NAME:
CHE 100 WINTER QUARTER 2008 9am CLASS MIDTERM 2
Marks for each question are as indicated. Total number of marks is 32. You are allowed to use
calculators and dictionaries. Time allowed is 50 minutes. Data sheets are attached; no other
materials are to be used to help answer questions.
1. What is the proper name for Br–?
(1 mark)
Bromide Ion
2. An ionic compound made from calcium and oxygen has what formula?
(1 mark)
CaO
3. What is the correct formula of an ionic compound made from phosphorus and calcium?
A) CaP2
B) Ca2P C) Ca3P2
D) Ca2P3
(1 mark)
C)
4. What term is used to describe the simplest ratio that makes up an ionic compound?
(2 mark)
Formula Unit
5. What is the formula of the ionic compound made from ammonium and sulfate?
A) NH4(SO4)2
B) NH4SO4
C) (NH4)2SO4
D) (NH4)2(SO4)2
(1 mark)
C)
6. Hg(OCN)2 is an explosive that forms elemental mercury, carbon monoxide and nitrogen
gas when detonated. Write and balance the equation for the decomposition of
Hg(OCN)2.
(2 marks)
Hg(OCN)2 → Hg + 2CO + N2
7. How many milligrams of O2 are needed to react completely with 28.0 g of Li in the
following reaction?
4Li + O2 → 2Li2O
4Li + O2 → 2Li2O
nLi = m/M
= 28.0/6.941
= 4.03 moles of Li
nLi = 4 x no2
no2 = 0.25 x 4.03
= 1.01 moles of O2
m=nxM
= 1.01 x 15.999 x 2
= 32.3 grams of O2
= 32.3 x 10-3 mg of O2
(3 marks)
Silver reacts with hydrochloric acid according to the equation:
2Ag + 2HCl → 2AgCl + H2
If 55.0 g of Ag is mixed with 45.0 g HCl, what is the limiting reactant?
(3 marks)
(Continue answer on top of next page if more space required)
nAg = nHCl = nAgCl
nAg = m/M
= 55.0/107.868 = 0.51 moles of Ag
nHCl = m/M
= 45.0/(1.0079 + 35.453)
= 1.23 moles of HCl
nHCl > nAg therefore Ag is the limiting reagent.
8. How is stoichiometry best defined?
A)
(2 marks)
The use of chemical equations for determining the materials in a given chemical
calculation.
B)
The use of balanced chemical equations for identifying the materials in a given chemical
reaction.
C)
The use of unbalanced chemical equations for quantifying the amount of materials in a
given chemical reaction.
D)
The use of balanced chemical equations for quantifying the amount of materials in a
given chemical reaction.
(D)
9. What is a saturated solution? (2 marks)
A saturated solution is formed when the maximum possible amount of a given solute is
dissolved in a particular solvent.
10. If the reaction AgNO3 + NaCl → NaNO3 + AgCl were written out as a total ionic
reaction, which ions would be the spectator ions?
A) Ag+ and NO3–
B) Na+ and Ag+
C) Na+ and NO3–
(1 marks)
D) Cl– and NO3–
C)
11. In the following reaction what chemical change occurs to the zinc metal?
2 HCl + Zn → H2 + ZnCl2
(2 marks)
The zinc is oxidized.
12. A solution with a pH = 3.5 is said to be what?
A) acidic B) basic C) neutral D) can't tell from the information given
A)
(1 mark)
13. What is the mathematical formula to determine pH from the hydrogen ion
concentration?
(2 marks)
pH = -log10[H+]
14. What is the process called when particles in a solution move from a region of high
concentration in some random fashion to a region of lower concentration? (2 marks)
The process is called diffusion.
15. The property of liquids that is a measure of how much energy is needed to increase the
surface area of a liquid is what?
(1 marks)
Surface Tension
16. What is the difference between osmosis and diffusion?
(2 marks)
A)
Osmosis always involves particle movement through a semi-permeable membrane.
B)
Osmosis almost always involves movement of particles through a non-permeable
membrane.
C)
Osmosis always involves movement of solvents through a semi-permeable membrane.
D)
Osmosis almost always involves movement of solvents through a non-permeable
membrane.
D)
17. How are London dispersion forces characterized?
A) as weak intermolecular forces
(1 mark)
B) as strong intramolecular forces
A)
18. Upon what do colligative properties depend?
(1 mark)
The number of solute particles.
19. What formula is used to compute freezing-point depression?
∆Tfp = Kfpmparticles
(1 mark)
The speed of light
c = 3.00 x 108 ms-1
Planck’s constant
h = 6.626 x 10-32 Js