For NaOH, since the molar ratio was 1:1, the following equation was used:
Molarity of HCl was determined using the values from the first experiment and another titration in this equation, the dilution equation, which can be used for titration if there is a
1:1 mole ratio:
or
(MNaOH)(VNaOH) = (MHCl)(VHCl)
In both experiments, the average of the results were taken from three trials.
Pre-Lab Questions:
1. Titration: method of quantitative chemical analysis that is used to determine the unknown concentration of a known reactant.
Monoprotic acid: acids that are able to donate one proton per molecule during the process of ionization.
Multiprotic acid: acids that are able to donate more than one proton per molecule during the process of ionization.
2. What volume of 0.2535M NaOH is required to titrate 0.8508g KHP to the end point?
M=40 x (0.8508 x 0.2535)=3.36
3. A volume of 18.95mL of 0.5025M NaOH was needed to titrate 10mL acetic acid. What is the concentration of the acetic acid?
(M)(10mL)=(18.95mL x 0.5025M)= 0.952M
II. Procedure:
For part one of the experiment, the student standardized the ~0.1M NaOH solution with ~0.2g KHP with exact mass taken to the forth decimal place for each trial. A 250mL Erlenmeyer flask was obtained and cleaned. A KHP sample was transferred from the weigh boat to the flask and washed with 20mL distilled water until dissolved as much as possible. 2 drops of indicator were added to the flask and stirred until the sample completely dissolved. A buret was then obtained and clasped to the ring stand appropriately. The buret was then rinsed with NaOH solution twice, all excess material went into a labeled waste container and disposed of in the sink with water. Enough NaOH was added to the buret using a funnel so that the buret was filled close to the top and that volume was recorded as the initial volume to the nearest hundredth milliliter. NaOH was slowly added to the flask until a pink spot appeared in the liquid and persisted for at least one minute with continuous stirring, reaching the reaction end point. Final volume of the buret was recorded to the nearest hundredth milliliter. This was conducted a total of three times and the average concentration of NaOH was calculated using the first equation above.
In part two, the flask was first cleaned. As close to exactly 10mL of acid as possible was added to the flask. 20mL of water was added to the flask and stirred, then 2 drops of indicator was also added to the flask and stirred with a stirring bar. The buret was filled with standardized NaOH, the initial volume was recorded, and the solution in the flask was titrated to the phenolphthalein end point as observed by the student. Final
volume of the buret was recorded. This was repeated for a total of three trials, and the average concentration of HCl was calculated using the second of the equations above.
The buret was rinsed with 100mL of tap water and drained until empty. The outside was wiped dry and returned to the drawer. along with the clean stir bar. Left over acid solutions were discarded under the hood and the lab station was left clean.
III. Tabulated Experimental Data:
Average M NaOH: 0.096 M
% Error: [(0.0959M-0.096M)/(0.096M)] x 100=0.10%
Average M HCl: 0.1052 M
% Error: [(0.1054M-0.1052M)/(0.1054M)] x 100=0.19%
IV. Sample Calculations:
(M)(10mL)=(0.096M)(10.90mL) =0.1046M
(M)(10mL)=(0.096M)(10.87mL) =0.1044M
(M)(10mL)=(0.096M)(11.10mL) =0.1065M
V. Tabulated Results of Calculations:
VI. Discussion of Results:
The results of the experiment are close to the actual value of the experiment given that the student is not experienced with titration. Values are logical relative to the given information, being that both substances were strong and in solution. The exact values were disclosed by the laboratory professor for purposes of calculating percent error and interpreting results.
Post Lab:
1. Assume the concentration of HCl is 0.1000M and calculate percent relative error in your experiment.
[(0.1054M-0.10000M)/(0.1054)] x 100=5.12%
VI. Conclusion:
Molar concentration of both samples of NaOH and HCl were determined. Though the results of each trial did not equal the actual value, the average of the three trials' results came very close. This experiment gave a better understanding of how neutralization reactions between and acid and a base are involved in titration to determine concentrations of substances with respect to another substance of known concentration that the substance will react with. Possible sources of error include KHP sticking to the weigh boat when being transferred to the flask, adding too much titrant, or human measuring errors. Given the average results and being a new process to the student, the results can still be interpreted overall as part of a successful experiment. In further experiments, it is recommended that more trials be conducted to achieve an average closer to the expected value. Trials using three drops of indicator instead of two may be conducted to see if results are more correct or more incorrect relative to the accepted value.