Answer:
0.8 liters of a 1.2 M solution is needed to prepare 1400 mL of a 0.8 M solution.
Step-by-step explanation:
To determine the volume of a 1.2 M solution needed to prepare 1400 mL of a 0.8 M solution, we can use the following equation:
```
M1 * V1 = M2 * V2
```
where:
* M1 is the molarity of the first solution
* V1 is the volume of the first solution
* M2 is the molarity of the second solution
* V2 is the volume of the second solution
Substituting the known values into the equation, we get:
```
1.2 M * V1 = 0.8 M * 1400 mL
```
```
V1 = (0.8 M * 1400 mL) / 1.2 M
```
```
V1 = 800 mL
```
Since the volume is in milliliters, we need to convert it to liters before answering the question.
```
V1 = 800 mL / 1000 mL/L = 0.8 L
```
Therefore, 0.8 liters of a 1.2 M solution is needed to prepare 1400 mL of a 0.8 M solution.