Lab: Molarity
Background:
One way to express concentration of a solution of a solution is using molarity. The symbol for molarity is M;
which means moles of solute per liter of solution.
Purpose: To investigate the concept of molarity and to determine the concentration of an acid that has an
unknown molarity.
Pre-Lab:
1. Write out and balance the following equation (including states of matter):
Calcium carbonate reacts with hydrochloric acid to yield calcium chloride, carbon dioxide, and water.
Use this data to answer the questions below.
Description
100 mL beaker
100 mL beaker + CaCO3 (before reaction)
CaCO3 before reaction
Beaker + CaCO3 (after reaction)
CaCO3 after reaction
CaCO3 used up in reaction
Volume HCl (40 mL)
Mass (g)
100.00
105.56
5.56
102.35
2.35
3.21
0.040 L
2. How many moles of calcium carbonate reacted?
3. How many moles of HCl reacted?
4. What was the molarity of HCl?
Procedure:
Day 1:
1. Carefully label and weigh a dry 100 mL beaker. Record the mass in the data table. Put a marble chip
into the beaker (calcium carbonate). Record the new mass.
2. Using a graduated cylinder, add 50.0 mL of hydrochloric acid, HCl, of an unknown concentration to the
beaker. Using a setting of 2-3, gently heat on a hot plate, while stirring, until the reaction is well under
way (15-20 min).
3. During this time, complete some questions on the backside.
4. Place the beaker in a designated area to finish the reaction over-night.
Day 2:
1. Discard the remaining solution (calcium chloride + water) by decanting (pouring off) into the sink, taking
care to leave the marble chip in the beaker.
2. Using the graduations on the beaker, wash the chips with three separate 25 mL portions of distilled
water. Decant and rinse water each time into the sink without losing the marble chip.
3. Add approximately 5 mL of acetone (located on the back center table). Acetone is a solvent for
removing any additional water. Swirl the acetone in the beaker for a minute and then decant into the
waste container on the center table.
4. Place the beaker and any unreacted marble chips on a warm hot plate (150˚C) until you are sure the
beaker and contents are completely dry.
5. After cooling, weigh the beaker and contents. Record. Discard unreacted marble chips in the
designated beaker.
Data:
Description
Mass (g)
100 mL beaker
100 mL beaker + CaCO3 (before reaction)
CaCO3 before reaction
Beaker + CaCO3 (after reaction)
CaCO3 after reaction
CaCO3 used up in reaction
_______ L
Volume HCl (50 mL)
Calculations:
1. Using the mass of calcium carbonate that was used up in the reaction, calculate the moles of calcium
carbonate reacted.
2. Using the balanced equation and the moles of calcium carbonate reacted calculated in #1; find the
moles of HCl reacted.
3. Using your answer from #2 and the volume of HCl used (in L); determine the molarity of the HCl
solution (mol/L).
Analysis Questions:
1. Assume that you use 2.00 g of NaCl to make a 50.0 mL solution with water. What is the molarity of the
solution?
2. You have a 3 M solution of NaOH that has a final volume of 1.5 L.
a. How many moles of NaOH were used to make the solution?
b. How many grams of NaOH were used to make the solution?
3. A 6 M solution of magnesium chloride was prepared for an experiment using 10 moles of solute. What
is the final volume of the solution?