1. Draw a mental model for how methanol, which has the formula of CH3OH and is a liquid at room
temperature with a boiling point of 65 °C, dissolves in water.
One would draw methanol molecules swimming about amongst water molecules. There are no CH3+ and
OH– ions present, as methanol is a molecular substance that is not acidic in water.
2. Does your model above account for the observation that solutions of methanol in water do NOT
conduct electricity? What explanations can you offer for why methanol does not conduct electricity in
water?
Methanol(aq) won’t conduct electricity well, since it is molecular, and there are no ions present.
3. Draw a picture of a saturated solution of NaCl. Think about how you can show that the solution is
saturated.
Draw a picture like B below. The remaining solid will show that it is saturated.
4. There are different concentrations of sugar solutions in beakers A, B, and C. Label each beakers'
contents as being saturated, unsaturated or supersaturated.
A supersaturated (more dots than B)
B saturated (no more will dissolve)
C unsaturated (more will dissolve)
5. Consider the following, and re-evaluate your answers to the above question. Look up the definitions
if you are unsure of the terms.
Assumptions: The dots represent the dissolved sugar molecules. The undissolved sugar in beaker B is
shown as a darkened area.
Questions:
a. What do the different patterns of dots in the diagrams represent? Dissolved sugar molecules
b. If you separate the solid from the solution in B by filtration, what would you call the remaining
solution? Saturated
c. If you had to prepare a supersaturated solution, how would you do it? Heat sugar in water, cool
slowly
6. Consider the following reaction between a non-metal and a metal to form an ionic compound, shown
by spheres representing the reactants and products. Which sphere represents the metal, and which is
the non-metal?
Metal (cations get smaller)
Non-metal (anions are larger)
7. Which of the following must be the same before and after a chemical reaction?
a.
b.
c.
d.
e.
The sum of the masses of all substances involved.
The number of molecules of all substances involved. incorrect
The number of atoms of each type involved.
Both (a) and (c) must be the same. ONLY d is correct
(e) Each of the answers (a), (b), and (c) must be the same.
8. Assume a beaker of water has been boiling for 30 min. What is in the bubbles in the boiling water?
a.
b.
c.
d.
e.
Air.
Oxygen gas and hydrogen gas.
Oxygen.
Water vapor. Water doesn’t decompose when heating, it just turns to vapor.
Heat.
9. 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?
a.
b.
c.
d.
Water evaporates from the milk and condenses on the outside of the glass. A little
The glass acts like a semi-permeable membrane and allows the water to pass, but not the milk.
Water vapor condenses from the air. Best answer, most condensation from this source
The coldness causes oxygen and hydrogen from the air combine on the glass forming water.
There isn’t much H2 or H in our air
10. What is the mass of the solution when 1 pound of salt is dissolved in 20 pounds of water?
a.
b.
c.
d.
e.
19 Pounds.
20 Pounds.
Between 20 and 21 pounds.
21 pounds. Unless you spill some, it has to be this answer
More than 21 pounds.
11. The diagram below 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: D is best answer, shows the SO3 molecules and 2 remaining S atoms
2S + 3O2 → 2SO3
12. 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 is best
answer,
see #8
13. 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?
a.
b.
c.
d.
e.
Breaking the H–H bonds releases energy.
Breaking the O–O bonds releases energy.
Forming hydrogen-oxygen bonds releases energy. (breaking bonds absorbs E!)
Both (a) and (b) are responsible.
(a), (b), and (c) are responsible.
14. Iron combines with oxygen and water from the air to form rust. If an iron nail was allowed to rust
completely, one would find that the rust weighs:
a. less than the nail it came from.
b. the same as the nail it came from.
c. more than the nail it came from.
c is Best answer, as Fe2O3 is formed, heavier due to mass of O
d. It is impossible to predict.
15. What is the reason for your answer to question 14?
a.
b.
c.
d.
e.
Rusting makes the nail lighter.
Rust contains iron and oxygen. Best answer, explains C above
The nail flakes away.
The iron from the nail is destroyed.
The flaky rust weighs less than iron. Wrong, but explains A
16. Salt is added to water and the mixture is stirred until no more salt dissolves. The salt that doesn’t
dissolve is allowed to settle out. What happens to the salt concentration if water evaporates until the
volume of the solution is ½ the original volume? (Assume temp remains constant.)
The concentration of dissolved salt
a. increases.
b. decreases.
c. stays the same. As water evaporates, salt will precipitate, leaving the concentration the same.
Evaporation from an unsaturated solution will lead to an increase in conc.
17. What is the reason for your answer to question 16?
a. There is the same amount of salt in less water.
b. More solid salt forms. Explains c above
c. Salt does not evaporate and is left in solution.
d. There is less water.
18. What mass of nickel (II) sulfate dihydrate is needed to make 1.00 L of a solution so that 25.00 mL of
that solution will react completely with 80.0 mL of 0.177 M NaOH?
The NiSO4 solution needs to be 0.2832 M, so to make 1 L 54.1 g of the hydrate needs to be used.
19. What is the molarity of a sulfuric acid solution if 40.00 mL of the solution is exactly neutralized by
14.97 mL of a sodium hydroxide solution prepared by dissolving 1.6428 g of the solid in H2O to make
300.0 mL of solution?
H2SO4 + 2 NaOH → Na2SO4 + 2 H2O
1.6428 g NaOH | 1 mol NaOH |
1
| 40.00 g NaOH | 0.3000 L
= 0.1369 M NaOH
0.01497 L NaOH | 0.1369 mol NaOH | 1 mol H2SO4 |
|
L NaOH
| 2 mol NaOH
1
= 0.02562 M H2SO4
| 0.04000 L H2SO4
20. Without looking at any data tables other than the periodic table, predict the larger of each pair:
Na or Si
Mg2+ or Na
O
or
O2–
Fe2+ or Fe3+