The hedgehog reversed: dissolving tin
What can you do with the tin hedgehog from one of the previous experiments? One of the possibility is to study the properties of tin. Like its interaction with acids and alkali. And at the same time to get tin salts for further experiments.
The following experiments with acids and alkali are less safe than those from the MEL Science sets (if you use any) and require some extra chemicals.
To “reverse” the tin hedgehog creation and turn it back to the tin chloride, it’s possible to dissolve it in hydrochloric acid. As the reaction is slow, it’s better to use higher concentrations of the acid (I used 30%) and heat (putting the test tube into the glass of hot water is sufficient). You can find the hydrochloric acid (also called muriatic acid) in a hardware store. Mostly it’s about 10%, so it will take more time for tin to get dissolved.
What are the other ways to dissolve the tin hedgehog? Tin can interact with both acids and alkali.
This video shows the tin interaction (or the absence of it) with hydrochloric acid, sulphuric acid and potassium hydroxide.
In the reactivity series tin comes before the hydrogen, so it should react with acids to produce hydrogen gas and tin salts. But at the same time tin is placed is in the middle of the series, close to the hydrogen. It is less reactive metal than for example magnesium or zinc, so its reaction with acids will go much slower.
K→Ca→Na→Mg→Al→Zn→Fe→Co→Ni→Sn→Pb→H→Cu→Ag
Hydrochloric acid is the best way to dissolve tin as you can see from both videos. Tin reacts with the diluted acid, but very slowly. Concentrated acid dissolves tin much quicker, especially when heated. The product of this reaction tin chloride interacts with hydrochloric acid and forms complex compounds.
Sn (s) + 2HCl (aq) → SnCl2 (aq) + H2 (g)
SnCl2 (aq) + HCl (aq) → H[SnCl3] (aq)
The reaction with a diluted sulphuric acid is very slow even at higher temperatures - I could hardly notice any hydrogen bubbles. The concentrated sulphuric acid slowly dissolves tin when heated (oxygen from the air seems to help too):
Sn (s) + 4H2SO4 (conc) → Sn(SO4)2 (aq) + 2SO2 (g) + 4H2O
Sulphuric acid can be bought at 37% concentration (used as a battery acid), but due to the lack of interaction, you can’t use it to dissolve tin.
Interaction with nitric acid varies depending on the acid concentration and the temperature.
Interaction with a very diluted nitric acid (3-5%) at low temperatures leads to tin nitrate formation without any visible gas release:
4Sn (s) + 10HNO3 (very diluted) → 4Sn(NO3)2(aq) + NH4NO3 (aq) + 3H2O
Higher concentrations of nitric acid and higher temperatures lead to nitrogen formation (with some impurities of nitrogen monoxide):
5Sn (s) + 12HNO3 (diluted) → 5Sn(NO3)2(aq) + N2 (g) + 6H2O
Concentrated nitric acid oxidizes tin to a stannic acid:
Sn (s) + 4HNO3 (conc) → SnO2•xH2O (s) + 4NO2 (g) + (2-x)H2O
Unfortunately nitric acid is not readily available and its use is restricted, so no demonstration in a house lab. But there is a video by Tuan Dang:
Tin can be also dissolved in sodium or potassium hydroxide. The result may vary depending on temperature and concentration:
Sn (s) + KOH (conc) + 2H2O → K[Sn(OH)3] (aq) + H2 (g)
Sn (s) + 2KOH (conc) + 4H2O → K2[Sn(OH)6](aq) + 2H2 (g)