A chemist makes a “stock” solution of KOH by dissolving 1050.0 grams in enough water to make 1.50 liters of solution. If later on the chemist wants to use this stock solution to make 200.0 mL of 0.10 M KOH, what would the chemist need to do? (Define the steps and show the calculations).
What's the molarity of the stock solution.
mols KOH = 1050 g/molar mass KOH = ?
Then M stock soln = ?mols/1.50L = x.
To dilute use the dilution formula.
c1v1 = c2v2
c = conc
v = volume.
c1 = M of the stock soln from above.
v1 = volume of the stock soln to use(in mL).
c2 = 0.1M
v2 = 200 mL
98
To make 200.0 mL of a 0.10 M KOH solution using the stock solution, the chemist needs to follow these steps:
Step 1: Determine the number of moles of KOH needed:
To calculate the moles of KOH required, we can use the formula:
moles = molarity x volume
moles = 0.10 M x 0.200 L
= 0.020 moles
Step 2: Calculate the volume of the stock solution required:
Using the stoichiometry of the balanced chemical equation, we know that 1 mole of KOH is equivalent to 1 mole of KOH in solution.
Since the stock solution is made up of 1050.0 grams of KOH in 1.50 liters, its concentration can be determined as follows:
concentration = mass/volume
concentration = 1050.0 g / 1.50 L
= 700 g/L
Now, we can calculate the volume of the stock solution required using the formula:
volume of stock solution = moles of KOH needed / concentration of stock solution
volume of stock solution = 0.020 moles / (700 g/L / 56.11 g/mol)
= 0.020 moles / 0.0802 L
≈ 0.249 L
Step 3: Convert the required volume to milliliters:
The calculated volume of the stock solution is in liters, but we need to express it in milliliters since the stock solution will be measured in a 200.0 mL container.
volume of stock solution in mL = volume of stock solution x 1000
volume of stock solution in mL = 0.249 L x 1000
≈ 249 mL
Therefore, to prepare 200.0 mL of a 0.10 M KOH solution using the stock solution, the chemist would need to measure approximately 249 mL of the stock solution and then carefully dilute it to the desired volume of 200.0 mL using water or a suitable solvent.
To determine what the chemist needs to do to make 200.0 mL of 0.10 M KOH from the stock solution of KOH, we can follow the steps below:
Step 1: Calculate the number of moles of KOH in the stock solution:
Firstly, we need to determine the number of moles of KOH in the stock solution by using its molar mass. The molar mass of KOH can be found by adding the atomic masses of potassium (K), oxygen (O), and hydrogen (H):
Molar mass of KOH = atomic mass of K + atomic mass of O + atomic mass of H
Molar mass of KOH = (39.10 g/mol) + (16.00 g/mol) + (1.01 g/mol)
Molar mass of KOH = 56.11 g/mol
The number of moles of KOH in the stock solution can be calculated using the formula:
moles of KOH = mass of KOH / molar mass of KOH
moles of KOH = 1050.0 g / 56.11 g/mol
moles of KOH = 18.72 mol
Step 2: Determine the volume of the stock solution required to make 200.0 mL of 0.10 M KOH:
We can use the equation:
moles = Molarity x Volume (in liters)
to determine the volume (in liters) of the stock solution required to make the desired concentration.
Rearranging the equation, we have:
Volume (in liters) = moles / Molarity
Volume (in liters) = 0.10 mol / 0.200 mol/L (since we want to make 200.0 mL or 0.200 L of 0.10 M KOH)
Volume (in liters) = 0.5 L
Step 3: Determine the volume of the stock solution needed to make 200.0 mL of 0.10 M KOH:
Now that we know the volume of the stock solution required in liters, we can convert it to milliliters.
1 L = 1000 mL, so
Volume (in mL) = Volume (in liters) x 1000
Volume (in mL) = 0.5 L x 1000
Volume (in mL) = 500 mL
Therefore, the chemist would need to use 500.0 mL of the stock solution to make 200.0 mL of 0.10 M KOH.