CHEM 1021 Lecture 8: Chemistry Chapter 8

Adding a strong Acid to a Buffer Part A Learning Goal : A beaker with 145 mL of an acetic acid buffer with a pH of 5,000 is sitting on a benchtop. The total molarity of acid and conjugate base in this buffer is 0.100 M. A student adds 8.60 mL of a 0.320 M HC1 solution to the beakerHow much will the pH change? The pK, of acetic acid is 4.740. To understand how buffers use reserves of conjugate acid and conjugate base to counteract the effects of acid or base addition on pH Express your answer numerically to two decimal places. Use a minus (-) sign if the pH has decreased. Hints A buffer is a mixture of a conjugate acid-base pair. In other words, it is a solution that contains a weak acid and its conjugate base, or a weak base and its conjugate acid. For example, an acetic acid buffer consists of acetic acid, CH, COOH, and its conjugate base, the acetate ion CH3 COO. Because ions cannot simply be added to a solution, the conjugate base is added in a salt form (eg., sodium acetate NaCH COO). IVO Aze s o o o ? ApH -- 0.363 Submit My Answers Give Up Incorrect, Try Again; 5 attempts remaining Buffers work because the conjugate acid-base pair work together to neutralize the addition of H' or OH ions. Thus, for example, if H ions are added to the acetate buffer described above, they will be largely removed from solution by the reaction of Hwith the conjugate base: Provide Feedback Continue H+ + CH, COO CH, COOH Similarly, any added OH ions will be neutralized by a reaction with the conjugate acid OH + CH3 COOHCHCOO + H2O This buffer system is described by the Henderson-Hasselbalch equation [conjugate base] pH = pK. log [conjugate acid)

.ill AT&T 9:44 AM Back Chem1B-W18-Homework5.pdf [1] This homework assignment郷due at the begining of class on March 9., 2018, write your answers on a separate piece of paper, and show your work to receive credt Protiem 1 What distinguishes a strong acid from a weak acid7 What distinguishes a strong base from a weak base? Write out examples of the proton-transfer reaction for each as well as the equilibrium expression (K or Ko) tor each ? Wrtie equations Probiem 2 In class we dscussed e autoionization of water, What is an for the autoionization reactions for H-O and H SO Assume that both are pure iquids Problem 3 In class on Friday, we calculated the [HO-1 and [OH in stomach acid at pH 1.5 The average volume of an adult human stomach is 1L. How many H0 ions are present in a human stomach i&the pH is 2.0? How many OH- ions? man body temperatre). Problem4 any equlbnum constant. Min changes with temperature. At 37 ℃ the pH of waner is 6.80. Caloulate the following for pure water at this temperature: b) IOH1 Problems whais a con ate acid-base pair? What is the relationship between the two members of pair? Prettem.6 Draw a Lewis structure ot each of thy tolowing acids. Then, wte balanced aciddssociaton reactions and equibrium expressions for each in water. a) Formic acid, HCOOH b) Chloric acid, HCIO, c) Dihydrogen arsenate, H As0 Probiem Z Dihydrogen arsenate is an ampiprotie substance, meaning tcan both accept and donane a proton Draw Lewis structures of the conjugate acid and the conjugate base of dihydrogen arsenate. Write the balanced base-dissociation reaction and equiibrium expression of dihydrogen arsenate in water Paatina successivo K.'s for polyprotic acids decrease. For thé polyproc phosphoric acid. HAo, K., 7.2 x10. KA6.3 x 10, Ka 4.2 x 10- Draw Lewis structures of each of the species involwed in each acid- dissociation roacton、Why d0the K.'s decrease for each successi e deprotaraton? Protiem 2 Hypochionous acid, HCIO, has a pka ol 7.54. What are the [Hs0-]. pH. [CO1 and [HCIO] in a 0.115 M solution of HCI0? Problema in a 0 735 M solution a weak acid is 12 5% dssoc ated. a) Calculatemo-1, pH·[OH 1, and pH of the solution. b) Calculate Ka of the acid Problemi! Acetyisaleyic acid (asprin, structure shown to the right). HC此:O4, is the most widely used pain reliever and tever reducer. Find the pH of 0.018 M aqueous aspirin at body temperature (K.: 3.6 x 104 at 37°C). Problem12 why郷aqueous NaF basic but aqueous NaCl neutral? Chit consider the reaction of each anion with water 1 of 1 Previous Dashboard Calendar To Do Notifications Inbox