8.3 The Concentration of Solutions

What is Concentration? Concentration tell us the amount of solute per quantity of solvent.

Concentration Units There are many units of measurement for concentration. Mass/volume Mass/mass Volume/volume Parts per million Parts per billions Molar Concentration Solubility Concentration

1. Mass/Volume (m/v) This quantity gives the mass of the solute dissolved in a volume of solution expressed as a percent. Mass/volume Percent = Mass of solute (g) x 100% Volume of Solution (mL)

Example A pharmacist adds 2.00 mL of distilled water to 4.00 g of a powder drug. The final volume of the solution is 3.00 mL. What is the concentration of the drug in g/100mL of solution. What is the (m/v) of the solution? % m/v = Mass of solute (g) x 100% Volume of Solution (mL) = 4.00 g / 3.00 mL X 100% = 133%

2. Mass/mass (m/m) Gives the mass of solute dissolved in a mass of solution and is expressed as a percent. This is used for alloys, example stainless steel Fe (78%), Cr (15%), Ni (7%) Mass/mass Percent = Mass of solute (g) x 100% Mass of Solution (g)

Example Calcium chloride, CaCl2 can be used instead of road salt to melt ice. A student collected a sample 23.47 g sample of slush and allowed it to melt. The residue that was left had a mass of 4.58 g (assume its only CaCl2). What is the mass/mass percentage of calcium chloride in the slush? X g = 4.58 g 100 g 23.47 g X = 19.5 g or 19.5 % CaCl2

3. Volume/volume (v/v) When mixing 2 liquids together to form a solution, it is easier to measure their volumes rather than their masses. Volume/volume %= Volume of solute (mL) x 100% Volume of Solution (mL)

Example Rubbing alcohol is commonly used as an antiseptic for small cuts. It is sold as 70% v/v solution of isopropyl alcohol in water. What is the volume of isopropyl alcohol used to make 500 mL of rubbing alcohol? v/v %= Volume of solute (mL) x 100% Volume of Solution (mL) 70 % = Volume of solute (mL) x 100% 500 mL Volume of solute (mL) = 70% 500mL = 350 mL is needed 100%

4. Parts per million (ppm) and 5. Parts per billion (ppb) The concentration of a very small quantity of a substance in the human body or the environment is usually expressing in ppm (or ppb, next slide)

ppm Calculations Or ppm = Mass of solute x 106 Mass of Solution Mass of solute = x (g) Mass of Solution 106 g of solution

ppb Calculations ppb = Mass of solute x 109 Mass of Solution Or Mass of solute = x (g) Mass of Solution 109 g of solution

6. Molar Concentration The most useful and widely used in chemistry Molar concentration is the number of moles of solute that can dissolve in 1L of solution

Is this a molar solution? Ouch!!

Completing the Bermuda Triangle