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Question Can you explain to me what are the chemical properties of a mixture of 64 ounces of tap water diluted with 3/4 ounce of sulfuric acid if I use it for my electrolysis? Any affect on our health and in environment? Answer First, I am assuming that you are talking about fluid ounces though it doesn't make much of a different to calculate a volume vs. volume percentage. 64 oz / 0.75 oz = 0.0117 x 100 = 1.17 % H2SO4 (Note: Another assumption being made here is the use of concentrated H2SO4, actual concentration of the available concentrated acid is ~98% but the two percent difference is ignored in the above calculation and is negligible.) From the Handbook of Chemistry and Physics(1) some properties for 1 and 2% acid are as follows (:
To get into the chemical properties of your solution, let's figure out the pH (or a reasonable facsimile thereof): .75 fl oz = 22.18 ml of concentrated sulfuric acid which has a density of 1.84 g/ml so you're adding 40.81 grams of sulfuric acid to (64 x 29.57 ml / oz) 1.893 Liters of water (Note: This equates to slightly more than 20 g/L, if you look above this would put it at beyond 2% which is contradictory to the percentage calculated earlier, meaning those percentages were either listed as weight vs weight or weight vs volume or vice versa). Converting the weight of sulfuric acid added to mols of sulfuric acid we divide by the molecular weight of sulfuric acid: 40.81 grams / (90.09 grams / mol) = 0.45 mols of sulfuric acid Now to convert to molarity we divide by the total volume: 0.45 mol / 1.893 liters = 0.24 M or since there are two acidic protons 0.48 N (normality is a measure of the active constituent in terms of molarity, in this case hydrogen ion) To get a quick and dirty idea of the pH we can just take the negative log of the normality, and the negative log of the molarity and the pH will lie somewhere in between: pH = -log (0.24) = 0.62 So, this is a fairly acidic solution from a pH perspective. Concentrated sulfuric acid solutions can be oxidizing but this is no where near concentrated. Because it is so dilute, the first proton on the sulfuric acid will be completely dissociated:
H2SO4
+ H2O <----> HSO4-
+ H3O+
(I) The dissociation of the first proton is shown in equation (I), that equilibrium lies almost entirely to the right. The second proton dissociates to a somewhat lesser degree (II) but because the solution is so dilute the equilibrium will also lie to the right. So you will have hydronium ions, sulfate anions, and bisulfate or hydrogen sulfate anions as well floating around in your solution. This will be conducive to conducting electricity and will help in electrolysis since it seems that is what you are going for. Now that I've gone through that aspect of things. Don't use tap water! Especially if you are trying to plate metals, even small amounts of impurities can have drastic impacts on the quality of deposition of metal films and in organic electrolysis it can impact byproducts and side reactions. Spend the money to buy a gallon of distilled water, they sell it in gallon jugs for less than $1 at nearly every chain grocery store near the bottled water. Tap water can vary greatly from location to location, yours might not be as bad as some, then again you might have very hard water in your area which could very easily hinder/hurt any electrolysis you might be doing. As for health and environment, sulfuric acid is considered toxic mostly for its corrosively and because it is an industrial chemical it is not made with consumption in mind so it contains some other nasties that would hurt you to consume. But really it itself is not that toxic, sulfates, bisulfates, they put them in food and water for various reasons, magnesium sulfate is the best example since you can purchase it as a 'pure' salt. The only side effect of its consumption is diarrhea which is something people intend to bring about by its consumption. This is such a dilute solution that any poisonous attributes should be nill, it will still irritate the skin and gloves are recommended but it's nowhere near the monster of the concentrated stuff. Just don't get it in your eyes. And on the note of the environment, the concentrated acid is used as a drain cleaner, conceptually liters of it can be dumped down the drain and the Environmental Protection Agency has no qualms against it being sold over the counter for that purpose. A few liters of dilute solution is nothing to worry about the environment over although you could be so kind as to neutralize it with some baking soda before disposal. Your only worry with respect to the environment is anything else you dissolve in your sulfuric acid, those have to be considered on a case by case basis to determine any impact that they might have. -Chemist
(1) Hodgman, Charles D. Handbook of Chemistry and Physics.
39th ed. Cleveland, OH: Chemical Rubber Publishing Co. 1957 |
