Melting Sand

This quick and simple activity can be utilized in a variety of lesson plans. I have personally used it to demonstrate both acid rain and ocean acidification. It can be used at the beginning of a lesson to surprise and hook their interests (my recommendation), or after the lesson as a hands-on wrap up. When you add the vinegar to the sand, it immediately begins to fizzle and bubble. The sand literally melts before your students eyes! To scaffold it up for older students, you can pair it with a video showing the phenomena in nature and a book or a peer-reviewed scientific article about the topic. However you decide to incorporate it, it is a very fun way for students to get involved!

Background Information

The Chemistry

I know, I know. Most people don’t see the word ‘chemistry’ and go ‘Yes! My favorite!’ It takes a special person to willingly delve deep into this field (like one of my advisors, bless his soul). However, the longer I have studied science, the more I see the importance of understanding at least the basics of chemistry. So much of the natural world is ‘controlled’ if you will, by the laws of chemistry. Not understanding chemistry means you don’t really ever understand fully what is going on in a given situation. So, any lesson, even a very short one, about melting sand with vinegar would not be complete without a dash of chemistry. So, let’s go over what’s going on quick to get it over with!

Ocean Acidification

In nature, there is a natural flow between what is in our atmosphere, and what goes into our oceans. At the surface, wind and waves create a constant mixing between the two. Compounds in the air, in this case carbon dioxide (CO2), dissolve into the water. When this dissolves into the water, it reacts with the molecules of water themselves (H2O). After a series of reactions, a new compound called carbonic acid (H2CO3) is created from the atoms. Normally, seawater is slightly basic (about 8 and change) on the pH scale. As an acid, this new compound lowers the overall pH of the seawater.

Calcium carbonate (CaCO3) is used by many marine animals to build their shells and skeletons (corals are probably the most well-known user of it). You will recognize it as the very fine, soft white sand seen on desirable tropical beaches. In the marine environment, this compound can be found dissolved in the water column. Animals, like corals, can take it up and use it. Under normal conditions, the shallow water where corals live is fully saturated with it. This means any extra calcium carbonate will remain a solid (hence why animals use it for their hard shells and skeletons). You can think of it similar to the process of making rock candy. When the water becomes more acidic however, its capacity to hold and dissolve calcium carbonate increases. What this means is that the water where these animals live will dissolve their shells and skeletons. This causes the animal to have to take up more of the compound and use more energy to repair itself. If the rate of dissolution (how fast something dissolves) is greater than the animal can replace itself, then the animal will dissolve away. They would no longer be able to grow, defend themselves, or in extreme cases, die. The sand used in this activity is crushed up shells and old coral, so it perfectly demonstrates what happens in the wild.

Acid Rain

Acid rain is produced when the air has high levels of sulfur dioxide (SO2) and nitrogen dioxide (NO2). These compounds react with the water molecules in the atmosphere to produce acids. So, when it rains in these areas, the rain drops are literally acidic! Acid rain effects the environment, people, and even buildings and structures. It can harm or kill trees, ruin soil, kill small animals and insects, turn lakes or streams acidic, cause buildings and structures to erode away and negatively impact human health. No one wins with acid rain. There are several sources of sulfur dioxide and nitrogen dioxide. Naturally, volcanoes, some wetlands and the oceans can produce them. The main source for them however is people. Electricity generation, factories and cars all produce an abundance of both. While the compounds used in this activity are not exactly the ones found in the real life situation, they still provide students a good visual that relates to what happens.

Materials

  • Old newspaper (optional)
  • Small bag of calcium carbonate based sand, sometimes labeled as ‘aragonite (can get at any pet store in the fish section)
  • Unlabeled squeeze bottle of vinegar (any kind will do)

Activity

  • If this lesson is to be conducted in a normal classroom and not in a laboratory, take out a pile of old newspapers, and instruct each student to take a piece and lay it on the top of their desk.
  • Walk around the room with a container of calcium carbonate sand, having each student use their hands to take a small scoop, making sure to keep their hands over the newspapers to prevent spilling onto the floor.
  • Once each student has a scoop of sand, walk around the room a second time, this time with the squeeze bottle of vinegar.
  • Squeeze a few drops of vinegar onto the top of the scoop of sand in each student’s hand
  • Let the fizzing and bubbles surprise and wow them!

Probing Questions

  • What do you see happening to the sand?
  • What do you think is happening chemically to the sand?
  • What in real life does this remind you of?
  • What does the vinegar represent?

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