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AP Chemistry Test / Solubility Rules

  • Thread starter cadillac
  • Start date
  • #1
10
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I'm finding a lot of inconsistency with the solubility rules from different sources.

especially when it comes to SO4(negative 2 charge).

my teacher told me: soluble except when combined with Ca2+, Ba2+, Sr2+, Pb2+... however, other sources sometimes include Hg(II) 2+, and some Ag+, and some both Hg(I) and (II).... so confusing.

any ideas?

also... not as important, but what is the format of the AP test?
I know its 75 MC and then 6 FRQs, but how much are the MC and FRQ sections scaled? And also, it seems that each FRQ varies in points?
 

Answers and Replies

  • #2
1,901
45
I'm finding a lot of inconsistency with the solubility rules from different sources.

especially when it comes to SO4(negative 2 charge).

my teacher told me: soluble except when combined with Ca2+, Ba2+, Sr2+, Pb2+... however, other sources sometimes include Hg(II) 2+, and some Ag+, and some both Hg(I) and (II).... so confusing.

any ideas?

also... not as important, but what is the format of the AP test?
I know its 75 MC and then 6 FRQs, but how much are the MC and FRQ sections scaled? And also, it seems that each FRQ varies in points?
Insoluble sulphates (in order from the most insoluble to the least insoluble):
Ra2+, Ba2+, Pb2+, Sr2+, Hg22+, Ca2+, Ag+.
Their pKsp:
10.4, 10.0, 7.7, 6.5, 6.2, 5.0, 4.8
 
  • #3
10
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Thank you very much, lightarrow!
 
  • #4
Borek
Mentor
28,327
2,716
You see, the problem is that soluble/insoluble is not zero or one, it is governed by Ksp - so you have to put the limit somewhere. CaSO4 is considered insoluble, but saturated soluition is about 0.005M - not bad for "insoluble" salt. For Ag2SO4 saturated solution has even higher concentraion.
 
  • #5
274
3
also... not as important, but what is the format of the AP test?
I know its 75 MC and then 6 FRQs, but how much are the MC and FRQ sections scaled? And also, it seems that each FRQ varies in points?
http://www.collegeboard.com/student/testing/ap/chemistry/samp.html --> Sample F/R Questions

College Board said:
The AP Chemistry Exam has two main parts, Section I and Section II, that contribute
equally (50 percent each) toward the final grade. Section I consists of 75 multiplechoice
questions that cover a broad range of topics. Section II consists of six freeresponse
questions: three multipart quantitative questions, one question on writing
balanced chemical equations and answering a short question for three different sets
of reactants, and two multipart questions that are essentially nonquanititative.
Teachers should not try to prepare students to answer every question in Section I
of the exam. To be broad enough in scope to give every student who has covered an
adequate amount of material an opportunity to make a good showing, the exam must
be so comprehensive that no student should be expected to make a perfect or nearperfect
score.
A period of 90 minutes is allotted for Section I of the exam. Section II is divided into
two parts: for Part A (55 minutes), students are allowed the use of a calculator, but for
Part B (40 minutes), no calculators are permitted.
Every Section II of the exam will contain one quantitative question that is based on
chemical equilibrium and one question that is based on laboratory. The laboratory
question may appear in Part A and be quantitative, or it may appear in Part B and
require little or no calculation.
Good luck!:biggrin:
 

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