Home Chemistry Some Basic Concepts of Chemistry The Mole Concept Calcium phosphide (Ca 3 P 2 ) formed by reac…
Chemistry Some Basic Concepts of Chemistry The Mole Concept Single Correct MCQ
Published on: August 14, 2026

Calcium phosphide (Ca 3 P 2 ) formed by reacting calcium orthophosphate (Ca 3 (PO 4 ) 2 ) with magnesium was hydrolyzed by water. The evolved phosphine (PH 3 ) was burnt in air to yield phosphorus pentoxide (P 2 O 5 ). How many grams of magnesium metaphosphate would be obtained, if 19.2 g of magnesium were used for reducing calcium phosphate.

Ca 3 (PO 4 ) 2 + Mg Ca 3 P 2 + MgO

Ca 3 P 2 + H 2 O Ca(OH) 2 + PH 3

PH 3 + O 2 P 2 O 5 + H 2 O

MgO + P 2 O 5 Mg(PO 3 ) 2

magnesium metaphosphate

A
145.8 gram
B
32 gram
C
50.4 gram
D
18.2 gram

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Text Solution

Verified by Experts
The correct answer is:
D

Balance chemical equations are :

Ca 3 (PO 4 ) 2 + 8Mg Ca 3 P 2 + 8MgO

Ca 3 P 2 + 6H 2 O 3Ca(OH) 2 + 2PH 3

2PH 3 + 4O 2 P 2 O 5 + 3H 2 O

MgO + P 2 O 5 Mg(PO 3 ) 2

moles of magnesium used = 0.8 moles

moles of MgO formed = 0.8 moles

moles of Ca 3 P 2 formed 0.1 moles

moles of PH 3 formed = 0.2 moles

moles of P 2 O 5 formed = 0.1 mole (limiting reagent)

moles of Mg(PO 3 ) 2 = 0.1 moles

mass of Mg(PO 3 ) 2 = 18.2 gram

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