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Mole Day Planning Pack Starter Ask students to think of as many words as they can beginning with the prefix mono. What does mono mean? What does monomolecular mean? Stimulus Remember to complete a risk assessment before beginning practical work. Demonstrate the formation of a monomolecular layer of oleic acid on water in a bowl. Using a pipette, place one drop of oleic acid from a solution of 0.05 ml oleic acid in 1 dm3 pentane. Explain what you are doing. Tell students that they are going to use this demonstration and some extra information to answer some questions. Split the class into groups, with students numbered 1, 2 and 3 in each group. Question 1 What is the length of an oleic acid molecule? Give students time to think about the question. Then ask them to write down on an index card one question that they will need to know the answer to in order to answer question 1. In groups of 3, ask students to share their questions by passing their index cards around the group, explaining to each other why they wrote this question down. Now give each group the information card and ask them to come up with a strategy to answer question 1. Hint cards are available if they are unable to move on from one step to the next. Recommend they attempt a solution before asking for hints. Ask the number 2 from each group to explain their idea to the class. Take each idea in turn and encourage students to decide whether it is a feasible strategy. Allow access to the equipment for students to answer the question. Question 2 What value does this experiment give for Avogadro’s number? Repeat the process used to solve question 1, this time ask the number 1 from each group to feedback the group’s strategy. Question 3 Compare your answer for 2 with the stated value of 6.02 x 1023. What are the uncertainties and sources of error in your calculations? Ask them to discuss question 3 in their group and list all of their answers. After 5 minutes ask all number 3s to feedback to the class. www.ulster.ac.uk/scienceinsociety/ 15 ANALYSING PROBLEM SOLVING F An enquiry approach to determining Avogadro’s Number T Mole Day Planning Pack Information Card ! ! ! ! ! ! ! ! ! ! ! ! ! This part of the molecule is hydrophilic. It can form hydrogen bonds so is more soluble in water than in oil. Oleic acid is less dense than water. A very small amount of oleic acid dropped onto the surface of water will spread out to form a monomolecular film (a layer 1 molecule thick on the surface of the water). Pentane evaporates from the surface of the water. The molar mass of oleic acid is 282 g mol-1 The density of oleic acid is 0.895 g mol-1 Area of a circle = πr2 Concentration of oleic acid = 0.05 cm3/ dm3 m= ρV Resources that you have access to in order to answer the question. Balance Small measuring cylinder Any material used in the demonstration Question 1 hints Question 2 hints 1 Volume = Area x length 1 Number of molecules = Number of moles x Avogadro’s number 2 Find the volume of oleic acid in one drop 2 Calculate the number of moles of oleic acid. 3 Volume of 1 drop = 5 cm3 divided by number of drops in 5 cm3 3 Number of moles = mass (g) divided by molar mass (g mol-1) 4 Find out how many drops are needed to reach 5 cm3 4 Calculate the mass of oleic acid used. m = ρV 5 Measure the area of the slick 5 Calculate the number of oleic acid molecules 6 Assume the layer of oleic acid is one molecule thick. 6 Assume oleic acid is a cube. V = l3. 7 Assume oleic acid is cubic 7 No. molecules = volume of oleic acid divided by volume of 1 molecule www.ulster.ac.uk/scienceinsociety/ 16 ANALYSING PROBLEM SOLVING Oleic acid (see below) has a hydrophobic end (the hydrocarbon end) and a hydrophilic end (the carboxylic acid end). S