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Chemistry: Observation Of Chemical Changes

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Category: Science

Autor: jon 08 March 2011

Words: 2762 | Pages: 12

Experiment 1: Observations of Chemical Changes

Purpose: To observe the macroscopic changes that occur in chemical reactions and attempt to interpret the microscopic changes of the atoms and molecules that allow for the macroscopic changes to happen; and to associate these chemical properties with household products.

Also, it is to learn the importance of how to separate mixtures into their component substances by solubility.

Procedure: Before starting with the official experiment, it was important that I dilute the chemicals in the Auxiliary Chemical Bag to change the chemicals to the molarity needed for the experiment. First I had to dilute the Hydrochloric Acid that had a molarity of 6 to a molarity of 1. So, I took the 24-well plate and placed 10 drops of distilled water into well A1. I then proceeded to take the Hydrochloric Acid from the Auxiliary Chemical bag that had 6M and carefully added 2 drops to well A1. Next, I stirred the water and the HCl in the well with a toothpick to ensure that the HCl was diluted as much as possible. Then, taking a pipet labeled Hydrochloric Acid, I sucked up the diluted HCl and placed the pipet upside down in a well plate for standby until needed for the experiment. For Ammonia and Sodium Hydroxide, I followed the same procedure that I did for HCl with the exception that the diluted solution for Ammonia was made in well A2 and the diluted solution for Sodium Hydroxide was made in well A3.

Now that the diluted solutions have been created and contained, I must move on the main experiment. In order to conduct this experiment, I must have a 96-wellplate, the diluted solutions in the pipets that contain them that I just created, a piece of white paper, a piece of black paper, and the chemicals from the Observation of Chemical Changes Experiment Bag.

For the following combinations of chemicals, and using a different well of the 96-well plate for each combination, I must place 2 pipet drops of the first chemical in one well and then add 2 drops of the second chemical, unless it is stated otherwise below. After combining the chemicals, I must observe the mixture against white and dark backgrounds by slipping white and black paper underneath the well plate. For ever reaction, I wrote down the chemical combination, the well number, and my observations of the chemical reactions against the white and dark backgrounds. The combinations are as follows:

a) NaHCO3 (sodium bicarbonate-baking soda) and HCl (hydrochloric acid)*

b) HCl* and BTB (Bromthymol blue)

c) NH3 (ammonia, a base) and 1 drop of BTB

d) HCl* and FDC Blue Dye#1

e) FDC Blue Dye#1 and NaOCl (sodium hypochlorite). Observe, then add 1drop of HCl.

f) NaOCl (sodium hypochlorite) and KI (potassium iodide). Observe, then add 1 drop of starch (shake well before using).

g) KI and Pb(NO3)2 (lead nitrate)

h) NaOH (sodium hydroxide – a base)* and phenolphthalein.

i) HCl* and phenolphthalein

j) NaOH and AgNO3

k) AgNO3 and NH3(ammonia)*

l) NH3* and CuSO4(Copper(II)sulfate)

After placing all the liquids in the well, I made sure to use a toothpick to stir up the chemical and recorded as many observations as I could.

Data Tables: (These data tables include observations)

DATA TABLE 1:

Chemicals Well# (Observations)

Chemical Reaction w/White Paper (Observations)

Chemical Reactions w/Black Paper

NaHCO3 (sodium bicarbonate-baking soda) and HCl (hydrochloric acid)* A1 Clear bubbles; bubbles did not fizz and continued to occur until all of the liquid from the well was gone. Homogeneous. Bleach-like smell Clear bubbles; bubbles did not fizz and continued to occur until all of the liquid from the well was gone. Homogenous. Bleach-like smell

HCl* and BTB (Bromthymol blue) B1 Turned orange, homogenous Turned into an amber color, homogenous

NH3 (ammonia, a base) and 1 drop of BTB C1 Turned dark blue, but did not leave a stain on the toothpick; homogenous Still resembled a dark blue, NOT black; did not leave stain on toothpick; homogenous

HCl* and FDC Blue Dye#1 D1 Turned dark blue, stained toothpick with dark blue color; homogenous Seemed to be entirely black; homogenous

FDC Blue Dye#1 and NaOCl (sodium hypochlorite). Observe, then add 1drop of HCl.** E1 Turned dark blue, but with time it turned into an aqua blue; stained toothpick with aqua blue; homogenous Looked nearly black at first, but as it grew lighter, it looked more grey; homogenous

NaOCl (sodium hypochlorite) and KI (potassium iodide). Observe, then add 1 drop of starch (shake well before using). ** F1 Turned yellow; homogenous Seems like a clear brownish color, but is NOT amber like; with time it grew a lot lighter; homogenous

KI and Pb(NO3)2 (lead nitrate) G1 Bold yellow, seems solid and cloudy; with time created white/yellowish solids at the bottom of the well; precipitated Bold yellow, seems solid and cloudy; with time created white/yellowish solids at the bottom of the well; precipitated

NaOH (sodium hydroxide – a base)* and phenolphthalein H1 Pink/Dark Fuchsia color; homogenous Still resembled a dark fuchsia; homogenous

HCl* and phenolphthalein A2 CLEAR; no bubbles; homogenous CLEAR; no bubbles; homogenous

NaOH and AgNO3 B2 Bold brown, chocolate milk color(?), seems solid and cloudy; with time create white/brownish solids at bottom of the well; precipitated Bold brown, chocolate milk color(?), seems solid and cloudy; with time create white/brownish solids at bottom of the well; precipitated

AgNO3 and NH3(ammonia)* C2 Clear Clear; seems to be some small bubbles/solids at the bottom

NH3* and CuSO4(Copper(II)sulfate) D2 Cloudy aqua blue, seems solid and cloudy; with time created white/blue-is solids at bottom of the well; precipitated Cloudy aqua blue, seems solid and cloudy; with time created white/blue-ish solids at bottom of the well; precipitated

**See Data Table two for adding the extra chemicals

DATA TABLE 2:

Chemicals Well#

(Observations)

Chemical Reaction w/White Paper (Observations)

Chemical Reactions w/Black Paper

FDC Blue Dye#1 and NaOCl (sodium hypochlorite). Observe, then add 1drop of HCl.** E1 Turned the blue into a sudden green which turned into yellow ; Homogenous Looks like a light yellow

NaOCl (sodium hypochlorite) and KI (potassium iodide). Observe, then add 1 drop of starch (shake well before using). ** F1 Turned yellow brown and then after stirring with a toothpick turned BOLD BLACK Looks BOLD BLACK

DATA TABLE 3:

Household Product Well# (Observations) Chemical Reaction w/White Paper (Observations)Chemical Reaction w/Black Paper

Windex + BTB A12 Super Dark Blue Looks nearly black

Palmolive Antibacterial Dish Liquid + BTB B12 Turned bold yellow Amber

Clorox Clean w/Bleach + BTB C12 Dark Blue Dark Blue

Calculations: (there are none required for this experiment)

Questions:

Questions within Procedure:

b. Bromthymol blue is one of many acid-base indicators. What color do you observe?

I observed an orange/amber color change that was homogenous in the chemical reaction.

c. What color do you observe? Record the colors you expect when BTB reacts with an acid and with a base.

I observed a dark blue color change that was homogenous in the chemical reaction. After the previous chemical combination, I am under the impression that when Bromthymol blue is mixed with an acid, it turns into an orange color and when mixed with a base it turns into a heavy, dark blue.

f. Test various foods (fruits: apples, bananas, etc.; vegetables: potatoes, corn, etc.; crackers, cookies, etc.) to confirm the presence or absence of starch.

It is to my understanding after testing with various foods, that food containing starch will turn yellow-brown to black.

g. Describe the precipitate formed:

The chemical combination made the mixture turn into a bold yellow that seemed to be solid and cloudy. The precipitate that forms was white/yellowish solids that formed at the bottom of the well; clearly heterogeneous.

h. What color do you observe?

I observed a pink/dark fuchsia color that was homogenous.

i. What color do you observe? When reacting phenolphthalein with an acid, what color change do you expect? What color change do you expect with a base?

The color I observed when mixing HCl and phenolphthalein was a clear homogenous mixture. I am under the impression that when phenolphthalein is mixed with an acid the mixture it remains clear, but when mixed with a base it turns pink/fuchsia.

k. Absorb this mixture onto a scrap of paper towel and expose it to intense light from a light bulb or the sun. Be patient and you will observe a change. Record your observation.

The mixture turned into a dark brown, and after leaving it for a few hours, it seemed as though the chemicals had separated on the paper.

Questions and Problems at End of Experiment:

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?

a. I would test it with multiple chemicals in separate well plates to see if they react the same way it did in Data Table 1. For example, one plate would have HCl + Sodium Bicarbonate and if it created clear bubbles and a bleach-like smell (which we know is the release of CO2) that would be one way of proving it. We could also add it to Bromthymol Blue and depending on the color it changed we would get a better understanding. Likewise, I would test it phenolphthalein to see if it changed into a pink/dark fuchsia color or if it remained the same. And perhaps I would also test it with Silver Nitrate to see if turned white and cloudy that would cause some precipitates to occur. In the end, the best way to tell would be doing all of these tests to ensure our evidence is correct.

B. You know what color phenolphthalein and Bromthymol 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 Bromthymol 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?

DATA TABLE 3:

Household Product Well# (Observations) Chemical Reaction w/White Paper (Observations)Chemical Reaction w/Black Paper

Windex + BTB A12 Super Dark Blue Looks nearly black

Palmolive Antibacterial Dish Liquid + BTB B12 Turned bold yellow Amber

Clorox Clean w/Bleach + BTB C12 Dark Blue Dark Blue

I would interpret my data observations that the Windex and Clorox Clean w/Bleach are both heavy bases, and that the Palmolive Antibacterial Dish liquid is an acid. I am surprised at this data, because I would've assumed that the bleach and Windex are the heavy acids since they do heavy amounts of cleaning and the Palmolive antibacterial dish liquid would've been a base so as to not damage skin as much as an acid could. However, now that I have this data collected, I am interpreting the results that the reason Windex and Clorox are heavy bases is because if they were acids, whatever surface they were used to clean would become damaged. And the reason that the Palmolive Antibacterial Dish liquid is an acid is so that it will be able to take as much food grease and grime off as possible, if not all.

C. You found a sample of a solution that has a faint odor resembling vinegar. You are verifying that it is indeed vinegar and you add a few drops of phenolphthalein. The sample turns pink. What assumption can you make about this sample?

a. We know that vinegar is an acid. Phenolphthalein ONLY turns pink when it is mixed with a BASE. This means that the sample of solution we thought was vinegar is NOT vinegar.

D. While performing a starch test on several different cookie brands, four tests result in the typical black color of starch-presence, but the fifth gives a yellow-brown color. How might you interpret this result?

a. I would interpret the result that the fifth cookie does not contain as much starch as the other four cookies. In my observations in Data Table 1, I noticed that the starch actually turned slightly yellow-brown and it didn't turn fully black until I had stirred them thoroughly with a toothpick. Therefore, I would assume that the first four cookies have A LOT of starch whereas the fifth cookie clearly has far less than the rest, but still contains some amount of starch.

E. You decided to investigate if the new wave of VitaminWater is pH neutral: neither too acidic nor too basic. Using BTB (Bromthymol blue), you select five flavors of VitaminWater to test. Three of the flavor-samples turn a murky green, indicating the likelihood of acid/base balance. Of the two remaining, one turns slightly yellow, while one remains blue. What can you assume about the acid/base content of these particular flavors of VitaminWater?

a. We have interpreted our data, so far, to be that when Bromthymol Blue is mixed with an acid it will turn yellow and that if it is mixed with a base it will turn/remain blue. I must interpret that the Vitamin Water that remained blue is more heavily weighted in its bases than its acids. Likewise, we can assume that the Vitamin Water that turned yellow is more heavily weighted in its acids that its bases.

F. You have read that a new brand of hair tonic is supposed to contain lead (an ingredient in Grecian Formula). Devise a simple test to confirm the presence of absence of lead in that hair tonic.

a. Well since we know that when lead, or at least lead nitrate, is mixed with potassium iodide it will turn into a bold yellow color, in which the mixture looks solid and cloudy and will eventually precipitate a white/yellowish solid, the best test I can come up with the current knowledge is as follows: I would mix an even amount of the hair tonic with potassium iodide and wait and see if a similar reaction occurred. If it turned into a bold yellow or formed a precipitate or both, I would assume that lead is indeed within the hair tonic. If nothing or something entirely different happened, I would assume that there is no lead in the tonic.

Conclusion:

The objective of this lab was to observe the macroscopic changes that occur in chemical reactions, and attempt to interpret the microscopic changes of the atoms and molecules that allow for the macroscopic changes to happen. This taught me the importance of interpreting acids and bases, how the same chemical can have many different kinds of reactions with different chemicals and how to interpret what each kind of reaction could mean.

It also forced me to think critically as to what microscopic changes were occurring for these macroscopic changes to occur. To the extent of my knowledge of chemistry, which will include Chapter 2 of our chemistry book, my best analysis is that charges of these chemicals and their placement on the periodic table (metal, non-metal, alakali,alkaline, etc) have an effect on these chemical reactions. To me, this analysis made the most sense because the only way for chemicals to combine and rearrange is when they are able to share electrons, which in the end, the product of the chemical reaction must create chemical formulas that allow for the products to be balanced. However, since I do not know how to write and interpret chemical formulas, I cannot prove this calculation wise.

It also taught me the importance of ratios within an experiment. If one chemical is greater in ratio than another chemical, an entirely different reaction would occur, or even how the reaction occurred could've been different..

Also, it is to learn the importance of how to separate mixtures into their component substances by solubility. If the molarity of Hydrochloric acid, or Ammonia, or Sodium Hydroxide were greater than the rest of the chemical substances, I believe that the reactions would've been either much different than what we have collected in our data OR the reaction would be far more intense.

In the end though, we must also account for error and uncertainty in our experiment. The first possible error/uncertainty that I can think of is that there is no such thing as the perfect drop. Some drops seem to be bigger and others seem to be smaller. As a result, it is possible that the chemical reactions were not a perfect 1:1 ratio. This could affect the chemical reaction in a number of different ways, such as a more violent reaction or even no reaction at all. However, since our drops and mixtures were a very small amount I also assume that any errors via our drop ratios are also a very small. Another error, I must confess, is that I did not and could not find a piece of solid black paper. Instead, I used a piece of black fabric instead. Since it was entirely different material that I used to see the effects of a dark background, it could affect the experiment in that the fabric allowed for a lot more light particles to go through and make contact with the chemical mixtures. This could affect the reaction in the sense that, as we saw with the Silver Nitrate and Ammonia that we left out in the sunlight for a while, it could affect the chemicals that are sensitive to light and cause for an entirely different reaction to occur or even separate the chemicals all over again.

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