a subgroup of four columns and three rows. The first column has the following: 0.10, negative x, 0.10 minus sign x. The second column is blank. The third column has the following: approximately 0, x, x. The fourth column has the following: 0.10, x, 0.10 plus sign x.
  3. Solve for x and the equilibrium concentrations. We find:
    x = 1.8 × 10 −5 M

    [ H 3 O + ] = 0 + x = 1.8 × 10 −5 M

    pH = −log [ H 3 O + ] = −log ( 1.8 × 10 −5 )

    = 4.74

  4. Check the work . If we calculate all calculated equilibrium concentrations, we find that the equilibrium value of the reaction coefficient, Q = K a .

(b) Calculate the pH after 1.0 mL of 0.10 M NaOH is added to 100 mL of this buffer, giving a solution with a volume of 101 mL.

First, we calculate the concentrations of an intermediate mixture resulting from the complete reaction between the acid in the buffer and the added base. Then we determine the concentrations of the mixture at the new equilibrium:

Eight tan rectangles are shown in four columns of two rectangles each that are connected with right pointing arrows. The first rectangle in the upper left is labeled “Volume of N a O H solution.” An arrow points right to a second rectangle labeled “Moles of N a O H added.” A second arrow points right to a third rectangle labeled “Additional moles of N a C H subscript 3 C O subscript 2.” Just beneath the first rectangle in the upper left is a rectangle labeled “Volume of buffer solution.” An arrow points right to another rectangle labeled “Initial moles of C H subscript 3 C O subscript 2 H.” This rectangle points to the same third rectangle, which is labeled “ Additional moles of N a C H subscript 3 C O subscript 2.” An arrow points right to a rectangle labeled “ Unreacted moles of C H subscript 3 C O subscript 2 H.” An arrow points from this rectangle to a rectangle below labeled “[ C H subscript 3 C O subscript 2 H ].” An arrow extends below the “Additional moles of N a C H subscript 3 C O subscript 2” rectangle to a rectangle labeled “[ C H subscript 3 C O subscript 2 ].” This rectangle points right to the rectangle labeled “[ C H subscript 3 C O subscript 2 H ].”
  1. Determine the moles of NaOH. One milliliter (0.0010 L) of 0.10 M NaOH contains:
    0.0010 L × ( 0.10 mol NaOH 1 L ) = 1.0 × 10 −4 mol NaOH
  2. Determine the moles of CH 2 CO 2 H. Before reaction, 0.100 L of the buffer solution contains:
    0.100 L × ( 0.100 mol CH 3 CO 2 H 1 L ) = 1.00 × 10 −2 mol CH 3 CO 2 H
  3. Solve for the amount of NaCH 3 CO 2 produced. The 1.0 × 10 −4 mol of NaOH neutralizes 1.0 × 10 −4 mol of CH 3 CO 2 H, leaving:
    ( 1.0 × 10 −2 ) ( 0.01 × 10 −2 ) = 0.99 × 10 −2 mol CH 3 CO 2 H

    and producing 1.0 × 10 −4 mol of NaCH 3 CO 2 . This makes a total of:
    ( 1.0 × 10 −2 ) + ( 0.01 × 10 −2 ) = 1.01 × 10 −2 mol NaCH 3 CO 2
  4. Find the molarity of the products. After reaction, CH 3 CO 2 H and NaCH 3 CO 2 are contained in 101 mL of the intermediate solution, so:
    [ CH 3 CO 2 H ] = 9.9 × 10 −3 mol 0.101 L = 0.098 M

    [ NaCH 3 CO 2 ] = 1.01 × 10 −2 mol 0.101 L = 0.100 M

    Now we calculate the pH after the intermediate solution, which is 0.098 M in CH 3 CO 2 H and 0.100 M in NaCH 3 CO 2 , comes to equilibrium. The calculation is very similar to that in part (a) of this example:
    Four tan rectangles are shown that are connected with right pointing arrows. The first is labeled “Determine the direction of change.” The second is labeled “Determine x and the equilibrium concentrations.” The third is labeled “Solve for x and the equilibrium concentrations.” The fourth is labeled “Check the math.”
    This series of calculations gives a pH = 4.75. Thus the addition of the base barely changes the pH of the solution ( [link] ).

(c) For comparison, calculate the pH after 1.0 mL of 0.10 M NaOH is added to 100 mL of a solution of an unbuffered solution with a pH of 4.74 (a 1.8 × 10 −5 - M solution of HCl). The volume of the final solution is 101 mL.


This 1.8 × 10 −5 - M solution of HCl has the same hydronium ion concentration as the 0.10- M solution of acetic acid-sodium acetate buffer described in part (a) of this example. The solution contains:

0.100 L × ( 1.8 × 10 −5 mol HCl 1 L ) = 1.8 × 10 −6 mol HCl

As shown in part (b), 1 mL of 0.10 M NaOH contains 1.0 × 10 −4 mol of NaOH. When the NaOH and HCl solutions are mixed, the HCl is the limiting reagent in the reaction. All of the HCl reacts, and the amount of NaOH that remains is:

Questions & Answers

Hi, I have a question. What factors influence social facilitation and social inhibition in groups?
Amritpal Reply
it really depends on that person on how the can task in life either they can work better with other people or you do worse working with people.
the task
they task
Do you know of any studies done to show social facilitation and social inhibition
Does anyone know how I can transfer my higher national diploma credits in usa?
Qwanta Reply
Oh wow. I never realised there was a chat on this app!
Amritpal Reply
Then welcome dearest
Thank you! ❤️
thank you
Hello Ana, good afternoon from here
Philip Reply
hello im new student here.
Junalyn Reply
o sorry madm
I m also student.
what is easier option to psychology?
I'm new too
As in the the specialisation or ?
good morning
understanding human nature is what we are going to talk about.
okay, go ahead
“ Every child is left to evaluate his experiences for himself, and to take care of his own personal development outside the classroom. There is no tradition for the acquisition of a true knowledge of the human psyche. The science of human nature thus finds itself today in the position that chemis
well, I think every individual is different and to a great extent we can't say confidently that we understand the human nature in its entirety
lack determines what we will become in life?.
Not 100% but it plays a huge role
Hi! I wasn't aware there was a chat feature on this app 😊
👍Philip Anyaegbu
yes Ana I'm here
alternatively we are different, we have basic similar qualities
Yes true Bridget.
hello there
who we are how we think what we do insight
@ bridget. yes that's true
Ana ioanidis? do you speak Greek?
Qwanta no I dont speak Greek my husband does
are you a psychologist? or your husband?
I need some reliable informations about my studies...
not a psychologist
I ask questions
so what is the cause why a person experiences a psychological disorder if it not of their own?
Junalyn Reply
it's partly genetics,culture, environment and substance abuse. generally these are the common factors which can lead to most of the disorders
r u proficcer
u r psychology subject
not a professor but a clinical psychologist
can i ask you, i keep getting headache, and had a history of hypothyroid ans diagnosed as having mild anxiety disorder. i want to finish. my undergraduate psychology thesis.. but always unable to have good ambition and energy to focus on writing the case and the theories... whats the best remedy
had a headache and have a history
how many disorders are there
Janareon Reply
interesting question
it is😅
I'm guessing it's in the tens of thousands, maybe hundreds if you include counter interactions and stuff like it. although I'm sure it's almost impossible to know for sure, unless you're very rich and connected to the right people. but as I said: guessing.
There are more than 200 classified forms of mental illness. Some of the more common disorders are: clinical depression, bipolar disorder, dementia, schizophrenia and anxiety disorders. Symptoms may include changes in mood, personality, personal habits and/or social withdrawal. that is what I think
too difficult to number. diagnosing a disorder is just checking off boxes on a compilation of symptoms that might match any particular condition on the DSM
what is psychology of the guest
Lirilong Reply
I don't understand the question can you elaborate?
the study of philosophy gives to the sociologist
Aman Reply
why women are viewed as far more emotional than men?
Wario Reply
because they actually are ,I guess.
May be they are biologically milder than man. It does not mean they are not equal with man. Man can also be emotional and can are oppressed with traditional norms. For example, man are not to be cry, in actual man are also emotional being and they cannot have the right to show their sentiment.
sollungal bro sollungal...
because of she has hormonal fluctuations than men..
usually women are more emotional than men and they are multi talented people
Both men and women are capable of expressing emotions. But women has the highest percentage of doing that. Because our society is conditioned by nature in such a way that men are expected to suppress their emotions and motivate them through their acts or thoughts, which has it's side effects of....
denial of any emotion which they feel that useless at that point. Women in the other hand were encouraged/not controlled to suppress their emotions and let them out what they feel about it. I feel that's the wonderful superpower of the women.
Men's emotion comes mostly with memories triggered by senses. That means, they thoughts have the power to decide whether to let go of emotions or not.
because women tend to be more agreeable than men.
women at a young age are conditioned to be more in tune with emotion than man should be less
The question is "Why women Viewed are as far more emotional than men ?" it's not a question whether women are more emotional than men. This is more an issue about the point of view from the observer, his/her assumption what emotional behavior is or what emotional behavior is.
The anwers are answers more to the question " Are women more emotional than men?"
hi are you on what'sap
Wunuji Reply
no not really a fan of social laziness
is there any way for a Btech E.C.E. graduate to take on MSC. PSYCHOLOGY
ya you can just by cracking entrance , if in India
Any stream in UG can go for M.Sc (Psychology)
classification of traits and how they are measured
chinedu Reply
what was Freud's first name?
Robin Reply
Sigismund Schlomo Freud
Sigmund Freud
Leon Vygotsky and Sergei Rubenstein please tell me contributions of these personalities in in 4 lines
sigmund Freud
Lev Vygotsky was the founder of socio-cultural theory
So psychology was based off of the Greek gods I that right or no?
Tanya Reply
psychology is the study. anything -ology is the study of a certain field. Psyche is a mortal woman who becomes divine in Greek mythology. The etymology of the word "psyche" in Greek means "spirit" or "soul"
seriously there is no scope of psychology all over the world.i hear those how have psychology degrees they have no careers
Madeeha Reply
psychology degree is the waste of time qnd waste of money.is this true?...
at least you know people's minds
well, i like this subject for helping myself and others as well, not for the scope or anything. and i think we shouldn't liberate everything on the basis of outcomes etc
very useful skill
It is not at all true that people who have psychology degree have no career scope
If u complete your M.Phil then you can work in hospitals as a clinical psychologist.You can also work in school, colleges and IT companies as a counsellor or clinical psychologist.
people are so stressful and tense, and they need a psychologist
yo fr tbh lol
if some one have only master degree in psychology what will he/she do...where he/she utilizes degree
Not if you have set goals and a plan. Look into what careers are available with your degree where you live. Also it helps to have a specialty along with your psychology degree. For example a Bachelor's degree in Psychology of Science in Addictions allows for you to become an addictions counselor.
Psychology is really a valuable degree. I would like to become an "EDUCATIONAL PSYCHOLOGIST "
there is no proper society of Psychology. so it doesn't get a good exposure in our country. we along with whole student need to discuss and approach to government
Psychology is not only a diverse field but also one that is expected to grow tremendously in the years to come. As a subject dealing with the study of the human psyche or mind, psychology finds applications across all avenues of life, be it family, work, relationships, sports, corporate spaces
Clinical Psychology As is suggestive, this branch of psychology is associated to the understanding, diagnosis and treatment of psychological disorders in humans. Clinical psychologists help people facing difficulties in their life to get through it using different treatment methods and therapies.
These professionals work with hospitals, NGOs and even drug rehabilitation centers. As people become increasingly aware of different psychological disorders with time, the need for experts in clinical psychology is only expected to grow.
Counseling Psychology Counseling psychology is a branch of psychology that helps solve people’s personal and interpersonal issues. These issues can be problematic but are different from serious mental health issues. Counseling psychologists or counselors help people deal with such issues when they
fail to do it on their own.Career counseling, guidance counseling, marital counseling and rehabilitation counseling are among the many applications of counseling psychology. These professionals either manage their own counseling set-ups or work with therapycenters, career centers, NGOs as well as
schools and universities. Industrial or Organizational Psychology Organizational psychologists are professionals who apply the principles of psychology in organizations or workplaces. They analyze the issues of the workplace at individual as well as organizational level, and work towards resolving
them to enhance the efficiency of the employees. Those specializing in organizational psychology can choose to work as – • Human resource development specialists • HR managers • Organizational consultants With increasing pressure and stress levels at work places, the need for emotional understandi
understanding and gauging social intelligence has become stronger. Child Psychology (Development psychology) Development psychology is a branch of psychology that is dedicated to studying the psychological development of human beings over the course of their lifetime. Child psychology is one of
the more popular variants of development psychology, and deals with emotional, cognitive, social and psychomotor development in infants and children. Child psychologists work with schools, child therapy centers and also NGOs. They also play big roles in special education centers for children.
Sports Psychology This branch of psychology deals with the study of elements that influence an athlete’s performance. These elements or factors could be emotional, cognitive, psychological or motivational. Sports psychologists can go on to work with sports coaching centers, leagues, academies or
sports teams. Sports psychologists aid sportspersons to stay in their best mental forms, thus improving their performances on the ground. With the frenzy regarding sports in India, sports psychology is a promising career to pursue.
Forensic Psychology Forensic psychology offers a unique opportunity to apply psychology to the benefit of legal organizations, especially pertaining to specific contents or witness testimony. Professionals in this field utilize their skills to look deep into the psyche of criminals and figure out
the intent behind the crime. This helps define the quantum and nature of sentence to be rendered. With the onset of new legal era, forensic psychology is expected to influence policy making.
psychology and the jobs in psychology are the ever growing fields. there are number of jobs available. but, yes, one needs the right qualification, such as, MPhil, PhD, NET, etc.
No. Psychology has a great scope all over world
Because of 90% people has stress or anxiety or any other mental problem. So they have a need of Psychologist.
how do you find theWhat are the wavelengths and energies per photon of two lines
caroline Reply
The eyes of some reptiles are sensitive to 850 nm light. If the minimum energy to trigger the receptor at this wavelength is 3.15 x 10-14 J, what is the minimum number of 850 nm photons that must hit the receptor in order for it to be triggered?
razzyd Reply
A teaspoon of the carbohydrate sucrose contains 16 calories, what is the mass of one teaspoo of sucrose if the average number of calories for carbohydrate is 4.1 calories/g?
ifunanya Reply
4. On the basis of dipole moments and/or hydrogen bonding, explain in a qualitative way the differences in the boiling points of acetone (56.2 °C) and 1-propanol (97.4 °C), which have similar molar masses
Kyndall Reply
Calculate the bond order for an ion with this configuration: (?2s)2(??2s)2(?2px)2(?2py,?2pz)4(??2py,??2pz)3
Gabe Reply
Which of the following will increase the percent of HF that is converted to the fluoride ion in water? (a) addition of NaOH (b) addition of HCl (c) addition of NaF
Tarun Reply
Practice Key Terms 3

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Ut austin - principles of chemistry. OpenStax CNX. Mar 31, 2016 Download for free at http://legacy.cnx.org/content/col11830/1.13
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Ut austin - principles of chemistry' conversation and receive update notifications?