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Description
Before this programme the student will have performed an experiment to determine the enthalpy change when magnesium is dissolved in acid. In the pre broadcast notes the student is asked to recall s...ources of error in his experiment and compare his method with the method Dr. Ross describes in the programme used by the National Physical Laboratory to determine the enthalpy change very accurately. Typically illustrated are techniques for handling and weighing the sample, use of the rotating bomb calorimeter, temperature measurement with a platinum resistance thermometer, a calibration experiment using the National Standards of voltage and current and the method the NPL use to record their results. The thermodynamic thinking behind both experiments is explained in detail and the enthalpy change related to measurable quantities. Later in the programme Dr. Johnson contrasts a modern value of the enthalpy change with a value obtained by Julius Thomsen an eminent 19"th. century thermochemist, and by suggesting a source of error in the earlier experimental work, describes how the value for the enthalpy change can be corrected for impuriter present in the metal sample.
Before this programme the student will have performed an experiment to determine the enthalpy change when magnesium is dissolved in acid. In the pre broadcast notes the student is asked to recall s...ources of error in his experiment and compare his method with the method Dr. Ross describes in the programme used by the National Physical Laboratory to determine the enthalpy change very accurately. Typically illustrated are techniques for handling and weighing the sample, use of the rotating bomb calorimeter, temperature measurement with a platinum resistance thermometer, a calibration experiment using the National Standards of voltage and current and the method the NPL use to record their results. The thermodynamic thinking behind both experiments is explained in detail and the enthalpy change related to measurable quantities. Later in the programme Dr. Johnson contrasts a modern value of the enthalpy change with a value obtained by Julius Thomsen an eminent 19"th. century thermochemist, and by suggesting a source of error in the earlier experimental work, describes how the value for the enthalpy change can be corrected for impuriter present in the metal sample.
| Item code: | S25-; 04 |
|---|---|
| First transmission date: | 04-03-1972 |
| Published: | 1972 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:24:29 |
| + Show more... | |
| Producer: | David Jackson |
| Contributors: | H A Gundry; Len Haynes; David Johnson; Robert Ross |
| Publisher: | BBC Open University |
| Keyword(s): | Calibration experiment; Handelling samples; Julius Thomsen; Magnesium enthalpy change; Rotating bomb calorimeter; Thermodynamics |
| Footage description: | Len Haynes introduces the programme. Bob Ross sums up the aims of the student home experiment which measures the value of the enthalpy change for a reaction between magnesium and an acid. Shots of the National Physical Laboratory (NPL). Shots of the rotating bomb calorimeter which would be used there for the same experiment. Commentary by Ross. Shots of the aluminium-iron oxide thermit reaction from unit 3 are shown to demonstrate the problem of oxide formation. Film shots at the NPL show how the problem is tackled there. H.A. Gundry uses a glove box to abrade a magnesium sample in a nitrogen atmosphere to remove the oxide coating. Ross explains how students determined the mass of their magnesium sample. Film shots at the NPL show how mass of a magnesium sample is determined there by weighing. Commentary by Ross. Ross with a rotating bomb such as that used in the NPL calorimeter. He explains its construction and how it works. Film shots show H.A. Gundry at the NPL preparing a bomb and calorimeter for an enthalpy experiment. Commentary by Ross. Ross compares the NPL calorimeter with that used by students in their home experiments. Further film shots of the NPL calorimeter being set up for an enthalpy experiment by H.A. Gundry. Ross with a platignum resistance thermometer such as is used by NPL. He explains how it works. Ross then explains how the NPL experiment is started. Shots of the NPL calorimeter. Shots of Gundry taking temperature readings before and during the reaction. Shots of a graph which shows the rise in temperature. Ross explains how the rise in temperature of the NPL experiment is calculated as this cannot be measured directly. He shows the resulting calibration graph. Ross uses a diagram to explain what is happening in the experiment. D.A. Johnson discusses the importance of sample purity when doing enthalpy experiments. He discusses and compares the results of the magnesium with acid enthalpy experiments of Julius Thomsen (1882) with those of Shomate and Huffman (1943). Johnson points out several possible reasons why Thomsen's results were less accurate. He goes on to explain the effects of an oxygen impurity in the magnesium on the reaction. Johnson works out the equation on a board, Johnson concludes from this that the MgO impurity in the sample was probably responsible for Thomsen's less accurate figure. Ross sums up by asking students to calculate H m for the reaction of magnesium with acid using the figures given in the Broadcast note appendix. |
| Master spool number: | 6LT/70357 |
| Production number: | 00521_2170 |
| Videofinder number: | 1772 |
| Available to public: | no |
