Question

Fresh milk has a pH of 6. When it changes into curd (yogurt), will its pH value increase or decrease? Why?

Answer 1

Hint:The pH value shows the acid and base nature of the substance. And $7$ is the neutral value of any substance. There are many types of bacteria in nature. Some chemical change happens in milk due to these bacteria, which is responsible for the formation of curd.

Complete step by step answer:
-pH scale-It is the kind of scale in which the range lies between $0 - 14$. One end shows the strong acidic nature while the other shows the strong base nature of the substance. If any substance has a pH value of less than $7$, that will be acidic. Another hand, if a substance has a pH value is more than $7$, that will be basic.
Therefore, according to pH value milk is acidic.

-Milk converted into curd due to fermentation. In this process, lactobacillus plays an important role. When milk is heated, then a small amount of curd adds to it. Afterward, these bacteria start to multiply and convert milk into curd. This whole chemical process is known as fermentation.
-The formation of lactic acid starts due to fermentation, which is acidic. The pH value of curd is $4.5 - 5.5$. So, the pH value of curd will decrease.

Note:
The pH scale was discovered by Soren Sorensen. The value of the pH scale depends on the concentration of ${H^ + }$ and $O{H^ - }$ ions. The high concentration of ion is directly related to strong acid, while more $O{H^ - }$ ion shows a strong base. Fermentation is the anaerobic process, which means it happens in the absence of oxygen.