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
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.
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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.
To determine which forms precipitate when the given solutions are mixed with the provided compounds, we can refer to solubility rules. Solubility rules provide guidelines for predicting the solubility of different compounds based on their ionic nature.
Here are the general solubility rules:
1. Most nitrate (NO3-) salts are soluble.
2. Most alkali metal (Group 1) salts and ammonium (NH4+) salts are soluble.
3. Most chloride (Cl-), bromide (Br-), and iodide (I-) salts are soluble, except for those of silver (Ag+), lead (Pb2+), and mercury (Hg2+).
4. Most sulfate (SO42-) salts are soluble, except for those of barium (Ba2+), strontium (Sr2+), lead (Pb2+), and calcium (Ca2+).
5. Most carbonate (CO32-), phosphate (PO43-), and sulfide (S2-) salts are insoluble, except for those of alkali metals and ammonium.
6. Most hydroxide (OH-) salts are insoluble, except for those of alkali metals and barium (Ba2+).
Now, let's go through each compound and determine if precipitation would occur when mixed with the provided solutions:
1. Cr(NO3)3:
- Cr(NO3)3 contains the nitrate ion (NO3-), which is generally soluble.
- Therefore, Cr(NO3)3 is soluble and will not form a precipitate.
2. Fe(NO3)3:
- Fe(NO3)3 contains the nitrate ion (NO3-), which is generally soluble.
- Therefore, Fe(NO3)3 is soluble and will not form a precipitate.
3. Bi(NO3)3:
- Bi(NO3)3 contains the nitrate ion (NO3-), which is generally soluble.
- Therefore, Bi(NO3)3 is soluble and will not form a precipitate.
4. Mg(NO3)2:
- Mg(NO3)2 contains the nitrate ion (NO3-), which is generally soluble.
- Therefore, Mg(NO3)2 is soluble and will not form a precipitate.
5. Pb(NO3)2:
- Pb(NO3)2 contains the nitrate ion (NO3-), which is generally soluble.
- However, according to solubility rule #3, lead (Pb2+) salts, including Pb(NO3)2, are insoluble with chloride (Cl-).
- When mixed with 6M HCl, Pb(NO3)2 will form a precipitate of lead chloride (PbCl2).
To summarize:
- Cr(NO3)3, Fe(NO3)3, Bi(NO3)3, and Mg(NO3)2 are all soluble and will not form precipitates.
- Pb(NO3)2 will form a precipitate (PbCl2) when mixed with 6M HCl.