COMMON-ION EFFECT AND BUFFER

M. MALATE1 and K. GINO2 1, 2 DEPARTMENT OF FOOD SCIENCE AND NUTRITION, COLLEGE OF HOME ECONOMICSUNIVERSITY OF THE PHILIPPINES, DILIMAN, QUEZON CITY 1101, PHILIPPINES DATE SUBMITTED: 23 FEBRUARY 2016DATE PERFORMED: 17 FEBRUARY 2016

ANSWERS TO QUESTIONS (Cambria 11, all caps, bold)

1. Account for the differences in color of solutions 1 and 2 after adding methyl orange indicator

After adding methyl orange to solution 1 it turned salmon pink and in solution 2 it turned to yellow

2. Account for the differences in color of solutions 3 and 4 after adding phenolpthalein indicator

After adding phenolphthalein to solution 3 and 4 it turned dark pink.

3. Which causes a larger change in pH, addition of 3 drops 1.0M HCl (or three drops of 1.0M NaOH) to solutions 1,2,3 or 4? Explain.

Based from the data obtained, addition of 3 drops of 1.0 M HCl caused a greater pH change in solution 1 and 3. It showed drastic change in color and a higher gap in pH reading. This is because the solution 1 and 3 are not buffer solutions. They do not have the capacity to counteract additional stress.

4. Compare the different methods of determining pH: visual indicators, pH meter and calculations. Compare the accuracy of the three methods employed.

Visual indicators include litmus paper and liquid indicators. pH is determined through looking at the color and comparing it to the standard color with corresponding pH. This method is less accurate to using pH meter and calculations. pH meter measures the voltage produced by the solution and uses the difference in voltage to determine the pH. This somehow identifies the concentration of hydrogen ions. Its accuracy however depends on if it is properly calibrated. pH calculation gives the expected pH of the solution based from the concentration of the solutions.

5. What are the possible sources of errors and their effect on the calculated parameters? Rationalize.

The possible errors are could be the solution preparation, not properly calibrated pH meter and also personal errors like prejudice. If the solutions were not properly prepared it will lessen or add the concentration of the solutions changing the pH. If the pH meter is not properly calibrated then the readings would not be accurate and if the numbers are constantly jumping from one number to another, personal preference will affect the values you chose for the data.

REFERENCES (CAMBRIA 11, ALL CAPS, BOLD) [1]Woodford, C. (2015). pH meters. Retrieved from EXPLAINTHATSTUFF: http://www.explainthatstuff.com/how-ph-meters-work.html

[2]

Petrucci, R., Herring, F., Madura, J., & Bissonnette, C. (2010). General Chemistry. Juron, Singapore: Pearson Education South Asia PTE.LTD.