Question

A beaker with 2.00×10² mLmL 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 MM. A student adds 4.20 mLmL of a 0.410 MM HClHCl solution to the beaker. How much will the pH change? The pKa of acetic acid is 4.740.

Answer 1

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Total imolarity of acid and conjugate base in buffer Sollution is 0.1 molar la Let us suppose concentration of acid is a (M) S o pKa So, concentration of conjugate base is (0.1-x) (M) lence concentration of sail I Coulon of acetic acid is 4.740 from flenderson Hasselbalch equation we can write и — Рka + Текс- (acid) 8 5 = 4.740 + dag (0.1-x)

08 dog love) = (5 - 4.790) = 0.26 0 00 Oll-x = 10 y 10 - 1.8197 = 1.8197 -1 = 18197 03.07. Ou = (1.5197 +i) = 2.8194 67, X = = 0.0354 (M) 2.8197 acetic So, concentration of acid = x (M) = 0,03 54 (M) concentration of conjugate base =[Salt) = (0.1-2) in (0.1-0.8354) (M) So, concentration of salt = 0.0646 (M) TCH Cor] = 0.0646 (M)

Volume of buffer solution = 200 me. 200 del 0.0554 (M) CalcooH = 20000 : 0354 mol Cty cooh 50.0070840 f HyCOOH, 4.2 ml of 0.410(M) Hel solutish is added to buffer solution. 4.2 use of o. Ata (и) ни (А. 2 xo. 410 ) и t of Roc h orn s - 0.001722 mol of Hee 0.001722 urol of Ht added combines with 0.001722 urol of Choo to produce 0.00 1722 urol of Chcool. H+ (tett Cherd (+Nat) = ell cooh (+ Nat & ee) Amount of acetic acid increases by 0.601722 mol. Amount of Chhod decreased by 0: 001722 So, amount of acetic acid - (0.00708 +0.001722) mol of in this solution CH₂ Crot = 0.008802 tual of Cute Total volume of solution = (288+4-2) — 204. 2 ml So, concentration of acetic acid = elle nott) = (0.008882 x 16 204,2 1000 KM So, Sc [Cty coot = 0.0431 (1)

2004 0.06 4 c (м) и е с 2 а х 0.0 646 back 100 оf еңгі - 0.012 2 4d of eц сов Studio».ly, asuut of c, tо - о 1202 - 6.00 (122) = 0.011198 mal mol м. (ен, есі) = 10 % уст) у - Imaa) — о ова 8 (0) З 04. 2 Now, pH = pka + log [ethycoo] с рец - сон ) pH = pka + day [Sale] on ỦY, PR - 4 740 + (x (01 48 0 043) 61, pH - 4. 140 +0. (048 п, рН 4, 844 Sa, pH Atevasd t (5 - 4 844) E 05%