We'll show you how to make your peas look fresher when you boil them, and then explain the chemistry involved. We used a bag of frozen peas, several identical pots, a pinch of baking soda and two pennies that were washed and scrubbed so the copper colour shows. We boiled the peas in two separate pots. In one pot we also added a pinch of baking soda. This is a trick that most good cooks know. The peas on the right above are the ones cooked with a pinch of baking soda. They are clearly greener and look more appetizing, while the ones on the left (no baking soda) are much paler. Here's another trick that's almost as effective. Before boiling some more peas, we added two copper pennies to one of the pots. You can see the results in the two photos below. The results are quite dramatic. The peas on the right, boiled with several pennies, are vibrantly green and far less wrinkled. Let's look at the chemistry so we can understand why these tricks work. Peas are green because, like all plants, they contain the molecule chlorophyll. Chlorophyll absorbs most of the colours in the light that hits it, except for green, which gets reflected. (That's why the peas look green). Chlorophyll, in a process called photosynthesis, converts the light's energy into chemical energy, which the pea plant uses to make glucose from water and carbon dioxide. Chlorophyll is a large molecule, with a magnesium atom at its centre. When the peas are cooked, acids are released from the peas which displace the magnesium atoms in the chlorophyll, replacing them with hydrogen ions. These changed chlorophyll molecules reflect less of the green light, resulting in paler peas after they're cooked. Adding a pinch of baking soda (sodium bicarbonate), which is a base, neutralizes some of the acids that are released in cooking, allowing the chlorophyll to retain its magnesium atoms, and resulting in greener peas! A similar effect can be obtained by boiling the peas in a large pot with lots of water; the acid released in cooking is greatly diluted and has less of an effect on the peas, so they remain greener. Adding the copper coins has a corresponding effect. Some copper atoms are dissolved into the water; these replace the magnesium atoms in the chlorophyll. Although this results in slightly paler peas, the chlorophyll molecules with copper in them instead of magnesium are more stable in the presence of the acids in the water, and the peas retain more of their 'greenness' than if nothing had been added. Resources Content, HTML, graphics & design by Bill Willis 2023