Elbone wrote:The MSDS of PBW mentions sodium metasilicate (30%), along with sodium percarbonate as the ingredients. Is there a cheap source of sodium metasilicate? (I assume that's the chelating agent used?)
Sodium metasilicate is used in lots of detergents to get the pH up to where the greases/fats get saponified so that's a source - buy a detergent that contains it. It is a sequestrant. If calcium is present calcium silicate will be formed but that is insoluble so metasilicates aren't used with hard water unless there is a chelating agent present as well. Chelation is not the same as sequestration (it's a type of sequestration). In chelation (the word comes from the Greek word for "claw") the metal ion is surrounded and grabbed by the chelating agent in multiple places (6 with EDTA) such that the ion no longer is available for other chemical reactions. The complex is soluble (at least with the chelants I know about). In simple sequestration the metal ion is tied up by formation of an insoluble precipitate (such as calcium silicate) which can leave streaks. That's why glassware comes out of your dishwasher streaky if the water is at all hard unless you add one of those rinses which is supposed to prevent that and I'll bet a couple of mugs of my best that those are based on EDTA.
I did find cheap EDTA tetrasodium salt. It's lot's less expensive than the ACS grade disodium salt (requires more processing to make the stuff) I have in the lab. AFAIK, its chelating properties should be no different as it is the deprotonated acid that does the job. $21 a pound. Now that's much better.
