To determine how many grams of potassium chloride (KCl) are in 300 mL of a 15% KCl solution, follow these steps:

1. Understand the percentage concentration: A 15% KCl solution means there are 15 grams of KCl in every 100 mL of solution.

2. Set up a proportion to find the amount in 300 mL:

   $\frac{15 \text{ grams}}{100 \text{ mL}} = x \text{ grams in 300 mL}$

3. Solve for $x$:

   $x = \left( \frac{15 \text{ grams}}{100 \text{ mL}} \right) \times 300 \text{ mL}$

4. Calculate the result:

   $x = 45 \text{ grams}$

So, there are 45 grams of KCl in 300 mL of a 15% KCl solution.

Would you like more details or have any questions about this calculation? Here are some related questions for further exploration:

1. How many grams of KCl are in 500 mL of a 10% KCl solution?
2. What volume of a 20% KCl solution contains 50 grams of KCl?
3. How do you prepare 250 mL of a 5% KCl solution from a 25% KCl stock solution?
4. What is the KCl concentration in a solution containing 30 grams of KCl in 150 mL?
5. How would you dilute a 30% KCl solution to obtain 1000 mL of a 15% solution?
6. If a solution has 60 grams of KCl in 400 mL, what is the percentage concentration?
7. How many milliliters of a 15% KCl solution are needed to obtain 30 grams of KCl?
8. What is the mass of KCl in 1 liter of a 12% KCl solution?

Tip: When working with solutions, always ensure that the units of measurement are consistent to avoid errors in calculations.