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Acids And Bases: Titrations, Reactions, And Standardizations

Acids & Bases:
Reactions, Standardizations, & Titrations
Experiments 21 & 22





Experimental Overview:

The procedure for this experiment was carried out as instructed in the laboratory manual, Experiments in General Chemistry, 4th ed., S.L. Murov, Experiment 21, Acids and Bases: Reactions and Standardizations, and Experiment 22, Acids and Bases: Analysis. There were modifications made by the instructor to dilute the 6M NaOH to 0.1M in 300mls instead of 500mls in Part B of Experiment 21.

One objective for performing these two experiments was to observe qualitatively the reactions between common acids, bases, and the indicators phenolphthalein, methyl orange, bromothymol blue, and red cabbage extract. Another focus of this experiment was to perform a standardization of sodium hydroxide solution using the titration technique with potassium hydrogen phthalate. By titrating the standardized NaOH, determine the percent by mass of acetic acid in an unknown vinegar solution as well as determine the molecular mass of an unknown acid.

Background Information:

When an acid such as HCl and base such as NaOH are mixed with each other they neutralize and produce salts and react as follows:

HCl + NaOH „³ NaCl + H2O + Heat

Heat can be quantitatively measured using a thermometer as a result of the reaction forming water.
Other times, combining an acid such as HCl with a base such as Na2CO3 will result in the following:

2HCl(aq) + Na2CO3 (aq)„³ 2 NaCl + CO2 (g) + H2O (l)

Another unique property of acids and bases are their high reactivity with certain metals. Often their reactions will often be violent.

NaOH + Al(s) + „³ AlO (s) + H2 (g) + Na+ (aq)

Chemical indicators of acids or bases work because their molecules change shape in the presence of ions. The following indicators were used in this lab:
Methyl Orange is often used as an indicator for strong acids. In the presence...