Prelab: What is a titration? Why is the starch indicator added near

1. What is a titration?
Why is the starch indicator added near the end of the titration and not at the beginning?
A drain cleaner is to be tested for its acid content (sulfuric acid). A 5.0 mL portion of the drain cleaner is pipeted
into a 100.0 mL volumetric flask and diluted to the mark. A 10.0 mL portion of that acid is then titrated with 0.55
M sodium hydroxide. It is found that 23.75 mL of the sodium hydroxide is required to neutralize the acid.
3. What is the molarity of the dilute acid solution?
What is the molarity of the concentrated (full strength) commercial drain cleaner?
If the density of the drain cleaner is 1.45 g/mL, calculate the percent, by mass, of the sulfuric acid.
1. Using proper pipeting techniques, transfer exactly 5.0 mL of bleach solution to a 100 mL volumetric flask. Fill
the flask with water to the required mark, place a stopper in the flask, and mix well.
2. Mass 1 gram of solid KI
3. Pipet 10 mL of the dilute bleach solution (from #1), as directed by your instructor, into an Erlenmeyer flask.
Place the KI from #2 in to the flask. Add approximately 25 mL of deionized water, and 5 mL of the 1M
sulfuric acid. The solution should be a deep yellow color at this point. Set this aside.
4. Fill the buret with the standard, provided, 0.100 M sodium thiosulfate solution. Record the initial buret reading.
5. Titrate the contents of the flask with the sodium thiosulfate in the buret. As the titration proceeds, the color of
the solution in the flask will turn a very light yellow. At this point, add eight drops of the starch solution. The
solultion should turn a dark bluish-purple color.
6. Continue titrating, drop by drop, until all the blue color disappears. Use a piece of paper underneath if
7. When the color just disappears record the final buret reading.
8. Rinse out all the equipment and return as directed.
Data and Calculations:
Initial reading of the buret = ______________
Final reading of the buret = ______________
Volume of sodium thiosulfate used = ______________
Molarity of the sodium thiosulfate provided = ______________
Volume of concentrated bleach used = _____________
Volume of volumetric flask used = _____________
Volume of diluted bleach used = _____________
1. Calculate the molarity of the diluted bleach.
Calculate the molarity of the concentrated bleach.
Look at the bleach bottle. If the active ingredients list the percentage of NaClO, then calculate the percentage
of NaClO in the bleach. If the active ingredients list percentage of ClO -, then calculate the percentage of ClOin the bleach solution.
Determine the percent error for your results using the listed amount on the bleach bottle as the actual value.