General Chemistry Problems

[DMD to Be]

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Just took one of the Gchem practice tests from the "Permanent Link to Quizzes, etc" thread, and got a 16!!!! OMG. I have been studying G Chem for the past week. Kaplan Blue Book mainly, but there were at least 10 that were not covered in the blue book. I'm going to list several questions that I had no idea on and maybe some of you can help me out. Also, I hope these Kaplan tests on this link are MUCH harder than the real thing b/c I was hoping to pull at least a 20 in G chem.

The ions K+ and Cl- differ in many ways. In which one way are they most similar?

A. atomic weight
B. number of occupied orbitals
C. atomic size
D. ionization energy
E. number of protons and number of neutrons

Answer: B.



When 0.95 g of MgCl2 are dissolved in 1 kg of water, the freezing pt. of the solution is found to be 0.0558 C. The molal freezing pt. depression constant for water is 1.86 C/m. What can be said about the ionization of MgCl2 in aqueous solution?

A. MgCl2 does not ionize.
B. MgCl2 is totally ionized.
C. MgCl2 is one-half ionized.
D. MgCl2 is ionized to a negligible extent
E. Cannot be determined from the info given

Answer: B



A solid cube of unknown material whose edge is 2 cm weighs 0.2 kg. What is the specific gravity of this material? (Water weighs 1 gram per cubic cm)

A. 0.25
B. 0.1
C. 25
D. 250
E. 1000

Answer: C


This question is probably stupid, but I'm confused...
What is the oxidizing agent in the following reaction?

2Fe^3+ + 2I^- --> 2Fe^2+ + I2

They say it is Fe^3+

I thought it would be I-, though b/c Iron is being oxidized (i.e losing electrons) which means it definitely couldn't be the oxidizing agent???

 

[tinman831]

The ions K+ and Cl- differ in many ways. In which one way are they most similar?

A. atomic weight
B. number of occupied orbitals
C. atomic size
D. ionization energy
E. number of protons and number of neutrons

Answer: B.

K+ and Cl- have the same number of electrons, so they have the same number of occupied orbitals.

When 0.95 g of MgCl2 are dissolved in 1 kg of water, the freezing pt. of the solution is found to be 0.0558 C. The molal freezing pt. depression constant for water is 1.86 C/m. What can be said about the ionization of MgCl2 in aqueous solution?

A. MgCl2 does not ionize.
B. MgCl2 is totally ionized.
C. MgCl2 is one-half ionized.
D. MgCl2 is ionized to a negligible extent
E. Cannot be determined from the info given

Answer: B

beats me

A solid cube of unknown material whose edge is 2 cm weighs 0.2 kg. What is the specific gravity of this material? (Water weighs 1 gram per cubic cm)

A. 0.25
B. 0.1
C. 25
D. 250
E. 1000

Answer: C

density = weight/volume = 200g/8cm^3 = 25g/cm^3
sg = density of object / density of water = (25g/cm^3)/(1g/cm^3 = 25

This question is probably stupid, but I'm confused...
What is the oxidizing agent in the following reaction?

2Fe^3+ + 2I^- --> 2Fe^2+ + I2

They say it is Fe^3+

I thought it would be I-, though b/c Iron is being oxidized (i.e losing electrons) which means it definitely couldn't be the oxidizing agent???

An oxidizing agent causes oxidation, and itself is reduced in the process. Since Fe^3+ gained electrons, it is reduced, and is what is doing the oxidation.

 

[DMD to Be]

Thanks tinman.

 

[allstardentist]

When 0.95 g of MgCl2 are dissolved in 1 kg of water, the freezing pt. of the solution is found to be 0.0558 C. The molal freezing pt. depression constant for water is 1.86 C/m. What can be said about the ionization of MgCl2 in aqueous solution?

A. MgCl2 does not ionize.
B. MgCl2 is totally ionized.
C. MgCl2 is one-half ionized.
D. MgCl2 is ionized to a negligible extent
E. Cannot be determined from the info given

Answer: B

First find the mol. weight of MgCl2. Then find how many moles are there. Then find the molality of the solution. Multiply the molality by the constant to get the delta Tf. If MgCl2 is not ionized, this number should equal to the number given in the problem. If MgCl2 is totally ionized into 1 molecule of Mg and 2 molecules of CL (a total of 3), then if you multiply the delta Tf by 3 should give you the number given in the problem. So the answer is B.

 

[Djapprentice]

First find the mol. weight of MgCl2. Then find how many moles are there. Then find the molality of the solution. Multiply the molality by the constant to get the delta Tf. If MgCl2 is not ionized, this number should equal to the number given in the problem. If MgCl2 is totally ionized into 1 molecule of Mg and 2 molecules of CL (a total of 3), then if you multiply the delta Tf by 3 should give you the number given in the problem. So the answer is B.

Damn, you guys beat me to it, my brain is fried, I'm gonna sleep on this one, work it out & see if come up with the same thing & will let you know tomorrow

 

[Djapprentice]

Damn, you guys beat me to it, my brain is fried, I'm gonna sleep on this one, work it out & see if come up with the same thing & will let you know tomorrow

Ok, I just woke up & feel a little more refreshed. As for that question about the MgCl2 compound, notice it is an ionic compound, and what happens with ionic compounds when they're dissolved in water, they are COMPLETELY ionized. So in a nutshell, I would believe they're asking you for the deifnition of an ionic compound. Hope that helps & thanks again for the help 🙂

 

[Djapprentice]

Allstar, thanks for helping me out as well. How's your studying? I was wondering how you were coping with that carb problem from last week, do you understand it better? All this week, I've been analyzing PAT Achiever 2, & going over topscore questions. I still gotta do some Qr, ::sighs::

 

[Djapprentice]

DMD, another thing to consider with the redox problem, is given a problem like that, when it comes to asking for oxidizing / reducing agents, the first thing you MUST do is eliminate the products side right off the bat, that will make your life much easier. Tinnman is right on with the K+ & Cl-. I was so tired last night, I wouldn't have been of much help, but let me know if you still need any further clarification.

 

[Djapprentice]

One thing I forgot in that net ionic equation, as I did in acid-base chem, was that H+ = H3O, a subtle detail I missed, lol

 

[DMD to Be]

🙂 Thank you guys...