Physical and Chemical Changes

Name______Date______Period____

Physical and Chemical Changes

Pre-Lab Discussion (Do not copy in your lab book)

Chemistry is the study of matter and the changes it undergoes. These changes can be broken into two classes – physical changes and chemical changes. In a physical change, one or more physical properties of a substance are altered. Examples of such physical properties include size, shape, color, and physical phase. No new substance or substances are formed as a result of a physical change.

A chemical change results in the formation of one or more “new” substances. These new substances differ in chemical properties and composition from the original substance. The rusting of iron and the burning of paper are two examples of chemical change.

This experiment will help you understand the difference between physical and chemical change and to recognize each type of change when it occurs.

Purpose

After reading the pre-lab discussion, determine the purpose of this lab and write it in your own words.

Equipment:

balancemicrospatula

Bunsen burnerdropper pipette

test tube racksmortar and pestle

test tube holdermagnet

watch glassgoggles

Materials:

Copper sulfate pentahydrate (CuSO4 •5H2O)Iron filings (Fe)

Sodium chloride (NaCl)Sulfur (powdered) (S)

1M Hydrochloric acid (HCl)Paper (5 X10cm)

0.1M Silver Nitrate (AgNO3)Birthday Candle

Magnesium Ribbon (Mg)Matches

Safety (Do not copy in your lab book):

  • Be sure to note all safety precautions listed in the procedure
  • Be sure to always point the open end of a test tube away from yourself and others. Always swirl a test tube being heated to avoid glass cracking.
  • Handle all acids with extra caution. Always wear safety goggles when handling acids. Report all spills to the teacher immediately, and flush with cold water and a dilute solution of sodium bicarbonate (NaHCO3)
  • Give heated glass time to cool before handling it. Glass retains heat. Tie back long hair and secure loose clothing before working with an open flame. Wear safety goggles at all times.
  • Be careful when handling silver compounds. They will stain your clothes and skin. Always wear gloves.

Procedure

This lab will be completed in a “merry-go-round” fashion. There will be 6 stations set up, and you will be given about 10 minutes to complete each station. Do not waste time while completing this lab. Do not move on to the next station until you are instructed to do so.

Station 1: Candle

  1. Place a small amount of wax from a birthday candle into a test tube. Heat gently over a burner flame until the wax melts completely, and then allow the sample to cool.
  2. Melt the bottom of the candle and affix it to the watchglass. Light the candle, and then allow it to burn until it extinguishes itself.

Station 2: Paper

  1. Tear a piece of paper (about 5 X 10cm) into small pieces. Place the paper onto a watchglass. Ignite the paper with a match and allow it to burn.

Station 3: Salt

  • Caution: Wear gloves when handling silver solutions. They will stain your skin and clothes black.
  1. Add a microspatula of sodium chloride (NaCl) into about 5mL of water. (That’s about 1 in. of water at the bottom of a test tube)
  2. Shake the contents of the tube.
  3. Use a dropper to add about 10 drops of 0.1M silver nitrate (AgNO3) to the sodium chloride and water mixture.

Station 4: Magnesium

  • Use extreme caution when handling acids. Hydrochloric acid will cause chemical burns if it comes in contact with your skin.
  1. Obtain a piece of magnesium ribbon about 5cm long. Tear the ribbon into 1cm pieces.
  2. Place the pieces of the magnesium to a test tube. Then add a few drops of 1M hydrochloric acid (HCl) to the test tube.
  3. Touch the bottom of the test tube with your fingertip.

Station 5: Copper Sulfate Pentahydrate

  1. Use a mortar and pestle to grind several crystals of copper sulfate pentahydrate (CuSO4 •5H2O) into a uniform powder.
  2. Place 1 microspatula of the powder into a test tube. Heat gently over a burner flame for 5 minutes. Allow the sample to cool completely.
  3. Add a few drops of water to the test tube using a wash bottle.

Station 6: Sulfur and Iron Filings

  1. Using a balance and weighing paper, measure out 0.50g of iron filings and 0.50g of powdered sulfur.
  2. Test each sample with a magnet by running the magnet under the weighing paper.
  3. Mix the samples thoroughly in a test tube. Run the magnet along the bottom and sides of the test tube.
  4. Heat the iron-sulfur mixture over a burner flame until the mixture “glows”. Allow the sample to cool and examine it by probing it with a microspatula. Run the magnet along the test tube again.

Observations and Data:

Record all Observations for each step of the procedure.

Station 1: Melting of the wax
Station 1: Burning of the Candle
Station 2: Ripping Paper
Station 2: Burning Paper
Station 3: Mixing salt with water
Station 3: Salt water + Silver Nitrate
Station 4: Ripping Magnesium Ribbon
Station 4: Magnesium + Hydrochloric acid
Station 5: Grinding Copper sulfate pentahydrate
Station 5: Heating Copper Sulfate pentahydrate
Station 5: Adding water after heating
Station 6: Powdered Sulfur
Station 6: Iron Filings
Station 6: Iron and Sulfur Mixture before heating
Station 6: Iron and Sulfur Mixture after heating

Conclusion and Questions:

  1. Indicate whether the following changes are physical or chemical. Support your conclusions (explain each one)
  2. Melting candle wax
  3. Burning a candle
  4. Tearing paper
  5. Burning paper
  6. Dissolving NaCl
  7. Mixing NaCl and AgNO3
  8. Tearing Mg ribbon
  9. Adding HCl to Mg
  10. Grinding CuSO4 •5H2O
  11. Heating CuSO4 •5H2O
  12. Mixing Fe and S
  13. Heating a mixture of Fe and S
  1. Name 3 possible indications that a chemical change has taken place. Give an example(s) from this lab.
  1. Chemical change involves the formation of “new” substances. Briefly describe “new” substances formed as a result of each chemical change in this experiment. (There were 6 of them)
  1. The following changes do not always indicate a chemical change. Give examples in which they may be the result of a physical change.
  2. Change of color
  3. Apparent loss of mass
  4. Apparent disappearance of a substance
  1. How can substances in a mixture be separated? How can substances in a compound be separated? Use examples from this experiment in your explanation.

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