Agata Łuszczyńska II LO. im. Stefana Batorego

Coffee and milk

D		DCP		CE
1 asp		1 asp		1 asp
2 asp		2 asp		2 asp
3 asp		3 asp		3 asp

Design:

Specific heat capacity is the measure of the heat energy required to increase the temperature of a unit quantity of a substance by a certain temperature interval.

If something has a greater heat capacity then it will take longer to lower it's temperature.

In this experiment my aim was to determine how the temperature of the milk will affect the time of cooling down the coffee to 50°C.

I assume that the time will fall down uniformly.

As coffee and milk consist of mostly water, in my later calculations I will use the specific heat capacity of water - 4200 J kg⁻¹ K⁻¹. So I will substitute water as coffee as it is easier to manage.

Variables:

Dependent:	Independent:	Controlled:
Temperature of milk (20°C, 15°C, 10°C and 5°C)	Time of cooling down to 50°C	Temperature of coffee (100°C) Volume of coffee (100 ml) Volume of milk (20 ml) Temperature of the surroundings

Apparatus:

• Electric kettle

• A cup made out of glass

• Thermometer (0-100°C ± 0.5°C)

• Refrigerator

• Stopper (±0.1s)

Procedure of data collection:

For the experiment I decided to use a 2.0 % milk as it is most commonly used. Before the start of the experiment I have to cool down the milk in a refrigerator to temperatures 20°C, 15°C, 10°C and 5°C.

Then I would boil water in an electric kettle and pour it into a cup. Then I would add milk and quickly put in the thermometer. At the same time as I started measuring the temperature I would start the stopper to measure the time in which the temperature will fall to 50°C. I will repeat this with all of the different temperatures of milk and repeat all of the experiment twice to reassure myself with the results.

The best way to present the outcome of this experiment will be a table and a diagram to illustrate the table and more clearly see the changes.

1. Table

Temperature of milk [± 0.5°C]	Time of cooling down [±0.1s]
20
15
10
5

2. Diagram

The chart would have time on the x-axis and temperature on the y-axis

Data Collection:

1. Raw data:

Temperature of milk [± 0.5°C]	Time of cooling down [±0.1s]
		1^st measurement	2^nd measurement
20.0	630.0		616.6
15.0	569.3		542.0
10.0	436.0		387.2
5.00	247.5		264.9

2. Data processing and presentation:




We can see from the diagram that the changes of time are irregular.

At first the time is only shorter by 60.7s and 74.6s while the next is 133.3s and 154.8s and the last ones ar 188.5s and 122.3s.

So my assumption that with a regular fall in the temperature the time will also fall regularly is false.

Conclusion and evaluation:

There are many ways in which the results could be affected to present false data. I assumed that no heat would be exchanged to the surroundings, the flow of energy could be only between the liquids, but the glass cup does not have good insulating characteristics and so the flow of energy between the surroundings could easily happen. Also the electric kettle could heat the water to different temperatures each time so the change of temperature could be different each time. Also there could be imperfections in reading the value from the thermometer and imperfection in starting/stopping the stopper.

To improve this experiment firstly I should take the measurements in a well-insulated container like a thermos.

Also I shout heat water in a normal kettle (on a gas stove) and measure the temperature as the water heats up.

To erase temperature reading errors I should take a more legible thermometer or with a more detailed scale.

To limit the time errors I should make sure that I start and stop at the exact moment the measuring starts and stops.

To increase the overall accuracy of the experiment I should repeat the measurements at least four times.

---