Solutions and Concentrations

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1 A02 Solutions and Concentration.notebook Solutions and Concentrations What is concentration? 1

2 The difference between concentrated solutions and dilute solutions can be determined qualitatively and quantitatively. 2

3 A02 Solutions and Concentration.notebook Qualitative Properties Colour, colour intensity, taste, odour, transparency, conductivity and reactivity. All these could be used as clues to estimate the amount of solute dissolved in an amount of solvent 3

4 Investigation: Repeated Dilutions p36 4

5 Practice Problems p39 #2 6 5

Quantifying Concentrations Frequently, a qualitative knowledge of the concentration of solutions is not enough information. Especially in Chemistry.

6 Quantifying Concentrations Frequently, a qualitative knowledge of the concentration of solutions is not enough information. Especially in Chemistry. It is useful to know concentrations quantitatively (numbers) In order to do this, we need to become familiar with the appropriate concentration formulae. 6

7 Three New Formulae for Concentration 1. Percent by Volume 2. Parts per Million 3. Molar Concentration 7

8 1. Percent by Volume This method of expressing concentration communicates the volume of a liquid solute dissolved in the total volume of a solution. Frequently used by manufacturers of consumer products. 8

9 Example Problem 1.6 p41 A hair product requires you to combine 20.0 ml of Hydrogen Peroxide with enough water to produce a solution with a total volume of ml Determine the percent by volume concentration of the solution. 9

10 Example Problem 1.7 p41 A mosquito repellent says that DEET makes up 45.0% of the total volume. If you have a 75 ml sample of this repellent, determine the volume of DEET within the sample. 10

11 Example Problem 1.8 p42 Insecticidal soap is an environmentally friendly way to control pests on plants. A gardener needs a solution with a percent by volume concentration of insecticidal soap of 5.0%. If the total volume of the solution was 4000 ml, calculate the volume of insecticidal soap needed to make this solution. 11

12 Practice Problems: p42 #

13 2. Parts per Million (ppm) This method of expressing concentration communicates levels of a substance (like a pollutant) in very dilute aqueous solutions. Frequently used by agencies that set health and safety standards. 13

14 Example Problem 1.9 p43 A 200 g sample from a bottle of water contains 5.4 x 10 3 g of mercury. a) Calculate the concentration of mercury in the sample in parts per million. b) Use the information in the table "Allowable Toxic Levels in Drinking Water" (p42) to determine if this water is safe to drink. 14

15 Example Problem 1.10 p43 Carbon monoxide, CO (g), is a deadly gas that takes the place of oxygen molecules and binds to hemoglobin in blood. If you are smoking, the concentration of carbon monoxide that reaches your lungs is approximately 200 ppm. Determine the mass of CO (g) that would be present in a sample of air having a mass of 9.6 g (approx one breath). Express your answer in scientific notation. 15

16 Practice Problems: p44 #

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18 3. Molar Concentration This method of expressing concentration communicates the amount of moles of a pure substance dissolved in the total volume of a solution. or Frequently used by scientists and lab technicians. 18

19 Example Problem 1.11 p45 A sample of water taken from a nearby lake is found to have mol of salt in a 100 ml solution. Determine the concentration of the salt in the lake. 19

20 Practice Problems: p46 #34 20

21 Additional formulae and concepts that may be useful: Molar Mass, M the mass of 1 mole of a substance measured in g/mol 21

22 Determine the molar mass of a: sulfuric acid molecule, H 2 SO 4 magnesium phosphate molecule, Mg 3 (PO 4 ) 2 22

23 ... also useful, the formula for moles and molar mass. Example what is the mass of 1.27 mol of CaCl 2? 23

24 Example Problem 1.12 p45 You dissolve 30.0 g of sodium sulfate, Na 2 SO 4, into 300 ml of water. a) Determine the number of moles of sodium sulfate in this solution. b) Calculate the molar concentration of this sodium sulfate solution. 24

25 Practice Problems: p46 #

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29 In industry, it is sometimes necessary to create standard solutions... these are solutions with precisely known concentrations. In order to accomplish this, chemists must use the previously mentioned formulae and calculations. 29

30 Diluting solutions How many "moles" of Oj are in each pitcher? 30

The number of moles remains the same: initial solution final solution let's keep the

31 In order to dilute a solution, we normally keep adding water until we obtain the desired concentration. The number of moles remains the same: initial solution final solution let's keep the moles the same: n i = n f but remember that c=n/v or n = cv, therefore: c i v i = c f v f This is the formula that is used to calculate accurate dilutions 31

32 Example Problem 1.13 p49 You have 65.0 ml of a mol/l solution of sodium chloride, NaCl (aq). a) Calculate the final concentration if the solution is diluted to a final volume of ml. b) Calculate the final concentration of a solution prepared by adding ml of water to the original solution. c) How much water do you need to add to the original solution to obtain a solution with a concentration of mol/l? d) How much water needs to evaporate from the original solution to obtain a solution with a concentration of mol/l? 32

33 p46 Developing Technological Skills with Solutions 33

34 Practice Problems: p50 #37, 38, 39 p52 #4, 6, 7 Chapter 1 Review Questions p54 #1, 2, 5, 6, 8, 10 18, 21, 27 34

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Science 20 - Solution concentration

Science 20 - Solution concentration The concentration of a solution is a ratio of the amount of solute dissolved in a specific quantity of solvent. A dilute solution contains a relatively low quantity