Making Molar Solutions

1. Making Molar Solutions From Solids

2. What are molar solutions? A molar solution is one that expresses “concentration” in moles per volume Usually the units are in mol/L mol/L can be abbreviated as M or [ ]

3. x 0.10 mol NaOH 1 L Calculations with molar solutions Q: How many moles of NaOH(s) are required to make 7.5 L of a 0.10 M solution? M=n/L, n = 0.10 M x 7.5 L = 0.75 mol # mol NaOH= = 0.75 mol 7.5 L

4. Preparing molar solutions from solids – LAB TIME! • DO this INDIVIDUALLY!! You are given provided with solid NaCl. Describe (in writing) how you can prepare 100 ml of a salt solution of 0.10 M NaCl in this lab. • How much NaCl do you need? • Bring up your work to the front.

5. Equations using moles n = N NA n = m MM n = C x V

6. Preparing molar solutions from solids • Molar solutions are prepared using: • a balance to weigh grams • a volumetric flask to measure litres • L refers to entire volume, not water! • Because the units are mol/L, we can use the equation M = n/L

7. Practice making molar solutions • Calculate # of grams required to make 100 mL of a 0.10 M solution of NaCl. Do this part individually. • Get 250 mL volumetric flask, squirt bottle. Rinse all with tap water. • Pour a little (20 - 30 mL) distilled H2O into flask. • Weigh NaCl. Add it to flask. • Mix (by swirling) until the NaCl is dissolved. • Add distilled H2O to the 100 mL line.. • Rinse & return equipment.

8. Calculating grams of NaCl • Molarity of solution = 0.5 M NaCl • Volume solution = 100 ml = 0.1 L • M = n/V  n = MxV = 0.5M x 0.1L = 0.05 moles NaCl • MM = m/n  m = MMxn = 58.44g/molx0.05mol = 2.9 g NaCl

9. Practice Unit conversion Do above question using unit conversion Page 290. Do Q 19 - 22 • Do all these questions using unit conversion • For any test/quiz, you can use either Unit conversion OR equations.