A field trip with geography class
In November 2019 I went on a fieldtrip with geography class. We went to a basalt quarry where we were told that there could be iron(oxide) and limestone (calcium carbonate) in the basalt stones. We also went to a big wall with all kind of stones. It's easy to believe and sometimes it's also easy to see that there are different types of stones and minerals in the basalt and other stones, but it's a lot more fun to prove it with some experiments.
To do this, we wanted to put together a ‘movable lab’ with a group of friends before we left. Though I was really excited about it, for me, the most important thing to think about is safety. Therefore, we first talked to our teacher to check if we could get permission to do some experiments during the trip. Communication turned out to be the key for this. Our teacher allowed us to take materials for experiments on the trip if we promised to teach the group what we were doing. This made us happy, we had permission and we were going to entertain people with chemistry! In total, it took us two weeks to get permission, think of possible experiments, think of what we would be needing for that, making sure it was possible to take chemicals with us and actually packing everything. I took the pencil case, which you can see in the picture below, to make the equipment portable. I filled it with pipettes, pH testing strips, gloves, a pen to write things down, a permanent marker to write on glassware, and plastic bags to take samples home. I also made a bag with small bottles to take water samples and small containers for sand samples. Last but not least, I brought a large sealable bottle to put the waste we made during experiments in. Everything we used could go into the sewer because we used low concentrations and small quantities, but at most places we went to there wasn’t one. By using the bottle, we were able to clean things up easily and save the environment by not dumping things in nature.
The experiments during the trip
The first experiment we did was in the basalt quarry. The most obvious things to find in the basalt were iron and limestone. To prove this, we took different little chunks. The ones most likely to contain iron were a bit orange, whereas the ones with limestone were a bit white. We dissolved all the chunks in separate glasses in hydrochloric acid (low molarity for safety). One of the solutions turned orange, making it likely to contain iron. While adding some sodium hydroxide flakes, the mixture started heating up and some precipitates started forming. Looking at the colour of the precipitates, we were able to tell this was iron (II/III) hydroxide. The stones in the other glass, which had been suspected to contain limestone, immediately started bubbling while adding hydrochloric acid. Because of this reaction, we were able to conclude that there was, indeed, limestone in it. The molecule formula for limestone is CaCO3. When reacting with hydrochloric acid, CO2 is released, which causes the bubbles. After this reaction we added a solution with sulphate in it and saw a suspension being formed. Some of the calcium ions precipitated with the sulphate, which caused the solution to form a suspension. The fact that this happened makes it even more safe to say that there was calcium in the stones.
The second experiment we tried was with water from a waterfall. This waterfall deposited lime on the wall so our hypothesis was that the water on top of the waterfall needed to contain more lime than the water below the waterfall. We tried testing this, but the concentrations were far too low, so it didn’t work. As, out in nature, we didn’t have all the resources necessary to safely execute our tests, we decided to take some samples home and instead do our tests in the lab at school.
The last place we went to was a wall with all sorts of stone in it and a limestone cave. Due to the weather we couldn’t do experiments, so we invested the time we had in taking as many samples as we could.
The experiments in the lab after the trip
A few weeks after coming home from the trip, we found some time to do experiments with the samples we took with us. We used the same method to create precipitates. First, we dissolved the two brown coloured samples with hydrochloric acid in a test tube. Then we added sodium hydroxide to the solutions to create iron (II/III) hydroxide. As you can see in the picture below, one of the samples got a brown/red colour, while the other one became grey/white. Even though it’s hard to see, this tube also contains an iron precipitate, though it’s clear that the darker one contains a lot more iron.
To be sure the yellow powder came from limestone we dissolved it in hydrochloric acid. It immediately started bubbling so much that it couldn’t be anything other than limestone.
We also tried some random things to see what precipitates we could get. Because the samples we took were not pure at all, we couldn’t determine what we’d made, but we had a lot of fun and a row of test tubes with different contents of all colours as a result.
During this trip I found out that it's really awesome to use the overlapping parts of subjects to get a better understanding of the topics! I have learned a lot about both geography and regional geochemistry, so I look back on a successful trip!