LABORATORY WORK No 9

Performed by:

Zdenka Strechova

Conditions:

t = 24.5 ^oC;  φ = 52.4 %; p = 1020.5 hPa

Topic:

Melting and Boiling Temperatures of Substancies
Used in Household

Tasks:

1.

Determine the melting and boiling  temperatures of various substancies in household.

2.

Compare the melting and boiling temperatures by means of a bar chart.

Theory:

Most substancies change their state when heated up or melted. Melting temperature is a temperature by which the substance melts, i.e. changes its state from the solid to the liquid one. Solidification temperature  is a temperature by which the liquid solidifies, i. e. changes into a solid substance. The solidification temperature of a crystalline substance is equal to its melting temperature. Boiling temperature is a temperature by which the liquid changes into vapour not only on the surface but also inside. Melting and boiling temperatures depend on pressure, purity of the substance etc.

Aids:

Alcohol burner, thermometer, test tube, substancies from the kitchen according to the table.

Procedure:

1.

Pour the liquid into the test tube and put the thermometer in.

2.

Heat the test tube slowly up and follow the rising temperature on the thermometer.

3.

Determine the boiling temperature as exactly as possible at the moment when the liquid is starting to change into vapour in the whole volume. Notice the same temperature measured at any moment of boiling.

4.

Let the test tube with thermometer cool loosely, or put it  to a fridge or freezer.

5.

Follow the sinking temperature attentively and try to determine the temperature period in which the first nuclei of solid substance start to take shape. Notice that the temperature of substance is the same during the whole time of solidification.

6.

Observe also the change in volume of the substance during the solidification. The horizontal liquid surface changes into convex one (e.g. lard), some liquid substances increase their volume while solidifying (e.g. water).

7.

Heat the solid substance in test tube slowly up and determine the melting temperature on the thermometer again. Check if the melting and the boiling  temperatures are equal for this substance.

8.

If the substance from the household is solid in laboratory conditions, then put its small parts into the test tube and heat up slowly. Determine the melting and boiling temperatures by means of the inserted thermometer.

9.

Make up a bar chart in which the length of the column is directly proportional to the melting or boiling temperatures.

10.

Indentify  the substances with biggest and smallest melting and boiling temperatures.

Chart:

Picture:

determining of melting temperature

determining of solidifying temperature

determining of boiling temperature

Table:

Substance

Melting temperature t (°C)

Boiling temperature t (°C)

mineral water Mattoni

0.5

99

paraffin (candle)

75.2

154

fermenting vinegar 8%

-3.5

82

medium-fat milk 1,5%

-4.6

87

camomile tea

-1.6

98

beef soup

-5.3

102

fresh butter

62.5

-

butter spread

47.2

-

Conclusion:

We measured the highest melting temperature from all the investigated foods by wax  31 ^oC and the lowest melting temperatures by milk -5 ^oC and by  tea 3 ^oC.

Milk had the lowest boiling temperature 81 ^oC and, on the contrary, tea had the highest boiling temperature 102 ^oC.