PART IV: Molarity

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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 = 0.00855 mol NaCl

58.45 g

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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)

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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 H2O, what is the m/v percent?

5.70 g x 100% = 10.4%

55.0 mL

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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 0.017 = x g__

2000 mL 0.017 x 2000 = xg

34 = xgHe would need to add 34g of TSP

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m/m and v/v percentages

• Same processes as m/v

• m/m (all in grams)

• v/v (all in mL)

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Parts per million (or billion)

• Usually mass/mass relationship

ppm = mass solute (g) x 106

mass solution (g)

or

ppb = mass solute (g) x 109

mass solution (g)

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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

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Example from Molarity sheet