Molarity Of A Solution By Performing A Titration Biology Essay

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In Natural science, scientists plan experiments and examine them, to support their claims. Scientists use special units like Grams (g), Milliliters (mL) and Molars with a symbol of M. Molars is a term expressing morality of each compound or element in a chemical reaction. Molarity is the only way scientists use to measure the concentration of a solution. Concentration of a solution means how much solute (which is the substance that is being dissolved by the solvent, which is the liquid that dissolves the solute) is present in a given amount of solution. To find the concentration (C) we divide, moles of solute (n), by the volume of a solution (v). The following formula is being used: .Another formula can be used to determine Molarity (M) is by dividing the moles of solute (mol) by liter of solution (L), to find the concentration: . However, to determine the molarities of a solution of acidic and basic solutions, which are often used to convert back and forth between moles of solutes and volumes of their solutions, titration is used. Titration is when one solution is added to another solution until a chemical reaction between the solution has run to completion. The first solution is called the titrant, which is used to titrate the other solution. The completion of the reaction is usually shown by a change of color caused by a substance called an indicator, like phenotolphthatein. The following formula is used to determine titration in a chemical reaction: C1 Ã- V1 = C2 Ã- V2. C stands for the concentration, and V is the volume in an acidic and basic solution. This formula enables scientists to differentiate acids from bases and, also determine the concentration and volume (Titration) of a chemical reaction.

Aim: Determine the molarity of a NaOH solution by performing a titration using 0.100 M HCl.

Hypothesis:

Common unites used to measure solutions in labs are grams, milliliter and molarities. Molarity (M) is basically the measure of the concentration of a solution. However when it comes to acidic and basic solution, titration is used to find the volume and concentration of a solution. Titration is when one solution is added to another solution until a chemical reaction between the solutions has run to completion. The completion of the reaction between the solution is shown by a change of color caused by a substance called an indicator. In this experiment I predict that the HCl solution will dissolve completely, when a light pink color occurs, because when NaOH was tested by phenolphthalein indicator, it gave a light pink color.

Method:

25mL of 0.10 M HCl solution was measured in a graduated cylinder, to then transfer it into 50mL Erlenmeyer flask , to be accurate and exact.

Then, 50mL of NaOH with unknown concentration was measured.

The 50mL Burette was rinsed with a small amount NaOH, to avoid mixing water with NaOH. After rinsing the burette, NaOH solution was filled till the top.

A beaker was labeled "HCl" under the burette. After that the stopcock of the burette was opened, to allow air bubbles to escape from the burette.

Three droplets of phenolphthalein indicator were added to the HCl in the Erlenmeyer flask. Then, the Erlenmeyer flask was placed under the NaOH burette, and the stopcock of the burette was opened to allow a few drops of the NaOH to flow into the flask while continuously swirling the flask. Then we observed the color changes that occurred. After that, we slowly continued to add NaOH while swirling the flask.

When a faint pink color appeared and persisted for about 10 seconds or more of swirling of the flask, then the endpoint was reached. Which means that the HCl solution was completely dissolved in NaOH.

After that, the endpoint was reached, and the volume of NaOH was recorded.

Then, we calculated the molarity of the NaOH solution.

Several trials of titration were made, to have an exact and accurate initial and final readings.

After the 3 trials, we calculated the average concentration of NaOH solution.

Independent variable: The variable that changed was the initial reading. As we started from 0mL in trial 1 and 2, then we changed and started from 13.2mL in trials 3 and in trial 4 we started at 26.2mL.

Dependant variable: The variable that was affected from the changing variable was the final initial readings, which will impact on the volume of NaOH solution needed to neutralize HCl.

Controlled variable: The variable controlled was the NaOH solution in the burette, because we physically closed and opened the stopcock to allow drops of NaOH solution to react with the HCl solution in the Erlenmeyer flask.

Materials

Ring stand and clamp

50 mL Erlenmeyer flask

50 mL Burette

25mL Graduated cylinder

One 50 mL beaker

Filter funnel

0.100 M HCl

150 mL of Unknown concentration of NaOH

Phenolphthalein ( Indicator)

Safety factors

Lab coat

Safety glasses

Gloves

Avoid sitting, while doing an experiment.

Follow teacher's instructions.

Use right equipments, in a right way.

Result/Data

Reading of NaOH volume:

Trials

Initial burette reading

Final burette reading

Observation

Trial 1

0mL

13.0mL

The solution was perfect. It gave a light pink color.

Trial 2

0mL

13.2mL

The solution turned to a light pink color. This was considered perfect.

Trial 3

13.2mL

26.2mL

The solution became perfect again. As, it gave a light pink color. My partner and I observed that the change of the color will occur by doubling the initial burette reading.

Trial 4

26.2mL

38.5mL

Our observation was incorrect, as the solution was overshot, due to times limitation, because we rushed to finish the experiment. However, if we had more time, our observation, may turn correct.

Figure.1 Initial and final burette reading and observation of NaOH volume.

Volume of NaOH needed to neutralize HCl:

Trial 1

Trial 2

Trial 3

Trial 4

Observations

13.0mL

13.2mL

13.0mL

12.3mL

To find the volume of NaOH, we subtracted the initial burette reading by the final burette reading. The first three trials, they all had common numbers, which is 13. This explains the accuracy of the point reached, when HCl solution was completely dissolved in NaOH. Therefore when the solution becomes light pink, it contains only NaOH solution. In trail 4 , it was 12.3 , which was overshot.

Figure.2 Trials and observation of the volume of NaOH solution needed to neutralize HCl solution.

Discussion

The experiment investigates HCl + NaOH ® NaCl + H2O equation and determines the molarity of NaOH solution by performing a titration using 0.100 M HCl. The experiment began by measuring 25mL of HCl into an Erlenmeyer flask. Then we measured 50mL of an unknown concentration of NaOH and filled till the top of a Burette. We added three drops of phenolphthalein indicator in the HCL solution. To start the experiment we placed the HCL under the burette of NaOH solution and opened and closed the stopcock of the burette. Till a light pink color occur, this meant that all the HCl solution was dissolved in NaOH. In trail one, two and three, the solution gave a light pink color, which was perfect. We observed that the change of the color will occur by doubling the initial burette reading. However, our prediction was incorrect, because in trail 4 the solution was overshot, which gave a dark pink color. The solution was overshot, due to times limitation, as we rushed to finish the experiment. In trails 1, 2 and 3, the volume that was needed to neutralize the HCl solution, was 13mL.But in trail 4, it was 12.3mL, which was overshot. After these observation and calculation, the molarilty was determined by first finding the concentration of the NaOH solution using the titration formula: C1 Ã- V1 = C2 Ã- V2

M

0.100 M Ã- 25mL = C2 Ã- 50mL

C2 =

C2 = 0.05 M

After finding the concentration, we need to find the mol of NaOH solution using:

0.05 M =

n = 0.05 M Ã- 50mL = 2.5 mols

Finally, using the mols and volume of NaOH solution, the molarity can be determined by using its rule:

M= = 50 M

50 M is the molarity of a NaOH solution by performing the titration using 0.100 M HCl.

Errors and Improvements

There were systematic and random errors in this experiment that affected the results. In this experiment, we did four trials in total. All three trials were perfect and had a light pink color .However; the fourth trial became overshot, and had a dark pink color. Trial four was overshot due to time limitation, as we rush to do finish it. We opened the stopcock and NaOH solution was flowing quickly in the HCl solution that is another reason for the solution to become overshot. Another error was that we didn't do enough trails. To become accurate and exact trials should be made, to improve our experiment. In all our four trails we weren't concentrating as much, as we rushed more on the last trail. To improve our experiment we should concentration and wait for the NaOH solution to completely dissolve in the HCl. We also wasted a lot of NaOH solution, as we started from 0 twice, we should start from the previous number, that the NaOH solution was completely dissolved in HCl solution. Also, we wasted the HCl solution, when we quickly poured it and spilt about 5mL of the 25mL solution. Random errors affected the results, as it is all based on calculation. However the systematic errors did affect the results too, observation and collected data. To improve all these errors, we should concentration, not rush and be patient, to allow the accuracy and completion of the reaction.

Conclusion

This lab report investigates a balanced equation of HCl + NaOH ® NaCl + H2O. It determined the molarity of a NaOH solution by performing a titration using 0.100 M HCl. The molarity of NaOH is equal to 50 M, According to the calculation. We found the molarity by using the concentration, molarity and titration formulas. Also, we used trials, to observe the changes in the reaction between NaOH and HCl solutions.

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