BR practice test questions

[2010premed]

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1.. .Which of the following gases would have a negative value for the .a. term?
A.. .C2H6
B.. .NH4+
C.. .H3COCH3
D.. .H3CNH2(.g.)
I know that a negative a term means that the molecules repel one another, but how would you choose the right answer from here?

2.. .How does a battery differ from a capacitor?
A.. .A battery discharges voltage at a steady rate over time, while a capacitor discharges it all at once.
B.. .A battery discharges voltage all at once, while a capacitor discharges it at a steady rate over time.
C.. .A battery always discharges voltage, while a capacitor always absorbs voltage.
D.. .A battery always absorbs voltage, while a capacitor always discharges voltage.
Is this purely a knowledge based question, or is there any way I can reason to the answer? what are some other random facts that I should know about capacitors and batteries?
3.. .If a seismic recorder whose design is built around a vertical hanging spring is too sensitive, what adjustments can be made to the instrument to correct its reading?
A.. .Increase the spring constant, and mount the sensor on more solid ground
B.. .Increase the spring constant, and mount the sensor on less solid ground.
C.. .Decrease the spring constant, and mount the sensor on more solid ground.
D.. .Decrease the spring constant, and mount the sensor on less solid ground.
How would you answer this?
4.. .What is the hybridization of carbon in CaCO3(s)?
Answer: sp2

My question: when exactly do you know when to include the cation in the structure? Is it only when the compound is not ionic (big difference in EN between the cation + anion)?

 

[PiBond]

1.Which of the following gases would have a negative value for the .a. term?
A.C2H6
B.NH4+
C.H3COCH3
D.H3CNH2(.g.)
I know that a negative a term means that the molecules repel one another, but how would you choose the right answer from here?

2.How does a battery differ from a capacitor?
A.A battery discharges voltage at a steady rate over time, while a capacitor discharges it all at once.
B.A battery discharges voltage all at once, while a capacitor discharges it at a steady rate over time.
C.A battery always discharges voltage, while a capacitor always absorbs voltage.
D.A battery always absorbs voltage, while a capacitor always discharges voltage.
Is this purely a knowledge based question, or is there any way I can reason to the answer? what are some other random facts that I should know about capacitors and batteries?
3.If a seismic recorder whose design is built around a vertical hanging spring is too sensitive, what adjustments can be made to the instrument to correct its reading?
A.Increase the spring constant, and mount the sensor on more solid ground
B.Increase the spring constant, and mount the sensor on less solid ground.
C.Decrease the spring constant, and mount the sensor on more solid ground.
D.Decrease the spring constant, and mount the sensor on less solid ground.
How would you answer this?
4.What is the hybridization of carbon in CaCO3(s)?
Answer: sp2

My question: when exactly do you know when to include the cation in the structure? Is it only when the compound is not ionic (big difference in EN between the cation + anion)?

1. Use POE first. We see that answer D has the capability of H-bonding which will result in attractive forces between molecules, not repulsive. Choice C is polar so there will be attractive forces as well. Choice B is not a gas, so I pick choice A

2. Use POE again. Eliminate C and D because we know that capacitors don't just absorb or discharge voltage, they can do both. Eliminate B since we know that batteries do not discharge all their voltage at once.

3. This is just a guess. If the recorder is too sensitive then I'm going to want to mitigate that by having my spring stretch less to compensate. This calls for a spring with a higher spring constant. So I eliminate C and D. More solid ground would be better because it would lead to less movement which is a good thing if our sensor is too sensitive (I presume that less solid ground would cause erratic readings). I arrive at choice A

4. CO3 is sp2 hydridized given that we have 3 areas of electron density surrounding our carbon. There is one double bond to an oxygen, and two single bonds to the other two oxygens. Therefore, there are two negative charges resulting in a -2 formal charge. Calcium is a dication (+2), so everything checks out.