Presentation on theme: "Title: Lesson 12 Solutions Learning Objectives: – Understand the relationship between concentration, volume and moles – Pose and solve problems involving."— Presentation transcript:
Title: Lesson 12 Solutions Learning Objectives: – Understand the relationship between concentration, volume and moles – Pose and solve problems involving solutions (of the chemical kind not the answers kind)
Main Menu Lesson 12: Solutions Objectives: Understand the relationship between concentration, volume and moles Prepare a standard solution of silver nitrate. Pose and solve problems involving solutions (of the chemical kind not the answers kind)
Main Menu Solutions Basics Aqueous copper sulfate solution: + SOLUTE SOLVENT SOLUTION
Main Menu Concentration This is the strength of a solution. Most ConcentratedLeast Concentrated
Main Menu Concentration The amount of solute dissolved in a unit of solution. The volume that is usually taken is 1dm 3. The amount of solute may be expressed in g or mol therefore the units of concentration are g dm -3 or mol dm -3. Unlike gases, the volume of a liquid is not directly related to it’s amount. For solutions, we express the amount through it’s CONCENTRATION.
Main Menu Molarity The number of moles of a substance dissolved in one litre (dm 3 ) of a solution. Units: mol dm -3 Pronounced: moles per decimetre cubed Units often abbreviated to ‘M’ (do not do this in an exam!) Volume must be in litres (dm 3 ) not ml or cm 3 This is the most useful measure of concentration but there are others such as % by weight, % by volume and molality.
Main Menu Example 1: 25.0 cm 3 of a solution of hydrochloric acid contains 0.100 mol HCl. What is it’s concentration? Answer: Concentration = moles / volume = 0.100 / 0.0250 = 4.00 mol dm -3 Note: the volume was first divided by 1000 to convert to dm 3
Concentration can also be expressed in mass (g dm -3 )
Main Menu Example 2: Water is added to 4.00 g NaOH to produce a 2.00 mol dm -3 solution. What volume should the solution be in cm 3 ? Calculate quantity of NaOH: n(NaoH)= mass / molar mass = 4.00/40.0 = 0.100 Calculate volume of solution: Volume = moles / concentration = 0.100 / 2.00 = 0.0500 dm 3 = 50.0 cm 3
Main Menu More questions… Complete the test yourself questions on page 45. Questions 40 and 41. Check your answers on page 559.
Parts per million (ppm) Another unit of concentration Denotes one part per 10 6 by mass. Useful for very low concentrations such as found in air and water pollution A concentration of 1 ppm for a substance means that each kilogram of solution contains 1 milligram of solute. Assuming a density of 1 g dm -3, 1ppm also means each dm 3 of solution contains 1 mg of solute.
You can make a dilution from a more concentrated starting solution, called a stock solution, by adding a solvent. As a solution is diluted, the number of moles of solute remains the same, but now they are spread over a larger volume. Hence, concentration is decreased. Number of moles is constant. n=cV Concentration x volume must be constant through dilution