Buffer Quiz – Flashcards
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Write a chemical equation that illustrates what happens when a strong acid is added to a buffer
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H+ + A- --> HA (the strong acid reacts to form a weak acid)
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Write a chemical equation that illustrates what happens when a strong base is added to a buffer
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OH- + HA --> A- + H2O (strong base reacts to form weak base)
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How can you determine the components for making a buffer
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should be made using protonated/deprotonated versions of weak acids or weak bases; strong acids or bases should not be used because they will not combine with the H+ or OH- to form the weak acid or weak base
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pH of the buffer when moles of components are equivalent
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this is found from the pKa of the weak acid or the pKb of the weak base, as long as the moles of each are equivalent
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how to tell if a pair would be a buffer?
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check to make sure that there is a weak acid or base; and that the components are conjugate weak acid/base pairs
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which ratio of buffer components makes the most effective buffer?
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ideal buffer has equal moles of the protonated and deprotonated components; this is ideal so that a maximum amount of strong acid/base can be added with minimal pH change
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buffer capacity
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amount of strong acid or strong base that can be added to the buffer before the capacity of buffer is reached
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experimental definition of buffer capacity
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the amount of acid or base that causes a particular finite change in pH, such as +/- 1 unit
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theoretical definition of buffer capacity
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point where the amount (moles) of the buffer acid or buffer base are used up
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how would you make an acetic acid/sodium acetate buffer with only acetic acid?
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find the sum of the moles of the acetate ion and the acetic acid, then titrate with NaOH to get to the correct pH, then there should be the correct number of moles of each buffer component
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what is true when there are equal moles of each buffer component, the protonated and deprotonated forms?
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pH= pKa
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how does changes in the log([A-]/[HA]) expression affect the pH of the solution
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think: the inside of the parentheses is equal to 10^ a certain power, and that power is added to the pH; e.g., if the components are changed so that log(1/100), you solve 1/100=10^?, x=-2, decrease pH by 2 units
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how do you calculate the pH of the buffer knowing the volumes and molarities of components added?
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use the Henderson Hasselbach equation; pH= pKa+ log([conjugate base]/[weak acid]); calculate NEW molarities using the total volume of the two components, then plug into equation
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what would happen if you added NaOH to the buffer solution?
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the OH- anion would react with the acid in the buffer solution to form water and the conjugate base
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how much of a certain molarity base could you add to a buffer solution before the buffer component is depleted?
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calculate the number of moles of acid present by first finding the molarity of the acid (use its original molarity and the total volume of buffer solution to find number of moles); then multiply by acid's ratio with NaOH-, use the molarity of NaOH to know the volume of NaOH that would need to be added to neutralize all the acid in the buffer solution
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how would you find the mass of acid needed to make a certain volume of buffer at a certain pH, knowing the molarity of the base?
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use the equation pH= pKa + log([base]/[acid]); solve for the concentration of the acid using given values; find the number of moles of acid that would be present in a certain volume sample, then using the molar mass to find the mass of acid that would need to be added
