Title: Physical and Chemical Changes
Purpose: Recognizing and differentiating between physical and chemical changes in matter.
Materials and Apparatus: chemical splash goggles; sodium chloride (NaCl); laboratory apron; glass stirring rod; latex gloves; micropipet with silver nitrate (AgNO3), 0.1M; birthday candle; 5 test tubes; magnesium(Mg) ribbon; test-tube tongs; scissors; laboratory burner; micropipet with hydrochloric acid(HC1),6.0M; test-tube rack, wood or metal; matches; copper sulfate pentahydrate (CuSO4 X 5H20); glass square; piece of paper, 2cm X 2cm; mortar and pestle; watch glass; laboratory balance; insulating pad, iron filings(Fe); tap water; powdered sulfur(S); graduated cylinder, 10-mL; magnet; microspatula
Drawings:
Procedures and Observations:
Procedures:
1. First, put on the goggles and lab apron. Break of a small amount of wax from a birthday candle and place this into a test tube. Heat the test tube over a burner flame until the wax is melted completely using test-tube tongs. Place the test tube in the rack, let it cool for then minutes, and record the observations in the data table.
2. Light a candle with the matches provided. Secure the candle to a glass square by dripping wax onto the square and put the candle in the molten wax until it hardens. Let the candle burns completely until it burns out. Record the observations.
3. Take a small piece of paper and tear it into tiny pieces. Place these pieces of paper in a watch glass. Put the watch glass on an insulating pad and ignite the paper with matches. Wait for the paper to burn completely and record the observations.
4. Using a graduated cylinder, measure 5mL of water. Pour this into a test tube and add a microspatula of sodium chloride (NaCl). Mix the contents by stirring them and then put on latex gloves. Using a micropipet, add 10 drops of silver nitrate (0.1M AgNO3) to the NaCl-water mixture, being careful not to get any silver nitrate on skin or clothes. Then record all observations and dispose of the silver nitrate as instructed.
5. Obtain the 5-cm piece of magnesium (Mg) ribbon and use scissors to cut it into 1-cm pieces. Place two of the pieces into a test tube and add a few drops of hydrochloric acid (6.0M HC1) using a micropipet, being careful not to touch it because it is very corrosive. Then touch the outside of the test tube using one’s finger tip. Record the observations and dispose of the solution as instructed.
6. Using a mortar and pestle, grind several crystals of copper sulfate pentahydrate (CuSO4 X 5H2O). Place a microspatula of the powder into a test tube. Heat this gently over a burner flame for 2 minutes and then let cool for 5 minutes. Once cooled add a few drops of water. Then touch the bottom of the test tube using one’s fingertip and record the observations in the Data Table.
7. Fold to pieces of weighing paper by folding them in half, and then again in quarters. Then measure out .20 g of iron (Fe) filings and powdered sulfur (S) using a laboratory balance. After that while keeping the samples towards the middle of the paper to prevent spilling, run a magnet along the bottom of the paper. Then mix the two samples in a test tube. Now run a magnet along the bottom and sides of a test tube and record the results.
8. Then heat the iron filing and sulfur mixture under a fume hood for a few minutes until the mixture starts glowing. Do not attempt this without a fume hood because noxious fumes are created which can be evacuated by a fume hood. Allow this sample to cool for 10 minutes. Notice the appearance and test once again with the magnet along the bottom and sides of the test tube. Record the observations.
9. Finally, clean up the work area and wash hands before exiting the lab area.
Step / ObservationsObservations:
1 / Once the wax cools it just turns the shape of the wax into the shape of the bottom of the test tube.2 / The candle eventually all melted down until the wax and wick were gone which extinguished the flame.
3 / It started to burn but didn’t burn completely.
4 / The solution became very milky white towards the surface and towards the bottom the NACl began to settle.
5 / When touched it was very hot. The hydrochloric acid heated the magnesium.
6 / After heating, it lost its color and turned grey. When water was added after cooling the powder turned blue again and sizzled a little. When it was touched it was hot again.
7 / The filings pick up a bit of sulfur and give the sulfur some magnetic properties so that the sulfur moves with the iron.
8 / The iron filings began to glow and the sulfur combined to the iron. When tested with the magnet, the combined iron and sulfur was magnetic.
Data: No data was acquired.
Calculations: No calculations were needed.
Conclusions: Different substances react differently with other substances. The substances and type of change they undergo can change from before and after heating. Some changes observed were physical and others were chemical.
Error Sources: There were no error sources.
Questions:
1. Indicate whether the following changes are physical or chemical. Support your conclusions.
a. Melting candle wax – Physical: it is still the same substance; its appearance is just different; its melting point is an intensive physical property
b. Burning candle wax – Chemical: is has a production of a gas; its creates new compounds and cannot be changed back
c. Tearing paper – Physical: it changes shape which is an extensive physical property
d. Burning paper – Chemical: it burns and turns into ash which cannot be turned back into paper
e. Dissolving NaCl – Physical: the appearance changes and it becomes a mixture
f. Mixing NaCl and AgNO3 – Physical: the NaCl begins to settle on the bottom and it is no longer a mixture; the AgNO3 repelled the NaCl
g. Cutting Mg ribbon – Physical: the shape, mass, and weight changed which are physical properties
h. Adding HCI to Mg – Chemical: the HCI heated the Mg; production of heat which is a chemical property
i. Grinding CuSO4 X 5H2O – Physical: the shape, mass, and weight changed which are physical properties
j. Heating CuSO4 X 5H2O – Physical: there was a change of color which is an intensive physical property
k. Mixing Fe and S – Physical: the appearance changed which is an intensive physical property
l. Heating Fe and S – Chemical: they chemically combined; the properties had changed which is a chemical property
2. Name two possible indications that a chemical change has occurred, using examples from this investigation.
One example is the heating of Fe and S which creates a chemical change when there is a change of properties. Another example is HCI to Mg which creates the production of heat which is a chemical change.
3. A change in color does not always indicate chemical change. Explain why it could be a result of a physical change.
It could be a result of a physical change because the change of color does not necessarily represent a change of substance and properties. Also, the change of color is an example of an intensive physical property.
4. Answer the following questions using examples from this investigation to support your answers.
a. How can substances in a mixture be separated?
They can be separated by adding some type of substance that splits them apart such as the silver nitrate to the NaCl and water mixture.
b. How can substances in a compound be separated?
They can be separated through distillation, evaporation, or condensation methods, such as when water was added to the copper sulfate pentahydrate.
5. Sodium chloride dissolves in water, leaving a clear homogenous mixture with no physical evidence of the crystals with which you started. Design an experiment that you could perform to separate the sodium chloride from the water.
Silver nitrate could be added to the mixture because the sodium chloride and silver nitrate will repel.
6. How would the experiment you designed in response to question 5 differ if some sand was mixed in the sodium chloride before it was added to the water?
When the silver nitrate is added the sodium chloride will still repel but the sand wont which separates the sand from the sodium chloride.