Question

The $ 0.250 $ of an element M reacts with excess fluorine to produce $ 0.547g $ of the hexafluoride, $ M{F_6} $. What is the element?
[Atomic mass of Cr $ = 52g $ , Mo $ = 96g $ , S $ = 32g $ , $ Te = 127.6g $ ]
(A) Cr
(B) Mo
(C) S
(D) Te

Answer 1

Hint: At first, we will write what is given the question. Then we will write the reaction. Then we will calculate the molar mass of the product. Then we will use mass conservation. From there we will calculate the mass of M and will choose the correct option.

Complete step by step solution:
Step1. We are given with a compound M which reacts with fluoride to produce hexafluoride.
The amount of M reacts = $ 0.250 $ g
The amount of hexafluoride formed is $ 0.547g $ . We need to know the element.
Step2. The reaction will be happening as given below.
 $ M + 3{F_2} \to M{F_6} $
Now we assume that m is the molar mass of the element given.
So the molar mass of the $ M{F_6} $ will be an addition of mass of M and fluoride. So the mass will be $ m + (6 \times 18.9) = m + 113.4g/mol $
Step3. So the $ 0.250 $ g of the element M will produce the $ \dfrac{{0.250}}{m} \times (m + 113.4)g $ of $ M{F_6} $ which would be $ 0.547g $ .
So the $ \dfrac{{0.250}}{m} \times (m + 113.4)g $ = $ 0.547g $
 $ M = 95.5g/mol $ .
Step4. We have found the molecular mass of the M now we need to find out the name of the element whose molar mass is 96g/mol. According to the periodic table, that compound is Molybdenum. Its sign is Mo.
Hence the correct option is B.

Note:
Molybdenum is silvery white metal. It is highly ductile. It is highly important because it is highly resistant to corrosion. It has one of the highest melting points in pure metals. It can be used as a substitute to the tungsten at many places.