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CHEMICAL PROJECTS Research Ideas for Young Chemists JAY A. YOUNG, King's College, Wilker-Barre, Penna. JOHN K. TAYLOR, National Bureau of Standordr, Worhington, D. C.
An Inexpensive Coulometer for Titrations with Externally Generated Reagents See HEAD,W . F., JR., AND MARSH,M. M., J. Ch,em. Educ., 38, 361 (1961). The products formed when a solution of sodium sulfate is eleotrolyeed are sulfuric acid and sodium hydroxide. A huret constructed in the form of an inverted "T" is fitted with two platinum elect,rodes, one in each arm of the "T." As a solution of sodium sulfate is allowed to run out of the huret during electrolysis, acid will run out of one arm, and base from the other. The total amount of acid, or base, formed during electrolysis is conveniently measured by a coulameter, for which a wiring diagram and constructional details are described. Hence, by collecting either the electrolytically formed acid, or the base, in a flask containing base, or acid (the unwanted electrolysis product is discarded), and a suitable indicator, a titration can be performed. The ooulometer is turned off when
the indicator changes color, and the amount of acid or base generated and therefore collected in the titrating flask is noted from a dial reading on the coulometer. By selecting other electrolytes other titrsnts can he electrolytically generated. For example, iodine from a.solution of potassium iodide, lithium methoxide from a solution of lithium chloride in methyl alcohol aresuggested in the article. Question:
Construct the ooulameter and s ~ e c i ahuret. l
Select a uroblem
A Thermobalance for Student Experiments See BOTTEI,R. S., A N D GERACE, P. L., J . Chem. Educ., 38,568 (1961). Many substances lose weight when heated, either by partial or complete decomposition into gaseous products or by reaction with the air to form gaseous products. I n thermogravimetric analysis, a substance is slowly heated from room temperature (usually) t o higher temperatures of about 300DC,or even higher, while being continuously weighed. A graph showing tho weight of the substance as a function of temperature can he used to interpret the reactions which occur when thesubstance is heated. Far example, the graph for copper sulfate pentahydrate shows more than one break. indicating that the water is driven from this salt in steps; that is, not all five water molecul~sare held with equal strength. The article describes the modification of an ordinary analytical balance so that i t can be used for thermogravimetric analysis. Although the authors used a. magnetically damped balance for
this nmdification, this feature is not essential. Also, i t is not necessary to provide a nitrogen atmosphere for the furnace used in the heating. Instead of the Temeo input controller, a manually operated rheostat or autotransformer could he used, or see M. M. MARKOWITZ, ET AL., J. CAEI. EDUC.,38, 96 (1061) for 3 simple motor driven variable transformer. Another type of balance, using s. strain gauge as the sensitive element, is d e J . CHEM.EDUC.,38,566 (1961). scribed by W. W. WENDLANDT, Question:
Scloet one or more substances, or mixtures of substances, which you think will change weight when heated and determine the weight loss curve by thermogravimetric analysis. Interpret the curve you obtain, and confirm your ideas concerning the chemical changes which take place by further lahoratory studies.
A Simplified lsoteniscope See STEINBACH, 0.F.,
AND
DEVOR,A. W., J.Chem. Educ., 22,288 (1945); ibid,22,496 (1945)
The isotenincope is a convenient instrument for the measurement of vapor pressures of liquids over an extended temperature range. The apparatus deerribed in the first reference is s simplified design that, could produce vapor pressure measurements of a research quality. Essentially the apparatus consists of a hailing flask containing a thermometer and an outlet side arm which is provided with a U-tuhe trap all immersed in a. wat,er bath. This vessel is connected to a manometer, a ballast bottle, and a water aspirator pump to vary the pressure of the system. The water bath is heated and the pressure a t which ebullition just ceases is measured as the vapor pressure of the liquid a t the temperature indicated by the thermometer. The only compliceted part of the apparatus is the series of bulbs constituting a trap and these could he eliminated provided the inveetigstor was careful in his manipulation of the external pressure. The authors discuss sources of error and illustrate the performance of the apparatus by measurements of the vapor pres-
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sures and calculations of derived heats of vaporization for five compounds. Agreement with the literature is excellent, the maximum error indicated for the heat of vaporization being 2.6 per cent. The second reference by the same authors describes a miero-modificstion of the apparatus that gives results of eomparable or higher precision with as little as 0.5 ml of sample. Questions:
Construct an isoteniscope as described in the references, measure the vapor pressures and cdculate the heats of vaporization of representative compounds. What improvement could you suggest that might improve the reliability of the measurements obtained with this apparatus? Use the apparatus to measure the boiling points of a nnmher of "pure" materials. Devise purification procedures or callahorste with others engaged in such sotivities and utilize your apparatus for measurements of the purification procedure.
