) A chemist dissolves 1.000 x 103 g of potassium hydroxide in enough water to make 1.5 L of stock solution. The chemist later wants 2.00 x 102 mL of 0.10 M potassium hydroxide. How much stock solution does the chemist need in order to make this second solution?
Molarity of first solution:
1000/molmassKOH*1.5=1000/56*1.5=11.9M
You want to dilute it 11.9/.1 times= 119 times
That means, one part stock solution, 118 parts water.
What is one part? 200ml/119=1.68ml
So, take 1.68ml stock solution, add water to the 200ml part, stir, label, and store properly.
To determine how much stock solution the chemist needs to make the second solution, we need to use the concept of dilution.
Dilution is the process of reducing the concentration of a solute in a solution. The formula to calculate the final concentration of a diluted solution is:
C1V1 = C2V2
Where:
- C1 is the initial concentration
- V1 is the initial volume
- C2 is the final concentration
- V2 is the final volume
Let's calculate it step by step:
Step 1: Determine the initial concentration (C1) and volume (V1) of the stock solution.
- Initial concentration (C1): The problem does not provide this information directly. However, it states that 1.000 x 103 g of potassium hydroxide is dissolved in enough water to make 1.5 L of stock solution. Since the mass is given and potassium hydroxide is a solid, we can assume it is the molar mass of potassium hydroxide.
The molar mass of potassium hydroxide (KOH) is:
[K (39.10 g/mol) + O (16.00 g/mol) + H (1.01 g/mol)] = 56.11 g/mol
To determine the initial concentration, we need to convert grams of potassium hydroxide to moles:
1.000 x 103 g / 56.11 g/mol = 17.81 mol
Now, we can calculate the initial concentration (C1):
C1 = 17.81 mol / 1.5 L = 11.87 M
- Initial volume (V1): Given as 1.5 L
Step 2: Determine the final concentration (C2) and volume (V2) of the desired solution.
- Final concentration (C2): Given as 0.10 M
- Final volume (V2): Given as 2.00 x 102 mL. Let's convert it to liters:
2.00 x 102 mL = 0.2 L
Step 3: Use the dilution formula to find the volume of stock solution needed.
C1V1 = C2V2
11.87 M x 1.5 L = 0.10 M x V2
V2 = (11.87 M x 1.5 L) / 0.10 M = 178.05 L
Therefore, the chemist needs to use 178.05 L of the stock solution to make the desired 0.10 M potassium hydroxide solution with a volume of 2.00 x 102 mL.