Observations of Chemical Changes
Objectives: (1 of 20 points)
The objectives of this experiment are:
1. To observe some properties of chemical reactions
2. To associate chemical properties with household products
Background Information: (2 of 20 points)
Chemical changes are often accompanied by physical changes. Three that you should not see in this lab are changes in temperature, presence of a flame, and evolution of light, as when as firefly glows. Three physical changes that indicate a chemical change may have occurred (and that may be seen in this lab) are:
1. Color changes
2. Precipitate (formation of a solid)
3. Formation of gas bubbles
Procedure: (1 of 20 points)
No preliminary dilution of my test chemicals were necessary as Lab Paq provided pre-diluted chemicals. Utilizing the 96-well plate, 2 pipet drops of each chemical were added to the wells in the following combinations: a) NaHCO3+HCl b) HCl+Bromthymol blue c) NH3+1 drop Bromthymol blue d) HCl+blue dye e) Blue dye+NaOCl followed by HCl f) NaOCl+KI followed by various test foods g) KI+Pb(NO3)2 h) NaOH+phenolphthalein i) HCl + phenolphthalein j) NaOH+AgNO3 k) AgNO3+NH3 l) NH3+CuSO4. Along the way, observations were made pertaining to the reactions witnessed. This experiment concluded with testing household chemicals and proper disposal of lab chemicals.
Observations: (10 of 20 points)
CHEMICALS Well # Reaction on white paper Reaction on dark paper
a. NaHCO3 + HCl A1 Bubbling Clear Liquid Bubbling Clear Liquid
b. HCl + BTB B1 Golden Yellow Clear Liquid Amber Clear Liquid
c. NH3 + BTB C1 Royal Blue Clear Liquid Dark Blue Opaque Liquid
d. HCl + blue dye D1 Emerald Green Clear Liquid Dark Green Opaque Liquid
e. NaOCl + blue dye E1 Bright blue that dissolved to yellow Same; just easier to see
then to pale yellow.
f. NaOCl + KI F1 Gold clear Liquid; then Black Dark Gold Clear; then Black
after starch added
g. KI + Pb(NO3)2 G1 Bright yellow “puddy-like” Bright yellow “puddy-like”
h. NaOH + phenolphthalein H1 Bright magenta Liquid Bright Red liquid
i. HCl + phenolphthalein A2 White cloudy Liquid White cloudy Liquid
j. AgNO3 + NaOH B2 Thick, mud-brown paste Same
Didn’t remain suspended;
Settled to bottom
k. AgNO3 + NH3 C2 White cloudy mixture; the paper towel readily took up the mixture. I attached the paper strip to a light fixture. It took on the appearance of being “tea stained”. Brown “veins” ran through the paper towel with concentration at the edges.
l. NH3 + CuSO4 D2 Robin’s egg blue, cloudy thick Same
liquid; Didn’t remain suspended;
Settled to bottom
RESULTS OF TESTING VARIOUS FOODS FOR STARCH: (Control color= golden yellow)
Food Tested Observations Is starch present?
1. Strawberry to Burnt Umber There was definitely a reaction;
scant starch present
2. Banana to Gray Reaction took place; some starch is present
3. Bread to Black YES, starch is present!
What color change do you expect in the reaction of phenolphthalein with a base?
Expected solution color change to magenta
Answers to Additional Questions and Problems: (3 of 10 points)
1. Suppose a household product label says it contains sodium hydrogen carbonate (sodium bicarbonate). How would you test this material for the presence of sodium bicarbonate?
Phenolphthalein could be used to test for the presence of NaO4. The combination of cleaner and phenolphthalein would yield a chemical reaction manifested by a solution color change to magenta.
2. You know what color phenolphthalein and bromthymol blue turn when testing an acid or base. Test at least three household products, including household cleaning products, with bromthymol blue and interpret your results.
Product Tested Observations Interpretation
Windex Chemical to Blue Windex is a base
Joy Dishwashing Soap Chemical to Lime Green (Blue/Yellow) Neutral
Lysol Tub Cleaner Blue Base