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The formula of metal chloride is MCl3.It contains 20% of the metal. The atomic weight of the metal is 


1. 27
2. 56
3. 127
4. 48

1 Answer

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Best answer
Correct Answer - Option 1 : 27

Concept:

Equivalent weight/ Equivalent mass :

Equivalent weight = Molecular weight (or) Atomic weight / Valency factor

Equivalent weight =  Molecular weight / n-factor

\(Eq.\,wt\, = \,\frac{{\text{M}}}{x}\)

Where n-factor varies for different species as follows:

1. For elements: x = valency of element

2. For acid: x = no. of replaceable H+ ions per acid molecule

3. For the base: x = no. of replaceable OHions per basic molecule

Calculation: 

Given: Formula of compound= MCl3, Percentage of metal (M) present= 20%

To Find: Atomic weight of metal=?

Assume that 100 g of compound MCl3 contains 20 g of metal (M) and 80 g of Cl.

\(\frac{{{E_M}}}{{{w_M}}} = \frac{{{E_{Cl}}}}{{{w_{Cl}}}}\)        ......(1)

Where, EM & ECl= eq. wt of metal and chlorine (35.5) respectively, w& wCl= mass of metal (20g) and Cl (80g) present in MCl3

On substituting the values in Eqn (1) 

\(\frac{{{E_M}}}{{20}} = \frac{{35.5}}{{80}}\)

\({E_M} = \frac{{35.5 \times 20}}{{80}} = 8.875\)

Therefore, the equivalent weight of metal = 8.875

Valency of metal in MCl3 = 3

Valency of Cl in MCl3 = 1

\({\text{Eq}}{\text{.}}\,{\text{wt}}\,{\text{of}}\,{\text{metal}}\,{\text{ = }}\,\frac{{{\text{Atomic}}\,{\text{weight}}}}{{{\text{valency}}\,{\text{of}}\,{\text{metal}}}}\)

\(8.875\,{\text{ = }}\,\frac{{{\text{Atomic}}\,{\text{weight}}}}{3}\)

So, the Atomic weight of metal is

= 8.875 × 3

= 26.625 g ≈ 27 g

Hence, the Atomic weight of Metal (M) in MCl3 is 27 g.

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