Question

The student decides to determine the molarity of the same Na2CO3 solution using a second method. When Na2CO3 is dissolved in water, CO3 ^2−(aq) hydrolyzes to form HCO3 ^−(aq), as shown by the following equation.

CO3 2−(aq) + H2O(l)  HCO3 −(aq) + OH−(aq)    Kb = [HCO3^ -][OH^- ]/ [CO3^2- ] - - - = 2.1 × 10^−4

(f) The student decides to first determine [OH−] in the solution, then use that result to calculate the initial concentration of CO3 2−(aq).

(i) Identify a laboratory method (not titration) that the student could use to collect data to determine [OH−] in the solution.

(ii) Explain how the student could use the measured value in part (f)(i) to calculate the initial concentration of CO3 2−(aq). (Do not do any numerical calculations.)

(g) In the original Na2CO3 solution at equilibrium, is the concentration of HCO3 −(aq) greater than, less than, or equal to the concentration of CO3 2−(aq) ? Justify your answer.

(h) The student needs to make a CO3 2−/HCO3 − buffer. Is the Na2CO3 solution suitable for making a buffer with a pH of 6? Explain why or why not.

Answer 1

The answer is attach below

ANSWER! CORE) + H2O G + HCG @u tohºijer) kn = [HC03][0m [co] Kb = 2.1 x64, is À laboratory method (note Hitration that the student could use to collect determine, Lon'] in the solution. by pH meter, from pH meter, the student determine pH, from pH he cand student calculated pol, pH+poll = 14 from pH meter pon = 14-pH y then [on-3 = -log[pont [ou] = -log [14 -pH] 1 Coroa + H2o (1) » Hool en tono az ibitical Lovers From equation one mole of cazzo produce one mole of one Hence, concentration of [ono]= Concentration of care or other method CO² e) + H₂OO) 2 HCOO (94) + ahora Notes fonc3 = [hcący, than Kb = Con:j? cog? = Ken Long² C020

Hence (20,43 = Cowg from pl molbiz Note: (Coz? I = m from given value. concentraction at equilibriun we know [Coz?] = @ initial coniginal concentratan calculated by [00,), (1-x)[003]. I [Cuz? 3. : [coz?leq7 ==> Coriginal concentractim of Cg2a © Naz (Os Solution at equilibrium - co² + H2O Ž HiGo tono Initial C Larze o o Change -xc tuc tac degree At equilibrium (1-4) Large ac Hence of equilibrium (1-2)< >> RC because d: is very small compare to 1 Thus, Nazcoz solution at equilibrium is greates than CO² (62) of disso - ciahon

41 Kb = 2.1x10-4 Kaxk6=1514 ka=1614 = 4.76 x 10 2- 2x 10-4 = pka=-1 og [ka] pka : - log (4.76X4011) = 10.3222 No, the studentorets does not needs to make a caz 20 LH COT buffer, because pka cis, close, to pH of butter, Hence your buffer ph= 6. while require pH is close to 10.3222... il 9.32 to 18:32