Questions on pH Indicators

Pages: 1 (611 words) Published: November 3, 2014

ANSWERS TO QUESTIONS
1. Account for the differences in color of Solution 1 and 2 after adding methyl orange indicator. After adding methyl orange indicator in Solution 1, the color turned to light red which has a pH value ranging from 3.1 to 4.5 while in Solution 2, the color turned to yellow which has a pH value greater than 4.5. This indicates that Solution 1 is more acidic than Solution 2. 2. Account for the differences in color of Solution 3 and 4 after adding phenolphthalein indicator. After adding phenolphthalein indicator in Solution 3, the color of the solution turned to purple while in Solution 4, the color of the solution turned to pink. This indicates that the solutions are basic. The color of Solution 3 is darker than that of Solution 4 which indicates that Solution 3 is more basic than Solution 4. 3. Which causes a larger change in pH, addition of 3 drops of 1.0 M HCl (or 3 drops of 1.0 M NaOH) to Solution 1, 2, 3, or 4? Explain. In Solutions 1 and 2, addition of 3 drops of 1.0 M HCl caused a larger change in pH, based on the pH reading from the pH meter, than the addition of 3 drops of 1.0 M NaOH. In Solution 1, since the solution is acidic, adding more acid in the solution increases the concentration of H+, thus becoming more acidic, which is also the case in Solution 2. In Solution 3, addition of 3 drops of 1.0 M NaOH caused a larger change in pH, since the solution is basic adding more base increases the concentration of OH-, thus becoming more basic. In Solution 4, addition of 3 drops of 1.0 M HCl caused a larger change in pH. Although there are changes in the pH in the solution, it is still minimal since the solutions are buffers, thus it resists a drastic change in pH.4. Compare the different methods of determining pH: visual indicators, pH meter, and calculations. Compare the accuracy of the three methods employed. In visual indicators, pH is determined by comparing the change in color of the solution after adding different indicators...

References: [1] Jones, A., Clemmet, M. et al. (1999). Access to chemistry. United Kingdom: The Royal Society of Chemistry.
[2] Petrucci, R., Herring, S. et al. (2001). General chemistry: Principles and modern applications (10th Ed.). Canada: Pearson Canada, Inc.
[3] Prichard, E. (2003). Measurement of pH. United Kingdom: The Royal Society of Chemistry.
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