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    in order to buffer a strong acid into a weak acid, which has a less dramatic effect on ph, what chemical should be used as the buffer?

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    14.9: Buffers are Solutions that Resist pH Change

    A buffer is a solution that resists dramatic changes in pH. Buffers do so by being composed of certain pairs of solutes: either a weak acid plus a salt derived from that weak acid, or a weak base …

    14.9: Buffers are Solutions that Resist pH Change

    Last updated Feb 21, 2021

    14.8: Water - Acid and Base in One

    14.9: The pH and pOH Scales - Ways to Express Acidity and Basicity

    picture_as_pdf Readability Cite this page Donate Learning Objective

    Define buffer and describe how it reacts with an acid or a base.

    Weak acids are relatively common, even in the foods we eat. But we occasionally come across a strong acid or base, such as stomach acid, that has a strongly acidic pH of 1–2. By definition, strong acids and bases can produce a relatively large amount of hydrogen or hydroxide ions and, as a consequence, have marked chemical activity. In addition, very small amounts of strong acids and bases can change the pH of a solution very quickly. If 1 mL of stomach acid [which we will approximate as 0.05 M HCl(aq)] is added to the bloodstream, and if no correcting mechanism is present, the pH of the blood would go from about 7.4 to about 4.9—a pH that is not conducive to life. Fortunately, the body has a mechanism for minimizing such dramatic pH changes.

    This mechanism involves a buffer, a solution that resists dramatic changes in pH. Buffers do so by being composed of certain pairs of solutes: either a weak acid plus a salt derived from that weak acid, or a weak base plus a salt of that weak base. For example, a buffer can be composed of dissolved acetic acid (HC2H3O2, a weak acid) and sodium acetate (NaC2H3O2, a salt derived from that acid). Another example of a buffer is a solution containing ammonia (NH3, a weak base) and ammonium chloride (NH4Cl, a salt derived from that base).

    Let us use an acetic acid–sodium acetate buffer to demonstrate how buffers work. If a strong base—a source of

    OH − (aq) OH−(aq)

    ions—is added to the buffer solution, those hydroxide ions will react with the acetic acid in an acid-base reaction:

    HC 2 H 3 O 2 (aq)+ OH − (aq)→ H 2 O(ℓ)+ C 2 H 3 O − 2 (aq) (14.9.1)

    (14.9.1)HC2H3O2(aq)+OH−(aq)→H2O(ℓ)+C2H3O2−(aq)

    Rather than changing the pH dramatically by making the solution basic, the added hydroxide ions react to make water, and the pH does not change much.

    Many people are aware of the concept of buffers from buffered aspirin, which is aspirin that also has magnesium carbonate, calcium carbonate, magnesium oxide, or some other salt. The salt acts like a base, while aspirin is itself a weak acid.

    If a strong acid—a source of H+ ions—is added to the buffer solution, the H+ ions will react with the anion from the salt. Because HC2H3O2 is a weak acid, it is not ionized much. This means that if lots of hydrogen ions and acetate ions (from sodium acetate) are present in the same solution, they will come together to make acetic acid:

    H + (aq)+ C 2 H 3 O − 2 (aq)→ HC 2 H 3 O 2 (aq) (14.9.2)

    (14.9.2)H+(aq)+C2H3O2−(aq)→HC2H3O2(aq)

    Rather than changing the pH dramatically and making the solution acidic, the added hydrogen ions react to make molecules of a weak acid. Figure

    14.9.1 14.9.1

    illustrates both actions of a buffer.

    Figure 14.9.1 14.9.1

    : The Action of Buffers. Buffers can react with both strong acids (top) and strong bases (bottom) to minimize large changes in pH.

    Buffers made from weak bases and salts of weak bases act similarly. For example, in a buffer containing NH3 and NH4Cl, ammonia molecules can react with any excess hydrogen ions introduced by strong acids:

    NH 3 (aq)+ H + (aq)→ NH + 4 (aq) (14.9.3)

    (14.9.3)NH3(aq)+H+(aq)→NH4+(aq)

    while the ammonium ion (

    NH + 4 (aq) NH4+(aq)

    ) can react with any hydroxide ions introduced by strong bases:

    NH + 4 (aq)+ OH − (aq)→ NH 3 (aq)+ H 2 O(ℓ) (14.9.4)

    (14.9.4)NH4+(aq)+OH−(aq)→NH3(aq)+H2O(ℓ)

    Example 14.9.1 14.9.1

    : Making Buffer Solutions

    Which solute combinations can make a buffer solution? Assume that all are aqueous solutions.

    HCHO2 and NaCHO2 HCl and NaCl CH3NH2 and CH3NH3Cl NH3 and NaOH

    Solution

    Formic acid (HCHO2) is a weak acid, while NaCHO2 is the salt made from the anion of the weak acid—the formate ion (CHO2−). The combination of these two solutes would make a buffer solution.

    Hydrochloric acid (HCl) is a strong acid, not a weak acid, so the combination of these two solutes would not make a buffer solution.

    Methylamine (CH3NH2) is like ammonia with one of its hydrogen atoms substituted with a CH3 (methyl) group. Because it is not on our list of strong bases, we can assume that it is a weak base. The compound CH3NH3Cl is a salt made from that weak base, so the combination of these two solutes would make a buffer solution.

    Ammonia (NH3) is a weak base, but NaOH is a strong base. The combination of these two solutes would not make a buffer solution.

    Source : chem.libretexts.org

    Chemistry of buffers and buffers in our blood (article)

    Acid/base equilibria

    Chemistry of buffers and buffers in our blood

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    Let’s go to a chemistry lab and conduct a simple experiment. As shown below, we have

    two solutions - 50 mL of A and 50 mL of B respectively

    a solution of 0.2M hydrochloric acid (HCl)

    a solution of 0.2M sodium hydroxide (NaOH)

    pH meter to measure pH of the solution

    Illustration of experiment 1 and experiment 2

    Experiment 1: The pH of solution A is 7.0 i.e. it’s neutral. When we add 10 mL of 0.2M HCl to it, the pH decreases to 1.5. On the other hand, when we add 10 mL of 0.2M NaOH to solution A the pH shoots up to 12.5. In both these cases we see a drastic change in pH due to either the increase or decrease of proton [H

    ^\text{+} +

    start superscript, start text, plus, end text, end superscript

    ] concentration. Remember, pH of a solution is dependent on the concentration of hydronium ions or simply put as [H

    ^\text{+} +

    start superscript, start text, plus, end text, end superscript

    ].

    Experiment 2: Let’s see what happens when we repeat the same experiment with solution B, whose pH is also maintained at 7.0. When we add 10 mL of 0.2M HCl to it, the pH decreases by only 0.2 units to 6.8. Next, when we add 10 mL of NaOH to solution B, the pH just slightly rises to 7.2 from 7.0. In both these cases we do not see a drastic change in pH, as we observed with solution A.

    So, our observation from this experiment is that solution A underwent drastic changes in pH upon addition of a strong acid or a strong base, while solution B resisted a change in pH.

    Can you guess what the difference might be between solutions A and B?

    Solution A is pure ‘water’, while solution B is a ‘buffer’.

    How do we define a buffer?

    “A buffer is an aqueous solution that resists changes in pH upon the addition of an acid or a base”. Also, adding water to a buffer or allowing water to evaporate from the buffer does not change the pH of a buffer significantly. Buffers basically constituent a pair of a weak acid and its conjugate base, or a pair of a weak base and its conjugate acid (as will be discussed next).

    How do we prepare a buffer?

    A buffer is essentially prepared in two ways

    mixing a large volume of a weak acid with its conjugate base (eg. acetic acid – acetate ion, CH

    _{3} 3 ​

    start subscript, 3, end subscript

    COOH – CH _{3} 3 ​

    start subscript, 3, end subscript

    COO ^\text{-} -

    start superscript, start text, negative, end text, end superscript

    )

    mixing a large volume of weak base with its conjugate acid (eg. ammonia – ammonium ion, NH

    _{3} 3 ​

    start subscript, 3, end subscript

    – NH _{4} 4 ​

    start subscript, 4, end subscript

    ^\text{+} +

    start superscript, start text, plus, end text, end superscript

    )

    Phosphate buffer is a very commonly used buffer in research labs. It falls under the second category. It's made up of a weak base (HPO

    _{4} 4 ​

    start subscript, 4, end subscript

    ^\text{2-} 2-

    start superscript, start text, 2, negative, end text, end superscript

    ) and its conjugate acid (H

    _{2} 2 ​

    start subscript, 2, end subscript

    PO _{4} 4 ​

    start subscript, 4, end subscript

    ^\text{-} -

    start superscript, start text, negative, end text, end superscript

    ). The pH of a phosphate buffer is usually maintained at a physiological pH of 7.4.

    How does a buffer work?

    Buffer, as we have defined, is a mixture of a conjugate acid-base pair that can resist changes in pH when small volumes of strong acids or bases are added.

    When a strong base is added, the acid present in the buffer neutralizes the hydroxide ions (OH

    ^\text{-} -

    start superscript, start text, negative, end text, end superscript

    ).

    When a strong acid is added, the base present in the buffer neutralizes the hydronium ions (H

    _{3} 3 ​

    start subscript, 3, end subscript

    O ^\text{+} +

    start superscript, start text, plus, end text, end superscript

    ).

    Let’s understand this principle through the two examples we listed above.

    Suppose we have a buffer that contains acetic acid (CH

    _{3} 3 ​

    start subscript, 3, end subscript

    COOH) and its conjugate base, acetate ion (CH

    _{3} 3 ​

    start subscript, 3, end subscript

    COO ^\text{-} -

    start superscript, start text, negative, end text, end superscript

    ), as depicted below.

    Illustration of beaker containing acetic acid and its conjugate base, acetate ion

    When a strong acid is added, the acetate ions neutralize the hydronium ions producing acetic acid (which is already a component of the buffer).

    Source : www.khanacademy.org

    Acid/Base Balance Flashcards

    Start studying Acid/Base Balance. Learn vocabulary, terms, and more with flashcards, games, and other study tools.

    Acid/Base Balance

    25 studiers in the last day

    In order to buffer a strong acid into a weak acid, which has a less dramatic effect on pH, what chemical should be used as the buffer?

    Click card to see definition 👆

    a weak base

    Click again to see term 👆

    A friend has acid indigestion after eating a big meal. Which of the following would act as a buffer and help ease his pain?

    - Pure water, pH 7 - Cola, pH 3

    - Milk of Magnesia, pH 10

    - Black Coffee, pH 5

    Click card to see definition 👆

    Milk of magnesia, pH 10

    Click again to see term 👆

    1/26 Created by hculverteubert

    Terms in this set (26)

    In order to buffer a strong acid into a weak acid, which has a less dramatic effect on pH, what chemical should be used as the buffer?

    a weak base

    A friend has acid indigestion after eating a big meal. Which of the following would act as a buffer and help ease his pain?

    - Pure water, pH 7 - Cola, pH 3

    - Milk of Magnesia, pH 10

    - Black Coffee, pH 5

    Milk of magnesia, pH 10

    If a person exercises for a long time, lactic acid will start to build up in his or her muscles. Which of the following would you expect to happen as the lactic acid first starts to be formed?

    weak bases in the muscles will act as buffers and resist or minimize any pH change

    Starvation would cause which of the following acid-base conditions? Also, determine what type of compensation (metabolic or respiratory) there would be.

    Metabolic acidosis with respiratory compensation

    A patient is admitted to the hospital with the following plasma values: pH = 7.2, pCO2 = 55 mmHG, and HCO3 = 30 mEq/L

    respiratory acidosis with metabolic compensation

    A patient is admitted to the hospital with the following plasma values: pH = 7.5, pCO2 = 45 mmHG, and HCO3 = 30 mEq/L

    metabolic alkalosis with not compensation

    A patient is admitted to the hospital with the following plasma values: pH = 7.2, pCO2 = 25 mmHG, and HCO3 = 18 mEq/L

    metabolic acidosis with respiratory compensation

    Diarrhea can lead to which acid/base disturbance? Assuming compensation, would it be a metabolic or respiratory compensation?

    metabolic acidosis with respiratory compensation

    Emphysema can lead to which acid/base disturbance? What would be the compensation?

    respiratory acidosis; Kidneys will retain more HCO3 and excrete H+

    Of the three buffering mechanisms in the body, which is the strongest?

    Renal System

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