Which of the following pairs of compounds will give a precipitate in a diluted solution?

Question 4 options:
A) Cu(NO3)2 and Na2CO3
B) KNO3 and NaCl
C) MgCl2 and Ba(NO3)2
D) NH4Cl and Al2(SO4)3

http://www.files.chem.vt.edu/RVGS/ACT/notes/solubility_rules.html

To determine which pair of compounds will give a precipitate in a diluted solution, you need to consider the solubility rules of compounds.

Solubility rules provide guidelines to determine whether a compound will dissolve in water or form a precipitate. Here are the solubility rules for some common compounds:

1. Most nitrates (NO3-) are soluble.
2. Most salts of alkali metals (Group 1) and ammonium (NH4+) are soluble.
3. Most chlorides (Cl-) are soluble, except for those of silver (Ag+), lead (Pb2+), and mercury (Hg2+).
4. Most sulfates (SO42-) are soluble, except for those of calcium (Ca2+), barium (Ba2+), strontium (Sr2+), lead (Pb2+), and silver (Ag+).
5. Most carbonates (CO32-), phosphates (PO43-), and sulfides (S2-) are insoluble, except for those of alkali metals (Group 1) and ammonium (NH4+).

Now let's go through the given options to determine which pairs will give a precipitate:

A) Cu(NO3)2 and Na2CO3
Cu(NO3)2 is a nitrate, and nitrates are soluble, so it will not form a precipitate. Na2CO3 is a carbonate, and carbonates are usually insoluble except for those of alkali metals (Group 1) and ammonium (NH4+) ions. Therefore, Cu(NO3)2 and Na2CO3 will form a precipitate.

B) KNO3 and NaCl
Both KNO3 and NaCl are nitrates and chlorides, respectively. As mentioned earlier, nitrates and most chlorides are soluble, so there will be no precipitate formed in this pair.

C) MgCl2 and Ba(NO3)2
MgCl2 is a chloride, and chlorides are generally soluble. Ba(NO3)2 is a nitrate, which is also soluble. Therefore, this pair will not form a precipitate.

D) NH4Cl and Al2(SO4)3
NH4Cl is an ammonium salt, and ammonium salts are usually soluble. Al2(SO4)3 is a sulfate, and sulfates are generally soluble except for those of calcium (Ca2+), barium (Ba2+), strontium (Sr2+), lead (Pb2+), and silver (Ag+). In this case, Al2(SO4)3 will form a precipitate with NH4Cl.

Based on the solubility rules, the pair that will give a precipitate in a diluted solution is:

A) Cu(NO3)2 and Na2CO3