01:160:163 Lecture Notes - Lecture 15: Equivalence Point, Conjugate Acid

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aquamarinetiger679

19 May 2016

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***we did additional problems, especially on the latter point of the notes*** ***those will be up as soon as he gives them to us! Half equivalence point: one half of the initial amount of acid (ha) has been converted to a- *******equal to the pka value of the solution********** Equal amounts of weak acid and conjugate base at this half equivalence point. The ph of the solution is equal to the concentration of half of the oh or. H substance added to the solution at the equivalence point (therefore the pka is the final answer for the ph) This is why you can use henderson hasselbach equation for the total reaction. Acid- base indicator: weak organic acid that will have a different color than its conjugate base has. The color you observe will differ depending on the ratio between the acid and its conjugate base. Equivalence point: moles of acid equal moles of base.

Related Questions

Calculate the pH of the solution after the addition of the following amounts of 0.0649 M HNO3 to a 70.0 mL solution of 0.0750 M aziridine. The pKa of aziridinium is 8.04.

a) 0.00 mL of HNO3

b) 7.30 mL of HNO3

c) Volume of HNO3 equal to half the quivalence point volume

d) 77.5 mL of HNO3

e) Volume of HNO3 equal to the equivalence point

f) 85.8 mL of HNO3

Please answer all parts of the question detailed with work. I will know if you are wrong, so please answer to the best of your ability.

Hint:

Aziridine (C2H5N), a weak base, reacts with a strong acid such as HNO3 to form its conjugate acid aziridinium (C2H5NH ). A strong acid reacts completely with a stoichiometric amount of weak base after each addition of the strong acid. In the titration of a weak base with a strong acid, there are four regions of the titration curve that require different calculations when determining the pH of the solution. 1) Before any strong acid is added to the solution. 2) Between the initial addition and the equivalence point. 3) At the equivalence point. 4) After the equivalence point.

I will thumbs up the answer .

please answer all parts!! running out of time!

a) You will be titrating a 1.50 M solution of HCN. What is the initial pH of this solution before the titration has begun? b) We measure out 21.00 mL of a 1.50 M solution of HCN for our titration with sodium hydroxide. If you add 1.00 mL of a 0.30 M solution of sodium hydroxide, what is the pH of the acid solution at this stage of the titration? The Ka for HCN is 4.9 x 10-10 1.00 mL of sodium hydroxide added to the weak acid 0.30M sodium hydroxide in the buret as the titrant 21.0 mL of original 1.50 M HCN sample c) If we add enough sodium hydroxide to neutralize 1/2 of our HCN, we will have converted 1/2 the HCN into CN. At this point the [HCN] = [CNT, what is the pH at this point that we call the half equivalence point? d) If we add enough sodium hydroxide to neutralize all of the HCN, we will convert it all into CN and we will have reached the equlvalence point. Since the only thing that remains at the equivalence point is the salt of the conjugate base, CN, the pH at equence will be determined by the hydrolysis of this salt. Since you know how many moles of HCN you started with, you know how many moles of CN must be present at the equivalence point. To calculate the [CN ] you must know the total volume at the equivalence point. How many mL of 0.30 M sodium hydroxide are needed to reach the endpoint? e) What is the pH at the equivalence point of this titration? Remember that since the conjugate base, CN, is hydrolyzing in solution, you will need a Kb value for this base f) If we pass the equivalence point then the pH of the solution is dominated by the strong base. It is like a limiting reagent problem where now, we have run out of the weak acid and there is excess strong base. Even though there will be CN in solution, the OH from the strong base will control the pH. Thus, it is like a strong base pH problem. If we add 115.00 mL of sodium hydroxide we will be well past the equivalence point of the titration. What will be the pH at this point. (Hint: how much strong base will remain unreacted in solution?)

01:160:163 Lecture Notes - Lecture 15: Equivalence Point, Conjugate Acid

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