calculate the pH of the following buffer a.7.8 x 10^-2 M HC_2H_3O_2 and 8.6 time
ID: 972033 • Letter: C
Question
calculate the pH of the following buffer a.7.8 x 10^-2 M HC_2H_3O_2 and 8.6 times 10^-2 M NaC_2H_3O_2 4. A buffer is made from 3.7 times 10^-1 M HC_2H_3O_2 and 2.9 times 10^-1 M NaC_2H_3O_2 a. what is the pH? b. If you added 3.0 times 10^-3 moles of NaOH to 0.100 L of buffer what is the final pH.(assume that any change in volume is negligible.) 5. How many grams of phenylalanine are needed to make 350.0 ml of a0.125M solution? 7. you titrate valine as we did in class today;dissolved it,acidified the solution with an excess of HCl,then titrated with NaOH unit A pH of 13.5 was reached.Use the following information to determine; a.The molecular weight of valine b.Calculate the percent errorExplanation / Answer
(3) pH = pKa + Log [salt]/[acid]
pH = 4.75 + Log (8.6 x 10-2)/(7.8x10-2) = 4.79
(4)
(a) pH = pKa + Log [salt]/[acid]
pH = 4.75 + Log (2.9 x 10-1)/(3.7x10-1) = 4.64
(b) Added NaOH reacts with H+ ions which causes increase in the ionisation of acid and thus concentration of salt.
0.003/0.1 = 0.03M salt reacts with 0.03 M acetic acid,
Hence new,
[HC2H3O2] = 0.37 - 0.03 = 0.34 M and [NaC2H3O2] = 0.29 +0.03 = 0.32M
Therefore, pH = pKa + Log [salt]/[acid]
pH = 4.75 + Log (0.32/(0.34) = 4.72
(5)
(a) Alanine
+H3N-CH(CH3)COO -
(b) Serine
+H3N - CH(CH2OH) - COO -
(6) Mass = Conc. x GMW x V (in L) = 0.125 x 165 x 350 / 1000 = 7.22 g.
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