You are provided with a beaker, a thermometer, a stirrer, a measuring cylinder, a bunsen burner, a wire gauze, a 50g mass, a pair of tongs, water, tripod stand, and other necessary materials.
i. Using the measuring cylinder, measure 150cm\(^{3}\) of water into the beaker.
ii. Record the volume v of the water in the beaker
iii. Calculate the mass m of the water, given that m = pv and; p = 1gcm\(_{-3}\).
iv. Measure and record the initial temperature \(\theta_{0}\) of the water in the beaker.
v. Hold the 50g mass with the pair of tongs in the flame of the bunsen burner for 2 minutes.
vi. Quickly transfer the 50g mass to water in the beaker.
vii. Stir gently and record the highest temperature \(\theta_{1}\), attained
viii. Evaluate \(\theta\) = (\(\theta_{1}\) – \(\theta_{0}\)).
ix. Empty the content of the beaker and repeat the procedures above for the values of v = 200cm\(^{3}\), 250cm\(^{3}\), 300cm\(^{3}\), and 350 cm\(^{3}\).
x. Tabulate your readings.
xi. Plot a graph with m on the vertical axis and \(\theta\) on the horizontal axis.
xii. Determine the slope, s, of the graph.
xiii. Evaluate k = \(\frac{50}{s}\).
xiv. State two precautions taken to obtain accurate results.
(b)i. Define heat capacity.
ii. An electric kettle rated 1.2kw is used to heat 800g of water initially at a temperature of 20 C. Neglecting heat losses, calculate the time taken for the kettle to heat the water to its boiling point. [Take the boiling point of water= 101 C specific heat capacity of water = 4200 Jkg’ K’1 (odv)
Explanation
| S/N | m/g | T/min | \(\theta\) = \(\theta_{1} - \theta_{0}\) |
| 1 | 150.0 | 2.0 | \(\theta\) = 88 - 34 = 56\(^{6}\) |
| 2 | 200.0 | 4.0 | \(\theta\) = 86 - 34 = 52 |
| 3 | 250.0 | 6.0 | \(\theta\) = 84 - 34 = 50 |
| 4 | 300.0 | 8.0 | \(\theta\) = 80 - 34 = 46 |
| 5 | 350.0 | 10.0 | \(\theta\) = 76 - 34 = 42 |
Initial temperature of water = 34°
Slope s = \(\frac{\bigtriangleup {m}}{\bigtriangleup \theta}\)
= \(\frac{m_{2} - m_{1}}{\theta_{2} -\theta_{1}}\)
= \(\frac{350 - 50}{62 - 42} = \frac{300}{20}\)
S = 150
Evaluate k = \(\frac{50}{S} = \frac{50}{150}\) = 0.333
Precautions;
- Avoided splashing of water
- Stirred continuously (for even distribution of heat).
- Avoided parallax error on the thermometer/measuring cylinder
- Repeated readings shown on the table
- Ensured the heated mass was gently dropped into the beaker.
(b)i. Heat Capacity Is the quantity of heat required to raise the temperature of a substance.
ii. Pt = mc\(\theta\)
1200 x t = \(\frac{800}{1000}\) x 4200 (101 x 20)
1200t = 0.8 x 4200 x 81
t = \(\frac{0.8 \times 4200 \times 81}{1200}\)
t = \(\frac{272160}{1200}\)
t = 2260.8 secs
