Observations of Chemical Changes

Lab 1: Observations of Chemical Changes

Student:

Lab Partners: None

Date of Experiment: 6 June 2013

Location: My garage at home

Course Number: CHE111

Abstract: In the experiment, the objectives were to observe some properties of chemical reactions, as well as, to associate chemical properties with various household cleaning products.  While the microscopic reactions of individual atoms and molecules were not visible during this experimentation, physical and chemical changes were observed allowing a better understanding at the macroscopic level what changes chemicals undergo when combined with one another.  Chemical changes included various changes in color, the formation of precipitates, or the formation of gas bubbles from the different chemical combinations.

Experiment and Observation:  The first step of this experiment was to combine the prescribed chemicals listed in Data Table 1 (below) using a different well of the 96-well plate for each combination.  Two drops of each chemical were used in the combinations unless otherwise directed in the instructions.  Next, the mixtures were observed against white and dark backgrounds using a thick black and white paper.  This enabled the observation of the various color changes, the formation of precipitates, and as noted in the first chemical reaction, the formation of gas bubbles that occurred throughout the experiment and recorded below in Data Table 1.  In well B2, the combination of silver nitrate and ammonia created a cloudy liquid substance and when exposed to the intense light of a light bulb, a brownish/black ashy color with some precipitate formed on the paper towel.  

[pic 1]

The experiment continued with the testing of common household solutions in order to record their reactions with bromothymol blue (BTB).  The following household items were tested for observation and in support of answering lab question 2:

[pic 2]

Calculations and Error:  Calculations were not necessary in this lab experiment.  The largest source of error was most likely the equal distribution (two drops or one drop, when directed) of the chemical combinations into the different wells of the 96-well plate for observation.  

Discussion and Conclusion:  As previously stated, the microscopic reactions of individual atoms and molecules were not visible during this experimentation, but the physical and chemical changes were observed allowing a better understanding at the macroscopic level what changes chemicals undergo when combined with one another.  As the experimentation progressed, it became clear through observation that chemical reactions with acid-base indicators resulted in acids forming a yellow color, bases forming a blue color, and green for pH neutral combinations.  It was fun anticipating the various chemical and physical changes that occurred as the chemical combinations occurred in Data Table 1 as the combinations began to show these acidic and basic characteristics when combined with the acid-base indicators.  It was also interesting to observe the precipitates formed and ways to potentially test common household products used with various ingredients.

Questions:

A. Suppose a household product label says it contains sodium hydrogen carbonate (sodium

bicarbonate). How would you test this material for the presence of sodium bicarbonate?

If a household product label says it contains sodium hydrogen carbonate (sodium bicarbonate), I would be testing this material for the presence of baking soda.  By adding hydrochloric acid, I can test the product for the presence of sodium bicarbonate.  If bubbles are formed creating carbon dioxide, then I know the household product label is accurate.

B. You know what color phenolphthalein and bromothymol blue turn when testing an acid or a base. Use the empty pipet in the Auxiliary Supplies Bag to test several (at least 3) household items including household cleaning products with bromothymol blue. Rinse the pipet well before using it on the next household chemical. When finished with this experiment rinse the pipet well and return it to the Auxiliary Bag for use in future experiments. Name the items tested and record their results. What do these results mean?

Based off the observations in Data Table 2, the first three household items were of particular interest.  I tested Windex, Pine Sol, and Meyer’s all-purpose cleaner.  Meyer’s is advertised as an all-natural cleaning product which does match the results below.  Based off Data Table 2, Windex and Pine Sol are both acidic-based cleaners based off the color change to blue while the green color of Meyer’s indicates an acid-base balance.  This matches its label of containing naturally occurring ingredients and essential oils.