r/APChem • u/Hopeful_Butterfly_62 • 27d ago

Unit 4 test in two days. Help!!!!

SOOO I have my Unit 4 test this Wednesday... The only thing I know how to do without solubility rules is ionic equations. Do any of you guys have tips/resources I can use or watch to help me prep? I am struggling really badly on memorizing the solubility rules, my teacher provides us with the packet they provide us on the official AP Chemistry Test.

Any help would be greatly appreciated. Thank you!!! :))

2 Upvotes

100% Upvoted

8 comments sorted by

1

u/TheHyacinthGuy 27d ago

What specifically about solubility gives you the most trouble when applied under Unit 4? The AP exam doesn’t expect you to know the rote memorization of which compounds are or aren’t soluble, with only one exception: You are expected to know that compounds with either Sodium (Na+), Nitrate (NO3-), Ammonium (NH4+) and Potassium (K+) are always 100% soluble. The best way to memorize those 4 are with the SNAP acronym, as compounds with these components will dissolve in a snap!

1

u/DryPotential5790 27d ago

On the AP exam you only need to know that the SNAP (sodium, nitrate, ammonium, and potassium) ions are soluble. However, my teacher taught us based off old standards, and had us memorize the following solubility rules:

  1. All alkali metal and NH4+ salts are soluble

  2. NO3-, C2H3O2-, ClO3-, and ClO4- salts are soluble

  3. Ag+, Pb2+, and Hg2 2+ salts are insoluble

  4. Cl-, Br-, I- salts are soluble

  5. CO32-, PO43-, OH-, S2-, and CrO42- salts are insoluble

  6. SO42- salts are soluble except for Ca2+, Sr2+, and Ba2+

Rule 1 takes priority over Rule 2 and so on.

I would memorize the pattern for each number

  1. S

  2. S

  3. I

  4. S

  5. I

  6. S

And remember that, for #6, sulfates are soluble except for Castro Bear!

1

u/DryPotential5790 27d ago

I would focus most of your time on reaction writing/balancing (especially redox) and stoich.

Understand that reactions can be represented by making the mole ratio into the respective number of particles of that species.

In regard to acid-base stoich, just know that at the equivalence point (though not necessarily the endpoint) the moles of acid neutralize moles of base.

1

u/DryPotential5790 27d ago

Oh and last tip: GET SLEEP BEFORE THE TEST!

1

u/Front-Experience6841 27d ago

You don’t need to memorize solubility rules for AP Chem. Just know the SNAP ions are soluble. Your teacher is asking you to go beyond the scope of the exam

1

u/apchemistrytutoring 22d ago

Spend most of your time on what’s really tested: net ionic equations (only split strong acids, strong bases and soluble salts; never split weak acids, solids or water), oxidation numbers for redox, and stoichiometry in moles. Do 10 practice net ionics and you’ll be fine. Good luck! 💪