Coffee, Conspiracy, and Citizen Science: An Introduction to Iodometry

I take coffee very seriously. It’s probably the most important meal of the day, and apparently the largest overall dietary source of antioxidants in the United States of America. Regardless of whether you believe antioxidants have a health effect (I’m skeptical), that’s interesting!

Unfortunately, industrially roasted and ground coffee is sometimes adulterated with a variety of unwanted ‘other stuff’: corn, soybeans, wheat husks, etc. Across Southeast Asia, there’s a lot of concern over food adulteration and safety in general, as the cost-driven nature of the market pushes a minority of vendors to dishonest business practices. Here in Vietnam, one of the specific rumors is that coffee from street vendors is not actually coffee, but unsafe chemical flavoring agents mixed with corn silk, roasted coconut husks, and soy. Local news reported that 30% of street coffee doesn’t even contain caffeine.

While I’ve heard some pretty fanciful tales told at street side coffee shops, some of them turned out to be based on some grain (bean?) of truth, and local news has certainly featured it often enough. Then again, I’ve been buying coffee at the same friendly street vendors for years, and take some offense at unfounded accusations directed at them.

This sounds like a job for science, but what can we use to quantify the purity of many coffee samples without spending a fortune? As usual, the solution to the problem (pun intended) was already in the room:

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Making high concentrations of hydrogen peroxide at home

Hydrogen peroxide – the same stuff you can pick up from a drug store or beauty supply store – is one of those very interesting chemicals that belongs on every maker’s cabinet. At concentrations of about 30%, it’s perfect for etching PCB boards, and at even higher concentrations – about 70% – it can be used as rocket fuel. Unfortunately for the home hacker, it’s very difficult and expensive to obtain peroxide in concentrations above 3% or so. That’s alright with [Charlie], though, because he’s come up with a way to concentrate peroxide and measure the concentration once he’s done.

There are a few YouTube videos of kitchen chemists concentrating peroxide by heating it on a stove to just under 100°C. Because hydrogen peroxide boils at 150°C, they’re simply boiling off the water and increasing the concentration of peroxide. This is a qualitative method, and you’ll never know what concentration you’re getting. [Charlie] rigged up a small-scale with a pipette to measure the weight of his concentrated peroxide per unit of volume, giving him the density of his concoction and thus the concentration.

We have to note that concentrated peroxide is dangerous stuff, but the results of [Charlie]’s lab work aren’t much more dangerous than what hair stylists work with every day. If you’re going for high-test peroxide, good job, that’s awesome, but do be aware of the risks.