A milkman adds a small amount of baking soda to milk. This makes the pH of the milk
- A.strongly alkaline
- B.weakly alkaline
- C.strongly acidic
- D.weakly acidic
Correct answer
Explanation
The correct answer is B, weakly alkaline. Baking soda, sodium hydrogen carbonate, is a mild base, so a small amount shifts fresh milk, whose pH is about 6.6, slightly above 7.
Milk turns sour when bacteria convert its lactose into lactic acid. A milkman adds a pinch of baking soda to neutralise this acid as it forms, so the milk takes longer to curdle. Because sodium hydrogen carbonate is a weak base and only a little is added, the milk becomes only weakly alkaline. The same compound is used as an antacid and in baking, where it releases carbon dioxide that makes cakes rise.
A is wrong: a strongly alkaline pH, near 13 or 14, needs a strong base like sodium hydroxide, not a little baking soda.
C is wrong: adding a base raises pH, so the milk cannot become strongly acidic.
D is wrong: fresh milk is already weakly acidic; baking soda moves it the other way, past neutral.
Exam tip: milk pH about 6.6; baking soda (NaHCO3) makes it slightly alkaline and delays curdling.
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