Acid Base Titration s1

Acid Base Titration

Titration is a common laboratory technique to determine the concentration of substances in a solution. It is very easy to use and is quite economical as well. A known volume of a sample to be analyzed is often placed in an Erlenmeyer flask for easy mixing. The solution in a buret is known as the titrant and is added drop by drop to the solution. These 2 solutions could be reversed and the titration will still work. TO help identify when the reaction is complete, an appropriate indicator is chosen. The indicator must have a dramatic colour change. Indicators used in titrations include:

INDICATOR ACIDIC BASIC Litmus Red Blue Methyl orange Red Yellow Bromothymol blue Yellow Blue Phenolphthalein Colourless Red

The point at which the indicator changes colour is called the endpoint. This is the point at which the titrant and the solution have completely reacted and neutralized one another. This is + - the point at which the number of moles of H3O and OH are equivalent (so it is also known as the equivalence point). This is the first point at which the colour remains stable after the addition of titrant.

Requirements for a titration: 1) spontaneous - chemicals must react on their own without a continuous addition of energy 2) fast - chemicals reactant instantaneously when mixed 3) quantitative – the reaction must be more than 99% complete and easily visible 4) stoichiometric – there is a single, whole number ratio of products and reactants

Titration experiments are often repeated 3 times to ensure precision and accuracy.

Example of a titration experiment:

Quality control technicians often check samples of their product to ensure that guidelines are met. A sodium hydroxide solution may be titrated with acetic acid to determine the concentration of the strong base. The reaction is as follows:

NaOH (aq) + HCH3COO (aq)  HOH (l) + NaCH3COO (aq)

If 3.15 mL of sodium hydroxide are titrated by an average of 27.6 mL of 0.250 M acetic acid, what is the concentration of the sodium hydroxide solution?

Answer: mol H+ (aq) = 0.250M x 0.0276 L = 0.0069 mol

To titrate the number of moles of H+ = number of moles of OH-

Thus n(OH-) = 0.0069 mol V (NaOH) = 3.15 mL = 0.00315 L

C = n/V = .0069mol / 0.00315 L = 2.19 M Work : 1) Calculate the volume of a 0.200 M KOH solution that is needed to neutralize 25.00 mL of a 0.115 M HCl solution. (14.4 mL)

2) An average volume of 57.50 mL of 0.200 M lithium hydroxide is required to neutralize 25.0 mL samples of HBr (aq). What is the HBr concentration? (0.460 M)

3) An average of 86.19 mL of 0.765 M sodium hydroxide is required to neutralize 30.0 mL samples of HCl (aq). What is the concentration of the acid? (2.20 M)

4) Analysis shows that 9.44 mL of 0.050 M KOH is required to titrate 10.0 mL samples of sulfuric acid. What is the acid concentration? (0.024 M)

5) An average of 150.01 mL of 0.0974 M barium hydroxide is required to neutralize 10.0 mL of hydrochloric acid. What is the concentration of the HCl (aq)? (2.92 M)