Why do some combinations of ionic compounds form a precipitate while others do not

Whether or not such a reaction occurs can be determined by using the solubility rules for common ionic solids.

tell me if i'm wrong

This is because of the solubility of the reacting metal salts.

Explanation:

The use of solubility of salts influences the formation of precipitates. Most precipitation reactions occur as a result of the replacement reactions or double placement reactions. A double replacement reaction occurs when two ionic reactants dissociate and bond with respective anion and cation of the other reactant. This is simply a switch over reaction.

A double replacement reaction occurs when a chemical reaction occurs and one of the products formed is insoluble.

Here is an example:

Both reactants are acqeous and the product is solid.

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !

a pan containing water is placed in a positio n where it is exposed to a 10 mile per hour wind. the pan contains a uniform depth of 1.27 cm of water, is quite wide, and has a length of 2.44 m in the wind direction. the water in the pan is at a constant temperature of 15.5 °c.