Chemical formula of HA is often written as Ca 10 (PO 4 ) 6 (OH) 2 to denote its

Question

Chemical formula of HA is often written as Ca10(PO4)6(OH)2to denote its crystal structure. In CHA carbonate ions can take place of both hydroxide (called A-type substitution) and phosphate (called B-type substitution) ions. In a general way, formula for the A-type CHA could be written as Ca10(PO4)6(OH)2-2x(CO3)x. In this case, one carbonate ion substitutes two hydroxyl groups to maintain charge neutrality, but occupies only one OH-position, leaving vacancy (VOH) in theplace of the second OH-group. The formula can be rewritten as Ca10(PO4)6(OH)2-2x(VOH)x(CO3)x. In a similar manner, write formula for B-type substituted CHA, specify at what positions vacancies are forming.

Explanation / Answer

From the provided data for the Ca10(PO4)6(OH)2

The fomula for the B-type substituted CHA is written as follows : Ca(10-x)/2.V(PO4)6-x(CO3)x(OH)2

The vacancy arises by Ca2+ shift and leaving an empty space.

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