Kaplan General Chem Subject Test 4

[Meas]

Kaplan General Chem Subject Test 4:

As mentioned in previous threads, I am posting questions I have about subject tests that I did. Hope to get responses you all!

4) Which of the following if added to a saturated aqueous solution of NaCl, would most effectively reduce the chloride ion concentration?

Answer choices:
AgNO3
Ba(NO3)2
K2SO4
H2S
CH3COOH

A: AgNO3

--I know this has sthm to do with the common ion effect but I seem to visualize what is going on. When they say saturated aqueous solution of NaCl, is that simply NaCl + H2O à Na+ + Cl- + H2O?

When replacing each answer choice’s anion with Cl- & using the solubility details that we are supposed to memorize, I still can’t figure out the answer!

5) Which reaction will not proceed?

Answer choices:
Li+CuCl2
Zn+NaNO3
CaCO3+HCl
K+H2O
H+ + OH-

A: Zn+NaNO3

--Okay, I have no idea where to start!

7) An unknown weak monoprotic acid HY found to be 0.002% ionized in a 1M aqueous solution. What is the Ka of HY?

A: 4X10^-10

--Another ionization question that I don’t know how to start! I don’t know how % can be plugged into the Ka equation.

16) Predominant intermolecular attraction between molecules of CO2 & CH4 is:

A: dispersion forces

--I thought the answer would be H-bonding b/c the O from CO2 & H from CH4 can bond.

--I read the following somewhere else but I am not sure if I remember it correctly: covalent as being between nonmetals only, whereas ionic bonding is between metals & nonmetals. Please confirm!

25) How many calories are needed to convert 8grams of ice at –23C to water at 52C?
(sp. heat: water=1ca/g C; ice = 1cal/g C; heat of fusion: water = 80cal/g)

A: 75(8) + (80)(8)

--I used q = mc(delta T) = [(8)(1)(0+23)] (this is the heat to convert ice to water at 0C) + [(8)(1)(52-0)] (this is the heat to convert water at 0C to 52C. As you can see, this is totally different from the answer. Am I on the right track?

Thanks!

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[toothdoc0121]

for number 7

since its 1M solution 0.002% of the acid would mean than [H+]= .00002M and because [H+]=[A-] and [HA] is already given as 1M plug into:

[H+][A-] = Ka = 4 X 10^-10
[HA]

 

[Meas]

Thanks toothdoc!

 

[yumi43]

Kaplan General Chem Subject Test 4:

As mentioned in previous threads, I am posting questions I have about subject tests that I did. Hope to get responses you all!

4) Which of the following if added to a saturated aqueous solution of NaCl, would most effectively reduce the chloride ion concentration?

Answer choices:
AgNO3
Ba(NO3)2
K2SO4
H2S
CH3COOH

A: AgNO3

this is because NaCl and AgNO3 will produce an insoluble compound: AgCl. this is going by your solubility rules. anything paired with Ag, Pb, or Hg is insoluble. therefore, you have no Cl ions left!

 

[UCB05]

16) CO2 and CH4 are both nonpolar molecules. The predominant interaction will be dispersion forces. Hydrogen bonding occurs between molecules that possess intramolecular H-O-, H-F, H-N- bonds. This creates polarity in the H and electronegative atoms which contribute to intermolecular forces. The bonds in this case are C-O and C-H, which do not polarize the H on CH4 or O on CO2 enough to cause hydrogen bonding.

25) You got half of it right
q = mc(delta T) = [(8)(1)(0+23)] + [(8)(1)(52-0)] = 75(8)
Which accounts for the heat needed to increase the temp from -23 to 52 You also have to add in the amount of heat required to convert the water from its solid to liquid phase using heat of fusion. This is where the 8(80) term comes in.
The total heat required then is [(8)(1)(0+23)] + [(8)(1)(52-0)] + 8(80)