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Chemistry LabReportbuffer

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Introduction

Chemistry Lab Report PART 1 Aim: 1) To make up 100 cm3 of a buffer solution of pH 5.2 To make an appropriate buffer, the ratio of the volumes of the acid and its salt needs to be calculated. To find the volumes: The pKa value for 0.5 M ethanoic acid and 0.5 M sodium ethanoate is 4.76. To make the buffer pH 5.2: CH3COOH + H2O - CH3COO- + H3+O CH3COONa � CH3COO- + Na+ Using the equation previously stated: 5.2 = 4.76 - log (A-)/(HA) 10-0.44 = (A-)/(HA) 0.363 = (A-): (HA) Therefore, 100 x 0.363/1.363 = 26.6 � 0.1 cm3 acid (ethanoic acid) is required 100 - 28.46 = 73.4 cm3 � 0.1 cm3 salt (sodium ethanoate) is required Apparatus: 250 mL beakers, 50 cm3 burette Method: 1) Using a burette measure out 73.4 � 0.1 cm3 of sodium ethanoate. (Rinse the burette with water at regular intervals) 2) Then, using the burette measure out 26.6 � 0.1 cm3 of ethanoic acid. Add them 3) Then, measure the pH of the solution and compare it with the value needed. ...read more.

Middle

3) Add HCl to one of the beakers, and NaOH to the other, using two separate burettes. 4) First drop 0.1 cm3, then 1cm3 up to 5cm3 measuring the pH after each step and recording it in a table. 5) Then make two solutions, the first one should be 1/10 dilution, and for this 10cm3 of buffer solution is measured and then 90cm3 of distilled water measured out using a burette should be added to it. 6) The second will be a 1/100 dilution; for this 2cm3 of buffer solution is measured and 198cm3 of distilled water should be added to it. 7) Then, using a pipette measure out exactly 25cm3 of dilute buffer solution and place it in a small beaker. Repeat this so that there are four small beakers each containing 25cm3 of buffer solution. 8) Then, add HCl to one of the beakers, and NaOH to the other for each dilute buffer solution, using two separate beakers. 9) First drop 0.1 cm3, then 1cm3 up to 5cm3 measuring the pH after each step and recording it in a table. ...read more.

Conclusion

There was a great deal of fluctuation in the pH meter hence recordings were not accurate. Using better equipment such as pH probes, which have minimal systematic error, could solve this problem. Although, there was such a huge error, our main hypothesis can be proved. The trends give us a fair idea of the buffer capacity of the buffer solution. From graphs 1 and 2, we can clearly see, using the curve fit, that there is a very small change in the pH when small amounts of acid and base are added to it. Furthermore, the buffer solution acts better when small amount of acid are added to it, as compared to the addition of base. This is observed from all the 4 graphs. The curve is less steep when 0.5 M HCl solution and 1/5th diluted HCl solution is added to it, as compared to when 0.5 M NaOH and 1/5th diluted NaOH is added to it. Another reason for the error in the buffer capacity is that 0.5 M HCl and NaOH is added. If we had used 0.1 M HCl and NaOH, then fewer moles of the acid and base would have been added, thus allowing the buffer to act for a longer time. Zahoor Rahimtoola IBD Chem HL - 1 - ...read more.

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