Name: ____________________________ Period: _____ Date: ________

AP CHEMISTRY LAB MANUAL

QUARTER 2

Page(s) Lab Name Date Performed

Possible Points Points Earned

2 Lab Equipment Diagrams

3－ 7 Separation of a Dye Mixture 10/24 － 10/25 45

9－ 15 Qualitative Analysis 10/27 － 10/28 60

17 － 21 Separation of a Drug Mixture 10/31 － 11/02 50

23 － 27 Determination of the Molar Mass of a Volatile Liquid TBD 40

1

Name: ____________________________ Period: _____ Date: ________

2

Name: ____________________________ Period: _____ Date: ________

SEPARATION OF A DYE MIXTURE

Purpose The purpose of this lab is to investigate the factors that influences the separation of food dyes using paper chromatography. The investigation begins by comparing the resolution of the FD&C food dyes in different solvents. The class will upload and review the data collected for further study and application towards determining the dye content (qualitative) of colored candies. Background The use of color additives increased dramatically in the United States in the second half of the nineteenth century. As the economy became more industrial and demographics shifted, fewer people farmed and the population became more dependent on mass-produced foods. Color additives were used to make processed food more visually appealing to the consumer, and in some cases, used to mask poor-quality, inferior or imitation foods. For example, meat was colored to appear fresh long after it would have naturally oxidized and turned brown. This is still a common practice in the farmed salmon industry, to make the salmon appear fresh and pink after time in shipping and in the market. Many food colorings or additives used in this time period were discovered to be harmful or toxic. In 1883, the United States Department of Agriculture (USDA) Bureau of CHemistry began regulating the food industry to help ensure a safe food supply. Food coloring regulation is just one of the agency’s efforts. By 1907, the number of synthetic food dyes that were approved as safe to consumers was reduced from 695 to just seven. As more data was collected and more dyes were tested, more dyes were eliminated or restricted. Only two of the original dyes from 1907 are still accepted for use today. In total, only seven foods dyes are used in all of the U.S. food industry today. All of these dyes are FD&C approved are water-soluble, organic compounds that bind to ionic and polar sites in food molecules, in particular proteins and carbohydrates. Chromatography is a useful way of separating and purifying organic compounds. There are many different types of chromatography, but most depend on the principle of adsorption (no that is not a typo! Absorption and adsorption are different. Adsorption refers to the capacity of a solid to retain a liquid or gas on the surface of its structure, while absorption refers to the capacity of a solid to carry a liquid within its structure. Subtle difference). The two components of chromatography are the adsorbent and the eluent . Adsorbents are usually solid materials that will attract and adsorb the materials to be separated. The eluent is the solvent, which carries the materials to be separated through the adsorbent.. In this experiment, porous chromatography paper will act as the adsorbent, while dilute solutions of sodium chloride and isopropyl alcohol will be the eluents. Chromatograph is based on the principle that components of a mixture have different affinities for the eluent and adsorbent and thus will travel differently through the adsorbent and will become separated. The components that have the greatest affinity for the eluent may travel farther through the paper, while the components with lower affinity will travel less and will be retained. The distance a sample moves along the chromatography paper is compared to the overall distance that the solvent travels － this ratio is called the Rf value, or rate of flow. In the diagram to the right, the solvent traveled 6.5 cm, while the dye moved from the origin to a distance of 4.5 cm. The Rf value is calculated as the percentage of the distance the dye moved compared to the solvent: 4.5/6.5 = 0.69. It should be noted that dye spots will spread as they travel, while others will remain as small, concentrated spots. Therefore, the class must decide on a uniform way to to measure the distance the spot traveled － will you measure from the top, middle or bottom of the spot?

3

Name: ____________________________ Period: _____ Date: ________

Prelab Questions (10 pts) 1. Figure 1 is a sample paper chromatogram for three samples: A, B and C.

Determine the Rf values for A and B. _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________

2. Sample C gave two spots on the chromatogram. What can you infer about the composition of the sample?

___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

3. What conclusions can you draw about the intermolecular attractions that the samples have for the eluent and the paper?

___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ Materials

FD&C food dyes Erlenmeyer flasks, 250-mL, 2 Isopropyl alcohol solution, 2% Graduated cylinder, 25-mL Sodium chloride solution, 2% Pencil Candy samples Ruler Water, distilled Toothpicks Beaker, 50-mL Wash bottle Beakers, 100-mL, 2 Watch glasses, 2 Chromatography paper strips

Safety Isopropyl alcohol is a flammable liquid and is slightly toxic by ingestion or inhalation. Use proper exhaust ventilation to keep airborne concentrations low. The FD&C dyes are slightly hazardous by ingestion, inhalation, and eye or skin contact. Red No. 40 may be absorbed through skin and Yellow No. 5 may be a skin sensitizer. All dyes are irritating to skin and eyes. Avoid contact with eyes, skin, and clothing. The candies provided in this lab are non-edible. Wear chemical safety glasses, gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines!

4

Name: ____________________________ Period: _____ Date: ________

Procedure ➸ Day 1 1. Cut a piece of chromatography paper and position it so that is 152 mm tall and 19 mm wide. Handle the paper only

by the edges so the area for analysis is not compacted or contaminated. See Diagram on Page 5.

2. Using a ruler and a pencil, lightly mark a line 15 mm from the bottom of the paper across the width of the strip. Measure 9.5 mm from the edge and place a dot on the line. The is the starting point for the sample. See Diagram on Page 5.

3. Using the same ruler, measure 20 mm from the top of the strip and fold

across the width of the strip. This will allow the sample to hand on the lip of the flask. See Diagram to the right.

4. Repeat steps 1-3 for a three more strips; a total of four.

5. Obtain the dyes the instructor assigns to your group. Record the identity of

the dyes in the Day 1 Data Table.

6. Using a capillary tube, spot the chromatography strip by placing the tube into the dye mixture and then touching the tip of the tube onto the designated pencil spot very briefly. Allow the sample to dry. Repeat this procedure two to three more times to concentrate the dye on the strip, but do not allow the size of the spot to increase.

7. Repeat this process for the other chromatography strips, so that you have

a total of four prepared chromatograms, two for each dye assigned.

8. While samples are drying, obtain four 250-mL Erlenmeyer flasks and watch glasses to cover the tops of the flasks. Pour 10-mL of 2% sodium chloride into two of the flasks and 10-mL of 2% isopropyl alcohol into the other two. Cover the flasks with a watch glass.

9. When the chromatograms are dry, remove the watch glass and carefully hang the strips into the flask with the

sample end down. Do not get any solvent onto the upper portion of the strip. The sample spots must remain above the level of the solvent or the sample will dilute int the solvent.

10. Carefully place the watch glass back on top of the flask. Allow the chromatograms to develop. Record observations

of the dye sample as the solvent travels up the paper and the chromatogram develops.

11. When the solvent is within 1-2 cm of the fold in the strip, stop the run by removing the strip from the flask.

12. With a pencil, lightly draw a line to mark the solvent front.

13. Measure the distance from the pencil line at the bottom of the strip to the solvent front. Record this distance in millimeters in an appropriate data table.

14. With a pencil, trace the shape of each dye band or spot to mark its location on the strip.

15. Measure and and record the distance in millimeters that each dye band or spot traveled. Measure from the line at the

bottom of the paper to the center of each band or spot.

16. Calculate the Rf values for each dye in each solvent.

5

Name: ____________________________ Period: _____ Date: ________

Data Table ➸ Day 1 (6 pts)

Chromatogram Dye Solvent Distance Solvent Traveled Distance Spot/Band Traveled Rf

1

2

3

4

Observations ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ Calculations ➸ Day 1 (5 pts) Calculate the R f values for the dyes analyzed in Day 1. Upload your results to the class data table (link given in class) . Procedure ➸ Day 2

1. Obtain a candy sample (3 candies). Record the brand and color of the sample in the Day 2 Data Table.

2. Place the candies in a petri dish with 5-10 drops of distilled water and stir until the candy shell dissolves. Remove the inner candy with a set of tweezers and discard. What remains in the petri dish is your dye sample to analyze.

3. Prepare at least two chromatograms as you did yesterday and spot them with the dye sample that you prepared

today.

4. Choose an eluent to use and record it in the Day 2 Data Table. Run the chromatograms as you did yesterday, recording observations about the run, as well as the solvent distance and spot/band distance(s). Note that you may have multiple bands or spots separating from the dye, so you may need to modify the Day 2 Data Table.

6

Name: ____________________________ Period: _____ Date: ________

Data Table ➸ Day 2 (8 pts)

Brand and color of candy sample

Eluent

Observations

Trial Solvent Distance Spot/Band 1 Distance

Spot/Band 1 Rf Spot/Band 1 Distance

Spot/Band 2 Rf

1

2

add additional data cells as needed for more spots/bands

Reflection Questions (8 pts) 1. Is there any evidence for the color of the candy shell being a mixture of dyes? Describe this using justification from

your Day 2 Data. Alternatively, describe the evidence that shows that the color is due to only one dye. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

2. What dye(s) is(are) the most likely source of color for the candy that you analyzed. Justify your statement using evidence from both the class data and you own Day 2 observations.

___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ Results (8 pts)

Brand/Color of Candy

Dye(s) Actual Dye(s) (for teacher)

Points (for teacher)

dye(s) determined correctly: 8 pts dye(s) mostly determined correctly: 6 pts dye(s) mostly determined incorrectly: 4 pts dye(s) determined incorrectly: 2 pts

7

Name: ____________________________ Period: _____ Date: ________

this page is intentionally blank!

8

Name: ____________________________ Period: _____ Date: ________

QUALITATIVE ANALYSIS Purpose The purpose of this lab is identify 12 unknown solids based on systematic testing of their physical and chemical properties. This will be accomplished by qualitatively analyzing solubilities in various solvents, conductivity in the solid and aqueous states and melting point. Based on the results of these tests, the student should be able to assign an identity to the 12 unknowns. Background Help! A chemical emergency has occurred! Twelve bottles were found in the stockroom with labels missing. Conveniently, the labels were found, but the lab technician does not know to which bottle each label belongs. Luckily, the tech took AP Chemistry and knows a bit about intermolecular forces and how they influence chemical and physical properties. The tech thinks back to his favorite class from high school and remembers the following… Groups of atoms are held together by attractive forces we call chemical bonds . It is important to remember that our representations of bonds, such as...

...are all man-made concepts. Atoms do not really appear this way, nor are there lines holding them together. In fact, a bond is to atoms as gravity is to humans. The force is tangible, consequential and very real, but invisible. There are different types of chemical bonds and each is a result of the type of atoms involved and their arrangements. These types of bonds Ionic bonding describes the attractive force that results when oppositely charged ions form a compound. Anions (-) and cations (+) form a tightly packed 3-dimensional crystal lattice (see Figure 1). Due to highly charged points of the lattice, ionic solids are water soluble, conduct a current when dissolved in water (but not in the solid state), have high melting points and are generally hard, but brittle solids. Ionic solids that contain a transition metal sometimes have vivid colors, while those with Group A metals are typically white solids.

Covalent bonding describes a different kind of attractive force that results from the sharing of electrons between atoms that have similar electronegativities. Atoms may share one, two or three pairs of electrons (see Figure 2). In general, the more electrons shared, the stronger the covalent bond is. A covalent bond can be classified as polar or nonpolar. When two atoms with similar electronegativities bond, the electrons are shared mostly equally and no poles form, thus the bond is nonpolar. When two atoms with differing electronegativities bond, the electrons in the bond are not shared equally and thus the bond takes on partial charges, or poles. This is a polar bond. The more electronegative atom attracts the electrons more strongly

9

Name: ____________________________ Period: _____ Date: ________

and so takes on a partial negative charge (noted with 𝛅－ ) while the less electronegative atom takes on a partial positive charge (𝛅＋ ). See Figure 3.

Figure 3.

Covalent solids can take on two forms. In a molecular-covalent solid, individual molecules form and are held together by intermolecular forces like hydrogen bonding, dipole－dipole attraction and dispersion forces. Depending on which IMF is present, molecular-covalent solids can have a range of properties. The weaker the IMF, the lower the melting point, the softer and waxier the solid will appear. On the other hand, a network-covalent solid can form, which consists of a huge network of strong covalent bonds extending in all directions (similar to ionic forces). Network-covalent solids have some of the highest melting points in existence. Unlike ionic solids, they are not brittle and thus are extremely hard and durable materials. All covalent solids, both molecular and network, do not conduct electricity in the solid state. The polarity of the molecule dictates the solubility: nonpolar compounds are soluble in nonpolar solvents, like hexane, while polar compounds are soluble in polar solvents, like alcohols. Network-covalent solids are generally insoluble in any solvent due to the strength of the network of bonds. Metallic bonding is the result of the unique structure of metals. The current accepted model for metallic bonding refers to the “sea of electrons” (see Figure 4), in which the valence electrons of the metal are not strongly attracted to the metal cations and free to move among the metal atoms. This lends metals unique properties, like heat and electrical conductivity in the solid state, ductility, malleability. Some semimetals share these properties as well. Before beginning this lab, you will review the properties described above and create a flow chart to use in the lab. You should design your flow chart to be as simple as possible, so that your time in the lab is as effective as possible.

10

Name: ____________________________ Period: _____ Date: ________

Prelab Questions (10 points)

1. Considering the data in the table above, explain the following observations, using justification based on chemical

bonding and/or intermolecular forces among the atoms, molecules or ions in the solid state.

a. Iodine has a much lower melting point than sodium iodide. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

b. Iodine is slightly soluble in water, while lactose is very soluble. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

2. Predict the properties of the following solids.

3. Complete the following chart. Use the information in the Background to help you.

Type of Solid

Type of Bonding

Melting Point

(high/low)

Solubility in water

(yes/no)

Solubility in alcohol (yes/no)

Solubility in hexane (yes/no)

Conductivity (solid)

Conductivity (aqueous)

Ionic

Network－ covalent

depends on polarity

depends on polarity

depends on polarity

Molecular－ covalent

depends on polarity

depends on polarity

depends on polarity

Metallic

11

Name: ____________________________ Period: _____ Date: ________

4. These are the identities of the “unknowns”. Assign a bond type to each solid － ionic, network-covalent,

molecular-covalent or metallic. If covalent, be sure to specify if the substance is polar or nonpolar as well.

Name Formula Bond Type

Glycine

Iron(III) oxide Fe2O3

Calcium carbonate CaCO3

Adipic acid

Aluminum Al

Dodecyl alcohol

Iron powder Fe

Potassium nitrate KNO3

Silicon Si

Salicylic acid

Sodium carbonate Na2CO3

Graphite powder C

Materials

Ethyl alcoho, CH3CH2OH Conductivity probe Hexane, C6H14 LabQuest Water, distilled Conductivity meter Unknowns, approximately 3 g each Hot plate Aluminum weighing dish Test tube, small Bunsen burner Thermometer Beaker, 100-mL Tongs

Safety Hexane and ethyl alcohol are flammable organic solvents and dangerous fire risks. Keep away from flames, heat and other sources of ignition. Cap the solvent bottles and work with hexane and ethyl alcohol in a fume hood. Addition of a denaturant makes ethyl alcohol poisonous; it cannot be made nonpoisonous. Powdered unknowns are potential fire and inhalation risks. Wear chemical safety glasses, gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines!

12

Name: ____________________________ Period: _____ Date: ________

Brainstorm ➸ Day 1 (8 points) Using information from the prelab and Background, sketch a flowchart to describe the order of the qualitative tests that will be performed. Each branch of the flowchart should end in a solid type －ionic, polar covalent, nonpolar covalent, metallic, network-covalent.

13

Name: ____________________________ Period: _____ Date: ________

Procedure ➸ Day 2 Using approved flowchart from yesterday and the testing procedures described below, carefully perform tests on the 12 unknowns and take detailed notes in the Data Table in order to identify the unknowns.

Data Table (10 points)

14

Name: ____________________________ Period: _____ Date: ________

Identification/Results (24 points)

Unknown Identity Rationale (cite Data)

1

2

3

4

5

6

7

8

9

10

11

12

12 correct － 8 points 10 correct － 6 points 8 correct － 4 points

6 or fewer correct － 2 points

15

Name: ____________________________ Period: _____ Date: ________

this page is intentionally blank!

16

Name: ____________________________ Period: _____ Date: ________

SEPARATION OF A DRUG MIXTURE

Purpose The goal of this lab is to separate a mixture that represents a synthetic pain reliever and determine the percent composition of the mixture. The mixture may contain a binder, acetaminophen and acetylsalicylic acid in varying amounts. In order to effectively separate the mixture, the solubility of the components must be understood. Background A mixture is a combination of two or more pure substances that retain their separate chemical identities and properties. Since the amount of each substance making up a mixture can be changed, the physical properties of the mixture will depend on its composition. Pharmaceutical companies manufacture different over-the-counter drugs formulations with varying amounts of active drug ingredients, binders and other inert materials. Binders are added to drug mixtures to form the pill, hold it together, and control release of the drug in the body at varying rates. Pain relievers usually contain a starch or silica gel as the binder. Two common active drug ingredients in pain relievers are aspirin and acetaminophen. When not combined into pill form, aspirin and acetaminophen, like all pure substances, have characteristic physical properties. Examples of physical properties that can be used to separate pure substances from a mixture and identify them include solubility, conductivity, magnetism, density, boiling point, and melting point. By taking advantage of the unique physical properties of individual components within a mixture, it is possible to separate a mixture into its components. For example, if one component in a mixture of two solids dissolves in water, while the second component does not, the substances can be separated by adding water to mixture and then filtering the residue. Subjecting the mixture to a physical change in this way would change the ratio of components in the mixture. This leads to one of the definitions of a mixture － a substance whose composition can be altered by a physical change. Physical changes that can be used to separate the components of a mixture include filtration, evaporation, crystallization, distillation, and extraction. Extraction is a convenient method for isolating and separating organic substances. Sold-liquid extraction is a familiar technqiue used to prepare beverages such as coffee or tea － organic compounds, including caffeine and various flavor ingredients are extracted using hot water. In liquid-liquid extraction, a substance that is at least partially soluble in two immiscible liquids can be transferred from one liquid to the other. This is usually done in a separatory funnel by combining the solution containing two or more solutes with a second, immiscible solvent that will dissolve only one of the solutes. The mixture is shaken vigorously to allow the solvents to come into contact with the solutes (see Figure 1). The act of shaking will volatilize the organic solvent, so the funnel should be vented to prevent a build-up of pressure (Figure 2). The liquids separate into two layers in the separatory funnel, with the more dense liquid in the bottom layer and the less dense liquid in the top layer (Figure 3).

17

Name: ____________________________ Period: _____ Date: ________

The stopcock (valve) of the separatory funnel can be opened to carefully separate the more dense lower layer from the less dense upper layer. Alternatively, the two solvents can be vigorously mixed in a beaker and the lower layer can be removed by pipetting (this will be the preferred lesson for this extraction). The structures of acetylsalicylic acid (aspirin) and acetaminophen are shown in Figure 4 below. Acetylsalicylic acid is an organic carboxylic acid (－COOH) that also contains as ester functional group (CH3CO2－) as a side chain on the benzene ring. Acetaminophen has two primary functional groups, a hydroxyl group on the benzene ring, as well as an amino side chain (CH3CON－).

Carboxylic acids that do not dissolve in water can be extracted from an organic solvent with an aqueous solution containing an inorganic base, such as diluted NaOH. The addition of base creates an ionic byproduct that is water soluble. An example of this reaction is shown in Equation 1. C6H5COOH (s) ＋ NaOH (aq) → C6H5COONa (aq) ＋ H2O (l) Equation 1 Mass percent composition is a method of expressing the amount of each component in a mixture. Mass percent composition is calculated as follows: Mass % of component = (mass of component/total mass of mixture) x 100 In order to accurately determine the percent composition of a mixture, it is necessary to separate the components quantitatively － ideally, without loss of material － and then measure the mass of each recovered component. Prelab Questions (5 pts)

1. The Department of Transportation uses a mixture of salt and sand to de-ice roadways in the winter. The mixture contains 8.35 tons of salt and 6.28 tons of sand. What is the mass percent of each component in the mixture?

___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

2. A bakery needs a mixture of flour and sugar to make cookies. The mixture should contain 62.5% flour and 37.5% sugar. How many pounds of flour and sugar should be ordered to make 275 pounds of the mixture?

___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

18

Name: ____________________________ Period: _____ Date: ________

3. Using Figure 4 in the Background section, predict which component in the synthetic pain relief mixture is likely to dissolve in aqueous sodium bicarbonate mixture? Explain.

___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ Materials

Acetaminophen, C8H9NO2, 10 mg Funnel Acetylsalicylic acid, C9H8O4, 10 mg Graduated cylinder, 50-mL Ethyl acetate, CH3CO2CH2CH3, 65 mL Hot plate Hydrochloric acid, HCl, 6 M , 40 mL Ice bath Silica gel, 10 mg Magnetic stirrer and stir bar Sodium bicarbonate solution, NaHCO3, 10%, 50 mL pH test strips Synthetic pain relief mixture, 450 mg Separatory funnel or pipette Water, distilled Spatula Balance Test tube rack Beakers, 150-mL, 2 Test tubes, 9 Erlenmeyer flask, 125-mL Watch glasses, 2 Filter paper Weighing dishes

Safety The 6 M hydrochloric acid is toxic by inhalation and ingestion. It is severely corrosive to all body tissues, especially skin and eyes. Ethyl acetate is a colorless, fragrant and flammable liquid. Handle ethyl acetate in a properly ventilated area such as a fume hood and keep away from flames, sparks and other open sources of ignition. Ethyl acetate is also slightly toxic by inhalation, ingestion and skin absorption. Acetaminophen is harmful by ingestion and irritating to skin and eyes and mucous membranes. It is a possible sensitizer. Aspirin (acetylsalicylic acid) is toxic by ingestion. It is an allergen and irritant and may cause internal bleeding. The acetaminophen and aspirin are not sold for human consumption. Avoid contact of all chemicals with skin and eyes. Wear chemical safety glasses, gloves and a chemical-resistant apron. wash hands thoroughly with soap and water before leaving the laboratory. please follow all laboratory safety guidelines! Procedure ➸ Day 1

1. Obtain small, pea-sized amounts (1-2 mg each) of acetylsalicylic acid, acetaminophen and silica gel in separate labeled test tubes so that you have three tubes of each solid (9 tubes total).

2. Add approximately 1 mL of ethyl acetate to test tubes with each of the three solids. Record observations before and

after agitating.

3. Add approximately 1 mL of distilled water to test tubes with each of the three solids. Record observations before and after agitating.

4. Add approximately 1 mL of 10% sodium bicarbonate solution to test tubes with each of the three solids. Record

observations before and after agitating.

5. Slowly and carefully add about 1-2 mL of 6 M hydrochloric acid drop-wise to each test tube in Step 4. Record observations.

6. Place the test tubes from Step 5 in an ice bath for 5 min and record any additional observations.

7. Dispose of all solutions by pouring down the sink drain and diluting well. Scrub test tubes with soap and give a final

rinse with distilled water.

19

Name: ____________________________ Period: _____ Date: ________

Data Table ➸ Day 1 (5 pts)

Acetylsalicylic acid Acetaminophen Silica gel

Observations when ethyl acetate is added

Observations when distilled water is added

Observations when 10% NaHCO3 is added

Observations when 6 M HCl is added dropwise

Observations after placed in ice bath for 5 min

Brainstorm ➸ Day 2 (8 pts) Using information from Day 1, sketch a flowchart below that could be used to separate the components of a synthetic pain relief mixture that contains acetylsalicylic acid, acetaminophen and silica gel binder. Methods will be discussed in class about how to recover separated components from their respective solvents. Get the flowchart approved, then use it to write a numbered procedure (10 pts). Attach your typed, numbered procedure to this lab report.

20

Name: ____________________________ Period: _____ Date: ________

Data Table ➸ Day 3 (5 pts) Record all observations throughout the execution of the procedure you wrote. Calculations (9 pts) Calculate the mass percent of acetylsalicylic acid in the mixture. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ Calculate the mass percent of acetaminophen in the mixture. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ Calculate the mass percent of silica gel binder in the mixture. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ Results (8 pts)

Experimental mass percent

Actual mass percent (for

teacher)

Percent error (for teacher)

Points (for teacher)

acetylsalicylic acid

acetaminophen

silica gel

0-20% error: 8 pts 20-40% error: 6 pts 40-60% error: 4 pts

21

Name: ____________________________ Period: _____ Date: ________

60%+ error: 2 pts

this page is intentionally blank!

22

Name: ____________________________ Period: _____ Date: ________

DETERMINATION OF THE MOLAR MASS OF A VOLATILE LIQUID

Purpose The objective of this experiment is to determine the identity of a volatile alkane using molar mass as a tool for identification. A pneumatic trough will be used to collect the gas and determine its pressure, volume and temperature. These variables will be used in the ideal gas law relationship to determine the number of moles of gas collected. The mass of gas collected will be determined by weight difference of the lighter before and after collection. From mass and number of moles of collected gas, the molar mass can be determined and the formula of the alkane can be identified. Background A volatile liquid (or solid, for that matter) is one which evaporates easily. (Note: volatile is not a synonym of reactive). From the 17th through the early 19th centuries, a number of scientists discovered simple relationships among the temperature, pressure, volume, and amounts of gases. Robert Boyle determined that the volume of a gas is inversely proportional to its pressure. Jacques Charles determined that the volume of a gas is directly proportional to its temperature. Joseph Gay-Lussac determined that the pressure of a gas is directly proportional to its temperature. Amadeo Avogadro determined that the number of moles of gas is directly proportional to its volume. The proportionality of all of these variables － P, V, n and T can be summarized by the proportionality statement in Equation 1 below.

α nP × V × T Equation 1 After many experiments and tedious calculations, it was determined that P, V, n and T were always related by a constant value of 0.082057. This constant is called R, the ideal gas constant and is given units of L atm/mol K in order to effectively balance the units of the other variables. Put together, the four gas variables and their constant make the ideal gas law, shown below as Equation 2.

nP × V = × R × T Equation 2

Where P = pressure (in atm), V = volume (in L), n = number of moles of gas (in mol), T = temperature (in K) and R = 0.082057 L atm/mol K. Other units may be used for volume and pressure, so long as the value and units of R reflect that change. In this lab, you will need to measure the pressure, volume and temperature of the volatilized gas in order to determine the number of moles of gas collected. Pressure To determine the pressure of a gas collected, you will volatilize the pressurized liquid alkane and collect the gas via pneumatic trough. A pneumatic trough is simply a shallow container of water with an inverted tube, like a graduated cylinder, also filled with water. A tube is fed through the water into the cylinder and as gas dispenses through the tube, it displaces the water (see Figure 1).

23

Name: ____________________________ Period: _____ Date: ________

When the water level inside the cylinder aligns with the water level outside the cylinder, then the pressure of gas inside the cylinder is equivalent to the pressure of gas outside the cylinder (in other words, atmospheric pressure). Atmospheric pressure, Patm can be determined using a barometer or a local weather source. There is a small amount of water vapor in the cylinder as well, although it is small because water has a low vapor pressure. This amount of water vapor can be determined as a function of water temperature, see Table 1 below.

Determine the partial pressure of gas, Pgas, using Equation 3 below.

PP atm = PH2O + gas Equation 3 Volume The volume of gas be determined by reading the graduation of the cylinder at the time of gas collection, when the level of water inside and outside of the cylinder are the same. Temperature The temperature of the gas will be nearly the same as the temperature of the water in the pneumatic trough. Since the gas must be vented through the water in a tube, the temperature of the gas will equilibrate to the temperature of the surrounding water. Mass The mass of gas collected can be obtained by taking careful mass measurements of the lighter before and after collecting gas and by examining the difference between the measurements. To avoid getting the body of the lighter wet, weigh the lighter without the venting tube. By rearranging the variables of the ideal gas law to solve for moles, the following equation is produced: ngas = R×Tgas

P ×Vgas gas Equation 4

Finally, the molar mass can be determined by using Equation 5: olar mass M = ngas

mgas Equation 5

Alkanes have the empirical formula CbH2n+2. You can find the identity of the alkane once you have an experimentally determined molar mass.

24

Name: ____________________________ Period: _____ Date: ________

Formula Name Formula Name

CH4 methane C6H14 hexane

C2H6 ethane C7H16 heptane

C3H8 propane C8H18 octane

C4H10 butane C9H20 nonane

C5H12 pentane C10H22 decane

Table 2: Alkane Series Prelab (10 pts) Note: “STP” indicates Standard Temperature and Pressure: 0 o C and 1 atm. Useful equalities 1 atm = 760 mm Hg = 760 torr = 101.325 kPa 0 o C = 273 K

1. Determine the volume of occupied by 2.34 grams of carbon dioxide gas at STP. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

2. At what temperature will 0.654 moles of neon gas occupy 12.30 liters at 1.95 atmospheres? ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

3. A gas tank initially weighed 538.48 g. A 4.167 L sample of gas was collected at 79.97 kPa and 30.0 °C. The tank weighed 518.10 g after collecting.

a. What mass of gas was collected? ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

b. How many moles of gas were collected? ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

c. What is the molar mass of the gas? ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ Materials

Pneumatic trough 100-mL graduated cylinder Plastic lighter Balance Thermometer

Safety

25

Name: ____________________________ Period: _____ Date: ________

Volatile gases are flammable, keep away from open sources of ignition and perform this lab in a well-ventilated area. Wear chemical safety glasses, gloves and a chemical-resistant apron. wash hands thoroughly with soap and water before leaving the laboratory. please follow all laboratory safety guidelines! Procedure Be careful not to depress the lighter between weighings unless collecting gas or your measurements will be highly flawed.

1. Remove the plastic tube from the lighter for now. Weigh the lighter to the nearest 0.001 grams and record. Reattach the plastic tube to the gas opening on the top of the lighter.

2. Submerge a 100-mL graduated cylinder in water so that the cylinder fills completely with water. Invert the cylinder.

Make sure there are no air bubbles remaining in the graduated cylinder.

3. Take the plastic tube and insert it in the graduated cylinder under the water. Carefully release the butane from the lighter and collect it in the cylinder. Release enough butane to fill the tube to between the 90 and 100-mL marks. Remove the plastic tube from the graduated cylinder and the lighter.

4. Then adjust the level of the water inside and outside the tube to be the same. With the pressure inside the same as

the pressure outside, record the volume as precisely as possible.

5. Measure the mass of the lighter again, ensuring that it is completely dry.

6. Repeat the steps 1-5 two more times for a total of 3 trials.

7. Record the water temperature and barometric pressure.

8. Clean your station. Data Table (6 pts)

Quantity Trial 1 Trial 2 Trial 3

Initial mass of lighter

Volume of gas collected

Final mass of lighter

Water temperature

Barometric pressure

Calculations and Questions (16 pts) Choose one trial to show calculations.

1. Determine the mass of gas collected. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

2. Determine the volume of gas collected, in L. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

26

Name: ____________________________ Period: _____ Date: ________

3. What was the partial pressure of water vapor collected? Use the water temperature and Table 1 from the Background section.

___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

4. Determine the partial pressure, Pgas in atm, using Equation 3 from the Background section. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

5. Determine the number of moles of gas collected, using Equation 4 ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

6. Determine the experimental molar mass of the gas, using Equation 5. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________

7. Repeat your calculations for any the remaining trials and record your answers in the Results table.

8. Average your molar masses for your trials and record in the Results table..

9. What is the identity of the alkane gas collected? Explain your answer. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ Results (8 pts)

Trial 1 Trial 2 Trial 3

Experimental molar mass

Average molar mass

Identity of gas

Actual molar mass (for teacher)

Actual identity (for teacher)

Percent error (for teacher)

Points (for teacher)

0-20% error: 8 pts 20-40% error: 6 pts 40-60% error: 4 pts 60%+ error: 2 pts

27