0.5g of a metal on oxidation gave 0.7 g of its oxide. The equivalent weight of the metal is -

Options

A. 40
B. 20
C. 14
D. 10

Answer

To find the equivalent weight of the metal, we can follow these steps:

### Step 1: Determine the amount of oxygen that reacted
Given:
- Mass of metal = 0.5 g
- Mass of metal oxide = 0.7 g

To find the mass of oxygen that reacted, we subtract the mass of the metal from the mass of the metal oxide:
\[ \text{Mass of oxygen} = \text{Mass of metal oxide} - \text{Mass of metal} \]
\[ \text{Mass of oxygen} = 0.7 \, \text{g} - 0.5 \, \text{g} = 0.2 \, \text{g} \]

### Step 2: Calculate the equivalent weight of oxygen
The equivalent weight of an element is calculated using the formula:
\[ \text{Equivalent weight} = \frac{\text{Atomic mass}}{\text{Valency}} \]
For oxygen:
- Atomic mass of oxygen = 16 g/mol
- Valency of oxygen in metal oxide (assuming it is a typical oxide) = 2

Thus, the equivalent weight of oxygen is:
\[ \text{Equivalent weight of oxygen} = \frac{16}{2} = 8 \, \text{g/equiv} \]

### Step 3: Relate the equivalent weight of oxygen to the equivalent weight of the metal
From the reaction, we know that 0.2 g of oxygen reacts with 0.5 g of metal. We can set up a proportion to find the equivalent weight of the metal.

Let \( E_m \) be the equivalent weight of the metal. The relationship can be expressed as:
\[ \frac{0.2 \, \text{g O}}{E_O} = \frac{0.5 \, \text{g metal}}{E_m} \]
Where \( E_O \) is the equivalent weight of oxygen (8 g/equiv).

Rearranging gives:
\[ E_m = \frac{0.5 \, \text{g metal} \times E_O}{0.2 \, \text{g O}} \]
Substituting \( E_O = 8 \):
\[ E_m = \frac{0.5 \times 8}{0.2} \]
\[ E_m = \frac{4}{0.2} = 20 \, \text{g/equiv} \]

### Final Answer
The equivalent weight of the metal is **20 g/equiv**.

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