Making pH 7 Buffers

Considering you have the necessary chemicals:

250mL of 0.100M Potassium Phosphate Monobasic KH2PO4 (3.4022g in ~250mL dH2O)

250mL of 0.100M Sodium Phosphate Dibasic Na2PO4 (6.7017g in ~250mL dH2O)

Mix in 500mL container, add colour key preservative if you have it.

- Obviously, use proper lab techniques. Don't just measure out 250mL of water and mix. Pour the amount in a beaker, add roughly half of the volume of water, dissolve, then dilute to 250mL in a grad cylinder.
- Solutions must be of exact concentrations, use an analytical balance if you have it.
- Water should be freshly distilled (deionized too if you can), do not use old stock dH2O as it tends to be acidic and it may cause the pH to shift a little.


Note on managing a science lab inventory Part I

Managing a lab is complicated work, especially when it comes to keeping a stock and track an inventory of equipment, glassware, chemicals and other materials.

It gets more complicated when your equipment and glassware is mostly for the use of highschoolers.

Let's take for example glassware. There's lots of brands, qualities and prices of glassware you can buy. You can go high end and get everything pyrex, VWR and the like. Or you can go low end and buy ML, some Chinese glass or any of the other cheapies.

High end glassware is expensive, but it's sturdier, it doesn't break as easily in heat, when falling or when exposed to mechanical forces. If one puts it under enough pressure sure, it'll break, but what it takes to chip a high quality piece will certainly smash the low quality one. And that's the thing about low end glassware, sure it's cheaper, but it's more delicate than your grandma's

I've broken ML 100mL grads by just flicking them with my middle finger.

So comes the dilemma. I have X amount of money so i can either go with less of the good quality stuff, or buy tons of the cheap stuff.

If you work in a school, you will have teenagers whose brains are still adapting to their rapidly growing bodies and are natually clumsy, and your glassware will break, high or low end.

But consider this, by buying more expensive glass you will ensure a lower rate of breakage. If you buy cheap stuff, you might run out of glassware due to breakage before year's end. By my estimation, annually we spend more in replacing cheap glassware that broke from simple accidents (like hitting it against the tap of the sink when washing, which is quite common) with more cheap glassware than we would in replacing with good quality glassware, since they would last longer.

It's just not cost effective, considering that even the cheap glassware is not all that much cheaper than high quality glass, and is a little more expensive each year that goes by.

If you have a small budget then by all means get the cheap stuff so you can have enough stock to operate, but then you must instruct, and enforce, proper handling of glassware.

But if you have a large budget, don't keep a large stock of cheapies. Keep a small one of good quality ones. Just because they don't break or chip when hitting the tap.