Question

How many grams of ${H_3}P{O_4}$ is required to completely neutralize $120g$ of $NaOH$ ?
A. $49$
B. $98$
C. $198$
D. $9.8$

Answer 1

Hint: The neutralization reaction is defined as the reaction between an acid (either strong or weak) and a base (either strong or weak) to produce a salt with the release of a water molecule during the formation of the salt. Hence, the number of equivalents of an acid is equal to the number of equivalents of a base during a neutralization reaction.

Complete step by step answer:

Phosphoric acid is a very strong acid and shows a rigorous reaction with a strong base like sodium hydroxide to give sodium phosphate which is a salt of a strong acid and strong base. The balanced chemical equation of the reaction is:
${H_3}P{O_4} + 3NaOH \to N{a_3}P{O_4} + 3{H_2}O$
Thus, from the above balanced chemical equation, we can deduce that 1 mole of phosphoric acid neutralizes 3 moles of sodium hydroxide to produce one mole of sodium phosphate and 3 moles of water.
The molecular weight of sodium hydroxide is =$40g$
As we know that, the number of moles =$n = \dfrac{w}{{{M_w}}}$
Where, $w = $ given weight of the substance
${M_w} = $ molecular weight of the substance
Hence, the number of moles of sodium hydroxide will be =$n = \dfrac{{120}}{{40}} = 3$
Thus, as per the question, the number of moles of sodium hydroxide available for the neutralization of phosphoric acid is 3.
According to the balanced chemical equation, 3 moles of $NaOH$ neutralize 1 mole of ${H_3}P{O_4}$ .
From the equation of number of moles, we have:
$n = \dfrac{w}{{{M_w}}} \Rightarrow w = n \times {M_w}$
Thus, the weight of ${H_3}P{O_4}$required to neutralize 3 moles of $NaOH$=$w = 1 \times 98 = 98g$
Where, molecular weight of phosphoric acid = ${M_w} = 98g$
Thus, the correct option is B. $98$ .

Note:
There are several applications of neutralization reaction. They include:
(i) In chemical laboratories, it is used during titration of chemicals.
(ii) In the digestive systems of our body.
(iii) During wastewater treatment.
(iv) To control the pH of the soil by maintaining the level of carbonates and hydroxides in the soil.