Experiment a5 evidence for chemical change answer key

Final Report

Exercise 1

CHEM 181 DL1 Observations of Chemical Changes

I would drop in some hydrochloric acid and see if the household product fizzes and releases gas. If so, it most likely has sodium bicarbonate in it.

1. Suppose a household product label says it contains sodium hydrogen carbonate (sodium bicarbonate). Using your results f rom Data Table 1 as a guide, how would you test this material f or the presence of sodium bicarbonate?

AgNO3 (aq) + NaOH (aq) ------> AgOH (s) + NaNO3 (aq)

2. Write the chemical equation for the reaction in well A6.

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This reaction occurred in A1 I believe. That was the only reaction that caused any type of fizzing or gas, which would be the CO .

3. One of the reactions you observed resulted in these products: NaCl + H O + CO (g)? What well did this reaction occur in? Describe how the observations for this reaction support your answer.

2 2

2

I would believe that the substance is actually sodium hydroxide. Vinegar is made up to acetic acid, and according to my table, phenolphthalein does not cause acids to turn pink.

4. You found a sample of a solution that has a f aint odor resembling vinegar (an acid). To verif y that it is vinegar, you add a few drops of phenolphthalein. T he sample turns pink. From this result, can you assume this sample is indeed vinegar or contains some vinegar? Explain your answer using your results f rom Data Table 1.

I would assume that the fifth cookie does not have as much starch as the other cookies. The starch has not been removed completely, but is in a lesser quantity than the others.

5. While performing a starch test on several dif f erent cookie brands, f our tests result in the typical black color of starch presence, but the f if th gives a yellow-brown color. How might you interpret this result?

I would drop some of the hair tonic into some potassium iodide. If the substance begins to turn yellow, there is some lead in the tonic

6. 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 conf irm the presence or absence of lead in that hair tonic. Use your observations in Data Table 1 to describe a posit ive result f or this test.

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Data Table 1: Chemical Change Observations

I believe that this is the result of a chemical change. When the chemicals in the soda mix with the air while being poured into the glass, a gas is released. That gas causes the bubbles and fizzing.

7. Is cutting a cake into 8 pieces a chemical or a physical change? Explain your answer.

I believe that this is the result of a chemical change. When the chemicals in the soda mix with the air while being poured into the glass, a gas is released. That gas causes the bubbles and fizzing.

8. When a soda is poured into a glass and the soda bubbles, is it the result of a chemical change? Explain your answer.

In the second step, the reactant was the direct sunlight. This is a chemical reaction because it turned the color of dark brown similar to rust on the paper towel

9. In well B1, what was the reactant in the second step? Did this reactant cause a chemical change? Use your observations to support your answer.

Phenolphthalein acts well as an acid/base indicator. The reactions in A5 definitely support this statement. Sodium hydroxide is a base and hydrochloric acid is an acid. So, according to the table, phenolphthalein causes bases to turn pink and acids to remain clear.

10. T hink about how phenolphthalein acts as an acid/base indicator. Do your observations in well A5 support this or contrast what you would expect to happen? Explain your answer.

Well Chemical #1 (4 drops)

A1 NaHCO Sodium Bicarbonate3

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A2 IKI indicator

A3 KI Potassium Iodide

A4 NaOH Sodium Hydroxide

A5 HCl Hydrochloric Acid

A6 NaOH Sodium Hydroxide

B1 AgNO Silver Nitrate

B2 NH OH Aqueous Ammonia

Well Chemical #1 Appearance

A1

A2

A3

A4

A5

A6

B1

B2

Well Chemical #2 (4 drops)

A1 HCl Hydrochloric Acid

A2 Starch

A3 Pb(NO ) Lead(II) Nitrate

A4 C H O Phenolphthalein

A5 C H O Phenolphthalein

A6 AgNO Silver(II) Nitrate

B1 NH Aqueous Ammonia

B2 CuSO Copper(II) Sulfate

3

4

no color, liquid

no color, liquid

no color, liquid

no color, liquid

no color, liquid

no color, liquid

no color, liquid

no color, liquid

3 2

20 14 4

20 14 4

3

4

4

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Well Chemical #2 Appearance

A1

A2

A3

A4

A5

A6

B1

B2

Well Observations

A1

A2

A3

A4

A5

A6

B1 Observation 1:

+ Absorb in paper towel and expose to sunlight Observation 2:

B2

no color, liquid

no color, liquid

no color, liquid

no color, liquid

no color, liquid

no color, liquid

no color, liquid

light blue

No color change, bubbling and fizz ing occurred

blue-black color

yellow

Became bright pink

No Change

light brown, black starches

Became white and cloudy

Became a brown, rusty color

blue

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Exercise 2

Well Chemical Change (Yes/No)

A1

A2

A3

A4

A5

A6

B1

B2

Yes

Yes

Yes

Yes

No

Yes

Yes

Yes

For the magnesium, both reactions produced a chemical change, resulting in the metal burning and turning to ash. The main difference in the two reactions came down to burning it. When directly over a flame, the magnesium bursts into a bright white light, whereas in the test tube it just glowed red and turned into ashes.

1. Describe the similarit ies and/or dif f erences between heating and burning the magnesium metal. Did either heating or burning produce a chemical change? Explain your answer using the observations collected in Data Table 2.

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I did not observe any differences between the heating and burning of the zinc. Both methods caused the zinc to heat up and melt into a liquid. Even when I kept the zinc over the flame after melting, no type of chemical reaction occurred.

2. Describe the similarit ies and/or dif f erences between heating and burning the mossy zinc metal. Did either heating or burning produce a chemical change? Explain your answer using the observations collected in Data Table 2.

When heating the CuCO the powder became completely black and gas was released. There was no reaction after that. When burning the chemical, the powder still turned black but (I assume) the gas that was released caused the flame to glow bright blue.

3. Describe the similarit ies and/or dif f erences between heating and burning the Cu(NO ) . Did either heating or burning produce a chemical change? Explain your answer using the observations collected in Data Table 2.

3 2

3,

The heating and burning of Cu(NO ) was exactly the same, other than the addition of the glowing flame when heated.

4. Describe the similarit ies and/or dif f erences between heating and burning the CuCO . Did either heating or burning produce a chemical change? Explain your answer using the observations collected in Data Table 2.

3

3 2

In this experiment, I learned that chemicals react in many ways when exposed to different things. Whether it is mixing two chemicals together or setting one on fire, the reactions differ based on the method that chemical was tested. I also learned that these chemical reactions could be very helpful when trying to identify the chemical makeup of items. You can learn exactly what a product might be made out of from watching the reaction it has with heat, air, or water.

5. How would you describe the dif f erences between heating and burning? Use your experiences in the experiment to describe these dif f erences.

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Data Table 2: Heating and Combustion

The only chemical that has a physical change when heated was the mossy zinc. It melted and boiled in the test tube, but did not burn or change in color.

6. Which of the four chemicals that was heated produced a physical change? Support your answer with observations made and recorded in Data Table 2.

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Chemical Initial Observations

Mg

Zn

CuCO

Cu(NO )

Chemical Heating Observations

Mg

Zn

CuCO

Cu(NO )

Chemical Burning Observations

Mg

Zn

CuCO

Cu(NO )

small, silver, shiny

large, rock-like, silver

3 fine sea-for green powder

3 2 salt-like blue crystals, compact

glowed bright red and became a white ash

melted into liquid

3 turned black

3 2 Melted and turned green, lots of fizz ing and gas released, then turned black

Glowed red, then turned into a bright white flame, then turned into ash

Melted into a liquid, glowed red

3 The flame glowed blue and the powder turned black

3 2 The flame glowed green, the crystals bubbled and turned black

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