Glencoe Chapter 10:
Chemical Reactions

Problem:

What are some clues that accompany chemical changes?

Introduction:

Chemical changes are accompanied by signals, many of which are visual.  We can represent chemical reactions by writing  chemical equations.  Because atoms are neither created nor destroyed, the equations must also be balanced.  In this lab, you will carry out four chemical reactions and make careful observations to determine which clues accompany chemical changes.

**Prelaboratory Assignment:

ON THE DATA TABLE, write and balance the chemical equations for the following reactions.  Include the state for each substance in the equation. 
**NOTE: IF YOU FAIL TO COMPLETE THIS PART PRIOR TO THE LAB, YOU WILL NOT BE ALLOWED TO PARTICIPATE IN THE LAB AND THERE IS NO MAKEUP.
          (g) for gas
          (l) for liquid
          (s) for solid
          (aq) for aqueous (means that the substance has been dissolved into water to make a solution)

1. Solid magnesium reacts with aqueous hydrochloric acid to produce aqueous magnesium chloride and hydrogen gas.

2. Aqueous sodium chloride reacts with aqueous silver nitrate to produce solid silver chloride and aqueous sodium nitrate.

3. Solid magnesium burns in the air to form solid magnesium oxide.

4. Aqueous potassium thiocyanate reacts with aqueous iron (III) nitrate in a double replacement reaction.

Materials:

Safety:

• The 3.0 M HCl is very corrosive.  Handle it with extreme care.
• Safety goggles and lab apron must be worn at all times in the laboratory.
• Silver nitrate solution permanently stains both skin and clothing (it will turn black when sunlight hits it).  Avoid contact with the solution.
• If you come in contact with any of the solutions, rinse with lots and lots of water.
• You will work with flame in this lab.  Tie back hair and loose clothing.

Procedure:

Print off this data table.

NOTE: For each reaction below, take the chemicals you need from the front preparation area, use them and then PUT BACK UP AT THE FRONT right away!  Also, you can start with ANY of the parts below....you don't need to start at Part I first.

    Part I:

1. Place about 5 mL of the 3.0 M HCl in a test tube.
2. Add a 2-3 cm piece of magnesium ribbon to the acid.  Make careful observations and record on your data sheet.
3. Place another test tube over the mouth of the test tube containing the acid and magnesium.  The mouths of the two test tubes should be the same size.
4. After the reaction is complete, light a wooden splint.  Quickly turn over the top test tube (so the mouth is pointing up) and place the burning wood splint near the mouth of the test tube.  Do NOT point the test tube at anyone! 
5. Make careful observations and record on your data sheet what you see during BOTH of these reactions - note that there are TWO reactions which occurred (one in the test tube and the other when you place the burning splint near the mouth of the test tube) and in your lab writeup, you will write and balance TWO equations. Cuidado observaciones y graba en su hoja de datos lo que usted ve durante tanto de estas reacciones.

    Part II:

1. Take a few crystals of silver nitrate and place into a clean test tube.
2. Add about 5 mL of distilled water and dissolve the silver nitrate using a CLEAN stirring rod.
3. In a different test tube, add sodium chloride (about the size of the end of a matchstick - the part that lights).
4. Add about 5 mL of distilled water using a CLEAN stirring rod to dissolve.
5. Add the solution of sodium chloride into the test tube that has the solution of silver nitrate.
6. Swirl gently to mix the two solutions together.
7. Let the test tube sit for a while.  Do you see any differences over time?
8. Make careful observations and record on your data sheet about what you see right after you mix the solutions and then after the solutions have been sitting for a while. Cuidado observaciones y graba en su hoja de datos sobre lo que usted ver derecho después de mezclar la soluciones.

    Part III:

1. Light the bunsen burner.
2. Use tongs to hold a 1-2 cm piece of magnesium ribbon in the flame.  Do NOT look directly at the magnesium as it burns.
3. Look carefully at what is being held in the tongs after it is burned.  What does it look like?
4. Make careful observations about what you see AS the magnesium burns and what it looks like after the burning is over. Cuidado observaciones sobre lo que usted ve como el magnesium quemaduras y lo que parece que después de la quema es más.

    Part IV:

1. Place a few drops of aqueous iron (III) nitrate into a clean test tube.
2. Slowly add a few drops of the aqueous potassium thiocyanate to the aqueous iron (III) nitrate.
3. Let the test tube sit for a while.  Do you see any differences over time?
4. Make careful observations and record on your data sheet about what you see right after you mix the solutions and then after the solutions have been sitting for a while. Cuidado observaciones y graba en su hoja de datos sobre lo que usted ver derecho después de mezclar la soluciones y después de la soluciones han sido sentado por un rato.

Clean Up:

• THOROUGHLY clean out all your glassware!  Then, after you are certain the test tubes are CLEAN, as a last step, rinse out each test tube with distilled water.  Turn the test tubes UPSIDE DOWN in the test tube rack and return to the front of the room.
• Bring all supplies back to the front of the room.
• Wipe down your lab table area with a wet paper towel and then dry off.
• Wash your hands thoroughly.

Analysis and Conclusions:

Answer the following in essay form. Word process your answers and turn in this paper to Turnitin.com. This is WRITING ASSIGNMENT #3. 
Si usted necesita ayuda con esto, ver la Sra. Weir en la mañana antes de la escuela.

Remember, never use indefinite pronouns in your narrative (e.g. "it") and use verbs that accurately describe what you observed.  For example, you did NOT observe anything "dissolving" (that would have been a physical change); instead, you observed substances "reacting."

1. Label this first section PART A:
   • Type each balanced equation (see note below on how to do superscripts and subscripts).  Be SURE to include BOTH reactions that occurred in Part I.
   • Then, right underneath each balanced equation, list the  the observations that led you to believe that a chemical reaction took place.  Remember, each reaction may have more than one characteristic that leads to you believe that a chemical reaction takes place.  Use "bullets" for each observation.
2. Label this second section PART B:
   • LIST the FIVE (yes, exactly five) characteristics that when you observe them, a chemical reaction may have taken place.  Number them 1, 2, 3, 4, 5.
3. Label this last section PART C:
   • For each of the FIVE characteristics you listed in step #3, describe one chemical reaction from everyday life that demonstrates each of the chemical reaction clues you observed in this lab.  Your examples should be something you can observe in your house or apartment or in your workplace - someplace OTHER THAN a chemistry lab!
   • A CHEMICAL REACTION is one where you get a NEW PRODUCT formed with DIFFERENT physical and chemical characteristics as compared to the reactants that you started with. 
   • A PHYSICAL CHANGE means that your substances may "look different" but you have NOT fundamentally changed the nature of the substances.  For example, when you dissolve salt into water, you cannot see the salt in the salt water.  BUT, by simple evaporation, you can get the salt back and the water is still water.  "Dissolving" or "Mixing" or "Tearing" or "Evaporating" are all examples of physical changes.  This is NOT what you observed in this lab.
   •  So, be sure to use examples which are CHEMICAL reactions - NOT physical changes.

   1. Not a single one of these are chemical changes.... they are all PHYSICAL changes (so don't use these!)
      Mixing kool-aid into water	Bartender mixing drinks
      Evaporating the water from a container of salt-water	Making steel from iron and other metals
      Putting marshmallows into a mug of hot chocolate and seeing them melt	Dropping mentos into diet coke
      Blood picking up oxygen in the lungs	Mixing white milk with Hershey's chocolate
      Melting gold to make jewelry	Putting sugar into iced tea
      Tearing a piece of aluminum foil	Light bulbs lighting up
      A hot glass cracking when it is placed into cold water	Chewing bubble gum to make a popping sound
      Opening a can of pop and the soda fizzes out	Mixing warm water and flour
      Popping a balloon	Sprinkling salt on your fried eggs

NOTE: To make special symbols and superscript and subscripts.

• Superscript is <Ctrl> plus <shift> plus <=>
• Subscripts is <Ctrl> plus <=>
• To go back to regular typing, <Ctrl> plus <spacebar>
• To make an "arrow", type two hyphens (the key just to the left of the = sign key) and then type >  (shift + "period" key)

If you are using a MAC instead of a Windows machine, use the "command" key above rather than the "control" key.