Base and Cm3
4.3 Exercise 4 - Titrations and indicators
1. 20 cm3 of methanoic acid (Ka = 1.8 x 10-4 moldm-3) of concentration 0.10 moldm-3 is titrated against sodium hydroxide of concentration 0.05 moldm-3. a) Calculate the pH of the solution: i) initially ii) after 10 cm3 of the alkali has been added iii) after 20 cm3 of the alkali has been added iv) after 30 cm3 of the alkali has been added v) after 50 cm3 of the alkali has been added b) Sketch a pH titration curve to show this reaction c) Explain why the pH at the end-point is greater than 7.
2. Calculate the pH after the following solutions are mixed together: a) 15 cm3 of 0.1 moldm-3 HCl and 10 cm3 of 0.1 moldm-3 NaOH b) 10 cm3 0.1 moldm-3 HCl and 15 cm3 of 0.1 moldm-3 NaOH
3. Sketch pH curves for the following titrations: a) 20 cm3 0.10 moldm-3 NH3 against 0.1 moldm-3 HCl b) 20 cm3 0.10 moldm-3 NaOH against 0.2 moldm-3 HCl c) 20 cm3 0.10 moldm-3 CH3COOH against 0.06 moldm-3 NaOH d) 20 cm3 0.10 moldm-3 CH3COOH against 0.15 moldm-3 NH3
4. Given the following pKIn values:
| |Indicator |pKIn | |
| |Methyl red |5.1 | |
| |Phenolphthalein |9.3 | |
State, with a reason, which of the indicators would be suitable for each of the titrations in question 3.
http://sat.collegeboard.org/register/sat-us-dates http://www.readmanga.eu/manga/4513/Sweety-Gem/3/55 http://www.paked.net/higher_education/hec_university_rankings.htm
1. 20 cm3 of methanoic acid (Ka = 1.8 x 10-4 moldm-3) of concentration 0.10 moldm-3 is titrated against sodium hydroxide of concentration 0.05 moldm-3. a) Calculate the pH of the solution: i) initially ii) after 10 cm3 of the alkali has been added iii) after 20 cm3 of the alkali has been added iv) after 30 cm3 of the alkali has been added v) after 50 cm3 of the alkali has been added b) Sketch a pH titration curve to show this reaction c) Explain why the pH at the end-point is greater than 7.
2. Calculate the pH after the following solutions are mixed together: a) 15 cm3 of 0.1 moldm-3 HCl and 10 cm3 of 0.1 moldm-3 NaOH b) 10 cm3 0.1 moldm-3 HCl and 15 cm3 of 0.1 moldm-3 NaOH
3. Sketch pH curves for the following titrations: a) 20 cm3 0.10 moldm-3 NH3 against 0.1 moldm-3 HCl b) 20 cm3 0.10 moldm-3 NaOH against 0.2 moldm-3 HCl c) 20 cm3 0.10 moldm-3 CH3COOH against 0.06 moldm-3 NaOH d) 20 cm3 0.10 moldm-3 CH3COOH against 0.15 moldm-3 NH3
4. Given the following pKIn values:
| |Indicator |pKIn | |
| |Methyl red |5.1 | |
| |Phenolphthalein |9.3 | |
State, with a reason, which of the indicators would be suitable for each of the titrations in question 3.
http://sat.collegeboard.org/register/sat-us-dates http://www.readmanga.eu/manga/4513/Sweety-Gem/3/55 http://www.paked.net/higher_education/hec_university_rankings.htm