Beatty 4. E2 6092 Thermometric Titration_Answers

1 Beatty Secondary School Science Department (Chemistry Unit) Chemistry 6092 Name: ___________________________________ ( ) Date: ________________ Class: 4E___ Practical 4: E2 – Thermometric Titration Skills: MMO: Manipulation, measurement, and observation PDO: Presentation of data and observations ACE: Analysis, conclusions and evaluation Aim: To find the concentration of an alkali using temperature changes. Apparatus and chemicals: burette funnel clamp and stand measuring cylinder styrofoam cup with lid thermometer distilled water 50 cm3 of solution U 60 cm3 of solution V 250 cm3 beaker Solution U contains 0.500 mol/dm3 of sulfuric acid. Solution V is aqueous sodium hydroxide of unknown concentration. When acids react with alkalis, heat is produced because the reaction is exothermic. When aqueous sodium hydroxide is steadily added to a volume of sulfuric acid, the temperature rises until all the acid has reacted. At this point, even if more alkali is added, there is no further increase in temperature as all the acid has been neutralise d. You are to add solution V to a volume of solution U, recording the temperature changes by the following procedure. From the results, you are to find the concentration of sodium hydroxide in solution V. Procedure: 1 Put the alkali V into a burette. 2 Use a measuring cylinder to place 50 cm3 of solution U into a styrofoam cup. Using a thermometer, measure the temperature of the solution in the cup and record this value (T0) in an appropriate table under the results section. 3 Add 5.0 cm3 of solution V from the burette into the styrofoam cup. Gently stir the mixture with the thermometer and record the maximum temperature reached (T1). You should reach the maximum temperature in about half a minute. 4 Without delay, add another 5.0 cm3 of solution V from the burette into the styrofoam cup and stir the mixture. Record the maximum temperature (T1) reached in the table. 5 Repeat Step 4 with further 5.0 cm3 portions of solution V until a total of 45.0 cm3 of solution V has been added to the styrofoam cup. Record all the results in your table. 35

2 Results: Total volume of solution U used = 50.0 cm3 Initial temperature (T0) of solution U = 29.5 °C total volume of V added / cm3 maximum temperature (T1) reached / °C total temperature change / °C 0.00 29.5 0.0 5.00 32.0 +2.5 10.00 34.0 +4.5 15.00 35.5 +6.0 20.00 37.5 +8.0 25.00 39.0 +9.5 30.00 39.5 +10.0 35.00 38.5 +9.0 40.00 38.0 +8.5 45.00 37.5 +8.0 [5]

3 Plot a graph of total temperature change in the styrofoam cup against total volume of solution V added to the cup. Draw two intersecting straight lin es passing through the points. One of the lines must pass through the origin. [4]

4 Calculations: 1 Answer the following questions with reference to your graph plotted. (a) What is