Question

Marble is composed largely of calcium carbonate. Splitting tomato juice on a slab of marble etches the surface. Explain what happens in chemical terms.

Answer 1

Marble is a fairly soft stone which is largely composed of calcium carbonate. When any amount of lemon juice or tomato juice splash on the marble surface, then it is going to leave a 'dull spot' on its surface. This dull spot is know as 'etches'.

This etching happens when a acidic substance fall on the marble surface. Here, many fruits and few vegetables contains organic acids. Generally tomatoes contains organic acids like, citric acid, oxalic acid, ascorbic acid.

These acids, reacts with calcium carbonate present in the marble and creates etches. These corrodes the shiny surface area of marble.

Now we will see the chemical property of calcium carbonate (CaCO₃) with acid:

Calcium carbonate reacts with any acid and releases carbon dioxide (CO₂), calcium salts and water. The general reaction is shown below.

In the same way, organic acid such as citric acid present in the tomatoes will react with calcium carbonate and forms calcium citrate and CO₂. This chemical change causes the etching.