Refresh  How many oxygen atoms are there in 0.20 mol of ethanoic acid, CH 3 COOH? A. 1.2 x B. 2.4 x C. 3.0 x D. 6.0 x 10 24

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Lesson 6: Moles and Molar Mass  Objectives:  Calculate the relative mass and molar mass of substances  Relate the mass of a substance to a quantity in moles  Apply the above by conducting an experiment to determine the number of moles of water of crystallisation

Questions 1. Calculate the mass of mol of benzene (C 6 H 6 ) 2. Calculate the mass of mol of ammonium nitrate (NH 4 NO 3 ) 3. What quantity of iron (III) oxide is present in a 1.00 kg sample? 4. What quantity of cobalt (II) chloride (CoCl 2 ) is present in a 2.40 g sample? moles of a compound has a mass of 1.41 kg. Calculate its molar mass mol of an oxide of hydrogen has a mass g. Deduce it’s formula. Answers: 1) 7.81g, 2) 60.0g, 3) 6.26 mol, 4) mol, 5) 160 g/mol, 6) 34.0 g/mol

Moles of Water of Crystallisation  Many compounds can incorporate water into their crystal structure, this is called the water of crystallisation.  CoCl 2 is blueCoCl 2.6H 2 O is pink  The ‘.’ means the water is ‘associated’ with the CoCl 2  It is loosely bonded, but exactly how is unimportant  In this experiment you will calculate the moles of water of crystallisation of a compoundthis experiment  Nearpod code: ULZOK

Main Menu Refresh  A student reacted some salicylic acid with excess ethanoic anhydride. Impure solid aspirin was obtained by filtering the reaction mixture. Pure aspirin was obtained by recrystallisation. The following data was recorded by the student.  Mass of salicylic acid used3.15 ± 0.02 g  Mass of pure aspirin obtained2.50 ± 0.02 g 1. Determine the amount, in mol, of salicylic acid, C 6 H 4 (OH)COOH, used.

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 Molarity  The number of moles of a substance dissolved in one litre 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 grams per litre, % by weight, % by volume and molality. moles concentration volume x

Main Menu Example 1:  25.0 cm 3 of a solution of hydrochloric acid contains mol HCl. What is it’s concentration?  Answer:  Concentration = moles / volume = / = 4.00 mol dm -3  Note: the volume was first divided by 1000 to convert to 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 =  Calculate volume of solution:  Volume = moles / concentration = / 2.00 = dm 3 = 50.0 cm 3

Main Menu Example 3:  It is found by titration that 25.0 cm 3 of an unknown solution of sulfuric acid is just neutralised by adding 11.3 cm 3 of 1.00 mol dm -3 sodium hydroxide. What is the concentration of sulfuric acid in the sample. H 2 SO NaOH  Na 2 SO H 2 O  Use: (C 1 x 25.0)/1 = (1.00 x11.3)/2 C 1 = ((1.00 x 11.3) / 2)/25.0) = mol dm -3 Where: n = coefficient in balanced equation C = concentration V = volume ‘1’ refers to H 2 SO 4 ‘2’ refers to NaOH

Main Menu Questions 1. You have 75.0 cm 3 of a mol dm -3 solution of zinc sulphate (ZnSO 4 ). What mass of zinc sulphate crystals will be left behind on evaporation of the water? 2. What volume of water should be added to 3.23g of copper (II) chloride (CuCl 2 ) to form a mol dm -3 solution? 3. A 10.0 cm 3 sample is removed from a vessel containing 1.50 dm 3 of a reaction mixture. By titration, the sample is found to contain mol H +. What is the concentration of H + in the main reaction vessel? 4. In a titration, 50.0 cm 3 of an unknown solution of barium hydroxide was fully neutralised by the addition of 12.2 cm 3 of mol dm -3 hydrochloric acid solution. What concentration is the barium hydroxide solution? Ba(OH) HCl  BaCl H 2 O 5. In a redox titration, 25.0 cm 3 of an unknown solution of Fe 2+ is found to react with 5.6 cm 3 of a mol dm -3 solution of manganate ions (MnO 4 - ). What is the concentration of Fe 2+ ions? What mass of iron was present in the solution? MnO Fe H +  Mn Fe H 2 O Answers: 1) 1.82g, 2) 3.23g 240 cm 3, 3)0.530 mol dm -3, 4) mol dm -3, 5) mol dm -3, 0.156g

Main Menu Preparing a Standard Solution  A standard solution is one whose concentration is well known  And usually a round number like 1.00 or mol dm -3  Prepare standard solutions sodium hydroxide with concentrations of mol dm -3 Prepare standard solutions sodium hydroxide  You will use these in a future lesson so make them well!

Main Menu Problem Time  Write three stoichiometry problems using any of the ideas from the unit so far (make sure you know the answer).  In ten minutes time you will need to give your problems to a classmate to solve.