Problem with SAT II CHEMISTRY

Discus: SAT/ACT Tests and Test Preparation: May 2004 Archive: Problem with SAT II CHEMISTRY
 By Thunder77 (Thunder77) on Sunday, May 16, 2004 - 02:43 pm: Edit

Help,

I have a few problems I need to find out about the SAT II CHEMISTRY

- Are we expected to know how to write out the chemical formula ourselves from the word problem?

ex: How many grams of aluminum will be completely oxidized by 44.8 liters of Oxygen?
I know howto do this, but I did not know how to write out the chemical fomula correctly. I wrote Al + 02 --> Al02
but it turns out that is is actually
4Al + 302 ---> 2Al203; How am I supposed to know the product?!?

-Also, the questions from the barrons book requrie a lot of mathematic calculations
ex: x/65 = 65/73
and so x= (65*65)/73
Am I supposed to waste time doing this by hand on the real test!? Theres only 60 minutes for 85 problems!!!

 By Newo54 (Newo54) on Sunday, May 16, 2004 - 03:02 pm: Edit

For you first question, you should know the product based on the Aluminum ion's expected charge, 3+. This is something you can either memorize or figure out based on Aluminum's group in the periodic chart (this doesn't work for transition metals to the left of Aluminum).

I don't remember there being any long calculations when I took it. The math was either very simple (multiplying by 2 or 4 or something) or the answers were groups of factors,
ex: (.567)(348)(.0821)

 By Thunder77 (Thunder77) on Sunday, May 16, 2004 - 03:11 pm: Edit

Thanks Newo!

I still have a few questions about my first question

1. If the element has multiple oxidation numbers, such as Pb, do they tell you something like Pb(II) ? But for cases like Cl, which has 5 oxidation numbers, they do not label them with parentheses. Why?
2. Also, For reactions like
Zn + H2SO4 --> ZnSO4 + H2 and
2K + 2H20 ---> 2KOH + H2
Do we just use our instincts to determine which compound will get replaced?

Chemical Formulas are my weakest subject, and I really appreciate your help Thanks !

 By Qwert271 (Qwert271) on Sunday, May 16, 2004 - 04:00 pm: Edit

1. For Pb or something like it, they will tell you the oxidation number. For Cl, for example, the overwhelmingly most common ion is the Cl-1 ion. You can assume this much. It's cause it's a halogen.

2. The element that is reaction with the compound has a certain tendency toward forming ions. Zn and K, in the examples that you gave, form positive ions. So, they replace the positive element in the compound and bond with the negative ion. You should know that all metals (left side of the PTOTE) form pos. ions and non-metals usually form negative ions. They won't give you anything too tricky.

 By Isnet396 (Isnet396) on Sunday, May 16, 2004 - 04:11 pm: Edit

Are the Chem SAT II tests now still vaguely based on the practice one they have in Real SAT II's? Specifically, that bizzare thing with those reactions going in all different directions toward the beginning of the test (like question 5-9 or so)?

 By Thunder77 (Thunder77) on Sunday, May 16, 2004 - 04:12 pm: Edit

Thanks Guys!

I understand now.

The Barrons seem very good. If I understand all of the stuff in it, do I still need another book? What do you guys have to say of the Kaplan book?

Thanks !

 By Qwert271 (Qwert271) on Sunday, May 16, 2004 - 05:52 pm: Edit

If you do well in the Barrons, you should get an 800. I looked over the Barrons practice tests and usually got 10-15 wrong, which correlates to well below 800. But on the real thing I got 800.