statescioly.org · Web viewFollow all lab safety protocols during the lab portion. Your workspace must be clean by the end of the lab section or you will receive a 7% reduction in

Team # ___________ School/Team name ___________________________________________

Chemistry Lab C – EXAM2019 UMD Invitational

Team Number: _____

Team/School Name:

___________________________________ No abbreviations / PRINT LEGIBLY

Student Names (First & Last): PRINT LEGIBLY

1. ____________________________________________

2. ____________________________________________

Total Points Possible (written test): 158

Total Points Earned: __________


Directions: - Show all of your work. SI units must be included. - It is acceptable to use a non-programmable calculator during all portions of the exam. - Follow all lab safety protocols during the lab portion. Your workspace must be clean by the end

of the lab section or you will receive a 7% reduction in your score. - Write all multiple-choice answers on the lines next to each question. Free response final

answers must be indicated by circling them.- Tiebreaker questions: #16C, #15B, #5B and C- Unless stated otherwise, ∆G, ∆H, and ∆S are per mole

Good Luck!-




Laboratory Portion 28 points (2 per box)

Hess’ Law

The enthalpy change for any reaction depends on the products and reactants and is independent of the pathway or the number of steps between the reactant and product.

In this experiment, you will measure and compare the quantity of heat involved in the reaction of sodium hydroxide solution with dilute hydrochloric acid solution.

Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) ---> Na+(aq) + Cl-(aq) + H2O

Safety:

Hydrochloric acid and sodium hydroxide are corrosive. Avoid direct contact. If any touches your skin, wash it off immediately. Be sure to close the lids of bottles of sodium hydroxide securely, immediately after using.

Materials:

2 large styrofoam cups 100 mL graduated cylinder 1 M sodium hydroxide solution 1 M Hydrochloric acid solution thermometers balance 250 mL beaker Stirring rod

Procedure:1. Measure 50 mL of 1.0 M Hydrochloric acid solution into your calorimeter and 50.0 mL of 1.0 sodium hydroxide into a 250 mL beaker.2. Record the temperatures and volumes of each solution.3. Add the sodium hydroxide solution to the acid solution in the Styrofoam cup. Stir the mixture and record the highest temperature reached. Discard the solution properly.

Data:Volume of 1.0 M HCl solution usedVolume of 1.0 M NaOH solution usedInitial temp of the NaOH solution (before mixing)Highest final temperature of mixture


Calculations: Calculations – Show all work! Answer

1. Change in temperature:

2. Moles of HCl used:

3. Moles of NaOH used:

4. Energy released:

5. Heat of reaction:


Written Portion - 28 Minutes Acids and Bases (40 points)

Choose the best answer to the following questions. You MUST indicate your answer on the line next to the question number to receive credit.

1. ____ Which of the following is a weak acid? (1 points)a. CO3

2-

b. NH3

c. HFd. HCl

2. ____ Which of the following is amphoteric? (1 points)a. C2H3O2

-

b. H3O+

c. C2H6

d. H2PO4-

3. ____ Which of the following, when dissolved in water, will create a solution with pH less than 7? (1 points)

a. HCO3-

b. HC2H3O2

c. NH3

d. C6H12O6

4. 0.307g sample of an unknown triprotic acid H3A is titrated to the third equivalence point using 35.2mL of 0.106 M NaOH. Calculate the molar mass of the acid. (7 points)

5. Hemoglobin (Hb) is a protein that transports oxygen in the blood of mammals. Oxygen binding to hemoglobin is pH dependent. The relevant equilibrium reaction is shown below:HbH4

+(aq) + 4O2(g) ⇆ Hb(O2)4(aq) + 4H+(aq)A. What form of hemoglobin is favored in the lungs? In the cells themselves? Explain each

phenomenon and describe how Le Chatelier’s principle applies. (4 points)


B. When a person hyperventilates, CO2 concentration in the blood decreases. How does this affect the oxygen-binding equilibrium? How does breathing into a paper bag counteract the problem? (5 points)

C. Sodium bicarbonate is injected into patients who have suffered cardiac arrest. What purpose does this serve? (4 points)

6. Explain the following reaction using the Lewis acid-base model (7 points):CO2(g) + H2O(l) → H2CO3(aq)

7. 0.1 mole of CH3NH2 (Kb = 5 x 10-4) is mixed with 0.08 mole of HCl and diluted to one liter. What will be the H+ concentration? (10 points)


Physical Properties (90 points)Choose the best answer to the following questions. You MUST indicate your answer on the line next to the question number to receive credit.

8. ____ Which of the following properties is NOT a physical property? (1 points)a. Flammability b. Boiling point c. Ductility d. Electrical Conductivity

9. ____ There are __________ molecules of NaCl in 5.00g of pure NaCl: (1 points)a. 0.085b. 4.95*1022

c. 0.580d. 5.15*1022

10. ____ The atoms that make up graphite molecules display this hybridization: (1 points)a. Sp2b. Sp3 c. All of the above d. None of the above

11. ____ What is the partial pressure of nitrogen, in torr, in the atmosphere when the atmospheric pressure is 760.0 torr? (1 points)

Components of Air Mole Fraction

Nitrogen 0.781

Oxygen 0.209

Argon 0.010

a. 430 b. 593c. 159d. 760

12. ____ The opposite process to deposition is: (1 points)a. Ionizationb. Evaporation c. Sublimation d. Fusion


13. For the following compounds, write the chemical formula when names are given and write the IUPAC name when chemical formulas are given. (16 points, 1 each)

a. Sulfurous Acid _____________

b. Sodium Phosphate _____________

c. Magnesium Nitrite _____________

d. Mercury(I) Oxide _____________

e.Lead(IV) Dichromate _____________

f. Propane _____________

g. Dinitrogen tetroxide _____________

h. Copper(I) Sulfate _____________

i. AgNO3 _____________

j. FeBr2 _____________

k. C2H6 _____________

l. CH3COOH _____________

m. SO3 _____________

n. NaHCO3 _____________

o. NH4MnO4 _____________

p. HBr _____________

14. A piece of metal with mass 16.0g is submerged in 46.0cm3 of water in a graduated cylinder. The water level increases to 48.0cm3. What is the density of the metal in g/m3? (6 points)

15. When 1.00L of 2.00M Na2SO4 solution at 30.0oC is added to 2.00L of 0.750M Ba(NO3)2 solution at 30.0oC in a calorimeter, a white precipitate forms. The temperature of the mixture increases to 42.0oC. The specific heat capacity of the solution is 6.37J/(oC*g), and the density of the (final) solution is 2.00g/mL.

A. Write the balanced equation of the reaction described above. (4 points)

B. Calculate the enthalpy change per mole of precipitate formed. (14 points)


16. A chemist performs a chromatography experiment in which she draws some small dots using a water-soluble marker near the center of a circular piece of filter paper. She then pokes a hole in the center of the filter paper and inserts a rolled up piece of filter paper as a wick. She places this chromatography setup into a cup of water and waits for the water to travel through the circular filter paper. A schematic of her experiment is shown in figure 1 below:

A. Is it important that the circular filter paper not be directly in contact with the water (i.e. only the wick is in direct contact with the water)? Why? (7 points)

B. What will happen to the dots of ink on the circular filter paper over the course of the experiment? How does polarity play a role in this process? (7 points)

C. Design a chromatography experiment in which you determine if purple and blue permanent markers (soluble in ethanol but insoluble in water) contain any of the same pigments in their respective inks. Describe the materials, procedures, possible results, and conclusions you will draw from your experiment. (12 points)


17. Freon-12 is used in home air conditioning as a refrigerant. The rate of effusion of Freon-12 to Freon-11 (molar mass = 137.4g/mol) is 1.07:1. The formula of Freon-12 is one of the following: CF4, CF3Cl, CF2Cl2, CFCl3, or CCl4. Which formula is correct for Freon-12? (8 points)

18. Consider the following gaseous samples (all at STP): 1.0L of H2, 2.5L Xe, 10L N2, and 1.5L O2. A. Rank the four gases in order of increasing average kinetic energy. Explain your reasoning. (5

points)

B. Rank the four gases in order of increasing average molecular velocity. Explain your reasoning. (6 points)

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statescioly.org · Web viewFollow all lab safety protocols during the lab portion. Your workspace must be clean by the end of the lab section or you will receive a 7% reduction in