Molarity Mastery Handout
Lab Notes: Molarity
Exp. 07-Concentration
Standard Operating Procedure: Concentration Analysis
Concentration Definition
Molarity (M) measures concentration by the number of moles of solute dissolved in exactly 1 Liter of total solution volume.
M = mol / L
Volume: mL → L
Convert milliliters to Liters. Divide by 1,000.
In: 250 mL » 0.250 L
Solute: g → mol
Convert mass to moles using the Molar Mass.
mol = grams / Molar Mass
Computation
Divide Result 02 (mol) by Result 01 (L).
Molarity = mol / L
Mnemonic
mol
M × V
The Triangle Trick
Cover the variable you want to solve for. mol = M × V | V = mol / M | M = mol / V
Concentration Worksheet
Researcher:
Date:
1
Molarity of 25.5g NaCl in 750.mL solution. (58.44 g/mol)
2
Mass (g) for 2.50L of 0.450M KNO3. (101.10 g/mol)
3
Volume (mL) of 2.00M glucose stock for 0.125mol.
4
Molarity of 0.80mol LiCl in 400.mL solution.
5
Mass (g) of NaOH in 50.0mL of 0.100M solution. (40.00 g/mol)
6
Volume (mL) of 0.25M stock for 5.00g NaHCO3. (84.01 g/mol)
Lab Ref: Concentration-SOP-01 Internal Use Only
Molarity Mastery Key
Molarity Master Key
Verified Solutions & Pathways for Exp. 07
mol
M × V
Instructor Key
A: NaCl Molarity 0.581 M
1. Volume: 750.mL = 0.750 L
2. Moles: 25.5g / 58.44g/mol = 0.436 mol
3. Calculation: M = 0.436 / 0.750 = 0.581 M
B: KNO3 Mass 114 g
1. mol: 0.450 M × 2.50 L = 1.125 mol
2. mass: 1.125 mol × 101.10 g/mol
3. Result: 114 g
C: Glucose Volume 62.5 mL
1. L: 0.125 mol / 2.00 M = 0.0625 L
2. mL: 0.0625 L × 1000 = 62.5 mL
D: LiCl Molarity 2.0 M
1. V: 400.mL = 0.400 L
2. M: 0.80 mol / 0.400 L = 2.0 M
E: NaOH Mass 0.200 g
1. mol: 0.100 M × 0.0500 L = 0.00500 mol
2. mass: 0.00500 mol × 40.00 g/mol
3. Result: 0.200 g
F: NaHCO3 Volume 238 mL
1. mol: 5.00 g / 84.01 g/mol = 0.0595 mol
2. V: 0.0595 mol / 0.25 M = 0.238 L
3. mL: 0.238 L × 1000 = 238 mL
Common Anomalies
Watch for decimal errors in mL-to-L conversions. Remind students to count sig figs on volume measurements (e.g. 750. vs 750).
Unit Consistency
Problems E and F require multiple conversions. Emphasize that final volumes in medicine and lab prep are almost always reported in mL.
