Question

How many grams of phosphoric acid (\[{{H}_{3}}P{{O}_{4}}\]) would be required to neutralize 68g of magnesium hydroxide?
A. 65.3g
B. 70.2g
C. 85.0g
D. 112.0g

Answer 1

Hint: Phosphoric acid is also known as orthophosphoric acid is a weak acid. It is white crystal like solid. It is colourless, viscous, and less dense. It is non volatile and non toxic in nature. Magnesium hydroxide is an inorganic compound which is less soluble in water. It is formed from mineral brucite.

Complete step by step answer:
 the equation when phosphoric acid and magnesium hydroxide react together is given below,
\[3Mg{{(OH)}_{2}}+2{{H}_{3}}P{{O}_{4}}\to Mg{{(P{{O}_{4}})}_{2}}+3{{H}_{2}}O\]
The molecular weight of I mole of magnesium hydroxide = 58.3g
In the equation three moles of magnesium hydroxide are reacting,
So the molecular weight of 3 moles of magnesium hydroxide = \[58.3\times 3\] = 174.9g
The molecular weight of 1 mole of phosphoric acid is = 98g
In the above equation 2 moles of phosphoric acid are reacting,
 so the molecular weight of 2 moles of phosphoric acid are = \[98\times 2=196g\]
so from the equation we get to know,
174.9g of magnesium hydroxide neutralizes= 196g of phosphoric acid
58g of magnesium hydroxide neutralizes = \[\dfrac{196\times 58}{174.9}\]
= 64.99g.
So the nearest value to 64.99g in the option is 65.3g.

so the correct option for the question is option A.




Note: Phosphoric acid can form dimmers, trimmers at high temperature. As it has three replaceable hydrogen so it forms three different types of salts. Phosphoric acid can be made by a wet process. Magnesium hydroxide is a food additive, used as fire retardant, in gold mining, warehouses. It is also used to soothe chronic constipation as laxative.