NAME ______________________________________________ LAB: EVIDENCE FOR A CHEMICAL CHANGE
OBJECTIVE: a) To identify and record data which relate chemical change and heat exchange.
THEORY:
Substances (elements or compounds) may be created by chemical change and may also undergo chemical change. When a substance (an element or a compound) is produced as a result of a chemical reaction, it is called a product of that reaction.
Some products of a chemical reaction may be solid (Solid products are called precipitates ). Other products may be molecular gases and bubble out of solution.
Soluble liquid products are difficult to “see”, but they (and insoluble liquid products) can be separated out of a mixture of substances, with some form of distillation. Distillation relies upon differences in boiling points to separate liquids.
Some products are soluble in water – and if the reaction were to occur in water, these products may be soluble ionic compounds and existing as (dissociated) hydrated cations and anions. These may be separated from the water with evaporation. Note, your college profs may not like the idea of un-bonded ions
(electrolytes) floating in the solution, being called “products”. However, it is a reasonable extension of term, given that the solid ionic salt can be obtained by evaporation and that, this ionic solid represents the new bonds.
Other products may be molecular compounds which are dissolved but not ionized or dissociated. Theses molecular species are whole molecules.
New bonds indicate a chemical reaction. One way of knowing that a chemical change has occurred is by observing that the physical properties of the product are different from those of the beginning reactant.
These physical properties may include, but are not limited to the melting point, density, solubility in water or alcohol ….
In this particular lab, we begin with a demonstration of copper metal and nitric acid, producing copper(II) nitrate (Cu(NO
3
)
2
), water, and various nitrogen oxides (essentially a mixture of nitrogen dioxide and nitrogen monoxide). I choose to demonstrate the reaction due to its hazards, in terms of the nitric acid and the poisonous nature of the nitrogen oxides. Your team will be provided with solution of copper(II) nitrate.

The solution will therefore contain Cu 2+
(aq)
and twice as many ions (NO
3
) 1-
(aq)
or rather, it will have hydrated ions of copper(II) and nitrate, in a 1:2 ratio.
Using this solution of copper ion, you will observe the sequence of changes that occur when it is involved in a series of different treatments. All of the reactions will take place in the same test tube. Look for evidence that a new substance is produced from each chemical change. Also, observe how the exchange of energy and chemical reactions are related.
This chemical conversion of one substance to another more desirable substance is what we speak of as recycling. The copper(II) nitrate solution used in this experiment is prepared originally from the element copper and nitric acid. After a number of steps the copper metal is recovered, ultimately. (Hence, we will be re-directing/re-arranging the electrons of the species involved …. making new bonds, in each step).
Recycling enables us to reuse scarce natural resources, such as copper and aluminum, by extracting the ions from compounds and converting those ions back into metal atoms. This is less expensive than mining, and when done properly, far less polluting.
This experiment has captured the minds of young chemists for years and years. Few have written about it with such wonder (and perhaps innocence) as a very young Ira Remsen.
Ira Remsen on Copper and Nitric Acid :
Ira Remsen (1846-1927) founded the chemistry department at Johns Hopkins University, and founded one of the first centers for chemical research in the United States; saccharin was discovered in his research lab in 1879. Like many chemists, he had a vivid "learning experience," which led to a heightened interest in laboratory work:
While reading a textbook of chemistry I came upon the statement, "nitric acid acts upon copper." I was getting tired of reading such absurd stuff and I was determined to see what this meant. Copper was more or less familiar to me, for copper cents were then in use. I had seen a bottle marked nitric acid on a table in the doctor's office where I was then
"doing time." I did not know its peculiarities, but the spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words "act upon" meant. The statement "nitric acid acts upon copper" would be something
more than mere words. All was still. In the interest of knowledge I was even willing to sacrifice one of the few copper cents then in my possession. I put one of them on the table, opened the bottle marked nitric acid, poured some of the liquid on the copper and prepared to make an observation. But what was this wonderful thing which I beheld?
The cent was already changed and it was no small change either. A green-blue liquid foamed and fumed over the cent and over the table. The air in the neighborhood of the performance became colored dark red. A great colored cloud arose. This was disagreeable and suffocating. How should I stop this? I tried to get rid of the objectionable mess by picking it up and throwing it out of the window. I learned another fact. Nitric acid not only acts upon copper, but it acts upon fingers. The pain led to another unpremeditated experiment. I drew my fingers across my
trousers and another fact was discovered. Nitric acid acts upon trousers. Taking everything into consideration, that was the most impressive experiment and relatively probably the most costly experiment I have ever performed. . . . It was a revelation to me. It resulted in a desire on my part to learn more about that remarkable kind of action. Plainly, the only way to learn about it was to see its results, to experiment, to work in a laboratory. from F. H. Getman, "The Life of Ira Remsen"; Journal of Chemical Education: Easton, Pennsylvania, 1940; pp 9-10; quoted in
Richard W. Ramette, "Exocharmic Reactions" in Bassam Z. Shakhashiri, Chemical Demonstrations: A Handbook for Teachers of
Chemistry, Volume 1. Madison: The University of Wisconsin Press, 1983, p. xiv:

PROCEDURE 1 (AND A SET UP FOR PROCEDURE 2)
Materials: 1 400 mL beaker
1 large test tube
1 250 mL beaker
1 micropipette
1 50 mL beaker 1 50 mL grad cylinder
1) PUT ON YOUR GOGGLES AND DO NOT TAKE THEM OFF.
2) Use the 400 mL beaker, to make a hot water bath, by heating about 300 mL of water to the boiling point.
Use a hot plate as your energy source for this. You will need this water for Procedure 2 … so as you work,
let it warm. Turn down the hot plate when the boiling becomes too riotous!
3) Into a nearby computer, plug in the temperature probe / open / prepare to take readings. Using a 25 mL or
50 mL graduated cylinder measure 15 mL of 1.0 M copper(II) nitrate solution and pour it into large test tube,
at your station. You can use the 250 mL beaker to support/hold the large test tube.
4) Rinse the graduated cylinder, well with distilled water and dispose of this waste water down a drain
5) Using the graduated cylinder, measure 15 mL of a 1.5 M sodium hydroxide solution and pour this solution into
the small (50 mL) beaker. Rinse the graduated cylinder and walk the beaker, and now rinsed cylinder to your
station.
BE VERY CAREFUL WITH THE SODIUM HYDROXIDE SOLUTION. IT IS A STRONG BASE
AND CAN CONVERT THE FATS OF YOUR SKIN TO SOAP! Call me over in the event of a spill.
6) At your station you should have a test tube with Copper(II) nitrate, resting in a beaker or test tube rack, a
temperature probe, ready to take measurements, a micropipette, and a small beaker with approximately 15 mL
of 1.5 M sodium hydroxide solution.
7) Insert probe into the test tube with the copper (II) nitrate solution and click collect on the logger pro lite
program. Allow the temperature to be collected for five to ten seconds.
8) As these data are collected, aspirate (squeeze) the bulb of the micropipette and insert it into the beaker holding
the sodium hydroxide. Be sure the tip of the micropipette is BELOW the level of the solution. Release the
bulb and draw up into up into the micropipette an aliquot (a sample) of the sodium hydroxide solution.
Carefully add this solution to the test tube with the probe and copper (II) nitrate solution. Repeat this, using
as much of the sodium hydroxide solution as is available. Rinse the 50 mL beaker, and discard the waste
water down the drain.
9) Continue to collect temperature data until the graph line begins to plateau. At this point stop the data collection
by clicking STOP on the Logger Pro Lite screen. Extract the probe and carefully rinse it with distilled water
and wipe it dry with a soft paper towel. Put it aside. You no longer need to use the probe.
10) Click on the Scale icon at the top of the screen. Print the graph screen for each partner. Label it as
Procedure 1: The Production of copper (II) hydroxide and sodium nitrate
11) Study the contents of the test tube. Record your observations. One product is copper(II) hydroxide and
the other is sodium nitrate.
(Note: This is not a phase change …this is the production of a new compound!!)
____________________________________________________________________________________
12) Go to the table of solubility in water on the next page. Study the chart to figure out its design. Once you know
how the table works, determine the identity of the new solid that has been produced.
13) On the graph classify the synthesis of this new solid as an exothermic or endothermic chemical reaction
Put your name, and that of your partner, on this graph. Staple it to this lab.

To help you learn how this table works
: Consider that the compound:

Iron(III) chloride will dissolve in water and it will dissociate into the Fe 3+ cation and the Cl

Zinc nitrate will dissolve in water and it will dissociate into the Zn 2+ cation and the (NO
3
) 1-
1 anion. (It is soluble in water.)
anion (It is soluble in water)

Calcium carbonate will NOT dissolve in water to any great extent. Some exceedingly small quantity may dissolve, but it is considered to be a solid in
20 ° C water(a precipitate) and tends to settle out at the bottom of a beaker.

Lead(II) bromide forms a cloudy solution when produced, if in water. Some small amount dissolves (more than calcium carbonate), but most remains undissolved.
Note: Solubility in water of an ionic compound is temperature dependent. Generally speaking, most dissolve to a greater extent at elevated temperatures. Most solubility tables indicate solubility in water at approximately 20 ° C.
Table of Ionic Compounds & Solubility in Water s = soluble (dissolves) i = nearly insoluble
(possibly a precipitate) ss = slightly soluble
(possibly a precipitate)
Aluminum (Al +3 )
Ammonium (NH
4
+1
)
Barium (Ba +2 )
Calcium (Ca
+2
)
Copper II (Cu +2 )
Iron II (Fe
+2
)
Iron III (Fe
Lead II (Pb
+3
)
+2
)
Lithium (Li
+1
)
Magnesium (Mg +2 )
Potassium (K
+1
)
Silver (Ag +1 )
Sodium (Na
+1
)
Zinc (Zn +2 ) acetate
CH
3
COO -1 s s s s s s s s s s s s s s bromide
Br -1 s s s s s s s ss s s s i s s carbonate
CO
3
-2 chloride
Cl -1 i s i i i i i i s i s i s i s s s s s s s ss s s s i s s chromate
CrO
4
-2 i s i s i i i i s s s ss s s hydrogen carbonate
HCO
3
-1 hydroxide
OH -1 iodide
I -1 s s s s s s s s s s s s s s s s s ss i i i i s i s i s i s s s s i s i ss s s s i s s nitrate
NO
3
-1 s s s s s s s s s s s s s s phosphate
PO
4
-3 i s i i i i i i s i s i s i sulfate
SO
4
-2 s s ss ss s s s s ss s s ss s s

PROCEDURE 2:
Materials: test tube tongs 1 alcohol thermometer* 1 250 mL beaker for support beaker tongs 1 50 mL grad cylinder
Note: *We are going to now use an alcohol thermometer, instead of a temperature probe. The acid used in this procedure could react with and damage the
metal of the probe. These thermometers can be read to 0.1°C.
SAFETY!!! GOGGLES ARE ON!!!!!!
1) Place the test tube, from Procedure 1, holding all of its contents into the hot water bath begun in Procedure 1.
Allow the water bath to continue to heat, but don’t let it boil …You want the water hot, but not boiling… Okay?
2) Allow the contents of the test tube to heat until a change no longer occurs. The products of the heating of the test
tube contents are copper(II) oxide and water .
(Were the change not to occur, or should it begin and then reverse, call me over.)
3) Once the copper(II) oxide and water are formed, you must allow the contents to cool to 20 °C before
moving on. The following will help you get the contents to the correct temperature:
Turn off the hot plate. Extract the test tube using test tube tongs or crucible tongs. ADD some cool water to the 250 mL
beaker, being used as a support for the test tube. Insert the test tube into this cool water bath, and allow the contents of the test
tube to cool to room temperature (20 °C). This may take 5 minutes or longer, and since the water bath will heat (as the
contents of the test tube cool) you will probably need to pour out the water bath and re-create the bath with more cool water.
While holding the test tube with crucible tongs (clasping the inner and outer lip) you may also run some cool water from your
faucet over the outside of the test tube, from your faucet.
4) Go to the hood and using your rinsed graduated cylinder, measure out about 15.0 mL of 1.5 M HCl
(aq)
. This is
hydrochloric acid. BE CAREFUL with it. Call me over, should any spills occur.
5) When the copper(II) oxide and water (the contents) of the test tube are near 20 °C, and/or no longer changing,
record the temperature.
6) Put the thermometer in the test tube and now carefully add the 15.0 mL of hydrochloric acid. (Remember, we
add acid to water … and this step meets that safety step, for there is water in the test tube, already)
7) Mix with your thermometer, very carefully. Read the thermometer, until no further changes in temperature occurs
Record the highest temperature of each thermometer, as a final temperature. You should read the thermometer
every 15 seconds or so …just to ensure you get the highest temperature correct.
The products of step 6) are copper(II) chloride and water. Is copper(II) chloride soluble in water? __________
Does your observation conform to the information on the Table of solubilities? _________________
Is there any similarity to the color of the solution with the copper(II) chloride, with the color of the original
copper(II) nitrate? _______
Did the chemical reaction between the copper(II) oxide and the hydrochloric acid generate (release) energy into
the surrounding environment (the water) of the test tube (thus increasing the overall temperature) or did the
temperature drop, due to the reacting chemicals absorbing energy? ___________________________ Given this
observation, is the reaction between copper(II) oxide and hydrochloric acid an endothermic or an exothermic
chemical reaction? ____________________ Defend your answer _____________________________________
_________________________________________________________________________________________ continue onto the next page

Procedure 2 continued:
8) Record the current temperature of the test tube contents.
9) Keep the thermometer in the test tube and place a strip of aluminum metal in the test tube. Allow it to remain, for
at least 2 to 3 minutes.
Recall that some visuals cues help to indicate a chemical reaction; a change in temperature, production of a new
solid (a precipitate), liquid or gas (indicated by fizzing/bubbling), or a bold color change When at least two of the five occur, the odds are favorable that a chemical change has occurred.
What visual clues tell you anther chemical reaction occurs? Is the reaction exothermic or endothermic?
Record your observations of what happens in the test tube, over the 2 to 3 minutes
Two different reactions occur in the test tube at Step 9 of Procedure 2. One produces copper metal and aluminum
chloride. The copper ion of the copper(II) chloride aqueous solution was converted back into (was reduced to) its
metallic form (The copper ion was re-cycled to copper metal).
The second reaction is between the aluminum metal and any un-reacted hydrochloric acid, to produce
aluminum chloride and dihydrogen gas.
Write the balanced chemical reaction for the reaction of aluminum metal with hydrochloric acid.
________________________________________________________________________________________
Should you expect a precipitate to be produced? _________
What would you predict would occur, if you were to isolate the copper metal produced in this reaction and
combine it with nitric acid? Defend your reasoning.
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
10) To extract the aluminum strip, you can pour out some of the test tube contents, into the sink. Add some tap water
to the test tube (diluting any remaining acid), and using a forceps, you can extract the metal strip. Rinse it in tap
water. Pour the remaining contents of the test tube down the sink. Clean the test tube using a test tube brush at
the main lab sink, near the door, at your station or up front, at the teacher station … please wipe up the mess.

A Few More Questions:
1) Based upon the table of ionic compounds and solubility in water, make a statement regarding the relative solubility in
water of: a) compounds made containing group 1 metal cations __________________________________________ b) nitrates: ______________________________________________ c) acetates: ___________________________________________ d) phosphates ___________________________ with exceptions _________________________
2) Based upon the table of ionic compounds and solubility in water would you predict sodium iodate (NaIO
3
) to be
soluble or insoluble in water? Defend your thinking Defend your reasoning. Have an argument, a setting (if required)
and some sort of proof or support using data/observations etc…)
_________________________________________________________________________________________
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__________________________________________________________________________________________
__________________________________________________________________________________________
3) Given a chemical reaction between silver nitrate and sodium chloride, what might you predict to see, as the products
are formed? Defend your reasoning. Have an argument, a setting (if required) and some sort of proof or support
using data/observations etc…)
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Using the Reflection Stems found on the website, write a metacognitive reflection as to your thoughts about processing the directions in the lab, your questions / concerns or insights.