Molarity final
Download as PPTX, PDF15 likes8,084 views
This document provides a comprehensive overview of molarity and dilutions, explaining the concept of molarity as a concentration unit and detailing calculations for preparing solutions. It includes several examples illustrating how to calculate molarity from moles and volume, as well as how to perform dilution calculations using the formula m1v1 = m2v2. The reader is expected to be able to calculate molarity, prepare solutions, and solve for moles or volume of solutions after studying the material.
Molarity final
- 1. Molarity and Dilutions By Shawn P. Shields, Ph.D. This work is licensed by Shawn P. Shields-Maxwell under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
- 2. Molarity Molarity (M) is a concentration unit that describes how much of a substance is dissolved in solution. Molarity = moles of solute Liters of solution M = molsolute Lsoln
- 3. Molarity Example Suppose we wanted to make a 1.0 M solution of NaCl. What should we do? Calculate the mass of 1 mole of NaCl, then weigh this amount on a balance. Molar mass = 22.990g + 35.453g = 58.443 g/mol NaCl Next, add this amount of NaCl to a flask, and fill it until the volume of the solution (water AND salt) equals one liter.
- 4. Molarity Example 2 What is the molarity of a 250 mL solution containing 0.35 moles NaCl? First, convert mL to L, 250 mL 1 L 1000 mL = 0.25 L Now, calculate the molarity of the solution M = molsolute Lsoln = 0.35 mol NaCl 0.25 L solution = 1.4 M NaCl
- 5. Molarity Example 3 Suppose we have 35 mL of a 0.85 M MgCl2 solution. How many moles of MgCl2 are present in the solution? Convert mL to L 35 mL 1 L 1000 mL = 0.035 L Now, rearrange the molarity equation and solve for moles. M = molsolute Lsoln molsolute = Lsoln × M = 0.035 L × 0.85 mol Lsoln = 0.030 mol MgCl2 Sig figs!
- 6. Molarity Example 4 How many mL of a 1.2 M MgCl2 solution are needed to have 0.35 moles MgCl2? Rearrange the molarity equation and solve for volume. M = molsolute Lsoln Lsoln = molsolute M = 0.35 moles MgCl2 1.2 moles MgCl2 Lsoln = 0.29 Lsoln Convert L to mL 0.29 L 1000 mL 1 L = 290 mL MgCl2 solution Sig figs!
- 7. Dilution Dilution is the process of adding solvent to a more concentrated solution to yield a solution of lower concentration. The equation for dilution calculations is 𝐌 𝟏 𝐕𝟏 = 𝐌 𝟐 𝐕𝟐 Where M1 is the initial molarity, V1 is the initial volume, M2 is the final molarity, and V2 is the final volume.
- 8. Dilution Recall that multiplying a volume in Liters and a molarity gives the moles of the substance. 𝐌 𝟏 𝐕𝟏 = 𝐌 𝟐 𝐕𝟐 Therefore, this relationship is simply moles = moles! The moles of solute remains constant, but the volume and molarity change.
- 9. Dilution Example How many mL of a 2.5 M HCl stock solution would we need to make 100 mL of 0.80 M HCl? 𝐌 𝟏 𝐕𝟏 = 𝐌 𝟐 𝐕𝟐
- 10. Dilution Example Solution How many mL of a 2.5 M HCl stock solution would we need to make 100 mL of 0.80 M HCl? 𝐌 𝟏 𝐕𝟏 = 𝐌 𝟐 𝐕𝟐 First, let’s identify what we have and what we are solving for… M1 is the molarity of the stock solution, but we don’t know how much we need. M2 is the final concentration (0.80 M) and V2 is the final volume (100 mL).
- 11. Dilution Example Solution How many mL of a 2.5 M HCl stock solution would we need to make 100 mL of 0.80 M HCl? 𝐌 𝟏 𝐕𝟏 = 𝐌 𝟐 𝐕𝟐 Plug everything in… (𝟐. 𝟓 𝐌)𝐕𝟏 = (𝟎. 𝟖𝟎𝐌)(𝟏𝟎𝟎𝐦𝐋) Solve for V1 𝐕𝟏 = (𝟎. 𝟖𝟎𝐌)(𝟏𝟎𝟎𝐦𝐋) (𝟐. 𝟓 𝐌) = 𝟑𝟐 𝐦𝐋 Watch sig figs… only 1 sf, so the final answer is 30 mL.
- 12. What You Should Be Able to Do Calculate the molarity of a solution Describe how to prepare a solution with a specific molarity Use the molarity relationship to solve for moles and/or volume of solution. Perform dilution calculations