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Introduction

Acid-Base Titration Lab By: Shawn Vickar Question: What effect does an indicators pH range have on the end point of the titration of vinegar and 1.00 mol dm-3 of sodium hydroxide solution? Equation: CH3COOH (aq) + NaOH (aq) ï NaCH3COO (aq) + HOH (l) Data Collection Table A: Table Representing the Initial Volume of NaOH in the Burette, the Final Volume of NaOH in the Burette and the Difference between Those Values for Specific Trials When Using Different Indicators. There were a minimum of three trials performed for this lab as there needed to be three of the same difference between the final and initial burette readings of the sodium hydroxide. This is due to the fact that a titration lab requires one to acquire three of the same values for this section to understand the exact amount of base required to reach the endpoint of the reaction. Indicator Initial Volume of NaOH solution (ml) ±0.05 Final Volume of NaOH solution (ml) ±0.05 Difference Between the Final and Initial Burette Readings (Volume of NaOH used) (ml) ±0.1 Qualitative Observations Phenolphthalein 0.0 0 0.90 0.9 The indicator is clear and transparent at first. However, when the base is added and the endpoint has been reached, the color changes to a light pink. If over titration occurs, the solution will be a fluorescent pink color. 0.90 2.30 1.4 2.30 3.20 0.9 3.20 4.10 0.9 Bromothymol Blue 8.00 9.50 1.5 The indicator is yellow at first. However, when the base is added and the endpoint has been reached, the color changes to olive green. If over titration occurs, the solution will be a dark blue shade. 9.50 11.10 1.6 11.10 12.90 1.8 12.90 14.40 1.5 14.40 15.90 1.5 Methyl Orange 15.90 16.90 1.0 The indicator is red at first when added to the acetic acid. However, when the base is added and the endpoint has been reached, the color changes to yellow. ...read more.

Middle

of sodium hydroxide pellets that was necessary for this experiment (1gram). This would ensure the sodium hydroxide pellets would not react with the carbon dioxide in air for very long before being put in the volumetric flask with water added. This is because there would be no need to measure these pellets on the electronic balance. A very common error with titration labs is that over-titration often occurs. This is the point in which too much titrant is added to the analyte during a trial. Therefore, the reaction passed the endpoint as too much of the basic sodium hydroxide was added to the acidic vinegar solution containing acetic acid. Unfortunately, this took place for most trials. For instance, phenolphthalein reaches its endpoint when it changes from being clear and transparent to becoming a light shade of pink. Though this may be, for all of our trials when using this indicator the color became a hot pink shade proving that over-titration had taken place. An improvement for this component of the lab is simple. An improvement to control this error would be to use a burette with a smaller opening. This is because the endpoint can be overshot quite easily and this would ensure the error would not take place. It would have been best to manage the amount of base entering the beaker as much as possible with greater accuracy. An additional error that took place was how the stopcock was not entirely effective. This is due to the fact that when the stopcock was turned to close the burette opening, little droplets of sodium hydroxide would still pour into the beaker. This means that if the solution had reached the endpoint and additional droplets were leaked from the beaker an inaccurate reading of the sodium hydroxide in the burette would be recorded. This error could have been improved by using a BT50 digital burette (Bibby, 2010). ...read more.

Conclusion

When comparing with the data of these groups it was determined that all of the results were mostly exactly the same or off by 0.1ml for the difference between the final and initial burette readings. For instance, for phenolphthalein, the value my group obtained for this was 0.9ml however, Yashna’s group got 1.0ml. This could have been due to a human error known as a parallax. A difference of 0.1ml could have taken place as one of our groups were unable to determine the position of the meniscus on the burette and therefore, the wrong readings of sodium hydroxide solution could have be collected. An acid base titration has several uses. One of the main real life uses of this experiment is to mix compounded drugs. A pharmacist will need to mix drugs appropriately in order for them to be in the appropriate pH range for the human body. Antacids are commonly used to help issues concerning heartburn, acid reflux and more. These feelings most likely take place due to excess hydrochloric acid in the stomach which causes an uncomfortable feeling. This subsequently allows a backflow of this acid to go up the esophagus which can make someone feel like their throat is burning. These tablets counteract the acidity as they go to the stomach area and react with the hydrochloric acid. These tablets are basic and change the liquid in the stomach to being not as highly acidic. Common antacid tablets contain Mg(OH)2 and Al(OH)2. A reaction equation by using an antacid tablet is shown as followed: HCl+NaOHï NaCl+H2O The acid base titration in this case is used to determine the amount of the stomach acid present in one’s body. Therefore, it can be discovered how much antacid will be needed for someone dealing with the issues mentioned above in order to make the hydrochloric acid present in their stomach less concentrated (Cavite, 2010). This will ensure the pH of the stomach will be less acidic. In other words, the lab will determine how much hydrochloric acid will be needed to be titrated by the base. ...read more.

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