How much water should be added to 200 c.c of seminormal solution
of NaOH to make it exactly decinormal?

Options

A. 1000 cc
B. 400 cc
C. 800 cc
D. 600 cc

Answer

To solve the problem of how much water should be added to 200 c.c of a semi-normal solution of NaOH to make it exactly decinormal, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Values:**
- The initial normality (N1) of the NaOH solution is semi-normal, which means:
\[ N1 = \frac{1}{2} \text{ N} = 0.5 \text{ N} \]
- The desired normality (N2) is decinormal:
\[ N2 = \frac{1}{10} \text{ N} = 0.1 \text{ N} \]
- The initial volume (V1) is given as:
\[ V1 = 200 \text{ c.c} \]

2. **Use the Normality Equation:**
The relationship between the normalities and volumes can be expressed as:
\[ N1 \times V1 = N2 \times V2 \]
Plugging in the values we have:
\[ 0.5 \times 200 = 0.1 \times V2 \]

3. **Calculate V2:**
Rearranging the equation to solve for V2:
\[ V2 = \frac{0.5 \times 200}{0.1} \]
Calculating the right side:
\[ V2 = \frac{100}{0.1} = 1000 \text{ c.c} \]

4. **Determine the Volume of Water to be Added:**
To find out how much water needs to be added, we subtract the initial volume (V1) from the final volume (V2):
\[ \text{Volume of water} = V2 - V1 = 1000 \text{ c.c} - 200 \text{ c.c} = 800 \text{ c.c} \]

### Final Answer:
The amount of water that should be added to the 200 c.c of semi-normal NaOH solution to make it exactly decinormal is **800 c.c**.

---