LABORATORY ACTIVITIES

SYNOPTIC DESCRIPTION OF SMALL EXPERIMENTS

The following synoptic experimentís descriptions have already been mentioned in the corresponding chapters. Here they are presented as a whole.

Reminder: As simple and harmless the experiment may be, and even for typical reasons, the advisable precautionary measures should be followed.

INFLUENCE OF THE CONCENTRATION

1) We separate a Na2S2O3 solution, from 0.1M to 0.6 M, in two parts with volume ratio 2:1. We add water to the solution with the smaller volume until its volume is equal to the second one. Thus, two solutions result and the first one has twice the volume of the second. In each one of these two solutions we add simultaneously the same quantity of hydrochloric acid. We observe that the solution that becomes turbid faster is the one with the higher Na2S2O3 concentration.

2) We place two cornflower floats, starchy powder, in two H2O2 solutions from witch the first has the double concentration of the second. (The peroxide solution is found in pharmacies and is diluted up to four or eight times its original volume with the addition of water). In each one of these solutions we pour simultaneously the same quantity of KI solution, almost 2% w/v, and make the observation that, in the beaker with the greater concentration of H2O2, the float is colored blue faster.

3) We pour a solution of hydrochloric acid, almost 3M, in a test tube up to 1/3 of its volume and in another test tube we pour a solution of hydrochloric acid, almost 1M. Next, we place in each test tube a piece of Zn and observe that in the solution with the higher density the production of bubbles is more intense.

INFLUENCE OF THE TEMPERATURE

1) We dilute a saturated solution of CuSO4 until it becomes three times its initial volume and separate it in two, almost equal, parts. One of these parts is heated on a water bath while the other one is placed on a beaker filled with ice. Next, we sink in each part an iron nail and observe that on the hotter solution the nail is covered faster with a copper layer. If the quantity of the solutions is relatively small we observe a change in their color, which occurs first on the hotter solution and afterwards on the colder.

2) We pour a solution of hydrochloric acid, almost 2M, in two test tubes up to 1/3 of their volume. One of the test tubes is heated on a water bath, while the other one is placed on a beaker filled with ice. Next, we place a piece of Zn in each one of the test tubes and observe that in the solution with the highest temperature the production of bubbles is more intense.

CATALYSTS ACT

  We place a small quantity of KClO3 in two separate test tubes and add a small quantity of MnO2 in only one of them. We heat simultaneously and uniformly the two test tubes and using a semi-extinguished little wooden stick we detect the Ο2 which is produced more intensively in the tube containing the catalyst.

 INFLUENCE OF THE PARTITION GRADE

If we add in KMnO4, which is found in fine partition, two drops of glycerin, inflection of the glycerin will take place almost immediately. On the contrary, if KMnO4 is not found in fine partition the inflection will either be delayed or not take place at all.

1) Detailed presentation of a laboratory exercise.

2) Detailed presentation of a laboratory exercise, with the deduction of measurements and the construction of a diagram.