Question

Solubility Rules!! Homework problem I desperately need help with

Solutions used: 6M HCl, 6M NaOH, 6M NH3, 3M H2SO4

Mixed with: Cr(NO3)3, Fe(NO3)3, Bi(NO3)3, Mg(NO3)2, Pb(NO3)2

please help me and tell me which form precipitates and which

Answer 1

There is no better time to learn the solubility rules then now. That's all it takes and a little practice helps of course. Here is a simplified version.
See below for an example of how to do these.

https://www.google.com/search?q=solubility+rules&client=firefox-a&hs=bg1&rls=org.mozilla:en-US:official&channel=sb&tbm=isch&imgil=eSgVJZM2Qry8hM%253A%253Bwuj7TohVYsLSMM%253Bhttp%25253A%25252F%25252Fyeahchemistry.com%25252Fsolubility-rules&source=iu&pf=m&fir=eSgVJZM2Qry8hM%253A%252Cwuj7TohVYsLSMM%252C_&usg=__Wv4bcTzS2j57NGbEUX3zndNDwy8%3D&biw=995&bih=601&ved=0CDEQyjc&ei=DNRSVK7_DYucNvzggegE#facrc=_&imgdii=_&imgrc=eSgVJZM2Qry8hM%253A%3Bwuj7TohVYsLSMM%3Bhttp%253A%252F%252Fyeahchemistry.com%252Fsites%252Fdefault%252Ffiles%252Fgeneralsolubilityrules.gif%3Bhttp%253A%252F%252Fyeahchemistry.com%252Fsolubility-rules%3B465%3B322

Let's take Fe(NO3)3 and add the four solutions to it.

With HCl it could form FeCl3 but all chlorides are soluble except Ag, Hg2^2+ and Pb so this one is no ppt.
With NaOH this could form Fe(OH)3 and that is insoluble so you get a ppt.

With NH3 you get NH3 + H2O ==> NH4^ + OH^- so the Fe(OH)3 will ppt here, too.
NOTE: NH3 can have two roles. One is that is forms OH^- in solution and OFTEN ppts the hydroxide if that is insoluble; at other times it is the NH3 molecule that form a complex ion as in Cu(NH3)4++.
Fe(NO3)3 + H2SO4 might form FeSO4 but sulfates are soluble except for BaSO4, SrSO4 and sometimes CaSO4 so no ppt.