LAB 16
STUDYING CHEMICAL REACTIONS
BACKGROUND: You know when a chemical reaction has occurred because one or more of the following takes place:
1. color change
2. ppt forms
3. gas produced (bubbles form)
4. change in temperature ( warmer or cooler)
But what is happening in a chemical reaction? Atoms must be rearranged from reactants to products. The formulae of the products must be different than the reactants. This is another way of saying bonds are broken (requires energy) and new bonds form (produces energy). The overall reaction is either exothermic (releases energy because more energy is produced than used) or endothermic (absorbs energy because more energy is used than produced).
In this lab you will not only look for evidence of a chemical change but also observe the rate of the reaction. You must determine if any of the following factors will affect the rate of a chemical reaction:
1. temperature
2. concentration
3. catalysts
For each part of the lab you must create a data table that should include a column for each of the following:
1. step #
2. a description of the reactants in each mix
3. detailed observations of each mix
4. did a reaction occur
5. evidence a reaction has or has not occurred
This is a qualitative lab and all amounts of reactants are to be estimated using the picture of a 13x100 mm test tube below:
Just lay your tt on top
and mark the lines with
the marking pen.
-----5 ml
-----4 ml
-----3 ml
-----2 ml
-----1 ml
SAFETY:
1. Wear goggles at all times.
2. Add concentrated acid to water.
PROCEDURE
PART I:
1. Add 5 ml of tap water to a tt and then add 15 drops of concentrated (18M) sulfuric acid one drop at a time. Record your observations. Always add conc. acid to water. Save this diluted acid for steps 4-5.
2. Add 3 pellets of KOH(s) to 2 ml of tap water. Shake it up and record your observations. Do not touch the KOH with you bare hands. Use this solution in step 3.
3. Add 5 ml of tap water to the 2 ml of KOH solution from step 2. Then add 2-3 drops of phenolphthalein (an indicator). Stopper the tt and shake gently. Record your observations.
4. Add 5 ml of tap water to 1 ml of H2SO4 solution from
step 1. Then add 2-3 drops of phenolphthalein (an indicator). Stopper the tt and shake gently. Record your observations.
5. Set up 4 tt, each with 5 ml of .1M Na2C2O4 (sodium oxalate). Add about 1 ml of the sulfuric acid solution made in step one to each of the 4 tt.
While you are making these tt your partner should set up a hot water bath. The front sink will have water that is hot enough for this bath.
Now place 2 of the tt made into the hot water and let them sit for 3-4 minutes, this will allow them to reach the same temp as the water bath, about 40˚-50˚C.
To one of the hot tt add 5 drops of .1 M MnSO4 (manganese II sulfate). Now add 2 drops of KMnO4 (potassium permanganate) to each of the hot tt. Shake each to mix and note the reaction time needed for each to reach the same product (color).
To one of the room temperature tt add 5 drops of .1M MnSO4. Then add 2 drops of .1 M KMnO4 to each of the room temp. tt. Shake each tt to mix and again compare the reaction time for each to reach the same product.
Record both the colors and time of reaction for each tt at each temperature.
PART II
1. Place 1 ml of solid NH4Cl (ammonium chloride) in a tt and add 5 ml of tap water. Stopper and shake the tt. Record your observations.
2. Place 1 ml of solid NaCH3COO (sodium acetate) in a tt and add 5 ml of tap water. Stopper and shake the tt. Record your observations.
3. Place about 1/4 ml of Na2SO3 (sodium sulfite) in a tt and CAREFULLY add about 3 ml of 3 M HCl. Record your observations.
4. Place about 5 ml of .1 M FeSO4 (iron II sulfate) in a tt. Add 10 drops of .1 M KMnO4, a drop at a time, shaking the tt after each drop. Record your observations.
5. Add 1 ml of .1 M NaCl (sodium chloride) to 1 ml of
.1 M KBr (potassium bromide). Record your observations.
6. Place 1 ml of .1 M NaCl in a tt. In another tt place 1 ml of
.1 M K2CrO4 (potassium chromate). Add a few drops of
.2 M AgNO3 (silver nitrate) to each tt. Record the results.
7. Add 1 ml of .1 M NaCl and 1 ml of .1 M K2CrO4 to a tt, shake to mix. Now add .2 M AgNO3 a drop at a time, shaking after each drop. Continue to add AgNO3 until no more changes are observed. This might take up to 20 drops or so.
PART III
1. Place 5 tt, each labeled 1,2,3,4,5 in a tt rack and the following to each :
Test tube / Add 5 ml of :1 / 6 M HCl
2 / 6 M HCH3COO
3 / 1 M HCl
4 / 1 M HCH3COO
5 / .1 M HCl
To make .1 M HCl just add 1 ml of 1 M HCl to 9 ml of tap water.
To each tt add one small piece of CaCO3 (calcium carbonate, or limestone). Put the CaCO3 pieces back in the reagent bottle, they can be reused. Record the relative rates of reactions.
2. Add about 1/4 ml of CuSO4.5H2O (copper II sulfate pentahydrate) to a tt. Note its color. Now heat the tt for few minutes using a Bunsen burner until a change is noted. Record the change. After the tt cools add a few drops of tap water and again record any changes seen.
3. Add about 1/2 ml of PbO2 (lead IV oxide) to a tt. Heat over Bunsen burner and note any changes. Light a wood splint, blow out the flame so a glowing ember remains and quickly place the glowing ember into the tt so it is just above the solid. Note what happens.
QUESTIONS:
To answer the questions just use a Roman Numeral to represent the part of the lab and a normal number to represent the step in that part. For example, question 1 asks in which experiment was there no evidence of a chemical change. My answer would be,
I-4. which tells me that in part I step 4 there was no change. Please list your answers to the questions vertically.
1. In which experiment was there no evidence of a chemical change?
2. Which reactions produced a new phase?
3. Which reactions were exothermic and which were endothermic? Label each vertical column with endo or exo.
4. In which reactions did an increase in temperature change the rate of the reaction?
5. In which reactions did an increase in concentration change the rate of the reaction?
6. In part I, step 5, what effect did the MnSO4 have on the rate of the reaction?