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Determination of the Molar Mass of a Volatile Liquid by the Ideal Gas Equation

Introduction:

1

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) The ideal gas law allows chemists to determine and derive important features of compounds by formula manipulation.

a. The formula: PV = nRT

i. P = pressure, V = volume, n = moles, R = ideal gas constant, T = temperature

1. R = 0.0

8

2

0

6

L ( atm/(K ( mol)

2) At standard temperature and pressure (STP), the volume for 1 mole of an ideal gas is 22.

4

L.

a. TSTP = 2

7

3

.1

5

K (0.00oC)

b. PSTP = 1 atm (760. mm Hg)

3) Volatile liquids are compounds that can be easily be vaporized.

a. If this vaporization takes place in a known volume and at a given temperature and pressure, the number of moles can be determined.

i. The rearranged formula: n = PV/RT

ii. The pressure in the container is equal to the barometric pressure as long as the container is open to the atmosphere.

1. Remember: 1 atm = 760. mm Hg

b. The molar mass of the volatile liquid can then be determined by knowing the mass of the vapor.

i. Molar mass (M) = mass of vapor/moles of vapor = g/mol.

The Known Volatile Liquids:

1) Acetone (2–Propanone)

2) Cyclohexane

3) Ethanol (Ethyl Alcohol)

4) Ethyl Acetate

5) Isopropyl Acetate

6) Isopropyl Alcohol (2–Propanol)

7) Pentane

Substances to include in the Table of Chemical and Physical Properties:

The boiling point for the seven known volatile liquids listed above.

Procedure:

1) Clean and completely dry a 125 mL Erlenmeyer flask.

2) Obtain a cap for the flask.

a. The cap is an appropriately sized stopper with a hole in the center. A small open glass tube (such as an eye dropper) has been placed through the stopper.

3) Record the mass of the clean and completely dried flask with the cap on an analytical balance.

4) Add approximately 7.5 mL of your volatile liquid to the inside of the flask.

a. Record the name of the volatile liquid assigned.

5) Set up a water bath in a 600 –

10

00 mL beaker using a hot plate as a heat source.

a. Place a few boiling stones into the water to promote even heating.

6) Immerse your flask into the water to cover the entire flask without allowing any water to enter the flask.

a. Secure the flask by using a utility clamp.

b. It is very important that water does not get into the flask!

7) Quickly bring the water to a boil and then lower the heat to allow for a gentile boil.

a. Record the temperature of the water once stabilized. (This temperature will also be the heat of your vapor.)

b. Record the pressure in the lab using a barometer.

8) Allow your sample to heat for 10 minutes once a gentle boil has been obtained. Ensure that all liquid material has been vaporized.

9

) Remove flask from water bath and allow to cool to room temperature.

a. The vapor may condense back into a liquid; do not be alarmed.

10) Remove ALL TRACES of water from the outside of the flask.

a. Water can condense on the edges of the cap; ensure removal of this water.

11

) Obtain the mass of the cool, dried flask on an analytical balance.

12) Dispose of extra/remaining volume of volatile liquid in the appropriately labeled waste containers.

13) Remove cap and ensure the Erlenmeyer flask has been rinsed well with water.

14) Fill up the flask to the top with deionized water.

a. CAREFULLY, transfer the volume into graduated cylinder(s) and record the total volume of the water that the flask could hold.

b. Repeat this volume determination for maximum precision.

15) Repeat experiment for a second trial.

a. Use a separate cleaned and dried 125 mL Erlenmeyer flask.

b. For this trial, add approximately 5.0 mL of the volatile liquid to the inside of the flask.

16) Using the example data table attached, determine the molar mass of your volatile liquid and compare to true value.

Clean – Up:

1) All water baths can be poured down the sink and the boiling stones discarded into the trash.

2) Extra volumes of volatile liquids should be placed in the appropriately labeled waste containers.

Sample Data Table:

a) Volatile liquid assigned: ________________

b) Mass of flask with cap in grams: ________

Trial 1: ________ Trial 2: ________ Trial 3: ________

c) Volume of unknown liquid added (mL):

Trial 1: ________ Trial 2: ________ Trial 3: ________

d) Stable temperature of water (oC):

Trial 1: ________ Trial 2: ________ Trial 3: ________

e) Stable temperature of water (K):

Trial 1: ________ Trial 2: ________ Trial 3: ________

f) Barometric pressure (mm Hg):

Trial 1: ________ Trial 2: ________ Trial 3: ________

g) Barometric pressure (atm):

Trial 1: ________ Trial 2: ________ Trial 3: ________

h) Mass of flask with cap with sample after heating in grams:

Trial 1: ________ Trial 2: ________ Trial 3: ________

i) Mass of volatile liquid in grams (h – b):

Trial 1: ________ Trial 2: ________ Trial 3: ________

j) Volume of water taken up by flask in liters:

Trial 1: ________ Trial 2: ________ Trial 3: ________

k) Moles of volatile liquid using n = PV/RT (mol):

Trial 1: ________ Trial 2: ________ Trial 3: ________

l) Experimental molar mass of volatile liquid in grams per mole (i/k):

Trial 1: ________ Trial 2: ________ Trial 3: ________

m) Average experimental molar mass of volatile liquid: _______________

n) True molar mass of volatile liquid: _______________

o) Percent error: _______________

Model Apparatus Set – Up:

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Barnett & Jones

General Chemistry-I Lab

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PAGE

1

General Chemistry – I Lab
Barnett

Pre-lab4

Title: Periodic Trends

Date: 9/12/18

Unknown: N/A

Purpose: The purpose is to observe chemical properties of elements in periods (rows) and in

groups/families (columns).

Balanced Equations:

Part 1: Chemical Properties of the Alkaline Earth Metal Nitrates

Mg(NO3)2(aq) + Na2CO3(aq)  MgCO3(s) + 2NaNO3(aq)

Ca(NO3)2(aq) + Na2CO3(aq)  CaCO3(s) + 2NaNO3(aq)

Ba(NO3)2(aq) + Na2CO3(aq)  BaCO3(s) + 2NaNO3(aq)

Part 2: Chemical Properties of the Halides

NaCl(aq) + AgNO3(aq)  AgCl(s) + NaNO3(aq)

NaBr(aq) + AgNO3(aq)  AgBr(s) + NaNO3(aq)

NaI(aq) + AgNO3(aq)  AgI(s) + NaNO3(aq)

Part 3: Reactivity of Third Period Elements with

Oxygen

2 Mg(s) + O2(g)  2 MgO(s)

4 Al(s) + 3 O2(g)  2 Al2O3(s)

Si(s) + O2(g)  SiO2(s)

Part 4: Reactivity of Third Period Elements with Hydrochloric Acid

Mg(s) + 2 HCl(aq)  MgCl2(aq) + H2(g)

2 Al(s) + 6 HCl(aq)  2 AlCl3(aq) + 3 H2(g)

Si(s) + 4 HCl(aq)  SiCl4(aq) + 2 H2(g)

Table of Chemical and Physical Properties:

Chemical Name Molecular

Weight

Boiling Point Density Safety

Barium nitrate

Ba(NO3)2

261.34

529 C 3.24 g/cm

3 Poisonous. Do

not mix with

flammable

materials.

Silver nitrate

AgNO3

169.87 440 C 4.35 g/cm
3 Corrosive and

toxic. Avoid

skin contact.

Sodium Chloride

NaCl

58.44 801 C (melting

point)

2.16 g/cm3 Nonhazardous

Magnesium

Mg

24.31 650 C (melting

point)

1.738 g/cm3 Flammable. Do

not stare are

flame during

reaction with

magnesium and

oxygen

Calcium

Ca

40.08 842 C (melting

point)

1.54 g/cm3 Flammable

gases produced

with in contact

with water

Aluminum

Al

26.98 2460 C 2.7 g/cm
3 Flammable

Silicon

Si

28.09 2355 C 2.33 g/ml Nonhazardous

Oxygen

O

15.999 u 90.188 K 1.429 g/L Flammable gas

Hydrochloric

acid

HCl

36.46 110 C 1.18 g/cm
3 Toxic and

corrosive. Can

cause irritation

or burns to skin.

Procedure Observation

Part 1

1. Add 1ml of each solution to each
labeled test tubes

2. Add about three drops of solution
from tube 4 into tubes 1-3 and record

observations.

Part 2

3. Repeat steps 1&2 for part 2 with
different solutions

Part 3

4. On a watch glass, add small pieces of
magnesium, aluminum and silicon and

observe physical appearances.

5. Take turns placing each substance
over an open flame and record

observations.

Part 4

6. Place a small piece of magnesium,
aluminum, and silicon in separate test

tubes and label appropriately.

7. Place 1ml of HCl into each test tube
and record observations.

All observations are documented in the data

tables below

Data Collected:

Part 1

Aqueous

substances

Observations after reacting with 0.02 M Na2CO3

Mg(NO3)2 No physical change observed

Ca(NO3)2 Semi-solid, cloudy substance formed and sunk to the bottom of the test tube

Ba(NO3)2 Solution became milky and slowly sunk to the bottom

Part 2
Aqueous
substances

Observations after reacting with 0.10 M AgNO3

NaCl Slow reaction. Started a bluish color and became milkier

NaBr Top layer of solution turned a milky color and slowly spread throughout

NaI Slow reaction. Went from a translucent yellow to a bluish color

Part 3

Metallic

substances

Observations during and after reaction with atmospheric O2

Mg Produced a bright white flame and sparks

Al The aluminum turned bight orange and produced an orange flame

Si No reaction observed

Part 4
Metallic
substances

Observations during and after reaction with aqueous HCl

Mg Immediately bubbled. Condensation and steam produced. Test tube was warm

Al Slow reaction. Solution bubbled and aluminum piece dissolved in solution

Si No reaction observed

Discussion:

In this lab we observed physical and chemical properties. For example, we observed a

chemical reaction when magnesium was introduced to oxygen. It produced a bright white flame.

Changes in color are physical changes like when AgNO3 was introduced to NaI.

Conclusion:

Some chemicals are more reactive than other. We can observe physical and some

chemical changes when we mixing chemicals together.

Date Completed & Signature:

Pre-lab4

Title: Periodic Trends

Date: 9/12/18

Unknown: N/A

Purpose: The purpose is to observe chemical properties of elements in periods (rows) and in

groups/families (columns).

Balanced Equations:

Part 1: Chemical Properties of the Alkaline Earth Metal Nitrates

Mg(NO3)2(aq) + Na2CO3(aq)  MgCO3(s) + 2NaNO3(aq)

Ca(NO3)2(aq) + Na2CO3(aq)  CaCO3(s) + 2NaNO3(aq)

Ba(NO3)2(aq) + Na2CO3(aq)  BaCO3(s) + 2NaNO3(aq)

Part 2: Chemical Properties of the Halides

NaCl(aq) + AgNO3(aq)  AgCl(s) + NaNO3(aq)

NaBr(aq) + AgNO3(aq)  AgBr(s) + NaNO3(aq)

NaI(aq) + AgNO3(aq)  AgI(s) + NaNO3(aq)

Part 3: Reactivity of Third Period Elements with

Oxygen

2 Mg(s) + O2(g)  2 MgO(s)

4 Al(s) + 3 O2(g)  2 Al2O3(s)

Si(s) + O2(g)  SiO2(s)

Part 4: Reactivity of Third Period Elements with Hydrochloric Acid

Mg(s) + 2 HCl(aq)  MgCl2(aq) + H2(g)

2 Al(s) + 6 HCl(aq)  2 AlCl3(aq) + 3 H2(g)

Si(s) + 4 HCl(aq)  SiCl4(aq) + 2 H2(g)

Table of Chemical and Physical Properties:

Chemical Name Molecular

Weight

Boiling Point Density Safety

Barium nitrate

Ba(NO3)2

261.34

529 C 3.24 g/cm

3 Poisonous. Do

not mix with

flammable

materials.

Silver nitrate

AgNO3

169.87 440 C 4.35 g/cm
3 Corrosive and

toxic. Avoid

skin contact.

Sodium Chloride

NaCl

58.44 801 C (melting

point)

2.16 g/cm3 Nonhazardous

Magnesium

Mg

24.31 650 C (melting

point)

1.738 g/cm3 Flammable. Do

not stare are

flame during

reaction with

magnesium and

oxygen

Calcium

Ca

40.08 842 C (melting

point)

1.54 g/cm3 Flammable

gases produced

with in contact

with water

Aluminum

Al

26.98 2460 C 2.7 g/cm
3 Flammable

Silicon

Si

28.09 2355 C 2.33 g/ml Nonhazardous

Oxygen

O

15.999 u 90.188 K 1.429 g/L Flammable gas

Hydrochloric

acid

HCl

36.46 110 C 1.18 g/cm
3 Toxic and

corrosive. Can

cause irritation

or burns to skin.

Procedure Observation

Part 1

1. Add 1ml of each solution to each
labeled test tubes

2. Add about three drops of solution
from tube 4 into tubes 1-3 and record

observations.

Part 2

3. Repeat steps 1&2 for part 2 with
different solutions

Part 3

4. On a watch glass, add small pieces of
magnesium, aluminum and silicon and

observe physical appearances.

5. Take turns placing each substance
over an open flame and record

observations.

Part 4

6. Place a small piece of magnesium,
aluminum, and silicon in separate test

tubes and label appropriately.

7. Place 1ml of HCl into each test tube
and record observations.

Data Collected:

Part 1

Aqueous

substances

Observations after reacting with 0.02 M Na2CO3

Mg(NO3)2

Ca(NO3)2

Ba(NO3)2

Part 2
Aqueous
substances

Observations after reacting with 0.10 M AgNO3

NaCl

NaBr

NaI

Part 3

Metallic

substances

Observations during and after reaction with atmospheric O2

Mg

Al

Si

Part 4
Metallic
substances

Observations during and after reaction with aqueous HCl

Mg
Al
Si

Discussion:

Conclusion:

Date Completed & Signature:

Banerjee

The lab notebook guidelines are included in this document.

1. Each lab period, in addition to coming to lab properly dressed, a pre-lab must be

prepared for the lab you are scheduled to perform that day. Failure to come to lab

without a complete pre-lab and improper dress will result in dismissal from the week’s

lab with a zero point allocation.

a. Each pre-lab should include the following sections: Name, Title, Date, Unknown,

Purpose, Balanced Equations, Table of Chemical and Physical Properties,

Procedure and an incomplete data table under Data Collected. This should be

uploaded on CANVAS before the start of lab and will be scanned for plagiarism.

This is due at the beginning of the lab period (mandatory).

2. Do not leave without checking out with your professor. You are allowed to use any

notebook or electronic notebook for this lab. Binded lab notebook is not needed for this

lab.

3. Lab reports (post-lab) are due 1 week following the completion of a lab. Each lab is

worth 100 points, comprising of pre and post lab. Your professor will provide further

instructions for completing your lab report.

a. Reports that are suspected to be plagiarized will be reported to the Dean, as

potential violators of the Academic Dishonesty guidelines (procedure 5026). This

will result in an F in the class. Self-plagiarism is also considered plagiarism.

4. The final lab report (post-lab) should comprise of 1) pre-lab sections, 2) Data collected,

3) Observations, 4) Discussion and 5) Conclusion and should be uploaded to CANVAS

placeholder.

Please upload at correct placeholder for each lab. Resubmissions are not allowed.

Please keep an eye on similarity score after submission.

Banerjee

Laboratory Notebook Guidelines

A proper laboratory notebook is one from which a given laboratory experiment can be repeated

by another chemist. Another chemist, chemical engineer or chemical patent lawyer should be

able to read your notebook and understand what you did and the results you obtained.

1. Every experiment should include the following sections listed below.

Title

Name

Date

Unknown (if any)

Purpose Describe the goal of the experiment.

Balanced Equation(s) (if any)

Table of Chemical and Physical Properties (including reference information, if

necessary)

Procedure & Do not provide a detailed, step-by-step procedure. The procedure is in

numerical form and should give the reader a general description of the procedure and any

special experimental details.

Observations . Throughout the lab, be sure to include any relevant observations: What

mass or volume did YOU use? Was the product a solid, liquid, gel, red precipitate, green

solution, etc?

Data Collected A sample data table is provided in each lab write-up. Record the

quantities of materials you used in the experiment. This includes calculations using

formulas, percent yield, percent error, etc.

Discussion Discussion should correlate expected data with obtained data in scientific

terms, without personal opinion.

Conclusion Conclusion should scientifically critic the success of the experiment, without

personal opinion and without over emphasis on errors.

The following sections must be completed prior to lab in the form of PRE-lab and uploaded to

CANVAS in correct placeholder: Name, Title, Date, Unknown, Purpose, Balanced Equations,

Table of Chemical and Physical Properties, Procedure and an incomplete data table under Data

Collected.

** All post-labs are due at the beginning of the next lab period on CANVAS, unless otherwise

specified. Each lab write-up is worth 100 points, including pre and post lab.

Banerjee

Lab reports must be written independently of lab partners,

students in other lab sections, and previous semesters’

students. Reports that are suspected to be plagiarized from any

of the previous sources will be submitted to the Dean, as

potential violators of the Academic Dishonesty guidelines

(procedure 5026). This will result in an F in the class.

THE FOLLOWING PAGE HAS A TEMPLATE ATTACHED FOR YOUR

CONVENIENCE:

Banerjee

Pre-lab

Your Name:

Title:

Date:

Unknown: (if none, write N/A)

(skip one line)

Purpose: Describe the goal of the experiment. Your purpose should answer the
following: What are you doing? Why are you doing it? How are you going do it?

This should be in your own words.

(skip one line)

Balanced Equations: (if none, write N/A)

(skip one line)

Table of Chemical and Physical Properties: The chemicals and
physical/chemical properties listed in the lab should be included in the table.

All the information can obtained from sigmaaldrich dot com.

Example:

Chemical

Name

Molecular

Weight

(g/mol)

Boiling

Point

(°C)

Density Safety

zinc 65.35 907 7.14

g/cm3

irritant,

combustible

copper

nickel

lead

polypropylene

water

Information obtained from:

http://www.sciencelab.com/msds.php?msdsId=9925476

http://pslc.ws/macrog/pp.htm

http://pslc.ws/macrog/pp.htm

Banerjee

Procedure
1. Obtain 50 mL H2O.
2. Tare graduated cylinder

on a balance.

3. Add a rubber stopper,
after recording size.

Observations:
Actual volume: xx mL

Color change:

Gas evolution:

Temperature change:

Data Collected: The provided data table can be pasted into this section or
rewritten for each lab. Include calculations for theoretical yield, actual yield,

percent yield, percent error, and any other calculations that were performed in the

completion of the data table.

(skip one line)

Discussion: Discussion should correlate expected data with obtained data in scientific terms,
without personal opinion.

Conclusion: Conclusion should scientifically critic the success of the experiment, without
personal opinion and without over emphasis on errors.

Contents of discussion and conclusion together should not exceed five scientifically written

sentences.

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