i) Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd ? Explain your answer.
ii) Why does distilled water not conduct electricity, whereas rain water does ?

i) Milk turns into curd as a result of the bacteria lactobacillus converting lactose in the milk into lactic acid. Formation of lactic acid and the dissociation of lactic acid to release hydrogen ions will result in a reduction in pH of milk. As a result of this, the pH will become more acidic as the milk changes into curd.

ii) Rainwater conducts electricity as it contains ions due to the presence of dissolved salts in it. However, distilled water does not contain these salts and therefore, does not conduct electricity.