Chemistry 102 Intro. GOB Chemistry
CHANGES IN MATTER
Your team is employed by MegaChem, Inc. in the process control department.
The production process for the extensive product line is being studied to
determine if steps can be eliminated or changed for improved recovery and
lower environmental impact. Your team has been assigned to determine if specific
procedures produce a physical or chemical change in the material(s).
You are also asked to give as much information as possible to the analytical
department on what these changes produce to make their job easier.
You should already know that in physical changes, some property like color,
shape or state (gas, liquid or solid) is altered, often temporarily, and
usually can be reversed easily. Examples include water vapor changing to
snow or sleet and then melting when the sun returns, sugar or salt dissolving
in water and then recrystallizing when the water evaporates, or a rock being
crushed to gravel. No new kind of matter is formed in a physical change.
A chemical change has occurred when a substance changes into a new substance.
But it is not always easy to look at a change and decide if it is a physical
or chemical one. Here are some indicators of a chemical change:
Chemistry texts are good sources of help with the differences.
- the initial substance (reactants) disappear,
- one or more new substances (products) are formed,
- an irreversible color change occurs,
- a gas is evolved (don't confuse this with liquid boiling),
- a precipitate (insoluble substance) forms when solutions mix, or
- energy (heat, light) is released or absorbed.
To determine, and support with evidence, which procedures give
physical, and which chemical changes in the materials.
To report as much information as possible on the products produced by the
You may have ammonium carbonate ((NH4)2CO3
), iodine (I2), ethanol, starch, ammonium dichromate ((NH
4)2Cr2O7), iron III chloride (FeCl
3), ammonium thiocyanate (NH4SCN), sodium sulfate (Na
2SO4), barium nitrate (Ba(NO3)2), copper
II sulfate (CuSO4), copper II oxide (CuO), dilute nitric acid
(HNO3), sodium thiosulfate (Na2S2O3
), sugar (C12H22O11), sodium bicarbonate
(NaHCO3), citric acid (C6H8O7
), zinc (Zn), hydrochloric acid (HCl), and magnesium ribbon (Mg) available.
Take and use the minimum amount you think you might need. You can
always get more, if necessary. Do Not return unused portions to the
stock bottles! Why not?
The following are some hints and questions to guide your work. They are
not inclusive; so you are encouraged, and indeed, expected to follow your
own ideas, as long as you consider safety issues. As with any new, or unknown
reaction, you should always start at a very small scale with extra safety
precautions. For example:
Safety: Never point the mouth of a test tube at ANYONE.
Never inhale with your nose directly over a tube,
beaker or bottle.
Your instructor will demonstrate wafting the fumes toward your nose with
Keep solutions containing alcohols far away from open
Your team will do the 10 tests chosen by your supervisor. Of course you
know it is critical to the success of these tests that the glassware used
be clean and dry!
Of course, Production needs your report yesterday, if possible. Again, they
want to know which were physical changes and which chemical, and why you
classed each as you did. Did you see sublimation in any test? Explain that,
- Production plans to heat ammonium carbonate ((NH4)2
CO3) to dry the crystals for packaging. Will it change physically
or chemically? If chemically, what could the products be? How will you know?
- Production also plans to heat iodine crystals (I2) to dry
them prior to packaging. Will this change it physically or chemically? How?
If chemically, what could the products be? How will you know? (Hint: Look
up the starch test.) They also plan to dissolve it in ethyl alcohol to make
a "tincture of iodine." Has the iodine changed?
- Ammonium dichromate ((NH4)2Cr2O
7) will also be heated. Since compounds containing Cr are poisonous,
you know never to attempt to smell this material. It is odorless.
You also know to work in the hood, pointing the mouth of the tube
in a safe direction, and not to touch the product. How should you
dispose of it?
- Production will add either ammonium thiocyanate (NH4SCN
) to an iron III chloride (FeCl3) solution, or potassium ferricyanide
(K3Fe(CN)6) into an iron II sulfate (FeSO4
) solution, without heating. Are there any changes?
- They also plan to add barium nitrate (BaNO3) to a sodium
sulfate (Na2SO4) solution without heating. Are
there any changes? Does it change on standing?
- Production plans to recover copper II sulfate (CuSO4) crystals
from a solution by heating. How should they do this? What happens at each
- They are going to heat crystals of sugar (C12H22
O11) or sodium thiosulfate (Na2S2O3
) gently without boiling it, and cooling to room temperature.
Is it still the same chemical or something else? How can you tell? What happens
if it is heated above boiling?
- Does magnesium ribbon (Mg) change when heated in the burner? Can it
be used for welding? How will you protect your eyes?
- Production wants to make a palatable liquid antacid by adding equal
amounts of citric acid (C6H8O7) to sodium
bicarbonate (NaHCO3) and dissolving it in water. Will this process
change the product at any step? Will it still work? How can you test it?
(Do not taste it!)
- Production wants to change from washing solid zinc (Zn) in water to
using dilute hydrochloric acid (HCl). Does the Zn change? Does the water?
How will you know?