Lab report

Chemical ReactionsGoals
To observe chemical reactions and balance chemical equations.
Background
Chemical and Physical Changes
Changes in matter are often classified as either physical changes or chemical changes. In a physical change, the basic
particle or substance remains unchanged, but its appearance may change. For instance, when water freezes, the
appearance changes, but the particles in the ice cube are still water. All phase changes are physical changes. Other
physical changes include crushing, dissolving, and cutting.
In a chemical change, also known as a chemical reaction, new substances are formed during the change. Propane burning
is an example of a chemical change. Propane and oxygen react to form new substances – carbon dioxide and water. Iron
and oxygen forming rust is another example of a chemical change. Chemical changes often (but not always) are difficult
to reverse – it is easier to thaw an ice cube than it is to un-rust a nail. Chemical changes may also be accompanied by a
change in heat (heat from the reaction of propane is used for cooking). Other things that may indicate a chemical change
are a change in color or the formation of a new solid or gas.
Balancing Chemical Equations
Chemists represent reactions in the form of chemical equations. The formulas for the starting materials known as
reactants are written on the left. This is followed by an arrow pointing to products of the reaction on the right. Phases of
reactants and products are often written next to the formulas as follows (s) – solid, (l) – liquid, (g) – gas, and (aq) – aqueous
(dissolved in water). A chemical equation for the reaction of lead and sulfur becoming lead (II) sulfide is shown below.
Pb (s) + S (s) → PbS (s)
Although new substances are formed during chemical reactions, the number and type of elements you start with will be
the same as the number and type of atoms you end up with. Atoms are not created or destroyed in a chemical reaction,
they are only rearranged. Consider the formation of sodium chloride below:
Na (s) + Cl2 (g) → NaCl (s)
The reaction is not balanced because the reactants have two chlorine atoms and the product only has one. When
balancing equations, it is important not to change or add subscripts. You cannot simply change NaCl to NaCl2 so that the
atoms balance – NaCl2 cannot exist because the ion charges do not sum to zero. Instead, we put stoichiometric coefficients
in front of the chemical formulas to balance. If we put the coefficient 2 in front of NaCl, the chorines will balance:
Na (s) + Cl2 (g)
→ 2 NaCl (s)
However, now the sodium does not balance – we have one sodium as a reactant, two in the product. If we add a coefficient
to the sodium, the all atoms finally balance:
2 Na (s) + Cl2 (g) → 2 NaCl (s)
This trial an error process is how we balance reactions. Keep changing coefficients until you have the same number and
type of elements on both sides of the reaction.
Laboratory Activity
Materials:
magnesium
1 M CuSO4
0.1 M CaCl2
0.1 M KSCN
bunsen burner
1 M HCl
0.1 M Na3PO4
Copper
tongs
Na2CO3
0.1 M BaCl2
Zinc
test tubes
wood splint
0.1 M Na2SO4
test tube rack
matches
0.1 M FeCl3
Procedure
1. Obtain a test tube rack and several clean test tubes (they do not have to be completely dry).
2. Measure 2 mL of water in a graduated cylinder and pour it into one of the test tubes. Use this as a reference for the
rest of the lab – instead of measuring 2 mL of reagents, just fill to approximately the same height as your reference test
tube.
A. Combustion of Magnesium
1. Obtain a small piece of magnesium and record its initial appearance on your data sheet.
2. Grab the end of the magnesium with tongs and hold it in a Bunsen burner flame. As soon as the magnesium begins
to react, remove it from the flame.
3. Record your observation of the reaction and the final appearance of the magnesium on your data sheet. Dispose of
any residue in the regular trash.
B. Reaction of Zinc with Copper Sulfate
4. Using the test tube of water as a reference, fill two other test tubes with about 2 mL of 1M CuSO 4. (1 M is the
concentration). Leave the first test tube as is for a color reference. Add one piece of zinc to the second test tube.
5. Record the appearance of the reference CuSO4 test tube without the zinc. Record the appearance of the test tube
with the zinc after 15 minutes and again after a total of 30 minutes.
6. Pour all materials in the waste jug. (Not down the sink!) Rinse test tubes with water.
C. Reaction of Metals with Acid
7. Obtain 3 test tubes and put 2 mL of 1 M HCl (hydrochloric acid) in each. Put one small piece of copper in the first
test tube, one piece of magnesium in the second test tube and one piece of zinc in the third test tube.
8.
Observe and record any changes that occur over the next 5 minutes.
9. Pour all materials in the waste jug. (Not down the sink!) Rinse test tubes with water.
D. Reaction of Carbonate with Acid
10. Obtain a test tube and add 2 mL of 1M HCl. Add a small amount of Na2CO3 (s) to the test tube.
11. Observe and record any changes.
12. Light a wood splint with a match. Place the burning end in the neck of test tube above the liquid. Record and
explain your observations. (Hint: think about the products formed in this reaction)
13. Pour the test tube contents down the sink. Rinse test tube with water. Put wood splint in the regular trash.
E. Reactions of Ionic Compounds
14. Obtain three test tubes. Record any changes after adding the following:
a. In test tube 1 put 10 drops of 0.1 M CaCl2 and 10 drops of 0.1 M Na3PO4.
b. In test tube 2 put 10 drops of 0.1 M BaCl2 and 10 drops of 0.1 M Na2SO4.
c. In test tube 3 put 10 drops of 0.1 M FeCl3 and 10 drops of 0.1 M KSCN.
15. Pour all materials in the waste jug. (Not down the sink!) Rinse test tubes with water.
Waste Disposal
●
Refer to the last step of each section A-E.
Name_________________________
Team Name ______________________
CHM111 Lab – Chemical Reactions – Grading Rubric
To participate in this lab you must have splash-proof goggles, proper shoes and attire.
Criteria
Points possible
Lab Performance
Lab work performed correctly. Proper safety procedures followed
and waste disposed of correctly. Work space and glassware
cleaned up. Participated actively in the experiment. Worked
actively in the lab group of 3 or fewer students. Did parts of the
experiment. (Collecting data is not doing part of the experiment)
3
Lab Report
Part A (accurate observations and reaction balanced)
2
Part B (accurate observations and reaction balanced)
2
Part C (accurate observations and reactions balanced)
2
Part D (accurate observations, reaction balanced, correct
explanation of splint)
2
Part E (accurate observations and reactions balanced)
3
Post Lab Q1
2
Post Lab Q2
1
Post Lab Q3
1
Post Lab Q4
2
Total
20
Subject to additional penalties at the discretion of the instructor.
Points earned
Combustion of Magnesium
Initial Appearance of Mg
Reaction observations
Final Appearance
Balance the reaction:
____ Mg (s) + ____ O2 (g)
→
B. Reaction of Zinc with Copper Sulfate
Initial Appearance of zinc and solution
____ MgO (s)
After 15 minutes
After 30 minutes
Balance the reaction:
____ Zn (s) + ____ CuSO4 (aq)
→
____ Cu (aq) + ____ ZnSO4 (aq)
C. Reaction of Metals with Acid
Metal
Initial Appearance
Reaction observations
Copper
Magnesium
Zinc
Balance the reactions:
____ Cu (s) + ____ HCl (aq)
→
____ CuCl2 (aq) + ____ H2(g)
____ Mg (s) + ____ HCl (aq)
→
____ MgCl2 (aq) + ____ H2(g)
____ Zn (s) + ____ HCl (aq)
→
____ ZnCl2 (aq)
+ ____ H2(g)
D. Reaction of Carbonate with Acid
Initial Appearance
Reaction observations
Observations for splint
Balance the reaction:
____ HCl (aq) + ____ Na2CO3 (aq)
→
____ CO2 (g) + ____ H2O (l) + ____ NaCl (aq)
Explain your observations of the splint based on the reaction products:
E. Reactions of Ionic Compounds
Reactants
Appearance before mixing
Reaction observations
CaCl2 + Na3PO4
BaCl2 + Na2SO4
FeCl3 + KSCN
Balance the reactions:
____ CaCl2 (aq) + ____ Na3PO4 (aq)
→
____ NaCl (aq) + ____ Ca3(PO4)2 (s)
____ BaCl2 (aq) + ____ Na2SO4 (aq)
→
____ NaCl (aq) + ____ BaSO4 (s)
____ FeCl3 (aq) + ____ KSCN (aq)
→
____ Fe(SCN)3 (aq) + ____ KCl (aq)
Q1. Balance the following reactions:
a)
____ H2SO4(aq)
+ ____ Sr(OH)2(aq)
b)
____ P4O10 (s)
+
c)
____ AlCl3 (aq)
d)
___C7H14O2(g) + ____ O2 (g)
____ H2O (l)
+
→
→
____ H2SO4 (aq)
→
____ H2O (l)
+
____ SrSO4(s)
____ H3PO4 (aq)
→
____ Al2(SO4)3 (aq)
____ CO2 (g)
+
+
____ HCl (aq)
____ H2O (g)
Q2. Are the following chemical (C) or physical changes (P)?
a)
____ Sugar dissolves in water
b)
____ Sugar is heated to form caramel.
c)
____ Water evaporates.
d)
____ Charcoal burns on a grill.
Q3. List 3 signs that a reaction occurred in your experiments. (How could you tell by looking at the mixtures that a
reaction had occurred.)
Q4. Give the balanced equation for the following reaction: aqueous solutions of lead (II) nitrate and sodium phosphate
are mixed resulting in the formation of solid lead (II) phosphate and aqueous sodium nitrate.
Decomposition of Sodium Hydrogen Carbonate
Goal: To experimentally determine decomposition reaction of sodium hydrogen carbonate on reaction stoichiometry.
Introduction
Stoichiometry is the study of mass relationships in chemistry. In this lab, you will decompose baking soda (sodium
hydrogen carbonate or sodium bicarbonate) and use the mass relationships to determine how baking soda decomposes.
Baking soda is commonly used in baking to provide a “rise” to baked goods. When baking soda decomposes it produces
a gas (carbon dioxide) which is trapped in pockets and giving the baked goods an airy texture. Sodium bicarbonate may
be more familiar to you as baking soda.
There are three theoretically possible chemical reactions that could occur during the thermal decomposition of baking
soda.
1)
sodium bicarbonate (s) → sodium hydroxide (s) + carbon dioxide (g)
2)
sodium bicarbonate (s) → sodium oxide (s) + carbon dioxide (g) + water (g)
3)
sodium bicarbonate (s)→ sodium carbonate (s) + carbon dioxide (g) + water (g)
By comparing the theoretical yields of the possible solid products with the actual experimental yield of the product, you
will be able to determine which of the above decomposition reactions occurred.
In this experiment, you will determine the products from the thermal decomposition of sodium bicarbonate. The
experiment is straightforward. A sample of sodium bicarbonate is weighed and heated. The final product will be weighed
and the mass of product will be compared to the theoretical yield of the three possible products to determine how sodium
bicarbonate decomposes, and whether its decomposition gives different products when heated to a low temperature
versus a high temperature.
Laboratory Activity
Equipment
hot plate
Beaker tongs
Chemicals
NaHCO3(s)
analytical top-loader balance
clean dry beaker
Safety Hazards – Caution – hot plates are hot! Even when they may not look hot. When determining if a beaker is still
hot, slowly bring the back of your fingers towards it. If you sense any heat radiating from the beaker, do not touch, wait!
PROCEDURE
1) (Run 1) Weigh a clean dry small beaker record the weight.
2) Add between 4 and 5 grams of sodium bicarbonate and reweigh. Record the weight.
3) Set the hot plate at 200 degrees C. Set the beaker on the hot plate and heat for 15 minutes.
4) Take the beaker off the hot plate and let cool until it reaches room temperature. reweigh.
5) (Run 2) Get a new clean dry beaker, weigh, add 4 to 5 grams of sodium bicarbonate and reweigh. Record all the
weights.
6) Set the hot plate to 400 degrees C. Put the beaker on the hot plate and heat for 15 minutes.
7) Remove the beaker from the hot plate and allow it to cool to room temperature and reweigh.
8) Dispose of waste in the sink.
Name_________________________
Team Name ______________________
CHM111 Lab – Decomposition of Sodium Bicarbonate – Grading Rubric
Criteria
Points possible
Lab Performance
Lab work performed correctly. Worked in a group of 3 or fewer.
Proper safety procedures followed and waste disposed of correctly.
Workspace and glassware cleaned up. Participated actively in the
experiment.
2
Lab Report
Data was recorded with correct units and significant figures
2
Question 1 (three balanced equations)
3
Question 2 (work shown clearly with units)
10
Question 3
1
Question 4
2
Total
20
Subject to other additional penalties as per the instructor
Points earned
DATA
Record all masses to the maximum number of
sig figs
1.
Mass of beaker
2.
Mass of beaker + NaHCO3
3.
Initial mass of NaHCO3
4.
Mass of beaker plus products after
heating.
Run 1
200°C
Run 2
400°C
5. Mass of product (actual yield)
PostLab Questions
1) Balance the reactions for the three theoretical decomposition reactions.
A. sodium bicarbonate (s) → sodium hydroxide (s) + carbon dioxide (g)
___NaHCO3(s)
→
___NaOH(s) +
___CO2(g)
B. sodium bicarbonate (s) → sodium oxide (s) + carbon dioxide (g) + water (g)
___NaHCO3(s)
→
___Na2O(s)
+
___CO2(g) +
→
___Na2CO3(s) +
___CO2(g) +
(Reaction B)
___H2O(g)
C. sodium bicarbonate (s)→ sodium carbonate (s) + carbon dioxide (g) + water (g)
___NaHCO3(s)
(Reaction A)
___H2O(g)
(Reaction C)
2) Using the initial mass of NaHCO3, calculate theoretical yield of each of the 3 possible solid products. Remember to
use your balanced equations from the previous section!
Run 1:
Initial Mass NaHCO3 ___________
Molar Mass NaHCO3 ______________
Initial moles NaHCO3 ______________
Molar Mass NaHCO3 ______________
Initial moles NaHCO3 ______________
Run 2:
Initial Mass NaHCO3 ___________
With the initial moles of sodium bicarbonate used for runs 1 and 2, calculate the theoretical yield (predicted mass) of
solid products from each of the possible decomposition reactions, then calculate the percent yield by dividing your
actual yield by the theoretical yield you calculate for each reaction.
𝑎𝑐𝑡𝑢𝑎𝑙 𝑦𝑖𝑒𝑙𝑑
Percent yield = |𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑| x 100
Run 1
Reaction A (balance the reaction)
___NaHCO3(s)
→
___NaOH(s) +
___CO2(g)
Run 1 200 °C:
Initial moles of NaHCO3
________________
moles of NaOH predicted: _________________
grams of NaOH predicted_______________
Grams of product actually produced ___________________
percent yield of NaOH Run 1 ____________
Show your work
Run 2 400 °C:
Initial moles of NaHCO3
________________
moles of NaOH predicted: _________________
grams of NaOH predicted_______________
Grams of product actually produced ___________________
percent yield of NaOH Run 2 ____________
Show your work
Reaction B (balance the reaction)
___NaHCO3(s)
→
___Na2O(s)
+
___CO2(g) +
___H2O(g)
Run 1 200 °C:
Initial moles of NaHCO3
________________
moles of Na2O predicted: _________________
grams of Na2O predicted_______________
Grams of product actually produced ___________________
percent yield of Na2O Run 1 ____________
Show your work
Run 2 400 °C:
Initial moles of NaHCO3
________________
moles of Na2O predicted: _________________
grams of Na2O predicted_______________
Grams of product actually produced ___________________
percent yield of Na2O Run 2 ____________
Show your work
Reaction C (balance the reaction)
__NaHCO3(s)
→
___Na2CO3(s) +
___CO2(g) +
___H2O(g)
Run 1 200 °C:
Initial moles of NaHCO3
________________
moles of Na2CO3 predicted: _________________
grams of Na2CO3 predicted_______________
Grams of product actually produced ___________________
percent yield of Na2CO3 Run 1 ____________
Show your work
Run 2 400 °C:
Initial moles of NaHCO3
________________
moles of Na2CO3 predicted: _________________
grams of Na2CO3 predicted_______________
Grams of product actually produced ___________________
percent yield of Na2CO3 Run 2 ____________
Show your work
3) For Run 1, which reaction was closest to 100% yield? For Run 2, which reaction was closest to 100% yield?
4) During Run 1 (heated to 200°C), do you think that the sodium bicarbonate turned into NaOH, Na2O, or Na2CO3?
What about during Run 2 (heated to 400°C)? Did they form the same product, or different products? Was this
expected or unexpected? Explain briefly.