Mcat practice question

[esla721]

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Hi guys, I'm new to this forum.
I've just started studying mcat and I've encountered questions! If you could kindly let me know why the answer to question 5 is a and to question 8 is b in the attached file, thank you so much!

another question added Jan 11

For the second attached thumbnail , I dont really know how to approach 46 (the answer is D) and for Q47, i thought pure gases should not be included in the equilibrium equation, could somebody help me clarify this?

 

[akim6890]

Ok for the first question think about what is similar and different about all the ions. They all have the same number of electrons but different number of protons. Their ion size is another way of saying how tightly the nucleus pulls on the electron cloud surrounding it (the positive charge from the protons pulls on the negative charge of the electrons). If there are the same number of electrons, then the relative size can be determined by the number of protons, which would correspond to how tightly it holds the electron cloud (smaller ion size). Number of protons increases in order of O, F, Na, Mg.

The second one is ambiguous because they need to mention that all lone pairs are as written. After you know that, it's simply a matter of looking at the number of valence electrons and seeing if they match with the lone pairs or charge. In this case, Cl is missing 1, each Se is missing 4, and F is missing 4. Only S has the correct amount with 4 valence electrons in bonds and 2 in a lone pair.

 

[esla721]

Ok for the first question think about what is similar and different about all the ions. They all have the same number of electrons but different number of protons. Their ion size is another way of saying how tightly the nucleus pulls on the electron cloud surrounding it (the positive charge from the protons pulls on the negative charge of the electrons). If there are the same number of electrons, then the relative size can be determined by the number of protons, which would correspond to how tightly it holds the electron cloud (smaller ion size). Number of protons increases in order of O, F, Na, Mg.

The second one is ambiguous because they need to mention that all lone pairs are as written. After you know that, it's simply a matter of looking at the number of valence electrons and seeing if they match with the lone pairs or charge. In this case, Cl is missing 1, each Se is missing 4, and F is missing 4. Only S has the correct amount with 4 valence electrons in bonds and 2 in a lone pair.

thank you for your reply, that was very helpful

 

[ChemTutor]

notice that a, b, d all have multiple halogen atoms each with 7 electrons. intuitively, one could suspect that we are likely to run into troubles trying to create octets around each atom.

on the other hand, Se=Se has a simple analog O=O (same group in the periodic table) that we know for a fact exists.

 

[NuttyEngDude]

just curious what this material is from, i want to make sure i dont look at something that i have planned in future? Thanks 😀

 

[CastleG8]

just curious what this material is from, i want to make sure i dont look at something that i have planned in future? Thanks 😀

That is from Exam Krakers 7th edition Inorganic Chem book. This isn't from the Lecture exams, just the chapter follow up questions to quiz you on covered topics.

 

[esla721]

just curious what this material is from, i want to make sure i dont look at something that i have planned in future? Thanks 😀

its from EK end of chapter practice questions

 

[esla721]

its from EK end of chapter practice questions

up

 

[esla721]

bump

 

[Deadlifts]

Hi guys, I'm new to this forum.
I've just started studying mcat and I've encountered questions! If you could kindly let me know why the answer to question 5 is a and to question 8 is b in the attached file, thank you so much!

another question added Jan 11

For the second attached thumbnail , I dont really know how to approach 46 (the answer is D) and for Q47, i thought pure gases should not be included in the equilibrium equation, could somebody help me clarify this?

Q46 gives you an equilibrium expression and a sealed environment of two beakers. Calcium isn't becoming gaseous. The gas is CO2. The amount of calcium is staying constant in each beaker so B and C are out. A isn't right because there will still be CaO in beaker 1 even it were to all shift to the right. So through the process of elimination and verified by it being a reversible reaction, D is correct.

Q47, you're thinking of pure solids, liquids/solvents.

For example,

NH4Cl(s) ⇄ NH3(g) + HCl(g) would be: K = [NH3][HCl]. You'd leave the solid out of the equilibrium expression.