The purpose of this experiment is to determine the concentration of a solution of sodium hydroxide by titration against a standard solution of potassium hydrogen phthalate.

 Concentration of acid = (inaccuracy of moles+ inaccuracy of volume of solution)

                                        = 0.04%+0.24%                     (inaccuracy is obtained from the previous experiment)

                                        = 0.28%

                                       = ± 0.0027286M

Volume of NaOH         = (inaccuracy/volume) x100

                                        = (0.06/25.54)x100

                                        =0.23%

                                         = ± 0.058742 ml

Concentration of NaOH = (inaccuracy of moles+ inaccuracy of volume of solution)

                                           = 0.04%+0.23%

                                           =0.27%

                                           = ± 0.00263115 M

From the last lab experiment we found that the moles of potassium hydrogen phthalate.

HA(aq) + Na+ OH-  (aq)  →Na + A- (aq)+ H2O

1 mole of acid reacts with 1 mole of NaOH solution.

Hence 0.02488 moles of potassium hydrogen phthalate will react with 0.02488 moles of NaOH solution.

Concentration of solution = Moles of solution/Volume of solution

                                               =0.02488/0.02554

                                               = 0.097450 M ± 0.00263 M

It is given that the concentration of NaOH solution is approximately 0.1M.

So if we take this as the literature value

Discrepancy = (experimental yield-theoretical yield/ literature value)x 100

                      = {(0.097450-0.100000)/0.1}x 100

                      = 2.55 %  

Conclusion

The main aim of this experiment was to find out the concentration of NaOH solution by titration against a standard solution of potassium hydrogen phthalate. We used the standard solution of known concentration from the previous lab experiment in which we made a standard solution of potassium hydrogen phthalate.

Discrepancy of the solution was calculated by subtracting the theoretical yield from the experimental yield, dividing by the theoretical value and then multiply by 100 to get the percentage.

The discrepancy % is found out to be 2.55%.Since the discrepancy % is low the experimental value can be taken for the literature value.

Since the discrepancy % is low, we have accepted the experimental value. The deviation from the theoretical amount is small and the errors that could have affected the result range from systematic errors such as calibration of the apparatus used to random human errors such as parallax in reading the values. If % difference is greater than experimental errors then there are systematic errors in the procedure.

Several trends were observed from the qualitative and quantitative observation :-

• The solution got its fade pink color between when 25ml-26ml of burette solution was titrated.
• The offshot experiments have a deep characteristic pink color that doesn’t goes away with in time of 2minutes in the solution.
• Before reaching the solution reaches the titrated value, when the burette solution is added to the conical flask the acid appears to be pink but after we swirl the solution it loses its color.
• The burette solution was titrated continuously until it reached the 20ml mark
• The pink color starts to appear from 20ml mark onwards
• The pipette completely drained the solution in the conical flask except only for a drop of solution to be left behind

Evaluation

• The NaOH solution was prepared by the lab technician of the concentration around 0.1M. The uncertainty in the error is unknown. This acts a drawback to our calculation and our experiment since we don’t know the amount of deviation the solution can have in its concentration. An improvement for this would be to use NaOH solution whose uncertainty is known so that we can calculate the error deviation in the final answer and hence be more precise and accurate in our calculation of the volume of NaOH solution titrated.
• Distilled water used in preparing the sodium hydroxide solution was 99.9% pure. The impurities present in the distilled water could have added to the error calculation, hence increasing the deviation. In order to reduce the error inaccuracy distilled water with higher purity should be used.
• An assumption is made that after the rinsing the burette and pipette with their respected solution there are no impurities left. This assumption could have added inaccuracies to the random error. Or another assumption that is the apparatus is clean and do not require rinsing could have also been made. Both of these assumptions stated above will lead to the reaction of the impurities  with the respected solution hence consuming the moles and increasing the volume of the solution used to be titrated  leading to an error in the calculation. An improvement for this would be to sterilize the lab apparatus in order to sure that even after rinsing no impurities are left behind.  
• While performing the experiment a drop was left in the pipette. The main reason of this is the pipette to be greasy. The drop is a constituent of the solution and contains moles of the solution which gets left behind. This error in experimental procedure will lead to less volume being used hence increasing the concentration and leading to an error in the titration procedure.an improvement for this error is to clean the pipette thoroughly by autoclaving the pipette, which will allow the pipette to deliver the complete solution or using other device of the same volume to create the standard solution.
• Difference in the colors of titrating the final solution could be obtained since the conical flask was kept on a black base. The problem with black base is that it makes it difficult to observe the color changes since black absorbs all colors. This will lead to slight differences in the shades of pink, which lead to differences in the volume of the solution used hence creating an inaccuracy. An improvement for this would be to either keep a white tile below the conical flask while performing the titration or keep a white sheet of paper. This will make it easier to observe color changes and hence will give more accurate burette readings
• Adding more / less than 2 drops of phenolphthalein indicator solution will cause inaccuracies in the burette volumes. By adding less indicator, when we titrate the solution the color change will come after a long time hence there will be more volume of the solution that is added than the necessary .If we add more indicator then while titrating the solution the color will change quickly and the volume of the solution from the burette used to titrate will be less than the required amount. An ideal improvement for this would be to carefully add 2 drops of the indicator of the almost the same size.
• An assumption made is the concentration C8H5O4K solution and NaOH solution were taken in the same room temperature as the experiment performed. When the room temperature is higher it leads to expansion in the volume and more amounts of moles are dissolved so when the room temperature cools then the concentration will rise as the volume will decrease.so if we take the readings while performing the experiment at different room temperature we can either have a greater or lesser value for our solution used for titration. An improvement in this would be to make the solutions and perform the experiments at the room temperature. So that there is no expansion of volume of the solution which can lead to inaccuracies in the concentration of the acid.
• Systematic errors such as bubble in the burette will lead to an increased reading of the volume of the solution used, which will cause error in the calculation of the concentration of the NaOH solution. The volume of the pipette solution was measured with the pipette inside the solution and not outside, by doing this the solution present inside the beaker adds to the pressure of the pipette holding the volume and hence it increases the volume of the solution, so when we take out the pipette from the solution the volume reading will drop down.

Questions

Q1.What effect would each of the errors described below have on the calculated value of the concentration of sodium hydroxide?

1. The burette is not rinsed with the sodium hydroxide solution
2. The pipette is not rinsed with the potassium hydrogen phthalate solution
3. The tip of the burette is not filled before titration begins
4. The conical flask contains some distilled water before the addition of potassium hydrogen phthalate.

1. If the burette is not rinsed with sodium hydroxide solution , there might be some impurities and when we add the sodium hydroxide solution , the molecules of the solution might react with the solution and hence will reduce the concentration of the solution
2. If the burette is not rinsed with the potassium hydrogen phthalate solution, there might be some impurities and when we add the potassium hydrogen phthalate solution , the molecules of the solution might react with the solution and hence will increase the concentration of the solution
3. If the tip of the burette is not filled , then a bubble remains in the tip of burette. This results in the solution taking a greater surface area in the burette and showing greater reading than the actual. So this will lead to decrease in the concentration because more volume will be used.
4. If the conical flask had some amount of distilled water before titration then more volume of the NaOH will be used to neutralize the acid , because the distilled water will dilute the acid, since more volume will be used the concentration of NaOH will reduce.