The problem with making a soluble salt is that it will instantly dissolve in the water that was used to dissolve the acid.

This means your salt solution will not be pure - it will be contaminated with un-reacted acid, or un-reacted base.

But there are ways around this problem.

If we use a metal that reacts with acid but does not react with water (most of them) then the only reaction that will happen is:

Metal + Acid --> Salt + Hydrogen

All we need to do is add enough metal to use up all the acid.

Any un-reacted Metal can be filtered off.

The solution will only contain salt which can be left to crystalise as the water evaporates.

We heat with a water-bath to reduce the temperature the salt is exposed to in case it is destroyed by the heat. 

We usually leave some water to evaporate away slowly - it's safer that way

The same method could be used with an insoluble Base such as Copper Oxide.

                    Base + Acid --> Salt + Water

Or an insoluble Carbonate such as Calcium Carbonate.

                   Carbonate+ Acid --> Salt + Water + Carbon Dioxide

Because this is likely to have hot salt crystals flying around the room as in the video clip below!

And because the heat might destroy the salt we want to make.

But we could heat just enough for some crystals to form on the surface of the water.

The solution is now saturated, letting it cool will see crystals form quickly.

If we have to evaporate to dryness then we shouldn't heat the salt directly, we should heat using a water bath - it's less dangerous and less likely to decompose the salt.