double indicator titration of phosphoric acid with sodium hydroxide
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To perform a double indicator titration of phosphoric acid with sodium hydroxide, you will need the following materials:
- Phosphoric acid solution
- Sodium hydroxide solution
- Two indicators: phenolphthalein and methyl orange
- Distilled water
- Burette
- Pipette
- Conical flask
- White tile or paper
Here is the step-by-step procedure for the double indicator titration:
1. Rinse the burette with the sodium hydroxide solution to ensure it is clean and free from any impurities. Fill the burette with the sodium hydroxide solution and record the initial volume.
2. Pipette a measured volume of the phosphoric acid solution into a conical flask. This volume will depend on the desired concentration of the acid and the stoichiometry of the reaction.
3. Add a few drops of phenolphthalein indicator to the conical flask. Phenolphthalein is colorless in acidic solutions and pink in basic solutions. This indicator will help you determine the endpoint of the titration.
4. Start titrating by slowly adding the sodium hydroxide solution from the burette into the conical flask while swirling the contents. The sodium hydroxide will react with the phosphoric acid to form water and sodium phosphate.
5. The phenolphthalein indicator will turn pink when the stoichiometric amount of sodium hydroxide required to neutralize the phosphoric acid is reached. This is the first endpoint and indicates the neutralization of the first hydrogen ion.
6. Continue titrating until there is a slight excess of sodium hydroxide in the solution. At this point, remove a small amount of the solution and transfer it to a white tile or paper.
7. Add a few drops of methyl orange indicator to the conical flask. Methyl orange is yellow in acidic solutions and red in basic solutions. This will help you determine the second endpoint.
8. Continue titrating by adding the sodium hydroxide solution drop by drop until the solution in the conical flask changes from yellow to red. This is the second endpoint and indicates the neutralization of the other two hydrogen ions in phosphoric acid.
9. Record the final volume of sodium hydroxide solution in the burette. The difference in volume between the initial and final readings gives you the volume of sodium hydroxide solution required to neutralize the phosphoric acid.
10. Repeat the titration process at least twice to ensure accuracy and consistency in your results.
11. Calculate the concentration of the phosphoric acid solution using the volume of sodium hydroxide solution used and the known molarity of the sodium hydroxide solution.
Remember to wear protective gloves and goggles while performing the titration and handle the chemicals with care.
A double indicator titration is a method used to determine the concentration of a solution of a known chemical compound by using two different indicators. In the case of the titration of phosphoric acid (H3PO4) with sodium hydroxide (NaOH), there are two common indicators that can be used: phenolphthalein and methyl orange.
Here are the steps to perform a double indicator titration of phosphoric acid and sodium hydroxide:
1. Prepare your chemicals: You will need a solution of known concentration of sodium hydroxide (the titrant) and phosphoric acid solution to be titrated, along with distilled water.
2. Set up the titration apparatus: Use a burette to deliver the sodium hydroxide solution and a conical flask to contain the phosphoric acid solution. Connect the burette to the flask using a rubber tube.
3. Add the indicators: Add a few drops of phenolphthalein to the conical flask containing the phosphoric acid solution. This indicator will change color from clear to pink as the solution becomes basic. Then, add a few drops of methyl orange, which will change color from yellow to pink as the solution becomes acidic.
4. Perform the titration: Slowly add the sodium hydroxide solution from the burette into the flask while stirring. The initial color will be yellowish because methyl orange is sensitive to a lower pH. As the sodium hydroxide reacts with the phosphoric acid, the solution will turn pink due to phenolphthalein.
5. Observe the color change: As you continue to add the sodium hydroxide solution, the pink color from phenolphthalein will become more intense. Once the titration reaches a point where the pink color persists for a while even after stirring, you have reached the endpoint of the titration.
6. Record the volume of sodium hydroxide used: At the endpoint, read the volume of sodium hydroxide solution required from the burette. This volume is used to calculate the concentration of the phosphoric acid solution.
7. Calculate the concentration of phosphoric acid: Using the volume of sodium hydroxide solution and its known concentration, you can calculate the concentration of phosphoric acid using the balanced chemical equation and stoichiometry.
It's important to note that the double indicator titration method is only one approach to determine the concentration of phosphoric acid with sodium hydroxide. Other methods, such as titration with a single indicator, can also be used. Additionally, accurate results can be obtained by repeating the titration multiple times to ensure consistency.