Conceptual Chemistry Questionnaire

Please do not write on this packet. You will indicate your answers on a scan-tron sheet.

Enter the following digits into the first eight bubbles of the ID Number box on the scan-tron: The month and day of your birthday, in the form mmdd, followed by the last four digits of your W#. For example, if Julie’s birthday is March 8 and her W# is W00105489, she would bubble in 03085489.

Do not put any other identifying information on your scan-tron.

This inventory consists of42 questions. Carefully consider each question and indicate the one best answer for each. Several of the questions are paired. In these cases, the first question asks about a chemical or physical effect. The second question then asks for the reason for the observed effect.

Your grade will be based on completion only, not on the number of questions you answer correctly.

1. Which of the following must be the same before and after a chemical reaction?

  1. The sum of the masses of all substances involved.
  2. The number of molecules of all substances involved.
  3. The number of atoms of each type involved.

d.  Both (a) and (c) must be the same.

  1. (e) Each of the answers (a), (b), and (c) must be the same.

2. Assume a beaker of pure water has been boiling for 30 minutes. What is in the bubbles in the boiling water?

  1. Air.
  2. Oxygen gas and hydrogen gas.
  3. Oxygen.

d.  Water vapor.

  1. Heat.

3. A glass of cold milk sometimes forms a coat of water on the outside of the glass (Often referred to as 'sweat'). How does most of the water get there?

  1. Water evaporates from the milk and condenses on the outside of the glass.
  2. The glass acts like a semi-permeable membrane and allows the water to pass, but not the milk.

c.  Water vapor condenses from the air.

  1. The coldness causes oxygen and hydrogen from the air combine on the glass forming water.

4. What is the mass of the solution when 1 pound of salt is dissolved in 20 pounds of water?

  1. 19 Pounds.
  2. 20 Pounds.
  3. Between 20 and 21 pounds.

d.  21 pounds.

  1. More than 21 pounds.

5. The reaction of element X with element Y is represented in the following diagram.

Which equation describes this reaction?

  1. 3X + 8Y à X3Y8
  2. 3X + 6Y à X3Y8

c.  X + 2Y à XY2

  1. 3X + 8Y à 3XY2 + 2Y
  2. X + 4Y à XY2

6. The diagram represents a mixture of S atoms and O2 molecules in a closed container.

Which diagram shows the results after the mixture reacts as completely as possible according to the equation:

2S + 3O2 2SO3


d

7. The circle on the left shows a magnified view of a very small portion of liquid water in a closed container.

What would the magnified view show after the water evaporates?

e

8. True or False: When a match burns, some matter is destroyed.

  1. True

b.  False

9. What is the reason for your answer to the question above?

  1. This chemical reaction destroys matter.
  2. Matter is consumed by the flame.
  3. The mass of ash is less than the match it came from.

d.  The atoms are not destroyed, they are only rearranged.

  1. The match weighs less after burning.

10. Heat is given off when hydrogen burns in air according to the equation

2H2 + O2 2H2O

Which of the following is responsible for the heat?

  1. Breaking hydrogen bonds gives off energy.
  2. Breaking oxygen bonds gives off energy.

c.  Forming hydrogen-oxygen bonds gives off energy.

  1. Both (a) and (b) are responsible.
  2. (a), (b), and (c) are responsible.

11. A 1.0-gram sample of solid iodine is placed in a tube and the tube is sealed after all of the air is removed. The tube and the solid iodine together weigh 27.0 grams.

The tube is then heated until all of the iodine evaporates and the tube is filled with iodine gas. Will the weight after heating be:

  1. less than 26.0 grams.
  2. 26.0 grams.

c.  27.0 grams.

  1. 28.0 grams.
  2. more than 28.0 grams.

12. What is the reason for your answer to the question above?

  1. A gas weighs less than a solid.

b.  Mass is conserved.

  1. Iodine gas is less dense than solid iodine.
  2. Gases rise.
  3. Iodine gas is lighter than air.

13. Figure 1 represents a 1.0 L solution of sugar dissolved in water. The dots in the magnification circle represent the sugar molecules. In order to simplify the diagram, the water molecules have not been shown.


Figure 1

Which response represents the view after 1.0 L of water was added (Figure 2).


Figure 2 b

14. 100 mL of water at 25°C and 100 mL of alcohol at 25°C are both heated at the same rate under identical conditions. After 3 minutes the temperature of the alcohol is 50°C. Two minutes later the temperature of the water is 50°C. Which liquid received more heat as it warmed to 50°C?

a.  The water.

  1. The alcohol.
  2. Both received the same amount of heat.
  3. It is impossible to tell from the information given.

15. What is the reason for your answer to the question above?

  1. Water has a higher boiling point then the alcohol.

b.  Water takes longer to change its temperature than the alcohol.

  1. Both increased their temperatures 25°C.
  2. Alcohol has a lower density and vapor pressure.
  3. Alcohol has a higher specific heat so it heats faster.

16. Iron combines with oxygen and water from the air to form rust. If an iron nail were allowed to rust completely, one should find that the rust weighs:

  1. less than the nail it came from.
  2. the same as the nail it came from.

c.  more than the nail it came from.

  1. It is impossible to predict.

17. What is the reason for your answer to the question above?

  1. Rusting makes the nail lighter.

b.  Rust contains iron and oxygen.

  1. The nail flakes away.
  2. The iron from the nail is destroyed.
  3. The flaky rust weighs less than iron.

18. Following is a list of properties of a sample of solid sulfur:

  1. Brittle, crystalline solid.
  2. Melting point of 113oC.
  3. Density of 2.1 g/cm3.
  4. Combines with oxygen to form sulfur dioxide

Which, if any, of these properties would be the same for one single atom of sulfur obtained from the sample?

  1. i and ii only.
  2. iii and iv only.

c.  iv only.

  1. All of these properties would be the same.
  2. None of these properties would be the same.

19. Consider three samples of water in three phases. The first is solid water (ice) at 0° C, the second is liquid water at 24° C, and the third is gaseous water at 100° C. The water molecules in the liquid phase ______the water molecules in the gaseous phase.

a.  move faster than

b.  move slower than

c.  move at the same speed as

d.  move more randomly than

e.  travel in the same direction as

20. Which of the following processes will make water molecules larger?

  1. freezing
  2. melting
  3. evaporation
  4. condensation

e.  none of the above

21. When water molecules in the gas phase are heated, the molecules themselves

a.  expand

b.  move faster

c.  become less massive

d.  change to a liquid

e.  release air

22. Which of the following processes will make molecules smaller?

a.  freezing

b.  melting

c.  evaporation

d.  condensation

e.  none of the above

23. When water at 25° C is heated and changes to a gas at 100° C, the water molecules

a.  become more organized

b.  move farther apart

c.  stop moving

d.  move closer together

e.  move more slowly

24. When water at 24° C is cooled to 0° C and freezes, the water molecules

a.  become less organized

b.  move much faster

c.  stop moving

d.  break apart

e.  move much more slowly

25. Hydrogen is a group 1 element, while fluorine is a group 7 element. Which of the following best represents the position of the shared electron pair in the HF molecule?

a.  b.

26. What is the reason for your answer to the question above?

  1. Non-bonding electrons influence the position of the bonding or shared electron pair.
  2. As hydrogen and fluorine form a covalent bond the electron pair must be centrally located.

c.  Fluorine has a stronger attraction for the shared electron pair.

  1. Fluorine is the larger of the two atoms and hence exerts greater control over the shared electron pair.

27. Nitrogen (a group 5 element) combines with bromine (a group 7 element) to form a molecule. This molecule is likely to have the following shape:

a. b. c.

28. What is the reason for your answer to the question above?

  1. Nitrogen forms three bonds which equally repel each other.

b.  The arrangement of the bonding and non-bonding electron pairs around nitrogen results in the shape of the molecule.

  1. The polarity of the nitrogen-bromine bonds determines the shape of the molecule.
  2. The difference in electronegativity values for bromine and nitrogen determine the shape of the molecule.

29. Oxygen is a group 6 element, while fluorine is a group 7 element. The polarity of the oxygen-fluorine bond would be best shown as:

a. b.

30. What is the reason for your answer to the question above?

  1. The non-bonding electron pairs present on each atom determine the polarity of the bond.
  2. A polar covalent bond forms as oxygen has six outer shell electrons and fluorine seven outer shell electrons.

c.  The shared electron pair is closer to fluorine.

  1. The polarity of the bond is due to the oxygen atom forming an O2- ion, whereas fluorine forms an F- ion.

31. Which of the following molecules is polar?

a. b. c.

32. What is the reason for your answer to the question above?

  1. The polarity of the molecule is due to the high electronegativity of fluorine.

b.  Non-symmetrical molecules containing different atoms are polar.

  1. Non-bonding electrons on an atom in the molecule produce a dipole and hence a polar molecule.
  2. A large difference in the electronegativities of the atoms in bonding results in a polar molecule.

33. Sodium chloride, NaCl, exists as a molecule.

a. True

b. False

34. What is the reason for your answer to the question above?

  1. The sodium atom shares a pair of electrons with the chlorine atom to form a simple molecule.
  2. After donating its valence electron to the chlorine atom, the sodium ion forms a molecule with the chloride ion.

c.  Sodium chloride exists as a lattice consisting of sodium ions and chloride ions.

  1. Sodium chloride exists as a lattice consisting of covalently bonded sodium and chlorine atoms.

35. Water (H2O) and hydrogen sulfide (H2S) have similar chemical formulae and have V-shaped structures. At room temperature, water is a liquid and hydrogen sulfide a gas. The difference in state between water and hydrogen sulfide is due to:

a.  Stronger intermolecular bonds between H2O molecules than between H2S molecules.

  1. Stronger chemical (intramolecular) bonds between O and H than between S and H.
  2. Slower moving H2O molecules compared to H2S molecules.

36. What is the reason for your answer to the question above?

  1. The small particles in gases move faster than the small particles in liquids.
  2. The bonds within each molecule of H2S are easily broken, whereas those within H2O molecules are not.

c.  The two molecules have different polarities.

  1. H2O is a polar molecule, whereas H2S is a non-polar molecule.

37. The following diagram represents a snapshot in time of a cross-sectional area of a steel tank filled with oxygen gas at room temperature. (The dots represent the distribution of oxygen molecules).

Which of the following diagrams illustrate a snapshot of the distribution of the contents of the steel tank if the temperature is lowered? (The oxygen remains in the gas phase).

a. b. c. d. e.

38. The following sets of drawings represent “snapshots” of a stoppered flask containing air particles before and after some of the particles were removed. Choose the best drawings of air before and after some was removed from the flask.

d

39. What is there between the particles inside the flask in figure A below?

a. Air

b. No material

c. Vapor

d. Oxygen

e. Pollutant

40. Choose the best explanation for the fact that particles of gas in a closed flask do not fall to the bottom in figure A below.

a. The particles have a very small density.

b. There are repulsive forces between particles.

c. The particles are in constant motion.

d. Air keeps the particles from falling.

e. There are more particles between those shown in the drawing.

41. A flask containing air was connected to a rubber balloon. Then the air in the flask was heated with a flame and the balloon inflated. Choose the drawing which is the best “snapshot” of the air after the balloon becomes inflated.

b

42. Following is a list of statements that may or may not describe what happens when sugar dissolves in water.

i. Chemical bonds within the sugar molecule break.

ii. Intermolecular bonds between sugar molecules break.

iii. The sugar melts.

iv. Intermolecular bonds form between water and sugar molecules.