Experiment # 3
IS IT A PHYSICAL OR A CHEMICAL CHANGE?

Objective
To identify the changes accompanying mixing various reagent  as  physical or chemical changes

Introduction
The entire natural world is continuously changing. The world is composed of chemical substance Those substances are subject to change.  Simple air and pure rain water erosion would cause a  mountain range to change its physical appearance over the centuries.  We would call this kind of transformation a physical change. However, the 20th century pollution created a phenomenon called the  acid rain. Erosion of the mountain range caused by the acid rain involves the chemical reaction between the acidic components of the rain and the basic components of the rocks. This type of erosion results  in the formation of new chemical substance and is  defined as the chemical change.
In a nut shell: a chemical change always involves a chemical reaction and results in a new chemical substance being formed, while a physical change alters the appearance of the substance without  changing its composition.
Physical changes may  include: phase transformation such as liquid turning into vapor (by boiling or room temperature evaporation), solid turning into vapor (subliming iodine), liquid turning into solid (e.g. by freezing),  solid turning  into liquid (e.g. smelting processes in the metallurgical technology), etc.
It is not always easy to distinguish between a chemical and physical transformations but a careful observation  may facilitate the detection of a chemical change. The clues that may  help you in making the decision  whether a chemical change has occurred are: evolution of a gas, formation of a precipitate or solid,  color change or  spontaneous temperature change.  Hence, your observations should include the  sense of sight, touch and smell.
The gas evolved upon mixing of two substances is usually detected by the presence of bubbles, a characteristic color, or smell.
Formation of  a precipitate (insoluble compound), with  characteristic color and texture, upon mixing of two solutions is indicative of a chemical reaction.
The color change of a solution  may be confusing and a careful investigation is necessary to make an educated decision whether it is a result of a chemical or physical change. For example adding water to a glass of ice tea lightens the color of the tea, but it is a physical process of dilution that is responsible for this change, not the change in the chemical composition of the tea.
Chemical changes are  usually accompanied by more pronounced color changes. Also, usually more than just color change occurs when a chemical reaction takes place.
Spontaneous temperature changes very often accompany the chemical reactions. The temperature of a solution  may drop when the occurring reaction is endothermic or rise if the reaction is exothermic. However, sometimes the temperature change will be a result of a physical process, such as dissolution of salt  crystals in water.

Safety tips
Sodium hydroxide (NaOH)and hydrochloric acid (HCl)  solutions are corrosive and toxic. Copper sulfate (CuSO4) solution is toxic and irritant. Prevent contact with eyes,  skin and clothes.

Equipment
The tools of your senses of sight, smell, and touch.
Minimum of 5 tiny test tubes labeled appropriately (wash and dry  between the experiments), test tube rack, test tube holder,  medicine dropper (rinse and dry when changing  solutions), 50 ml  beaker to hold about 10 ml of distilled water, and a porcelain, glass or plastic well plate or tray.

When recording observations of any reaction/process, pay particular attention to color changes (from....to...), precipitate/solid formation (include texture, e.g. gelatinous ppt, color), temperature changes (increase or decrease),  formation of bubbles, etc.
The best way to test for a temperature change is to touch the bottom of the test tube to the INSIDE of your wrist before and right after the reagents were mixed.

Procedure
1. A. Sodium hydroxide (NaOH) and phenolphthalein
Place 10 drops of 2 M NaOH  in a clean and dry, small test tube. Add a drop of phenolphthalein solution to the NaOH. Observe the contents of the test tube and record your observations.
B. NaOH and HCl
Add 13 drops of 2 M HCl to the test tube with the  mixture.  Observe the contents of the test tube and record your observations on a data sheet.
Dispose of the mixture in the  waste container (labeled: exp. 1,2, 6, 7).

2. Baking soda (sodium hydrogen carbonate, NaHCO3) and hydrochloric acid (HCl)
Obtain a ver small amount of baking soda (barely covering one fifth of a tip of a spatula) and place it  in a small, clean and dry test tube. Slowly add 8 to 10 drops of 3 M or 2 M hydrochloric acid (HCl). Observe the contents of the test tube. Record your observations on the data sheet.
Dispose of the contents of  the test tube in a designated waste container (labeled: Exp. 1,2, 6, 7). Squirt a small amount of  water into the test tube, rinse and pour the rinse into the waste beaker.

3. Copper sulfate (CuSO4) solution and water (H2O)
 Place 3 drops of 0.1 M copper sulfate solution into a clean and dry  well of a glass or porcelain spot plate. Add 5 drops of distilled water. Observe the contents of the test tube. Record your observations on a data sheet.
Dispose of the mixture into a waste container labeled: Exp. 3, 4 and 5.

4. Copper sulfate (CuSO4) solution and sodium hydroxide (NaOH)
Place 3 drops of 0.1 M copper sulfate solution into a well of a glass or porcelain spot plate.
Add 3 drops of  1 M or 2 M sodium hydroxide. Stir the mixture with a toothpick. Record your observations on a data sheet.
Dispose of the mixture  as in exp. 3.

5. Magnesium (Mg)  and copper sulfate (CuSO4) solution
Place 3e to 4 tiny  pieces of   magnesium turnings (use tweezers)  into a well of a glass or porcelain spot plate.
Add 4 drops of 0.1 M copper sulfate solution. Record your immediate observations. Leave the mixture  for about 10 minutes. Then stir it with a toothpick. Record your observations again.
Dispose of the mixture  as in exp. 3.

6. Magnesium (Mg)   and hydrochloric acid (HCl).
Place  5 to 6 shavings of  magnesium turnings  into a small, clean and dry  test tube. Add 5 drops of 3 M hydrochloric acid. Record your observations.  Dispose of the mixture  as in exp. 1.

7. Ammonium chloride (NH4Cl) and water.
Transfer one fourth  of the spatula  of  solid ammonium chloride into a small, clean and dry  test tube. Add approximately 1 mL of distilled water. Mix well.  Record your observations.
Dispose of the mixture  as in exp.1.

Data and Observations
1. A. NaOH and phenolphthalein
Observations:
 
 
 
 
 

Physical or Chemical Change?
 
 
 

B. NaOH/phenolphthalein  and HCl
Observations:
 
 
 
 
 
 

Physical or Chemical Change?
 

2. NaHCO3 and HCl  (baking soda and hydrochloric acid)
Observations:
 
 
 
 
 

Physical or Chemical Change?
 

3.CuSO4 and H2O (coper sulfate and water)
Observations:
 
 
 
 
 
 

Physical or Chemical Change?
 

4. CuSO  and NaOH
Observations:
 
 
 
 
 

Physical or Chemical Change?
 

5. Magnesium and CuSO4 solution
Observations:
 
 
 
 
 

Physical or Chemical Change?
 
 

6. Magnesium and HCl
Observations:
 
 
 
 
 
 
 

Physical or Chemical Change?
 
 

7. Ammonium chloride (NH4Cl) and water
Observations:
 
 
 
 
 

Physical or Chemical Change?

PRELAB
1. Explain the difference between chemical and physical changes.
 
 
 
 
 
 
 
 

2. Determine whether the following observations are the results of a physical or a chemical change:
Explain your answer.
a. The temperature of hot coffee drops upon addition of some cold milk.
 
 
 
 
 
 
 
 
 

b. “Dry” ice virtually disappears over time from your picnic ice chest. Hint: Start with finding out what "dry ice" is.
 
 
 
 
 
 
 
 
 
 

c. On a hot day, drops of water collect on the outside of a glass of Coke with ice.
 
 
 
 
 
 
 
 
 
 
 

POSTLAB
1. Based on the results of your experiment, is it correct to say that only one observable change accompanies a single chemical reaction? Explain using  examples from the experiment.
 
 
 
 
 
 
 
 
 

2.  Based on your experimental results, can you conclude that heat is always noticeably released in a chemical reaction? Explain using examples from the experiment.
 
 
 
 
 
 
 
 
 
 

3.  If some milk was added to a cup of coffee, would the resulting color change be due to a chemical or a  physical change? Explain.
 
 
 
 
 
 
 
 
 
 
 

4. Using only ingredients commonly available in the house, how can you verify the presence of  baking soda in Arm and Hammer laundry detergent ? Hint :Use your experiment as  a guideline, but remember that HCl is not a common household item, but it is an acid.