Ammonium hydroxide solution

In the strong acid-weak base titration, 0. 1 M ammonium hydroxide ( NH4OH ) was titrated with 0. 1 M hydrochloric acid ( HCl ). 2-3 drops of phenolphthalein were added as indicator into the conical flask which contains 25mL of hydrochloric acid. Ammonium hydroxide was then titrated slowly into the conical flask and the conical flask was swirled gently to ensure the reaction is reacted completely. The titration stops when the colour of the titrand changed from colourless to pale pink. The average titrant (29. 55 mL) of 0. 1 M of ammonium hydroxide was added into the conical flask.

By using screened methyl orange as indicator, the average titrant (26. 45 mL) of 0. 1 M of ammonium hydroxide was added to change the colour of the titrand from red to grey in conical flask. In weak acid-strong base titration, 0. 1 M sodium hydroxide ( NaOH ) was titrated with 0. 1 M acetic acid (CH3COOH). 2-3 drops of phenolphthalein as the indicator were added into the conical flask which contains 25mL of acetic acid. Sodium hydroxide was then titrated slowly into conical flask and the conical flask was swirled gently to ensure the reaction is reacted completely.

The titration stops when the colour of the titrand changed from colourless to pale pink. The average titrant (28. 60 mL) of 0. 1 M of sodium hydroxide was added into conical flask. By using screened methyl orange as indicator, the average titrant (2. 20 mL) of 0. 1 M of sodium hydroxide was added to change the colour of titrand from red to grey in conical flask. In experiment part II (A), pH titration curve in the strong acid-weak base titration indicate that the initial pH value of titrand is pH 1. 33 due to the strong acid, 0.1 M hydrochloric acid ( HCl ).

During titration, the pH value increases steadily but not significant due to the presence of buffer solution even when extra base was added. It increases to pH 2. 94 after 25. 00 mL of ammonium hydroxide was added. However, the pH value increases greatly from 3. 59 to 5. 99 when added extra 0. 50mL of ammonium hydroxide as shown in the graph 1.

The pH values increase slowly as extra ammonium hydroxide was continuously added. The equivalence point, which is the steepest point of graph, is pH 4.79 when ammonium hydroxide was added. In experiment part II (B), pH titration curve in the weak acid-strong base titration illustrates that the initial pH value of titrand is pH 2. 32 due to the weak acid, 0. 1 M acetic acid. Firstly, the pH value rises progressively and the presence of buffer solution which makes the curve slightly increases in steep. The changes in pH is small even when extra base was added.

It increases to pH 7. 00 after 26. 00 mL of sodium hydroxide was added. However, it rises rapidly when added another 0.50mL of sodium hydroxide which changes the pH from 9. 03 to 10. 08 as in the graph 1. 2, the equivalence point, which is the steepest point of graph, is pH 9. 915 when sodium hydroxide was added. The differences between the two titration curves The starting value of pH in strong acid-weak base titration is lower than the value in weak acid-strong base titration. The pH value of the equivalence point in strong acid-weak base titration is below 7. 00 whereas the pH value in weak acid-strong base titration is above 7. 00.

In the strong acid-weak base titration, which phenolphthalein was used as an indicator, the average titre to cause colour change in the indicator is 29. 55 mL. When the indicator is changed to screened methyl orange, average titre of 26. 45 mL of ammonium hydroxide was required to change the colour of the indicator from red to grey. However, based on Graph 1. 1, the volume of ammonium hydroxide added was 25. 70mL. The difference between the volume of ammonium hydroxide added when phenolphthalein was used as the indicator in acid-base titration and the titration curve is 3.85mL.

There is also a small difference of 0. 85 mL between screened methyl orange was used as the indicator in acid-base titration and titration curve. For the weak acid-strong base titration, phenolphthalein was added, the equivalence point obtained is 24. 20 mL. When screened methyl orange was added, it needed 4. 45 mL to change the colour from purple to grey green. However based on the result which recorded from the titration curve in graph 1. 2, the volume of sodium hydroxide added is 24. 75mL.

The slightly difference when phenolphthalein was added in acid-base titration and titration curve is 0. 55 mL, whereas it has a 20. 30 mL difference between screened methyl orange was added in the acid-base titration and titration curve. The causes of the slightly different between acid-base titration and titration curve is system errors and random errors. The Eye level is not perpendicular to the meniscus level of the burette when taking the reading which leads to the system error. Furthermore, the colour changes of the titrand were hard to be determined.

Thus, this cause the difference in the results. Other than that, different colour perspectives which differentiate by different people will also lead to inaccurate results. Overshot might happened during titration which cause inconsistency reading and results. Furthermore, water droplet remain in the burette after washing will lower the concentration of the titrant which lead to the inaccurate reading and results. [3] The colour change and pH range of the indicators: Indicators Colour change pH range Phenolphthalein Colourless to light pink 8.

3 – 10. 0 Screened methyl orange Red to grey-green 2. 9 – 4. 4 Phenolphthalein is not a suitable indicator in the strong acid-weak base titration because the range of colour change is at pH 8. 3 to 10. 0. However, the equivalence point of the titration is pH 5. 36 based on graph 1. 1. Ammonium hydroxide was added excessively as the equivalence point is off from the pH range. By changing the screened methyl orange for strong acid-weak base titration. It is more suitable to use as the indicator from red to grey green which is between pH 4.01 and pH 6. 71.

Compare to the phenolphthalein, screened methyl orange is much closer pH range which is 2. 9 to 4. 4. Thus, screened methyl orange is a more suitable compared to phenolphthalein. [5] On the other hand, screened methyl orange is not a suitable indicator in weak acid-strong base titration. Its pH range of colour change is at pH 2. 9 to 4. 4 from purple to grey green. However, the equivalence point of the titration is pH 9. 385 which will changed colour before the equivalence point of titration was reached.

By changing the phenolphthalein for weak acid-strong base titration, the colour changes from colourless to light pink which is between pH 7. 97 to pH 10. 80. In the equivalence point, pH 9. 385 locate in the range of pH 8. 3 to 10. 0. Thus, phenolphthalein is a more suitable compared to screened methyl orange. [5] Conclusion: According to this experiment, there are two ways to determine the average amount of volume of base needed to react in this acid-base titration which is the suitability of indicators and titration curves.

Suitable indicators can determine the equivalence points of the titration. Other than that, pH meter can be used to capture the pH values at every 0. 5mL interval when adding base into acid. A titration curve can be plotted by recorded data. In conclusion, screened methyl orange is more suitable indicator than phenolphthalein for strong acid-weak base titration. Contrastively, phenolphthalein is suitable indicator for weak acid-strong base titration. [6]