Why do most reagents have potassium instead of sodium?

[ShawnD]

Many reagents have potassium as the cation instead of sodium. Permanganate is always potassium permanganate. Chlorate is always potassium chlorate. Nitrate is always potassium nitrate. Iodide is potassium iodide.
If potassium costs more money, why is it used in everything?

 

[movies]

You can usually get the sodium salts too. We use sodium iodide in the lab all the time, but rarely KI. Also, sodium chlorite is used in commercial bleach, not potassium. Sometimes its a solubility issue, sometimes it's just availability. There is sometimes a reactivity difference as well.