Presentation on theme: "Making Molar Solutions From Solids. What are molar solutions? A molar solution is one that expresses “concentration” in moles per volume Usually the units."— Presentation transcript:
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 [ ]
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= 7.5 Lx 0.10 mol NaOH 1 L = 0.75 mol
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. Preparing molar solutions from solids – LAB TIME!
Equations using moles n = N N A n = m MM n = C x V
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 Preparing molar solutions from solids
Practice making molar solutions 1.Calculate # of grams required to make 100 mL of a 0.10 M solution of NaCl. Do this part individually. 2.Get 250 mL volumetric flask, squirt bottle. Rinse all with tap water. 3.Pour a little (20 - 30 mL) distilled H 2 O into flask. 4.Weigh NaCl. Add it to flask. 5.Mix (by swirling) until the NaCl is dissolved. 6.Add distilled H 2 O to the 100 mL line.. 7.Rinse & return equipment.
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
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.