What happens if you add metallic lithium to a glass of 7-Up? First, it bubbles like Alka-Seltzer. Then, it starts to heat up and boil. As it does so, the colour changes: to green, yellowish-brown, and reddish brown, until it is pretty much black sludge.
“By the time I went to the lab, it looked like beer,” observes Sir Martyn Poliakoff, our host and his impressively wild white hair—sort of Albert Einstein meets Doc Brown. The experiment comes from the latest episode of The Periodic Table of Videos from the chemists at the University of Nottingham in England. This particular entry was inspired by the fact that 7-Up really did contain lithium.
Apparently the colour change were pretty surprising, since lithium salts are pretty much colourless. But as Poliakoff explains, it’s the result of a sharp increase in acidity (Ph). Check out the whole thing, especially the control experiment, where they mixed sodium hydroxide pellets with 7-Up to see if this also made it change colour.