08:46 – I’m back to working heads-down on the forensics book and kit, with occasional breaks to do something down in the lab.
One thing I’m going to do today is convert some of that copper(II) sulfate I bought at Home Depot over the weekend into 1.00 molar copper(II) sulfate solution. The label of the last batch of Root Kill I had showed an assay of 99.8% copper(II) sulfate. I confirmed that gravimetrically. The molar mass of copper(II) sulfate pentahydrate is 249.68 grams/mole, so I dissolved 500.44 grams of the Root Kill in just under two liters of water. If the assay was correct, that 500.44 grams of Root Kill should have contained 499.36 grams or 2.00 moles of copper(II) sulfate. I filtered the solution using a weighed piece of filter paper, washed as much as possible of the soluble material out of the filter paper, dried the paper, and reweighed it. The mass difference was 1.13 gram, made up I’m sure of insoluble copper(II) oxide, which confirmed the assay of 99.8% copper(II) sulfate. Bizarrely, that $13 bottle of Root Kill contains 908 grams of what is for all practical purposes reagent-grade copper(II) sulfate. It even includes the CAS number on the label.
Alas, the assay on the new bottles lists the copper(II) sulfate content as “only” 99.0%. I think I’ll trust them and simply use 249.68/.99 = 252.20 grams per liter to make up the 1.00 molar solution today. I suspect that if I repeated the gravimetric tests I’d find that this stuff is in fact 99.0%. I’ll make up several liters. The 1.0 M solution is used as is in the chemistry kits, for which I need two liters per 60 kits. I can also use it to make up various solutions for the biology kits, including Barfoed’s, Benedict’s, and Biuret reagents, so it won’t hurt to have several liters made up. Copper(II) sulfate takes literally a week to dissolve, so having it made up ahead of time may save time later.