Greenwich chemistry lab session - titration


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Greenwich chemistry lab session - titration

  1. 1. The University of Greenwich is running a practical session for Chemistrystudents in Year 13Assessed Chemistry Practical Lab Session for A2Thermometric Titration of a Strong AcidWednesday 28 March at 12.30 – 3.00 pmUniversity of Greenwich, Medway CampusThis free session is open to all students on a first come first servedbasis. Please see accompanying information for further information.Programme:12.30 Arrival and briefing1.00 Chemistry Practical session begins2.30 Post-activity Assessment3.00 EndFor bookings and enquiries, contact Division, University of Greenwich at Medway, Pembroke Building, Chatham Maritime ME4 4TB
  2. 2. Thermometric Titration of a Strong Acid (Time required for this experiment: 1.30 hr with an addition of 30 min for post assessment) Start: 1.00 PM on Wednesday the 28th of March till 3.00 PM Location: Link Lab (School of Science, University of Greenwich, Medway)Aims:The aims of the practical session are to use thermometric titration to determine theconcentration of a strong acid HA. Neutralisation is an exothermic reaction and the maximumtemperature is reached at the end-point. From your results, you will draw a graph oftemperature against the volume of strong acid HA added.Assessment on:  Your ability to work carefully and safely, making accurate measurements and detailed observations and record all your results clearly in an appropriate way.  Carrying out the titration (reading and recording burette volumes and temperature values accurately).  Drawing and interpreting the graph to find the volume added of the strong acid.You will be supplied with the followings: • 1.0 M sodium hydroxide solution • Concentrated hydrochloric acid (HA)The neutralisation point in this titration occurs when the optimum volume of sodiumhydroxide solution (needed to exactly neutralise the amount of strong acid used) has beenadded to the acid. Neutralisation is an exothermic reaction and the maximum temperature isreached at the end-pointPartnership Division, University of Greenwich at Medway, Pembroke Building, Chatham Maritime ME4 4TB
  3. 3. At the end point of the titration of a strong avid and base the temperature is maximum. Anaddition of a little amount of the acid in solution will take the temperature down.Methods:  Transfer 50cm3 of sodium hydroxide solution to a polystyrene cup. Allow it to stand for a few minutes, and then record the temperature of the solution.  Add 5.0cm3 of hydrochloric acid from a burette to the cup.  Immediately stir the mixture with the thermometer and record its temperature.  Repeat the above step until you have added a total of 50.0cm3 of acid (total 10 steps additions of 5.0cm3 HCl).Analysis:  Plot a graph of temperature (vertical axis) against total volume of acid added (horizontal axis).  Draw straight lines of best fit and extend them until they cross (see diagram above). The point at which the two lines meet corresponds to the volume of acid needed for neutralisation and to the maximum temperature.  Record the volume needed for HCl  Use information from your graph to calculate the concentration of the acid. Evaluations and post assessments:Comment on your results, their accuracy, and the likely sources of error in the experiment.Consider the limitations of the experiment, and possible improvements to it.Use the equation below to calculate the acid concentrationPartnership Division, University of Greenwich at Medway, Pembroke Building, Chatham Maritime ME4 4TB
  4. 4. C b x Vb = C a x VaWhere,Cb = concentration of base (NaOH)Vb = Volume of the base (NaOH)Ca = Concetration of HClVa = Volume used of HCl  Now calculate the volume of HCl needed to neutralise 25cm3 of NaOH 1.0M solutions. At this volume the solution shows the highest temperature during the titration. The concentration for the HCl used is 2.0M.Health and Safety NotesHydrochloric acid: Corrosive. Refer to Hazcards for correct method to prepare the 2M(approx.) solution.Ethanoic acid: Corrosive. Harmful vapour.Refer to Hazcards for correct method to prepare the 2M (approx.) solution.Sodium hydroxide solid and solutionsSodium hydroxide is very caustic and forms strongly alkaline solutions.Exercise care in handling - wear gloves, Goggles, Labcoats and eye protection.If spilt, wash with a lot of water.Partnership Division, University of Greenwich at Medway, Pembroke Building, Chatham Maritime ME4 4TB