Lab Report Acid Base Titration

Topics: PH indicator, Titration, PH Pages: 5 (1352 words) Published: November 4, 2012

1. To determine the concentration of acid using titration. 2. Skills of titration techniques.

1. 250 volumetric flask
2. 10mL measuring cylinder
3. 25mL pipette
4. 50mL burette
5. 250mL beaker
6. 150mL conical flask
7. Retord stand
8. White tile
9. Stopwatch
10. Pipette bulb

1. HCl solution
2. 0.1M NaOH solution
3. H2SO4 solution
4. Distilled water
5. phenolphthalein

An acid-base titration is the determination of the concentration of an acid or base by exactly neutralizing the acid/base with an acid or base of known concentration. This allows for quantitative analysis of the concentration of an unknown acid or base solution. It makes use of the neutralization reaction that occurs between acids and bases and the knowledge of how acids and bases will react if their formulas are known. Acid–base titrations can also be used to find percent purity of chemicals. When a weak acid reacts with a weak base, the equivalence point solution will be basic if the base is stronger and acidic if the acid is stronger. If both are of equal strength, then the equivalence pH will be neutral. However, weak acids are not often titrated against weak bases because the colour change shown with the indicator is often quick, and therefore very difficult for the observer to see the change of colour. The point at which the indicator changes colour is called the end point. A suitable indicator should be chosen, preferably one that will experience a change in colour (an end point) close to the equivalence point of the reaction. First, the burette should be rinsed with the standard solution, the pipette with the unknown solution, and the conical flask with distilled water. Secondly, a known volume of the unknown concentration solution should be taken with the pipette and placed into the conical flask, along with a small amount of the indicator chosen. The known solution should then be allowed out of the burette, into the conical flask. At this stage we want a rough estimate of the amount of this solution it took to neutralize the unknown solution. The solution should be let out of the burette until the indicator changes colour and the value on the burette should be recorded. This is the first (or rough) titre and should be discluded from any calculations. At least three more titrations should be performed, this time more accurately, taking into account roughly where the end point will occur. The initial and final readings on the burette (prior to starting the titration and at the end point, respectively) should be recorded. Subtracting the initial volume from the final volume will yield the amount of titrant used to reach the endpoint. The end point is reached when the indicator just changes color permanently. This is best achieved by washing a hanging drop from the tip of the burette into the flask right at the end of the titration to achieve a drop that is smaller in volume than what can usually be achieved by just dripping solution off the burette. Acid–base titration is performed with a phenolphthalein indicator, when it is a strong acid – strong base titration, a bromthymol blue indicator in weak acid – weak base reactions, and a methyl orange indicator for strong acid – weak base reactions. If the base is off the scale, i.e. a pH of >13.5, and the acid has a pH >5.5, then an Alizarine yellow indicator may be used. On the other hand, if the acid is off the scale, i.e. a pH of <0.5, and the base has a pH <8.5, then a Thymol Blue indicator may be used.

Indicator| Color on acidic side| Range of color change| Color on basic side| Methyl Violet| Yellow| 0.0–1.6| Violet|
Bromophenol Blue| Yellow| 3.0–4.6| Blue|
Methyl Orange| Red| 3.1–4.4| Yellow|
Methyl Red| Red| 4.4–6.3| Yellow|
Litmus| Red| 5.0–8.0| Blue|
Bromothymol Blue| Yellow| 6.0–7.6| Blue|...
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