PART IV: Molarity

2 Review: How to you go from grams of a substance to moles (and vice versa)? Use molar mass! Ex: How many moles are in 0.50g NaCl? 0.50g x 1mol NaCl = mol NaCl g

3 Concentration The amount of solute per quantity of solvent Types of concentrations: 1.Mass/volume percent 2.Mass/mass % 3.Volume/volume% 4.ppm or ppb 5.Molar concentration (molarity)

4 Mass/volume % m/v % = mass of solute (g)___ x 100% volume of solution (mL) Ex: A chemist adds 5.70g of CuCl to 55.0 mL of H 2 O, what is the m/v percent? 5.70 g x 100% = 10.4% 55.0 mL

5 Example # 2: A clean wants to make a 1.7% (m/v) solution of TSP, what mass is needed to make 2.0L of solution? First change % to decimal ( 1.7%  0.017) Don’t forget to change L to mL!! Then use formula, solve for x = x g__ 2000 mL x 2000 = xg 34 = xg He would need to add 34g of TSP

6 m/m and v/v percentages Same processes as m/v m/m (all in grams) v/v (all in mL)

7 Parts per million (or billion) Usually mass/mass relationship ppm = mass solute (g) x 10 6 mass solution (g) or ppb = mass solute (g) x 10 9 mass solution (g)

8 Molarity Molar concentration is the number of moles in 1.0 L of solution Molarity (mol/L) = moles solute_______ volume (L) of solution Also expressed as C = _n__ V

9 Example from Molarity sheet