Chemistry Lab Reports

Acid-Base Titration: OnlineStudent Name:
• Carefully read the entire document. Insert values, calculations, and explanations where necessary
• Please be mindful of document formatting when done.
This Lab Report component contains 85 points. The remaining 15 points for this experiment are
earned through completion of the Lab Quiz questions.
Report
Component
Points
Available
Criteria & Maximum Point Deductions
0
–5 for live experiments for incomplete notebook
preparation according to the “Laboratory Notebook
Guidelines” document
10
–7 Title page not present
–5 Missing Results Statement
–3 Results statement lacking experimental findings
–3 Incorrect Title Page format
–5 Overall document formatting is ‘sloppy’
15
–1 to –15 Based on correct insertion of missing values
as determined from video (units, Sig Figs, and
magnitude)
Lab
Calculation
Section
20
–1 to –20 Based on correct calculations (final number,
and some degree of work shown where necessary)
Post-Lab
Questions
20
–1 to –20 Based on Answer Key.
20
Include 1-2 paragraph explanation of the general
principles used in the experiment, how they relate to
each other, the results of the experiments, and
whether they were accurate.
See specific requirements later in this document.
Limited to a maximum 1-2 paragraphs
–1 to –5 Poor grammar, punctuation, sentence
structure or not writing in past tense.
Notebook
Prep
Title Page,
Results
Statement,
and Overall
Formatting of
document
Lab Data
Section/Data
Tables
Discussion &
Conclusion
Total points (out of 85):
Points
Earned
NA
(Remote)
Acid-Base Titration: Online
(Remove this, and insert your title page and results statement here)
Acid-Base Titration: Online
General Directions: All work should be completed and typed directly into this word
document whenever possible. Alternatively, students may insert images of hand-written
work/calculations. Save the file with your last name in the title (i.e.
Student_AcidBaseTitration_Lab.) Upload the completed document to Canvas in the
correct assignment tab by the due date.
Specific Directions: Complete all data sections by typing in data after reading the background
and watching the appropriate experiment videos carefully. After reporting necessary data in
“Data Tables”, complete the “Calculations and Results Section” that follow. Write a ~1-2
paragraph “Discussion/Conclusion” for the entire lab This should include a brief explanation of
the general principles (in your own words) used in the experiment and how they relate to each
other, the results of the experiments, and whether they were accurate according to your
calculations.
OBJECTIVES
The objectives of this experiment are:
1. To prepare a solution of sodium hydroxide (NaOH) by dilution
2. To accurately determine the concentration (molarity) of the NaOH dilution by titrating
against a standard solution of hydrochloric acid (HCl)
3. To determine the molar mass and identity of an unknown acid by titration with this
standardized NaOH solution
BACKGROUND
Acids are compounds that yield a proton, H+ in a chemical reaction (i.e., H+ donors). Bases are
compounds that react with H+ (i.e., H+ ion acceptors). An acid base reaction is a proton transfer
reaction.
A titration is a technique used in the laboratory to determine the amount of an acid or base present
in a sample. During a titration, a standardized (i.e., one in which the concentration of the base is
accurately known) solution containing a base may be slowly added from a buret to a flask
containing an unknown amount of acid- the acid and base could be reversed, of course. By
measuring the amount of titrant (the solution in the buret) required to complete the reaction, and
the stoichiometry of the reaction (the ratio of moles of acid and base needed), the amount of the
acid in the sample can be determined.
Acid-Base Titration: Online
The equivalence point of a titration is where the amount of added titrant is stoichiometrically
equivalent (i.e., in the exact ratio of moles predicted by the balanced chemical reaction) to the
substance being titrated. The end point of the titration is where some change is observed that
indicates that the equivalence point has been reached. The end point can be observed by using
either a chemical indicator (if the solutions are not colored) or a pH meter. An indicator is a
chemical compound that exhibits specific color in acidic solution and a different color in basic
solution. Ideally the equivalence point and the observed end point are the same, however in practice
this is never true.
In this experiment you will first prepare a dilute NaOH solution, and then determine its molarity
by using it to titrate a standardized solution of HCl. After you have prepared and standardized the
NaOH solution, you will use it to titrate an unknown acid to determine its molar mass.
Phenolphthalein will be used as the chemical indicator. Phenolphthalein is colorless in acidic
solution and red/pink in basic solution.
Standardizing a Base (NaOH) by Titrating with a Known Amount of Acid
A titration is used in this experiment to standardize an aqueous solution of NaOH (i.e., to accurately
determine its concentration). A known volume of an HCl solution that has a known
concentration/Molarity (
moles HCl
L soln
) is placed into a flask, and water is added to provide enough
volume making it easy to observe. An indicator is added that will change color when the solution
turns basic. Then, the NaOH solution (whose concentration is unknown) is slowly added from a
buret, causing this reaction to occur:
HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq)
(1)
The solution in the flask (HCl alone, initially) is of course acidic at first. As NaOH is added in
small increments, the solution remains acidic, but becomes less acidic as more NaOH is added and
more of the HCl is consumed by reacting with it. Eventually the HCl in the flask is used up
completely, and the next single drop of NaOH turns the solution basic, causing the indicator to
change color. At the equivalence point in a titration, the amount of base added is exactly equal to
the amount necessary to react with all of the acid originally present in the flask.
# moles NaOH = # moles HCl
at the equivalence point.
We can calculate the amount of base that reacted by first calculating the amount of acid that reacted.
All the acid that reacted was present in the flask when the titration started. The number of moles
of acid can be calculated from the volume (# L) you put into the flask and its concentration
(moles/L) in that volume:
# moles HCl = (
# moles HCl
1L
) × # L HCl solution
Acid-Base Titration: Online
The stoichiometry of reaction 1 tells us that each mole of HCl reacts with exactly 1 mole of NaOH.
Therefore,
# moles NaOH = # mole HCl ×
1 mole NaOH
1 mole HCl
The concentration of the NaOH solution can then be calculated from the number of moles of NaOH
and the volume that it was dissolved in (i.e. the volume of NaOH solution that you added from the
buret):
Molarity of NaOH (M) =
# moles NaOH
# L NaOH soln
Titrating a Diprotic Acid
When a diprotic acid, e.g. H2SO4, is titrated with NaOH, both hydrogen ions on the acid are
transferred during the neutralization reaction. Write the balanced reaction of H2A with NaOH.
What does the balanced reaction tell you about the amounts of acid and base required for the
reaction?
To find the molar mass of H2A, both the mass of acid and moles of acid must be known:
Molar Mass =
g H2A
mole H2A
Techniques for Using Burets Accurately
1. Clean the buret by rinsing it with tap water and brushing it with a buret brush – don’t use
soap. Water in the buret should drain freely, without leaving clinging drops on the inside.
2. After cleaning the buret, rinse it thoroughly with ~5-10 mL portions of the solution that
goes into the buret. This prevents dilution of the solution with water left in the buret. Your
instructor will demonstrate this technique
3. The easiest way to fill/refill a buret is to use a small (100-250 mL) beaker and a liquid
funnel.
4. Initially, fill the buret to within a couple of mL from the top – above the 0.00 mL mark.
5. Ensure the tip of the buret is filled and free of air bubbles by opening and closing the
stopcock rapidly several times to allow the liquid running through the tip to dislodge the
bubbles. Remove any drops hanging from the buret tip with a wash bottle.
Acid-Base Titration: Online
6. Record the value exactly in your notebook. Some find it helpful to read a buret while holding
a piece of white paper behind the buret to blank out objects or people across the room. This
makes the meniscus darker and easier to see.
7. Double-check your readings. Burets are calibrated from top to bottom. The buret reading is
the number of mL read to the one hundredths place (0.0X mL) indicated by the bottom
of the meniscus.
Techniques for Using Pipets Accurately
1. Pipetting takes practice. Your instructor will demonstrate the use of a pipet and pipet bulb.
Before pipetting chemicals, practice with water until you are proficient. Avoid getting
liquid into the pipet bulb!
After practicing:
2. Clean the pipet by drawing the solution that you are pipetting into it, filling it completely
(to above the mark), and allow it to drain into a waste beaker. Repeat this step at least once
more.
3. Draw the solution past the mark on the pipet. Quickly replace the bulb with your finger and
slowly release the liquid into a waste container until the meniscus is on the line. Wipe off
any drop hanging from the pipet tip and any liquid on the outside of the pipet.
4. Angle the pipet while delivering the solution and touch the pipet tip to the inside of the
container to help remove the last drop. No drop should be left hanging.
5. Do not “blow out” the liquid that remains in the tip of the pipet when it is finished draining.
Pipets are calibrated to leave a small amount of liquid in the tip.
Acid-Base Titration: Online
Procedure:
Part A: Standardization of ‘unknown’ concentration NaOH Solution with HCl
Watch the video then use the data given below to complete the Data Table for Part A

Video Copyright: North Carolina School of Medicine
15 Points Total. Lab Data Section:
5 Points for Complete and Correct Table. Part A: Use the table and associated data to determine the
actual concentration of NaOH.
Molarity of HCl used: [Insert Value]
Volume of HCl used: [Insert Value]
Data Table Part A: Standardization of NaOH Solution with HCl
Volume of NaOH soln. used
Trial 1
Trial 2
Trial 3
21.50
21.15
21.90
Moles of NaOH used
Moles of HCl titrated
Volume of HCl soln. titrated:
Calculated molarity of NaOH
Procedure: Part B: Determining the Molar Mass of an Unknown Acid by Titration with NaOH
5 Points for Complete and Correct Table. Part B: There is no video for Part B. Use the table below and
associated data to determine the molar mass of the unknown acidic compound.
Molarity of NaOH Solution used in Part B: ___0.15 M NaOH_____
Trial 1
Trial 2
Trial 3
Mass of Unknown Acid 0.242 g
0.222 g
0.223 g
Volume of NaOH soln. 32.50 mL
titrated
31.2 mL
30.01
Moles of NaOH
Moles of unknown acid
Acid-Base Titration: Online
Calculated Molar mass
of acid
Average Molar Mass of unknown acid [Insert Value]
Procedure, Part C:
Watch the video then use the data given below to complete the Data Table for Part C

Video Copyright: Anne Schmidt
5 Points for Complete and Correct Table. Part C: Complete the table to determine the concentration of
acetic acid in vinegar.
Note: the molarity of NaOH in this experiment = 0.5 M NaOH
Trial 1
Trial 2
Trial 3
Volume of NaOH initial 0.60 mL 0.85 mL 0.45 mL
Volume of NaOH final 35.45 mL 34.30 mL 33.80 mL
Volume Vinegar Sample (L)
Volume NaOH Consumed (L)
Moles NaOH
Moles acetic acid present
Molarity acetic acid in vinegar
Trial 1
Trial 2
Trial 3
0.020
0.020
0.020
Acid-Base Titration: Online
20 Points Total. Lab Calculation Section
General Directions for inserting calculations:
A. Either insert photos of your (neatly) written out calculation,
Or
•
B. Type out the equations that you are solving. Remember to include proper units!
For this choice, use the “Insert→Equation” function in MS Word. This is a good opportunity to
practice typing equations.
Show examples of the following calculations below.
Calculations Part A.
3 Points. Calculate the molarity of the standardized NaOH solution for each of the three trials. Show one
calculation.
[Remove this statement and enter calculation here]
Calculations Part B.
3 Points. Write the balanced chemical equation for the reaction of a generic diprotic acid (H2A) with
NaOH:
[Remove this statement and insert equation here]
4 Points. Calculate the molar mass of the unknown diprotic acid for each of the three trials. Show the full
calculation for one.
[Remove this statement and enter calculation here]
Calculations Part C.
2 Points. Write the balanced chemical equation for the reaction of acetic acid with NaOH
[Remove this statement and insert equation here]
2 Points. Calculate the moles NaOH consumed for each of the three trials. Show one calculation.
[Remove this statement and enter calculation here]
2 Points. Calculate the moles acid present for each of the three trials. Show one calculation.
Acid-Base Titration: Online
[Remove this statement and enter calculation here]
2 Points. Calculate the molarity of acetic acid for each of the three trials. Show one calculation.
[Remove this statement and enter calculation here]
2 Points. Calculate the average acetic acid molarity for all trials:
[Remove this statement and enter calculation here]
Acid-Base Titration: Online
Discussion/Conclusion Statement (20 points):
[Insert Discussion/Conclusion paragraphs here. Discussion and conclusion statements should be standalone paragraphs that anyone could read and quickly understand what you determined, how precise and/or
accurate your results were, sources of error, potential improvements to the experiment and applications of
the experiment to a broader topic. Some discussion of the topics and how they relate is expected]
Discussion/conclusion statements should be stand-alone paragraphs that anyone could read and quickly
understand what you determined, how precise and/or accurate your results were, sources of error,
potential improvements to the experiment and applications of the experiment to a broader topic. For
example, do not simply state that the objective of the experiment was met but rather state what the actual
result was.
Avoid repeating the procedures from the experiment but be clear when you discuss sources of error and
improvements: “It was difficult to get the volume correct” vs “Due to lack of experience it was difficult
to use the pipet bulb and the volumetric pipets which may have resulted in significant errors in the
volume.” Do not include personal statements about the experiment –I did not understand the
procedures….
For this experiment, be sure to address the following in your statement:
(5 points) Part B: what is the (average) molarity of the base, how close were your three values (precision),
(5 points) Part C: what is the (average) molar mass of the unknown acid, how close were your three values
(precision), what is your accuracy for the molar mass
(5 points) Find a real-world example related to any topic covered in this experiment, discuss it briefly and
include a citation.
(5 points) For both parts: Did you observe any sources of error? How would these affect your calculated
results? Would the results be erroneously high or low?
Acid-Base Titration: Online
Post Lab Questions (20 Points).
Answer the following question on this sheet.
1. (4 points.):
When reading the buret in the lab, it is read to __________ of a mL (i.e. how many decimal places).
[Insert answer here]
2. A 0.500-gram sample of a weak, nonvolatile monoprotic acid, HA, was dissolved in sufficient water to
make 50.0 milliliters of solution. The solution was then titrated with a standard NaOH solution. Predict
how the calculated molar mass of HA would be affected (too high, too low, or not affected) by the
following laboratory procedures. Explain each of your answers for full credit.
A. (4 points.). After rinsing the buret with distilled water, the buret is filled with the standard NaOH
solution; the weak acid HA is titrated to its equivalence point.
[Insert answer here]
B. (4 points.) Extra water is added to the 0.500-gram sample of HA.
[Insert answer here]
C. (4 points.) An indicator that changes color at pH 5 is used to signal the equivalence point.
[Insert answer here]
D. (4 points) An air bubble passes unnoticed through the tip of the buret during the titration.
[Insert answer here]
Gas Laws: Online
Student Name:
• Carefully read the entire document. Insert values, calculations, and explanations where necessary
• Please be mindful of document formatting when done.
This Lab Report component contains 85 points. The remaining 15 points for this experiment are
earned through completion of the Lab Quiz questions.
Report
Component
Points
Available
Criteria & Maximum Point Deductions
0
–5 for live experiments for incomplete notebook
preparation according to the “Laboratory Notebook
Guidelines” document
10
–7 Title page not present
–5 Missing Results Statement
–3 Results statement lacking experimental findings
–3 Incorrect Title Page format
–5 Overall document formatting is ‘sloppy’
15
–1 to –15 Based on correct insertion of missing values
as determined from video (units, Sig Figs, and
magnitude)
Lab
Calculation
Section
20
–1 to –20 Based on correct calculations (final number,
and some degree of work shown where necessary)
Post-Lab
Questions
20
–1 to –20 Based on Answer Key.
20
Include 1-2 paragraph explanation of the general
principles used in the experiment, how they relate to
each other, the results of the experiments, and
whether they were accurate.
See specific requirements later in this document.
Limited to a maximum 1-2 paragraphs
–1 to –5 Poor grammar, punctuation, sentence
structure or not writing in past tense.
Notebook
Prep
Title Page,
Results
Statement,
and Overall
Formatting of
document
Lab Data
Section/Data
Tables
Discussion &
Conclusion
Total points (out of 85):
Points
Earned
NA
(Remote)
Gas Laws: Online
(Remove this, and insert your title page and results statement here)
Gas Laws: Online
General Directions: All work should be completed and typed directly into this word document
whenever possible. Alternatively, students may insert images of hand-written work/calculations.
Save the file with your last name in the title (i.e. Student_GasLaws_Lab.) Upload the completed
document to Canvas in the correct assignment tab by the due date.
Specific Directions: Complete all data sections by typing in data after reading the background and
watching the appropriate experiment videos carefully. After reporting necessary data in Data Tables,
complete the Calculations and Results Section that follows. Write a ~1-2 paragraph
Discussion/Conclusion statement for the entire lab This should include a brief explanation of the general
principles (in your own words) used in the experiment and how they relate to each other, the results of
the experiments, and whether they were accurate according to your calculations.
OBJECTIVES
1. To determine the molar mass of a volatile unknown organic compound
2. To determine the ideal gas constant, R, experimentally
Background:
Gases, unlike solids and liquids, have neither fixed volume nor shape. They expand to fill the entire container
in which they are held. The gas particles are in constant motion. When they collide with a surface, they exert
a force on it which we describe as pressure. Therefore, the pressure of a gas is defined as force per area. The
more collisions, the higher the gas pressure. The greater the force of the impact with the surface, the higher the
gas pressure.
The standard or SI unit for pressure is the Pascal (Pa) which is the force exerted by the gas in Newtons divided
by area in square meters, N/m2. However, atmospheres (atm) and several other units are also commonly used.
Once must be careful when using the ideal gas laws to ensure proper ‘unit matching’ between pressure,
temperature, volume, and the gas constant (R). The table below shows the conversions between these units:
Common Units of Pressure
1 Pascal (Pa) = 1 N/m2
1 bar = 100,000 Pa
1 atmosphere (atm) = 101.325 kPa
1 atm = 760 torr = 760 mm Hg
1 atm = 29.92 in. Hg
1 atm = 14.70 psi (pounds per square inch)
Gas Laws: Online
Part A Background:
Determining the Molecular Weight of a Volatile Unknown Organic Compound
There are several methods by which the molecular weight of a compound can be determined in the
laboratory. In this part of the experiment you will use a method useful for volatile liquids. Volatile
liquids are those liquids that have a low to moderate boiling point at atmospheric pressure or moderate
to high vapor pressure at room temperature.
In the Ideal Gas equation, P is the pressure of the gas, V is the volume of the gas, n is the amount of the
gas in moles, and T is the Kelvin temperature of the gas. R is called the ideal gas constant. The value of
R depends on the units used for pressure and volume. When P is in atmospheres and V is in liters, the
value of R is 0.08206 (L*atm) / (mol*K).
The Ideal Gas Equation:
PV=nRT
In this experiment, a volume of an unknown volatile liquid is heated in an Erlenmeyer Flask until it
completely vaporizes. Excess gas will leave the flask so that the vapor that fills the flask will be at
atmospheric pressure. When the flask is cooled only the vapor in the flask condenses into a liquid which
can then weighed.
As seen in the video in Part A, after determining the atmospheric pressure, temperature of boiling, the
mass of the condensed liquid, and the volume of the flask, you will have all the data required to calculate
the molar mass (molecular weight) of the unknown organic compounds as follows:
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑔𝑎𝑠 = 𝑛 =
𝑃𝑉
𝑅𝑇
𝑀𝑜𝑙𝑎𝑟 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑈𝑛𝑘𝑛𝑜𝑤𝑛 𝐶𝑜𝑚𝑝𝑜𝑢𝑛𝑑 =
𝑔𝑟𝑎𝑚𝑠 𝑜𝑓 𝑔𝑎𝑠
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑔𝑎𝑠, 𝑛
Background for Part B: Determination of the Ideal Gas Constant “R”
The ideal gas constant, R, can be calculated by rearranging the Ideal Gas Equation:
𝑅=
𝑃𝑉
𝑛𝑇
The value of R can calculated from experimentally measured values of pressure, P, of a sample of gas in
atmospheres; the volume of gas, V, in liters; the number of moles, n, of the gas; and the temperature, T,
of the gas in Kelvin. In this experiment, a known amount of hydrogen gas, H2(g), is generated by the
reaction of a known amount of magnesium metal with excess hydrochloric acid (HCl):
Mg (s) + 2 HCl (aq) → H2 (g) + MgCl2 (aq)
Gas Laws: Online
Since the magnesium metal is the limiting reactant, the moles of product hydrogen gas, H2, can be
calculated from the mass of reactant magnesium used. The hydrogen gas that is produced is collected in
a gas tube over water, so its volume and temperature can be directly measured.
The pressure measured in this experiment is atmospheric pressure, but the hydrogen gas is collected over
water so the gas collected will be a mixture of water vapor and hydrogen gas. Recalling that Dalton’s
Law of Partial Pressures states that the total pressure of mixture of gasses is the summation of all the
individual gas pressures, the pressure for the hydrogen gas can be determined as follows:
PTotal = PA + PB+ PC + PD . . .
Patm = PH2 + PH2O
PH2 = Patm – PH2O
The pressure exerted by the water vapor, PH2O, is the vapor pressure of water for a given temperature of
water. From the atmospheric pressure and the vapor pressure of water at this temperature (use Table 1
below), the pressure of the hydrogen gas itself can be calculated.
Gas Laws: Online
Procedure
Video for Part A: Determining the Molecular Weight of a Volatile Unknown Organic Compound
For details on the procedure, experiement set up, and data collection, watch:
https://www.youtube.com/watch?v=0UJXa9Hd88I.
Copyright: the North Carolina School of Science and Mathematics
15 Points Total. Lab Data Section:
6 Points for Complete and Correct Table. Part A: From the information provided in the video above,
complete the data table below. Include all units.
Data Table Part A: Determining the Molecular Weight of a Volatile Unknown Organic Compound
Atmospheric Pressure
Temperature of Boiling Water:
Volume of flask:
Mass of Florence Flask, foil, and copper wire
Mass of Florence Flask, foil, copper wire and condensed vapor:
Mass of condensed vapor
Moles of vapor (n) =
Molar mass of vapor (g/mol)
Unknown Volatile Gas ID:
% Error in Molar Mass:
Possible Volatile Unknowns:
Hexane, Molar Mass = 86.18 g/mol
2-Butanol, Molar Mass = 74.122g/mol.
Acetone, Molar Mass = 58.08 g/mol
Procedure
Video for Part B: Determination of the Ideal Gas Constant “R”
For details on the procedure, experiement set up, and data collection, watch:

Copyright: University of Texas, Arlington, Chemistry
9 Points for Complete and Correct Table. Part B: From the information provided in the video above,
complete the data table below. Include all units.
Gas Laws: Online
Data Table Part B:
Mass of magnesium
Temperature of Water:
Volume of H2 gas collected
Atmospheric Pressure
Vapor Pressure of Water (see Table 1 in Background section)
Vapor Pressure of Water (convert to units of atm)
Pressure of H2 gas (Use Dalton’s Law, see Background)
Moles of H2 gas produced
Value of Ideal Gas Constant, R
% Error in R
24.0 °C
137 mL
1.00 atm
20 Points Total. Lab Calculation Section
General Directions for inserting calculations:
A. Either insert photos of your (neatly) written out calculation,
Or
B. Type out the equations that you are solving. Remember to include proper units!
•
For this choice, use the “Insert→Equation” function in MS Word. This is a good opportunity to
practice typing equations.
Show examples of the following calculations below.
Calculations Part A.
4 Points. Calculate the moles of vapor/condensed liquid using the ideal gas law. Ensure the units for P,
V, and T match those of gas constant, R = 0.08206 (L*atm) / (mol*K)
[Remove this statement and insert equation here]
4 Points. Calculate the molar mass of the unknown volatile liquid.
[Remove this statement and insert equation here]
Calculations Part B.
2 Points. Based on the video, what would happen if two much magnesium was added to the experiment?
Briefly explain 1-2 sentence.
[Remove this statement and insert explanation here]
Gas Laws: Online
2 Points. Calculate the pressure of H2 gas produced based on the data in the Data table and Dalton’s
Law of Partial Pressures discussed in the background.
[Remove this statement and enter calculation here]
4 Points. Based on the balanced chemical equation in the background for the reaction of magnesium
with acid Calculate the moles of H2 gas produced.
[Remove this statement and enter calculation here]
2 Points. Calculate the value of the gas constant, R, in units of (L*atm/mole*K) based on your data
table and value for moles calculated above.
[Remove this statement and enter calculation here]
2 Points. Calculate the percent error between your experimentally determined value for R and the
known value for R:
[Remove this statement and enter calculation here]
Gas Laws: Online
Discussion/Conclusion Statement (20 points):
[Insert Discussion/Conclusion paragraphs here. Discussion and conclusion statements should be standalone paragraphs that anyone could read and quickly understand what you determined, how precise and/or
accurate your results were, sources of error, potential improvements to the experiment and applications of
the experiment to a broader topic. Some discussion of the topics and how they relate is expected]
For example, do not simply state that the objective of the experiment was met but rather state what the
actual result was. Avoid repeating the procedures from the experiment but be clear when you discuss
sources of error and improvements: “It was difficult to get the volume correct” vs “Due to lack of
experience it was difficult to use the pipet bulb and the volumetric pipets which may have resulted in
significant errors in the volume.” Do not include personal statements about the experiment –I did not
understand the procedures….
For this experiment, be sure to address the following in your statement:
(8 points) Part A: what is the identity of the liquid, what is the accuracy of your molecular weight (%
error), sources of error and improvements to the experiment.
(8 points) Part B: how accurate was your average (or best calculated) value to the known value for the
gas constant, sources of error and improvements to the experiment
(4 points) Find a real-world example related to any topic covered in this experiment, discuss it briefly and
include a citation.
Gas Laws: Online
Post Lab Questions (20 Points).
Answer the following question on this sheet.
1. (2 points) What type of reaction (i.e. precipitation, acid-base, oxidation-reduction, combustion, etc…)
is conducted in part B of this lab? Explain how you know.
Mg (s) + 2 HCl (aq) → H2 (g) + MgCl2 (aq)
Questions 2-4 are based off the following information and scenario:
The Dumas method (Part A of this lab) is one of the simplest procedures for determining the molar mass
of an unknown volatile liquid. In the Dumas method, a sample of a liquid in a flask with a tiny opening is
heated until the entire sample vaporizes. Because the volume occupied by the vapor at atmospheric
pressure is much larger than the volume occupied by the liquid, some of the vapor will escape from the
flask. However, the vapor remaining in the flask will contain the number of moles of the substance that
fills the volume of the flask at the experimental pressure and vapor temperature.
2. (4 points) Why is the barometric (i.e., atmospheric) pressure considered to be the pressure of the
vapor, i.e., how does the experimental procedure ensure this?
[Insert answer here]
3. (4 points) Why is it not necessary to weigh the amount of liquid initially put into the flask? Explain.
[Insert answer here]
4. (10 points)
A volatile hydrocarbon (a binary compound of carbon and hydrogen) was determined to be 92.3 % carbon,
by mass. In a separate experiment, utilizing the Dumas method, 4.00 mL pure liquid sample of this
hydrocarbon is vaporized in an Erlenmeyer flask when the barometric pressure is 768.0 torr.
The empty flask was fitted with a foil cap pierced with a pinhole and weighed 25.3478 g. After the excess
gas escaped, the temperature was measured as 98.0 °C. The flask and contents were subsequently cooled
to 25 °C and the vapor condensed into a liquid. The weight of the flask and contents is found to be 25.6803
g. The exact volume of the flask was determined to be 128.5 mL.
Using this information, determine both the empirical and molecular formula of this hydrocarbon.
Show/explain the steps of your work.
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