Q19 of 270 Page 79

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

When fresh milk changes into its sour version(curd), the ph value will decrease because of the formation of lactic acid.

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17 Two solutions X and Y have pH = 4 and pH = 8, respectively. Which solution will give alkaline reaction and which one acidic? 18 Fill in the following blanks with suitable words:

(a) Acids have a pH.................than 7.


(b) Alkalis have a pH.............. than 7.


(c) Neutral substances have a pH of ...............


(d) The more acidic a solution, the ................... the pH.


(e) The more alkaline a solution, the.................... the pH.

 20 (a) What is a universal indicator? For what purpose is it used? 20 How does a universal indicator work?