Question

Which of the following substances has the lowest pH-value?
(a)- Tomato
(b)- Vinegar
(c)- Washing soda
(d)- Human blood

Answer 1

Hint: pH-value defines the acidity or basicity of the substance. More the acidic substance lower is the acidic value.

Complete step by step solution:
pH- value helps us to know whether the substance is acidic or basic.
Its value ranges from 0-14.
0-6.9 is considered as an acidic substance, 7 is considered as neutral and 7.1 to 14 is considered as basic.
Now let study all the options one by one:
(a)- Tomato: Tomato contains two types of acids, these are malic acid and citric acid. Both of them are mild acids. Hence the pH-value of tomato ranges from 3.5-4.7
(b)- Vinegar: Vinegar is an aqueous solution of acetic acid (\[C{{H}_{3}}COOH\]). Acetic acid is a weak acid. Hence, the pH-value of vinegar is 2.5.
(c)- Washing soda: Washing soda commonly called as sodium carbonate (\[N{{a}_{2}}C{{O}_{3}}\]). Because of carbonate present, when washing soda is dissolved in water it gives carbonic acid. Hence, its pH-value is 11.
(d)- Human Blood: Human blood has a normal pH range of 7.35 to 7.45. Since it is greater than 7, it shows that human blood is slightly alkaline.
  From all the above options vinegar has the lowest pH-value that means it is the most acidic from the above and the washing soda is most basic.
Hence, the correct option is (b)- vinegar.

Note: You may get confused by the pH range. It should be noted that the lesser the pH value, the stronger is the acid, and the higher the pH-value, the stronger is the base. From \[{{H}^{+}}\] and \[O{{H}^{-}}\] we can know the pH- value. More \[{{H}^{+}}\]ions lesser the pH-value and more \[O{{H}^{-}}\]ions higher is the pH-value.