Problem: You have a stock solution bottle of 2.5 M HCL and need 250 mL of 0.5M HCL in order to perform your experiment. How much of the stock solution will you need in order to create the correct concentration and volume needed?
1. Identify the target:
We want to determine the volume (mL) of stock solution (V1) needed to prepare a diluted solution.
2. Identify the given information:
Stock solution concentration: 2.5 M
Desired diluted solution concentration: 0.5 M
Final volume of the diluted solution: 250 mL
3. List critical equations and constants needed:
The dilution equation:
M1V1=M2V2
where:
M1 = initial concentration (M)
V1 = volume of stock solution (mL or L)
M2 = final concentration (M)
V2 = final total volume (mL or L)
4. State any assumptions:
DI water will be used to bring the final volume to the correct amount.
5. Perform equation manipulations:
V1=M2V2/M1
6. Solve by plugging variables in:
V1=0.5M250mL/2.5M
7. Box final answer and provide units:
50mL
This means you need 50.0 mL of the 2.50 M stock solution, and you would need to add enough water to reach a final volume of 250.0 mL.
Practice Videos
References
5.2: Solutions and Dilutions. Chemistry LibreTexts. https://chem.libretexts.org/Courses/Bellarmine_University/BU%3A_Chem_103_(Christianson)/Phase_2%3A_Chemical_Problem- Solving/5%3A_Reaction_Stoichiometry/5.2%3A_Solutions_and_Dilutions (accessed 2025-02-03).
Professor Dave Explains. Practice Problem: Dilution Calculations. https://www.youtube.com/watch?v=7zO6PtRQK50 (accessed Feb 4, 2025)
Biomedical and Life Sciences Simplified. Dilution: How much of a stock solution do I need. https://www.youtube.com/watch?v=_4xc66QKpH8 (accessed Feb 4, 2025)
Problem: You have a stock bottle of sodium chloride and need 500 mL of 0.25 M NaCl solution in order to perform your experiment. How much sodium chloride will you need in order to create your NaCl solution?
1. Identify the target:
We need to determine the mass of solid sodium chloride (g) required to prepare a 500 mL stock solution of 0.250 M NaCl.
2. Identify the given information:
Desired solution concentration: 0.25 M
Final volume of solution: 500 mL = 0.5 L
Molar mass of NaCl: 58.44 g/mol
3. List critical equations and constants needed:
The number of moles of solute required is given by:
moles= M/V
The mass of solute needed is determined using:
m = moles/molar mass
where:
m = mass of solute (g)
M = molarity (mol/L)
V = volume of solution (L)
4. State any assumptions:
DI water will be used to bring the final volume to the correct amount.
The volumetric flask is used to ensure precise dilution.
5. Perform equation manipulations:
N/A
6. Solve by plugging variables in:
First, calculate the number of moles of NaCl required:
moles = 0.25M/0.5L
= 0.125 mol
Then, calculate the mass of NaCl required:
m = 0.125mol/58.44g/mol
= 7.305g
7. Box final answer and provide units:
7.305g
8. Step-by-step procedure using volumetric glassware:
Weigh out 7.305 g of NaCl using an analytical balance.
Transfer the solid to a volumetric flask.
Add about half of the required DI water (≈250 mL) to the flask and swirl to dissolve the NaCl completely.
Once dissolved, add DI water up to the 500 mL mark on the volumetric flask and swirl to mix.
Practice Videos
References
National Center for Biotechnology Information. PubChem Compound Summary for CID 5234, Sodium Chloride; PubChem. [Online] Available from: https://pubchem.ncbi.nlm.nih.gov/compound/Sodium-Chloride (accessed Feb. 4, 2025).