You are provided with a beaker, a thermometer, a stirrer Stopwatch/clock, measuring cylinder, table salt, water, and other necessary materials.
i. You Measure 200cm\(^{3}\) of water into the beaker.
ii. Heat the water until it boils steadily for about 2 minutes.
iii. Read and record the boiling point b\(_{0}\).
iv. Add table salt of mass M = 10.0 g to the boiling water and stir continuously until another boiling point b\(_{1}\) is attained.
v. Read and record b\(_{i}\).
vi. Evaluate \(\theta_{i}\) = (b\(_{i}\) – b\(_{0}\))
vii. Using the same mixture, repeat the procedure four more times by adding 10.0 g of salt each time to give the cumulative mass M\(_{i}\) of salt as 20 g, 30g, 40g, and 50g.
viii. In each case allow the mixture to boil steadily for at least 2 minutes then read and record the boiling point b.
ix. Tabulate your readings.
x. Plot a graph with M\(_{i}\) on the vertical axis and \(\theta_{1}\) on the horizontal axis.
xi. Determine the slope, s, of the graph.
xii. State two precautions taken to ensure accurate results.
(b) i. Define the boiling point of a liquid.
ii. What effects do impurities have on the boiling point of a liquid?
Explanation
bo = 102°c
| S/N | M/g | bi/ °c | \(\theta_{1}\)=(bi-bo)/° |
| 1.0 | 10.0 | 104.00 | 104 - 102 = 2.00 |
| 2.0 | 20.0 | 106.00 | 106 - 102 = 4.00 |
| 3.0 | 30.0 | 108.00 | 108 - 102 = 6.00 |
| 4.0 | 40.0 | 110.00 | 110 - 102 = 8.00 |
| 5.0 | 50.0 | 112.00 | 112 - 102 = 10.00 |
Slope, s = \(\frac{\bigtriangleup M_{2} - \bigtriangleup M_{1}}{\bigtriangleup\theta_{2} - \bigtriangleup\theta_{1}}\)
= \(\frac{40}{8} - \frac{10}{2} = \frac{30}{6}\)
S = 5
PRECAUTIONS
1. stirred the water gently to ensure uniform temperature.
2. avoided splashing of the water
3. avoided error due to parallax in reading the thermometer and the stop clock.
(b) i. Boiling point is defined as the point when liquid changes to vapour when the saturation vapour pressure is equal to the atmospheric pressure.
ii. Impurities affect the boiling of a liquid because their presence inicreases the boiling rboint of the liquidelcom- pared to the boiling point of a pure solvent.
