Question

Hydrangeas are flowers that have different colours depending on the pH of the soil in which they grow. Helen wants to change the colour of her flowers. To do so, she must increase the pH of her soil from 5.2 to 6.6. She has compost made from vegetable and fruit peels, coffee grounds and tea bags. She also has a bag of lime. Which should she use? Describe the type of reaction that will occur.

Answer 1

To increase the soil pH and change the color of her hydrangea flowers, Helen should use the bag of lime, as it induces a neutralization reaction following Le Chatelier's principle.

Step-by-step explanation:

Helen wants to increase the pH of her soil to change the color of her hydrangea flowers, which can vary with soil acidity due to the solubility of aluminum affecting the anthocyanin pigments. To increase the pH from 5.2 to 6.6, she should use the bag of lime, as it will raise the pH level to be more alkaline. The addition of lime will cause a neutralization reaction, where the acidic components in the soil are neutralized, thereby increasing the pH. Using compost with coffee grounds and tea bags would likely maintain or lower the pH, as they tend to be acidic. The reaction here is a classic example of Le Chatelier's principle, adjusting conditions to shift the equilibrium in favor of a particular outcome—in this case, less soluble aluminum for red flowers.