Thermodynamics
Mr. Miller

Lab 7: Specific Heat – Formal Write-Up

Introduction:
We know that different materials heat more or less quickly depending upon their heat conductivities.  But what will happen if you take exactly equal amounts of different substances and apply the exact same amount of heat to each?  What if you have twice as much material?  In this lab we will find out.

Materials:
Hot Plate
Beakers
Graduated cylinders
Oil (vegetable)
Water
Timer (accurate to the second)
Thermometer

Procedure:
Get into your assigned lab groups.  Send one person to collect all the materials.

Using the graduated cylinder, measure into your beakers the water and oil as exactly as you can: you will be heating 75ml of water, 150ml of water, 225ml of water, 75ml of oil, and 150ml of oil.  You may need to re-use beakers if we don’t have enough.  In this case, do your three water-trials first, then do the two oil-trials (see below).  DO NOT put oil in a beaker and then use it for water without thoroughly cleaning it out first.

For each trial, you will first place the CLEANED thermometer in the liquid and wait for its temperature to stabilize. Turn your hot plate to its highest temperature.  NEVER MOVE THE BURNER, OR TURN ITS KNOB, even between trials – this gives consistent results by continuously providing the same amount of heat.  Wait 4 minutes for the hot plate to heat up to maximum temperature.

Get ready to use the second hand of your watch or the clock at the back of the room, and carefully place a beaker on top of the hot plate.  The temperature of the liquid at time = 0 seconds is the initial starting temperature.

You will be taking temperature measurements every 10 seconds for 180 seconds (three minutes), and no longer – record these results below.  Be very careful not to break the thermometer.  Once you are finished, carefully remove the beaker with the tongs.  If the substance in the beaker is water, pour it into the sink.  If it is oil, set it aside in a safe place and let it cool (or pour it into another beaker) – use the other beakers to continue the experiment.  Once you are done and all your oil is cooled down, pour it back into the original bottles using a funnel.  DO NOT POUR THE OIL DOWN THE SINK.

Repeat the above heating and measuring procedure for each trial – you will have five total trials.  Everyone in the lab group should record the temperatures in the chart below in degrees Celsius.

 0s 10s 20s 30s 40s 50s 60s 70s 80s 90s 100s 110s 120s 130s 140s 150s 160s 170s 180s Water 75ml Water 150ml Water 225ml Oil 75ml Oil 150ml

Make note of any other observations here (sights, sounds, smells):

Analysis:
Once you have all the data above, you will need to put the data into a single graph, in order to check for patterns.
On a piece of graph paper, create a graph that contains all of the above data.  Color code each row above, and plot your points in the same color.  Put time on the x-axis and temperature on the y-axis.  Your graph needs to fill the entire sheet (and therefore should be made in landscape format rather than portrait).  You must have a title on the graph, and you must put in a legend or key showing which colored points belong to which ‘data set’ (or row: in this case, for example, “Water, 75ml”).

Now you will look for a pattern or trend in a particular part of the data, for which you can draw in a “trendline” or a “best-fit curve”.  A best-fit curve or trendline expresses in a single gesture the nature of the data and allows you to extrapolate beyond the data set you obtained observationally.  This is NOT, I repeat, NOT, a connect-the dots line.  A trendline is like an average of all the data points and is a smooth curve or line.

Things to include in the Analysis/Conclusions section of your MLB write-up:
Compare the graphs made by each row of data.  What kinds of conclusions can you draw from this data?

Can you say anything in general about the nature of substances given the fact that the same amount of heat was applied to each beaker?

What makes one liquid heat up more quickly than the other?  Can you form a hypothesis that is testable with a new experiment?

What were the probable sources of error in this experiment?

What could be done to improve this experiment?

What do you think would happen if you repeated the experiment but with a flame twice as hot?

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