4 g of copper was dissolved in concentrated nitric acid. The copper nitrate solutio on strong heating gave 5g of its oxide. The equivalent weight of copper is

Options

A. 23
B. 32
C. 12
D. 20

Explanation

To find the equivalent weight of copper based on the information provided, we can follow these steps:

### Step 1: Determine the mass of copper used
We know that 4 g of copper (Cu) was dissolved in concentrated nitric acid.

### Step 2: Identify the reaction and products
When copper reacts with nitric acid, it forms copper nitrate (Cu(NO3)2). On strong heating, copper nitrate decomposes to form copper oxide (CuO) and nitrogen oxides (NOx).

### Step 3: Analyze the mass of copper oxide produced
The problem states that the strong heating of the copper nitrate solution produced 5 g of copper oxide (CuO).

### Step 4: Calculate the mass of oxygen in copper oxide
The formula for copper oxide is CuO. The molar mass of Cu is approximately 63.5 g/mol, and the molar mass of O is approximately 16 g/mol. Therefore, the molar mass of CuO is:
\[ \text{Molar mass of CuO} = 63.5 + 16 = 79.5 \text{ g/mol} \]

### Step 5: Determine the mass of copper in the copper oxide
From the mass of copper oxide produced (5 g), we can find the mass of copper in it. The mass fraction of copper in CuO can be calculated as follows:
\[ \text{Mass fraction of Cu} = \frac{63.5}{79.5} \]
Now, we can calculate the mass of copper in 5 g of CuO:
\[ \text{Mass of Cu} = 5 \times \frac{63.5}{79.5} \approx 3.98 \text{ g} \]

### Step 6: Calculate the mass of oxygen in the copper oxide
The mass of oxygen in the copper oxide can be found by subtracting the mass of copper from the total mass of copper oxide:
\[ \text{Mass of O} = 5 \text{ g} - 3.98 \text{ g} \approx 1.02 \text{ g} \]

### Step 7: Determine the equivalent weight of copper
The equivalent weight of an element is defined as the mass of the element that combines with or displaces 1 mole of hydrogen or 8 grams of oxygen. In this case, we can use the mass of oxygen that reacted with copper:
- The mass of oxygen that combines with 4 g of copper is approximately 1.02 g.

Using the equivalent weight formula:
\[ \text{Equivalent weight of Cu} = \frac{\text{Mass of Cu}}{\text{Number of equivalents}} \]
Since 1 mole of oxygen (16 g) combines with 2 g of copper, we can find the equivalent weight:
\[ \text{Number of equivalents} = \frac{1.02 \text{ g O}}{8 \text{ g O}} = 0.1275 \]
Thus, the equivalent weight of copper can be calculated as:
\[ \text{Equivalent weight of Cu} = \frac{4 \text{ g}}{0.1275} \approx 31.43 \text{ g} \]

### Final Answer
The equivalent weight of copper is approximately 32 g.

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