Part 1 (0.3 point) i See Periodic Table See Hint A chemist performs an acid-base
ID: 555548 • Letter: P
Question
Part 1 (0.3 point) i See Periodic Table See Hint A chemist performs an acid-base titration using 0.118 Maqueous NaOH as the titrant with 27.95 mL of 0.102 MH2S04. The endpoint of the titration is detected using phenolphthalein as the indicator. The balanced equation for the reaction is shown below: 2NaOH(aq) + H2SO4(aq) 2NaCl(aq) + 2H2O(1) What volume of NaOH is expected to be required to consume all of the acid initially present? mL NaOH solution Part 2 (0.3 point) See Hint This reaction is monitored using an acid-base indicator to detect the endpoint. What is the difference between the endpoint of the titration and the equivalence point? Choose one: The equivalence point is the point at which the moles of H30+ moles of OH-. These terms mean the same thing. The endpoint occurs at pH 7.00 regardless of the equivalence point. The equivalence point is the point at which the indicator changes color The endpoint is always reached after the equivalence point. Part 3 (0.3 point) Some acid-base indicators are listed along with their pKa values. Which indicators would be most suitable for monitoring a titration involving a strong acid and a strong base? Choose one or more: methyl yellow; pKa- 3.5 phenolpthalein; pKa-9.2 alizarine yellow; pKa 11.0 phenol red; pKa = 7.2Explanation / Answer
1. Since H2SO4 is a diprotic acid , for 1 mole of acid ,2 moles of NaOH are consumed. Keeping this in mind we first calculate the no. of moles of acid present.
Moles of H2SO4 = M1V1= (0.102 x 27.95)/1000 = 0.00285 moles
For the above neutralisation reaction, the number of moles NaOH will be twice the number of H2SO4
therefore, number of moles of NaOH = 2 x 0.00285 = 0.0057
To calculate the volume of NaOH required for the neutralisation reaction is
V2 = n / M2 =( 0.0057 / 0.118 ) x 1000= 48.32 mL
2. The end point is always reached after the equivalence point.
3. Phenol red and bromothymol blue