CHEM 108 Chemistry Lab Report

CHEM 108 – Lab Experiment 5Chemical Reactions
Introduction
By definition, changing one or more substances into new substances is termed a chemical change
(chemical reaction). Knowing when a chemical reaction has taken place requires clearly observable
evidence that indicates that the atoms within the original substances have been rearranged to form new
substances. Using chemical analysis techniques, atomic and molecular‐level information can be
collected that provides this evidence. However, even without advanced chemical techniques and
instrumentation there are still some simple macroscopic observations that can provide evidence that a
chemical reaction may be occurring when substances are combined. Some observable behaviors that
provide evidence of a chemical reaction:
 Color changes
 Formation of a solid from a previously clear/transparent solution
 Formation of a gas, as seen by bubbles forming, when adding a substance to a solution
 Emission of light
 Emission or absorption of heat
When conducting these types of observations, you should keep in mind several important factors
regarding chemical reaction behavior:
(1) Chemical reactions occur at a variety of speeds. Some reactions occur slowly and may even take
hours or days for changes to be observed (in this lab all reactions will occur in several minutes).
As an observer, you should give reactions time to occur before assuming nothing is happening.
(2) Chemical reactions may be subtle. For instance, color changes may not be bright but rather faint
or pale such as a clear solution that turns slightly yellow during a reaction.
(3) Gas‐forming reactions may bubble violently creating a fast, frothing type of reaction or these
types of reactions may only create small, slow‐forming bubbles in solution.
(4) Reactions may increase or decrease their temperature (becoming hotter or colder) depending
on whether the reaction is exothermic (releasing energy) or endothermic (absorbing energy).
Energy changes and the accompanying temperature change often takes time and may not be
observed immediately after chemical substances are mixed together. In addition, monitoring
temperatures with the human hand can be deceptive since human skin is already warmer than
room temperature. For instance, most people will describe room temperature glass as feeling
‘cold’. To monitor temperature changes by hand, energy changes should be large enough to
make the containers in which they occur feel noticeably ‘hotter’ or ‘colder’ than when the same
container is held empty.
(5) Solid formation does not necessarily mean ‘chunky’ or ‘powdery’ solids. Solids also appear as
‘cloudy’ or ‘milky’ appearances that take a transparent solution (see‐through) and make it
opaque (not see‐through).
(6) Not every combination of chemical substances will result in observable reaction behavior. The
lack of observable changes says nothing about whether any chemical reaction is actually
occurring at the molecular level – just that no macroscopic changes are being observed.
In this lab, you are going to mix a variety of chemical substances and observe what, if any, changes
occur. Keep in mind the ideas above. Be patient and give any reactions that have no noticeable initial
changes several minutes before assuming that nothing is occurring. Look closely for subtle changes.
Chemical Reactions
© Colorado State University Department of Chemistry
Page | 35
Pre‐lab Questions (10 pts) ‐ must be typed and submitted on Canvas after taking safety quiz
1. There are safety hazards in this lab experiment. Specifically, what are the safety hazards associated
with the experimental procedure? Be sure to clearly identify and explain why these are hazards.
2. Identify the waste produced in this lab and explain how and where it should be properly discarded.
3. Identify four observable behaviors that provide evidence that a chemical reaction is occurring when
substances are combined.
4. Explain the difference between an endothermic reaction and an exothermic reaction.
5. Using a specific example to illustrate, explain what occurs in a precipitation reaction.
Experimental Procedure
Part A – Test Tube Reactions
Mix the following combinations of chemicals in test tubes. Be patient, some reactions will take longer
than others and the observable changes will be less noticeable. Carefully record your observations for
sight, touch, and smell on your report form.
Reaction A1 ‐ Magnesium metal and hydrochloric acid
 Place 20 drops of hydrochloric acid into a test tube. Add a 1 cm strip of magnesium ribbon to the
test tube.
Reaction A2 ‐ Potassium chloride and sodium chloride
 Place 20 drops of sodium chloride into a test tube. Add 10 drops of potassium chloride.
Reaction A3 ‐ Sodium hydrogen carbonate and hydrochloric acid
 Place a small amount (match head size) of solid sodium hydrogen carbonate into a test tube.
Slowly add 10 drops of hydrochloric acid into the test tube.
Reaction A4 ‐ Ammonium chloride and water
 Fill the test tube approximately ¼ full with solid ammonium chloride. Fill the test tube about ½
way with distilled water and mix well by shaking the test tube.
Reaction A5 ‐ Sodium chloride and silver nitrate
 Place 20 drops of sodium chloride into a test tube. Add 3 drops of silver nitrate.
Reaction A6 ‐ Sodium sulfate and copper(II) sulfate
 Place 20 drops of sodium sulfate into a test tube. Add 3 drops of copper(II) sulfate.
Reaction A7 ‐ Hydrochloric acid and sodium hydroxide
 Place 20 drops of hydrochloric acid into a test tube. Add 1 drop of the indicator solution. Slowly
add 25 drops of sodium hydroxide.
Page | 36
Chem 108 Laboratory Manual
© 2019 Colorado State University Department of Chemistry
Reaction A8 ‐ Sodium iodide and iron(III) nitrate
 Place 20 drops of sodium iodide into a test tube. Add 3 drops of iron(III) nitrate.
Reaction A9 ‐ Hydrogen peroxide and potassium iodide
 Place 20 drops of hydrogen peroxide into a test tube. Add 3 drops of potassium iodide.
Reaction A10 ‐ Iron(III) chloride and potassium ferrocyanide
 Place 20 drops of iron(III) chloride into a test tube. Add 3 drops of potassium ferrocyanide.
When you are done with Part A, carefully rinse the contents of your test tubes into the liquid waste
container. A single rinse of the test tubes may be placed in the waste container. Excessive rinsings
and/or soapy water should NOT be placed into the hazardous chemical waste. Thoroughly clean your
test tubes with a brush, soap, and hot water.
Part B – Spot Plate Reactions
Mix the following combinations of chemicals on a spot plate. Record observations on your report form.
For each reaction combination, mix 3 drops of each substance in a clean well on the spot plate:
Reaction B1 ‐ Iron(III) chloride and sodium hydroxide
Reaction B2 ‐ Sodium phosphate and silver nitrate
Reaction B3 ‐ Copper(II) sulfate and sodium hydroxide
Reaction B4 ‐ Cobalt(II) nitrate and sodium phosphate
Reaction B5 ‐ Potassium bromide and silver nitrate
Reaction B6 ‐ Sodium hydroxide and cobalt(II) nitrate
Reaction B7 ‐ Lead(II) nitrate and sodium iodide
Reaction B8 ‐ Sodium carbonate and lead(II) nitrate
Reaction B9 ‐ Sodium hydroxide and nickel(II) nitrate
When you are done with Part B, carefully rinse the contents of your spot plate into the liquid waste
container. A single rinse of the plate may be placed in the waste container. Excessive rinsings and/or
soapy water should NOT be placed into the hazardous chemical waste. Thoroughly clean your spot
plate with a brush, soap, and hot water.
Chemical Reactions
© Colorado State University Department of Chemistry
Page | 37
This page intentionally left blank for double-sided printing.
Page | 38
Chem 108 Laboratory Manual
© 2019 Colorado State University Department of Chemistry
CHEM 108 – Lab Experiment 5: Chemical Reactions I
Name:
Section:
In‐Class Activities (20 pts)
Part A – Test Tube Reactions:
Reactants
A1
Mg(s) + HCl(aq)
A2
KCl(aq) + NaCl(aq)
A3
NaHCO3(s) + HCl(aq)
A4
NH4Cl(s) + H2O(l)
A5
NaCl(aq) + AgNO3(aq)
A6
Na2SO4(aq) + CuSO4(aq)
A7
HCl(aq) + NaOH(aq)
A8
NaI(aq) + Fe(NO3)3(aq)
A9
H2O2(aq) + KI(aq)
Visual
Observations
Touch
Observations
Smell Observations
A10 FeCl3(aq) + K4Fe(CN)6(aq)
Chemical Reactions
© Colorado State University Department of Chemistry
Page | 39
Part B – Spot Plate Reactions:
Reactants
Visual Observations
B1 FeCl3(aq) + NaOH(aq)
B2 Na3PO4(aq) + AgNO3(aq)
B3 CuSO4(aq) + NaOH(aq)
B4 Co(NO3)2(aq) + Na3PO4 (aq)
B5 KBr(aq) + AgNO3(aq)
B6 NaOH(aq) + Co(NO3)2(aq)
B7 Pb(NO3)2(aq) + NaI(aq)
B8 Na2CO3(aq) + Pb(NO3)2(aq)
B9 NaOH(aq) + Ni(NO3)2 (aq)
Page | 40
Chem 108 Laboratory Manual
© 2019 Colorado State University Department of Chemistry
Post‐lab Assignment (36 pts)
1. (4 pts) Some of the mixtures in Part A have no observable changes. Identify these reactions and
discuss whether this provides evidence that a chemical reaction has not occurred in these situations.
2. (4 pts) List the endo/exothermic reactions from Part A (it is sufficient to just give the labels A1, A2,
etc).
3. (28 pts) All the reactions in Part B were examples of precipitation reactions in which cation and
anion pairs are exchanged (general form: AB + CD  AD + CB). For each reaction, write the complete
and balanced molecular equation including phase labels. Refer to general solubility rules for
identifying the precipitates – the solubility rules can be found online or in your chemistry textbook.
B1
B2
B3
B4
B5
B6
B7
B8
B9
Chemical Reactions
© Colorado State University Department of Chemistry
Page | 41
This page intentionally left blank for double-sided printing.
Page | 42
Chem 108 Laboratory Manual
© 2019 Colorado State University Department of Chemistry