Solution ConcentrationSolution Concentration

Concentration = quantity of solute quantity of solution (not solvent)

There are 3 basic ways to express concentration: 1) percentages,2) ppm and ppb (used for very low concentrations) 3) molar concentrations

1. Percent concentration

% concentration can be in 1a) % V/V1b) % W/W1c) % W/V

%V/V = volume of solute (mL or L) X 100% Volume of solution (mL or L)

1. 140 mL of acetic acid is present in a 500 mL bottle of solution? What is the percentage by volume concentration of acetic acid? 28% V/V

2. Gasohol fuel is a solution of ethanol and gasoline. A typical gasohol mixture available across Canada contains 4.1 L of ethanol in a 55-L tank of fuel. What is the percentage by volume concentration of ethanol? 7.5

3. What is approximate % V/V if 30 mL of pure ethanol is added to 250 mL of water? 11% V/V

1a) Percent volume by volume concentration

• %W/W = Weight of solute (g or kg) X100% Weight of solution (g or kg)

1. What is the % W/W if 8.0 g copper is added to enough zinc to produce 100 g of an alloy? 8% W/W.

2. Brass is a copper-zinc alloy. If the concentration of zinc is relatively low, the brass has a golden color and is often used for inexpensive jewellery. If a 35.0 g pendant contains 1.7 g of zinc, what is the percentage weight by weight of zinc in brass? 4.9% W/W

3. What is the % W/W of copper in an alloy when 10 kg of Cu is mixed with 250 kg of Zn? 3.8 % W/W

1b) Percent weight by weight concentration

• % W/V = weight of solute (g) X 100% volume of solution (mL)

• Can use g/ml or kg/L

1. Solder flux, available at hardware stores, contains 16 g of zinc chloride in 50 ml of solution. The solvent is HCl (aq.). What is the percentage weight by volume of zinc chloride in the solution? 16 g / 50 mL = 32% W/V

2. If 250 g of sodium chloride is present in 3 L of solution, what is the percentage weight by volume of sodium chloride? 250g/3000ml = 8.5% W/V

1c) Percent weight by volume concentration

2. Very low concentrations• Expressed in parts per million (ppm) or parts per billion (ppb)• A type of W/W or W/V concentration• E.g. chlorine concentration in a swimming

pool may be expressed as ppm • 1 mg/L 1 ppm 1 mg/1000L 1 ppb

1 mg/kg 1 mg/1000kg1) Convert 45 ppm to g/L, 45 ppb to g/L.2) Convert 3.75 mg in 50 mL to ppm.

3. Molar concentration

Molar concentration = amount of solute (in moles)(C) Volume of solution (in L)

C = n/V Units are mol/L or M or Molar1)If a reaction produced 0.186 mol of sodium hydroxide in 0.250 L of solution. Calculate the molar concentration of sodium hydroxide.2)64 g of oxygen gas (02) are dissolve in 100 L of air, what is the concentration?

Activity

• Work on assignment: due next class.