CHEM 1A Lecture Notes - Lecture 14: Molar Mass, Minnesota State Highway 1

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29 Nov 2016

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UCSB

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Chemistry and Biochemistry

Course

CHEM 1A

Professor

Joseph C A

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Recap: p and v are directly proportional to t, p is indirectly proportional to v. M = the mass of the gas in g. M = the molar mass of the gas. D = m/v = pm/nrt = pm/rt: the higher the molar mass, the higher the density is going to be, molar mass (m) of a gaseous substance. Air is a mixture: nitrogen is usually 78% in atmosphere, oxygen = approx. 21: argon = 0. 9, carbon dioxide = 0. 03, other gases, this is for dry air, higher altitude, stuffy roo(cid:373)s, city (cid:448)s forest . all de(cid:448)iate fro(cid:373) this, places that have high pollution = more dust. Mixture of n2 and o2 in a container. The pressure of one gas does not affect the pressure of another gas. Mole fraction (x: (x)a = (cid:3040)(cid:3042)(cid:3039)(cid:3032)(cid:3046) (cid:3042)(cid:3033) (cid:3002) (cid:3040)(cid:3042)(cid:3039)(cid:3032)(cid:3046) (cid:3042)(cid:3033) (cid:3003) (cid:3046)(cid:3048)(cid:3040) (cid:3042)(cid:3033) (cid:3040)(cid:3042)(cid:3039)(cid:3032)(cid:3046) (cid:3042)(cid:3033) (cid:3039)(cid:3039) (cid:3042)(cid:3040)(cid:3043)(cid:3042)(cid:3041)(cid:3032)(cid:3041)(cid:3047)(cid:3046) (cid:3046)(cid:3048)(cid:3040) (cid:3042)(cid:3033) (cid:3040)(cid:3042)(cid:3039)(cid:3032)(cid:3046) (cid:3042)(cid:3033) (cid:3039)(cid:3039) (cid:3042)(cid:3040)(cid:3043)(cid:3042)(cid:3041)(cid:3032)(cid:3041)(cid:3047)(cid:3046, (x)b =

Related Questions

I need the ones that I did checked, and c, f, l, and m done please.

Molar Volume of Oxygen Experiment

Please give me Post lab questions 2 and 3 at the bottom.

Experiment 7 - Molar Mass of a Volatile Liquid

Introduction. Given the mass of vapor at conditions of known pressure, volume, and temperature, one can determine the molar mass of the vapor. The Ideal Gas Law mathematically relates the quantities of pressure (P in atm), volume (V in liters), and temperature (T in Kelvin) and the quantity of gas (n in moles). Using the expression PV=nRT where R equals the Ideal Gas Constant 0.0821 L*atm/K*mol, one can determine the quantity of gas under given conditions of pressure, volume and temperature. The number of moles of gas is found by

n =

Because the molar mass (MM) is defined as the mass of one mole of substance in units of g/mol, the molar mass of the vapor can be determined by

MM= mass of vapor in grams/moles of vapor

In this experiment, an unknown volatile liquid is heated in a boiling water bath and is vaporized. The vapor forces air from the flask until the pressure within the flask equals the barometric pressure of the lab. As with all gases, the vapor occupies the entire volume of its container. The temperature of the vapor equals the temperature of the boiling water bath. After 8-10 minutes, the vapor is cooled. The mass of the condensed liquid is determined and the molar mass is calculated as described above.

Notes:

Check out unknown from stockroom

Record unknown number

Before weighing your condensed vapor, thoroughly dry the outside of the flask and make sure that no water is trapped under the foil cover

Do not rinse your flask with water between trials

Dispose of waste in appropriate container

Procedure. You will record your data and calculations in your lab notebook.

Obtain an unknown liquid and a 3 inch aluminum foil square. You will need two 600 or 800 mL beakers, and 3 or 4 boiling chips.

Add 3 or 4 boiling chips to the water in an 800 mL beaker and heat the water to the boiling point. Continue heating for 8 to 10 minutes after the water comes to a rolling boil. The temperature of the boiling water is 100.0^oC. This will be the temperature of the vapor. Convert the temperature to Kelvin and record in your lab notebook.

800 mL Beaker

250 mL Flask

11.

Chemical Molar Mass

1-chlorobutane 92.6 g/mol

t-butyl chloride 92.5 g/mol

trichloroethylene 131 g/mol

2-propanol 60.1 g/mol

Ethyl acetate 88.1 g/mol

n-hexane 86.2 g/mol

cyclohexane 84.2 g/mol

2-butanone 72.1 g/mol

Post Lab Questions: Answer the following questions using complete sentences. Include them after your conclusion.

1. If a lab group did not keep the flask submerged in boiling water for a full ten minutes, and some unknown never vaporized, how would that affect the calculated molar mass? In other words, would it make the calculated value too high or too low? Explain why.

2. While performing this experiment, ten lab groups have ten different unknown volatile liquids with a range of molar masses. If all lab groups have exactly the same size of flask (255 mL), and all groups took their unknown vapor to the same temperature (100.0^oC) and pressure (760.0 mmHg), how would the number of molecules within the different flasks compare? Would it vary with molar mass? How? Explain.

3. A student has determined that an unknown liquid is either 1-chlorobutane or t-butyl chloride. What other physical property(s) could be used to determine the identity of the unknown?

* Circle the intermolecular force(s) that is/are present in each of the following species. [Hint: there may be more than one correct answer.]

Ar (hydrogen bonding, dipole-dipole forces, dispersion forces)

CH4 (hydrogen bonding, dipole-dipole forces, dispersion forces)

HBr (hydrogen bonding, dipole-dipole forces, dispersion forces)

HF (hydrogen bonding, dipole-dipole forces, dispersion forces)

CHCl3 (hydrogen bonding, dipole-dipole forces, dispersion forces)

* For the following pairs of atoms/molecules, circle the species that has the higher boiling point.

Ne or Xe

Cl2 or F2

HBr or HF

HCl or HI

H2O or H2S

* Phase changes always associate with change of enthalpy. For the following situations, name the phase

transition and indicate whether the process is exothermic or endothermic.

(a) Dry ice (solid carbon dioxide) turns to gaseous carbon dioxide.

Answer:

(b) Water vapor turns to liquid water.

Answer:

(d) Iodine vapor turns to solid iodine.

Answer:

(e) Liquid helium turns to helium gas.

Answer:

* True or false

1. Intermolecular forces are stronger than ionic and covalent bonds. Answer:

2. For molecules with similar size and molar mass, those with higher polarity would have higher boiling

point. Answer:

3. Ion-dipole forces exist between ionic potassium bromide and polar water.

Answer:

4. Dispersion forces exist between argon and helium. Answer:

5. Instantaneous dipoles exist in all molecules and atoms. Answer:

6. The strength of dispersion forces depends on the molar mass but the shape of the molecules have no effect on dispersion forces. Answer:

7. Ice has a higher density than water because ice has an ordered cagelike structure. Answer:

8. Liquids with weaker intermolecular interactions have lower viscosity. Answer:

9. Viscosity decreases with increasing temperature. Answer:

10. For any molecules, the heat of vaporization is always lower than the heat of fusion because it takes more energy to make molecules to move past one another in a solid lattice. Answer:

CHEM 1A Lecture Notes - Lecture 14: Molar Mass, Minnesota State Highway 1

CHEM 1A Full Course Notes

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