Some Basic Concepts Of Chemistry Question 138
Question: Apatite is a mineral that is found in tooth enamel. When fluoride toothpastes are used, this mineral is converted to fluoroapatite, which is more resistant to tooth decay. The formula of apatite is $ Ca _5{{(PO _4)} _{x}}F $ . What is the value of $ x $ if the compound contains 18.45% by weight of phosphorus? (Atomic weight of $ P=31,Ca=40, $ $ F=19 $ and $ O=16 $ )
Options:
A) 2
B) 4
C) 5
D) 3
Show Answer
Answer:
Correct Answer: D
Solution:
[d] % of $ P=\frac{x\times 31}{5\times 40+31x+64x+19}\times 100=18.45 $
$ \Rightarrow $ $ x=3 $
