Coffee Problem

Lab 01: Coffee Problem

Purpose of Experiment: To perform specific heat calculations and check those calculations using the virtual lab example.

Deliverables:

  • A screenshot of the correct answer and all calculations and explanations

Instructions:

For this lab assignment, you will need to read the instructions for the Metals Density Problem on the ChemCollective website. After you complete this reading, return to this assignment to read an example problem that will help you to complete the lab on the ChemCollective page.

Go to lab page: http://chemcollective.org/activities/autograded/115

To complete the lab, all calculations and an explanation of how you will make the coffee must be shown in the provided box below the virtual lab. Once the green check box is clicked and the lab shows you have a correct answer, take a screen shot and submit the screenshot of the lab for your grade.

Lab Assistance:

The following will help you to complete out the Coffee Problem lab.

All glassware used in this lab (even the pipets) must be insulated. Once the coffee and milk are selected, you must change the temperature to the initial temperature and insulate the glassware or it will quickly lose temperature.

Hint: the coffee is in an insulated travel mug, so no heat escapes. To insulate a piece of glassware in Virtual Lab, Mac-users should command-click (or open-apple click) on the beaker or flask; Windows users should right click on the beaker or flask. From the menu that appears, choose “Thermal Properties.” Check the box labeled “insulated from surroundings.” The temperature of the solution in that beaker or flask will remain constant.

All calculations and an explanation of how you will make the coffee must be shown in the provided box below the virtual lab. Once the green check box is clicked and the lab shows you have a correct answer, take a screen shot and submit the screenshot of the lab for your grade.

Example question and calculation:

You decided to make hot water for your favorite flavored tea drink. The water, after boiling, was at about 98 ˚C when you poured it over the tea bags. You now have 100 mL hot tea at 98 ˚C and want to dilute the tea and bring it to room temperature at about 25 ˚C. To make the tea to the correct temperature, you will add a portion of cold water at a temperature of 5 ˚C. How much cold water should you add to the hot tea water? (Hint: the density of tea and water is 1 g/mL and the specific heat of tea and water is 4.184 J/g∙˚C).

First convert the volume to mass using density:

100mL⋅1g1mL=100g100mL⋅1g1mL=100g

Next, use the following equation: q=m×C×ΔTq=m×C×∆T. This problem requires an endothermic and an exothermic reaction; therefore the equation is modified: q=−qq=−q. The cold water absorbs heat and is the endothermic reaction; therefore, the cold water portion is the qq. The tea temperature being brought down is releasing heat and therefore is the −q−q side of the equation. Now we can substitute the m×C×ΔTm×C×∆T for each qq, making sure to keep the signs of each qq.

(m×C×ΔT)=−(m×C×ΔT)(m×C×∆T)=−(m×C×∆T)

(m×C×(Tf−Ti))=−(m×C×(Tf−Ti))(m×C×(Tf−Ti))=−(m×C×(Tf−Ti))

(m×4.184Jg⋅℃×(25℃−5℃))=−(100g×4.184Jg⋅℃×(25℃−98℃))(m×4.184Jg⋅℃×(25℃−5℃))=−(100g×4.184Jg⋅℃×(25℃−98℃))

(m×4.184Jg⋅℃×(20℃))=−(100g×4.184Jg⋅℃×(−73℃))(m×4.184Jg⋅℃×(20℃))=−(100g×4.184Jg⋅℃×(−73℃))

(m×83.68Jg)=−(−30,543.2J)(m×83.68Jg)=−(−30,543.2J)

(m×83.68Jg)=30,543.2J(m×83.68Jg)=30,543.2J

m=30,543.2J83.68Jg=365gm=30,543.2J83.68Jg=365g

Convert the grams into mL with the density: 365g×1mL1g=365mL365g×1mL1g=365mL

Once you have completed the calculation, check you work by doing the virtual lab as explained.

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