Experiment: Physical and Chemical Change

Experiment: Physical and Chemical Change

Theory:

Have you ever thought of your eyes as powerful tools for studying chemistry? Many of the properties of matter and the changes it undergoes can easily be determined thorough careful observation. Physical properties include color, density, solubility, and the state of the matter. Chemical properties describe the changes that take place when new substances are formed during a chemical reaction.

When matter undergoes a change, it is classified a either a physical change or a chemical change. During a physical change, only the size, temperature, or physical state of the substance changes. Melting, dissolving, grinding, and evaporating are all physical changes. No new substances are produced during a physical change. However, chemical changes always result in the formation of one or more new substances. The rusting of iron, during which the new substance iron (III) oxide forms from iron (Fe) and oxygen, (O2), is an example of a chemical change.

In this experiment you will observe a variety of materials and describe their physical properties. You will then cause some of the substances to undergo changes. Based upon your observations, you will determine whether the changes are physical changes or chemical changes.

Purpose:

To observe the physical and chemical properties of several substances and to classify observed changes as physical or chemical.

Safety:

Always wear safety goggles when working in the lab.

Hydrochloric acid is very corrosive and can cause severe burns.

Do not look directly at the burning magnesium. The intense light may damage your eyes. View the magnesium reaction by looking to the side of the reaction. Do not inhale the smoke that is produced when magnesium burns.

Powdered sulfur is irritating to the moist membranes of the eyes, nose, and throat. Avoid getting the dust into the air.

Do not taste any of the substances or touch them with your hands.

Procedures:

Part A. The Physical Properties of Matter

Record you observations for Part A in Table 2.1

1. Create seven pieces of 10 cm x 10 cm white paper

2. Label the seven pieces of paper for each of the following substances.

#1 Sulfur (powdered) (S) #2. Iron Filings (Fe)

#3. Sodium hydrogen carbonate (NaHCO3) #4. Sodium Chloride (NaCl)

#5 Sucrose (C12H22O11) #6. Sand (SiO2)

#7. Magnesium ribbon (Mg)

3. Copy both data tables 2.1 and 2.2 onto you lab worksheet. You will record all observations on this worksheet. Label both tables as 2.1 and 2.2.

4. Place two pieces of magnesium ribbon, one 5 cm long and one 1 cm long on the paper labeled “magnesium”.

5. Using a clean spatula, transfer a pea-sized sample of the other substances numbered #1 - #6 to their correctly labeled papers.

6. Examine each substance #1 - #7 with a magnifying glass. Record your observations (texture, shape, etc) under the physical state column .in table 2.1. Be sure to note the color and the smell of each substance.

7. Test the effect of a magnet on each substance by placing the watch glass in the concave position over each sample and pass the magnet under the over the watch glass. Record your data in table 2.1.

8. In separate small test tubes, test the solubility of each substance by mixing a small amount of each sample with 3 ml. of distilled water. (For the smaller test tubes this would be about 1/3 to 1/2 filled. “Flick” each test tube to thoroughly mix the contents.

9. Return the strip of magnesium ribbon in the test tube to its paper. Follow your teacher’s instructions for proper disposal of the other materials.

Part B Causing a Physical or Chemical Change

Record your observations for Part B in table 2.2

1. Mix the sodium chloride and sand on its appropriate piece of paper. Examine the mixture with a magnifying glass. And, test the effect of a magnet under the paper. Record your observations in table 2.2.

2.  Transfer the salt-sand mixture to a clean 100-ml beaker. Add 30 ml. of tap water

and stir. Record your observations in table 2.2. Prepare a filtration set up as described by your teacher. Filter the aqueous mixture and record your observations in table 2.2. Then, pour approximately 10 ml of the filtrate into an evaporating dish. Prepare a setup to evaporate the water from the evaporating dish. Examine both the dry residue in the evaporating dish and the wet residue on the filter paper. Record your observations in table 2.2.

3. Mix a small sample of iron filings and sulfur on its appropriate piece of paper.

Examine the mixture with a magnifying glass. And, test the effect of a magnet

under the paper. Record your observations in table 2.2. Discard this mixture as

instructed by your teacher.

4. CAUTION: DO NOT LOOK DIRECTLY AT THE BURNING MAGNESIUM.

Position a watch glass next to a Bunsen burner. Using the crucible tongs, grasp

the end of the 5 cm magnesium strip and hold it in the burner flame until it

ignites. Quickly position the burning strip over the watch glass so that the burnt

material falls onto the glass. Compare the appearance of the combustion product

to the 1 cm strip of magnesium. Record your observations in table 2.2.

5. CAUTION: HCl IS CORROSIVE

Place the unburned 1-cm strip of magnesium into a test tube. Place the

combusted magnesium from step #4 into another test tube. Add 10 drops of 6M HCl to each test tube. As you record your observations for both test tubes, feel the bottom of each test tube. Record in table 2.2.

6. CAUTION: HCl IS CORROSIVE

Transfer the sodium hydrogen carbonate sample to a clean test tube. Carefully add 5 drops of 6M HCl. As you record your observations for the test tube, feel the bottom of the test tube. Record in table 2.2.

7. CAUTION: DO NOT POINT A TEST TUBE OPENING AT ANYONE AND

HOT GLASS LOOKS EXACTLY LIKE COOL GLASS

The teacher will demonstrate the following procedure. Put half of the sucrose

sample into a clean test tube. Gently heat the sucrose over a flame. Watch and

record all of your observations in table 2.2. Then scrape a portion of the residue

onto your watch glass. Examine the residue and test its solubility in a clean test

tube. Record your results in table 2.2.

8. Follow your teachers instructions for proper disposal of the materials.

9. USING SOAP AND WATER, CLEAN ALL GLASSWARE AND YOUR

LAB AREA.

** Pre-lab: Go to WebAssign and complete assignment.

Data/Observations

Recreate the following qualitative tables in your lab notebook:

Data Record

2.1 Data Table for Part A
Substance and Formula / Physical State / Color / Odor / Solubility in water / Effect of Magnet
Iron filings, Fe
Sodium hydrogen carbonate,
NaHCO3
Sodium chloride, NaCl
Sucrose,
C12H22O11
Sand, SiO2
Magnesium, Mg
Sulfur, S
Table 2.2 Data Table for Part B
System Observation
Fe and S mixture
-tested with magnet
NaCl and sand mixture
-mixed with water
-filtered
-filtrate slowed to evaporate
Mg
Burned in air
Mg
Reacted in 6M HCl
Combustion product
-reacted with 6M HCl
C12H22O11
-heated
NaHCO3
-reacted with 6M HCl

Questions

1. For each of the reaction performed a change took place. Indicate whether the change was a physical or chemical change and provide data for your reasoning.

a)  mixing iron and sulfur

b)  mixing salt, sand, and water

c)  burning magnesium

d)  heating sucrose

e)  mixing sodium hydrogen carbonate and hydrochloric acid

2. How can you decide whether an observed property of matter is physical or chemical?

3. Explain the difference between a physical and chemical change

4. From table 2.1 which columns would be physical properties? How do you know?

5. What was unique about the heating of the sucrose, in terms of changes, as compared

to all of the other reactions.

Conclusion (Refer to Formal Lab Report rubric)

References (This lab is adapted from the following sources;)

Chemistry: Wilbraham, Staley, and Matta; Addison Wesley Publishing Company