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Starter for 10 Connect your learning Sit back to back – label yourselves A & B
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Starter for 10 Connect your learning Solvent
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Starter for 10 Connect your learning Solution
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Starter for 10 Connect your learning Solute
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Starter for 10 Connect your learning Concentration
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Match up the following words and definitions. Solvent Solute Solution Formed when a substance dissolves in a liquid. The liquid part of the solution that the substance dissolves in. The substance that dissolves in the liquid. Concentration How much solute is dissolved in the solvent
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Learning outcomes (c) State how to make a standard soluton (B) Calculate the amount of substance in mol, using solution volume and concentration (A/A*) Calculate the mass of a solute needed to prepare a certain volume of a standard solution
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What units are used to measure concentration? g cm 3 mol dm -3 cm 3 mol dm 3
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If the volume of the solution is measured in dm 3. n = c x V Where n = amount of substance, in mol c = concentration of substance, in mol dm -3 V = volume of solution, in dm 3 NB if the volumes are small (i.e. cm 3 ) divide V by 1000 Complete question 1 from the text book
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Standard solutions Solution of known concentrations Used in titrations You will firstly calculate an example and then use your results to make up a standard solution Use a volumetric flask – two types available, find out what they are and when you should use each type
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To calculate a standard solution you need to; 1.Consider the volume of solution required 2.Work out the amount, in mol, of solute needed 3.Convert the amount of solute to a mass, in g, so you know how much to weigh out
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Examples In a solution with a concentration of 4 mol dm -3 there are 4 moles of solute dissolved in every 1 dm 3 of the solution. In 1 dm 3 there are 4 mol of dissolved solute In 2 dm 3 there are 8 mol of dissolved solute In 0.25 dm 3 there is 1 mol of dissolved solute If you know the concentration in mol dm -3, you can find the amount, in mol, in any volume of solution
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Worked example Find the mass of KOH required to prepare 250 cm 3 of a 0.200 mol dm -3 solution
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Worked example Find the mass of KOH required to prepare 250 cm 3 of a 0.200 mol dm -3 solution 1.Find the amount of KOH, in mol, required in the solution: n (KOH) = c x V/1000 = 0.200 x 250/1000 = 0.0500 mol 2. Convert moles into grams Molar mass, M(KOH) = 39.1 + 16.0+ 1.0 = 56.1 g mol -1 Amount n = mass m molar mass M Hence, m = n x M = 0.0500 x 56.1 = 2.805g
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Calculate Find the mass of sodium chloride required to prepare 250cm 3 of a 0.300 mol dm -3 solution When calculated we are going to make up a standard solution based on the results
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Molar solutions Referred to as ‘M’ on bottles e.g. 2M HCl M means molar and refers to a solution with a concentration in moles per dm -3 2 mol dm -3 and 2M means the same thing! Question 3 from the text book
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Complete questions 1-3 on pages 17 in the text book Last weeks homework (exam questions, on the wiki lesson 6) – complete questions 1iii and 2ii Homework
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