Formula unit mass of `K_(2) CO_(3)` is
(Atomic mass of `K = 39 u , C = 12 u` and O = 16 u)

Options

A. 67 u
B. 138 u
C. 150 u
D. 134 u

Answer

To calculate the formula unit mass of \( K_2CO_3 \) (potassium carbonate), we need to sum the atomic masses of all the atoms present in the formula. Here’s the step-by-step solution:

### Step 1: Identify the components of \( K_2CO_3 \)
The formula \( K_2CO_3 \) consists of:
- 2 potassium (K) atoms
- 1 carbon (C) atom
- 3 oxygen (O) atoms

### Step 2: Write down the atomic masses
From the information provided:
- Atomic mass of potassium (K) = 39 u
- Atomic mass of carbon (C) = 12 u
- Atomic mass of oxygen (O) = 16 u

### Step 3: Calculate the total mass contributed by each element
1. **Potassium (K)**:
\[ \text{Mass from K} = 2 \times \text{Atomic mass of K} = 2 \times 39 = 78 \, \text{u} \]

2. **Carbon (C)**:
\[ \text{Mass from C} = 1 \times \text{Atomic mass of C} = 1 \times 12 = 12 \, \text{u} \]

3. **Oxygen (O)**:
\[ \text{Mass from O} = 3 \times \text{Atomic mass of O} = 3 \times 16 = 48 \, \text{u} \]

### Step 4: Add the masses together
Now, we add the contributions from each element to find the total formula unit mass:
\[ \text{Total mass} = \text{Mass from K} + \text{Mass from C} + \text{Mass from O} \]
\[ \text{Total mass} = 78 \, \text{u} + 12 \, \text{u} + 48 \, \text{u} = 138 \, \text{u} \]

### Conclusion
The formula unit mass of \( K_2CO_3 \) is **138 u**.

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