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Midterm Exam Prep - Flashcards

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Class:CHEM 1045 - General Chemistry Lab
Subject:Chemistry
University:Virginia Polytechnic Institute And State University
Term:Fall 2010
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How can you determine the amount of heat (q) that is lost of gained by a substance? use this equation: q= (mass x specific heat capacity x deltaT)
Correction factor (CF) How was it used in the Measurement lab? CF= temp probe measurement -- thermometer measurement In the Measurement lab, recall the fact that we used the temp probe to calibrate the thermometer, by subtracting the temperature that we got from both instruments, then applying the value to all of our thermometer calculations.
Apply a correction factor to the following data: A temperature probe and thermometer are used to measure the temperature of H2O. The temp probe gives a reading of 25.6 deg C and the thermometer gives a reading of 26.8. Calculate the CF, then apply it to the following data: 1)temp from probe=76.14 deg C temp from thermom.=80.4 deg C 2)temp from probe=81.56 deg C temp from thermom.=78.2 deg C CF= 26.8 deg C--- 25.6 deg C CF=1.2 deg C (this means the thermometer readings are 1.2 deg C too high) 1)temp from probe=76.14 deg C temp from thermom= 80.4--1.2= 79.2 deg C 2)temp from probe=81.56 deg C temp from thermom=78.2--1.2= 77.0 deg C
Law of Conservation of Energy The heat that is lost by a substance equals the heat that is gained by the other substance (ie: the heat lost by hot H2O=the heat gained by the cold H2O)
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T-hot Initial temp of H2O
How would you interpolate the density of H2O at 36.7 deg C based on the density table in Appendix E? 1) Choose 2 temperature from the chart that 36.7 is between. Lets use 35 deg C and 40 deg C. Find the difference of these temperature and the density. 35 deg C------->40 deg C = 5 deg range .9941 deg C----->.9922 deg C=.0019 density range 2) Of the 2 temperatures, which one is closest to 36.7 deg C? YEPP! 35 deg C is. NOW subtract. 36.7--35=1.7 deg C .9941--(1.7 x .0019 / 5)= .9935 g mL
How many sig figs does a reading from the thermometer have to have? 3 sig figs
Accuracy vs Precision Accuracy=tells how close your measurement is to the true value (Accuracy=measured value -- true value) Precision= tells how close your repeated measurements are to each other
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Systematic uncertainty/error means that there is a definite cause that makes your data wrong This error occurs because the system is all f#ck%d up. (ie: incorrectly labeled graduated cylinder)
Density of water depends on its____________. Temperature Recall that the table in Appendix E gives you the density of H2O at various temperatures.
Random uncertainty/error Random uncertainty/error affects the precision of your data by causing to scatter. It is caused by uncontrollable factors that are apart of all of your measurements.
Experimental uncertainty/error The overall uncertainty of your measurements Experimental uncertainty/error= (Random Uncertainty + Systematic Uncertainty)
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What affects the rate at which H2O cools? The container that the H2O is in
Buret A buret is a vertical cylindrical device that has volumetric markings on it that allows the operator to add a fixed volume of a solvent (in the measurement lab, recall that we used a buret to add 10mL of "cold" water to the cup of hot water, every 5 minutes.)
How many sig figs can a measurement from the temperature probe have? 4 sig figs
T-cold Temperature of cold H2O
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T-final Temp of H2O in cup after adding cold H2O
How do you know many sig figs to include in a mass calculation? Mass must have the same amount of sig figs as volume
gH mass of hot water
gC mass of cold water
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deltaT-hot vs delta T-cold deltaT-hot= (T-hot)---(T-final) deltaT-cold=(T-final)---(T-cold)
Specific heat capacity The amount of heat it takes to raise the temp of one gram of substance by one degree celsius
Specific heat capacity of H2O The specific heat capacity of water is a constant.
Heat (q) The amount of heat energy (q) gained or lost by a substance is equal to the mass of the substance (m) multiplied by its specific heat capacity multiplied by the change in temperature (deltaT) q= mass x specific heat capacity x deltaT
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 How can you determine the amount of heat (q) that is lost of gained by a substance?use this equation:

q= (mass x specific heat capacity x deltaT)
 Correction factor (CF) How was it used in the Measurement lab?CF= temp probe measurement -- thermometer measurement

In the Measurement lab, recall the fact that we used the temp probe to calibrate the thermometer, by subtracting the temperature that we got from both instruments, then applying the value to all of our thermometer calculations.
 Apply a correction factor to the following data: A temperature probe and thermometer are used to measure the temperature of H2O. The temp probe gives a reading of 25.6 deg C and the thermometer gives a reading of 26.8. Calculate the CF, then apply it to the following data: 1)temp from probe=76.14 deg C temp from thermom.=80.4 deg C 2)temp from probe=81.56 deg C temp from thermom.=78.2 deg C CF= 26.8 deg C--- 25.6 deg C
CF=1.2 deg C (this means the thermometer readings are 1.2 deg C too high)

1)temp from probe=76.14 deg C
temp from thermom= 80.4--1.2= 79.2 deg C

2)temp from probe=81.56 deg C
temp from thermom=78.2--1.2= 77.0 deg C
 Law of Conservation of EnergyThe heat that is lost by a substance equals the heat that is gained by the other substance

(ie: the heat lost by hot H2O=the heat gained by the cold H2O)
 T-hotInitial temp of H2O
 How would you interpolate the density of H2O at 36.7 deg C based on the density table in Appendix E?1) Choose 2 temperature from the chart that 36.7 is between. Lets use 35 deg C and 40 deg C. Find the difference of these temperature and the density.
35 deg C------->40 deg C = 5 deg range
.9941 deg C----->.9922 deg C=.0019 density range
2) Of the 2 temperatures, which one is closest to 36.7 deg C? YEPP! 35 deg C is. NOW subtract. 36.7--35=1.7 deg C

.9941--(1.7 x .0019 / 5)= .9935 g mL
 How many sig figs does a reading from the thermometer have to have?3 sig figs
 Accuracy vs PrecisionAccuracy=tells how close your measurement is to the true value
(Accuracy=measured value -- true value)

Precision= tells how close your repeated measurements are to each other
 Systematic uncertainty/errormeans that there is a definite cause that makes your data wrong

This error occurs because the system is all f#ck%d up. (ie: incorrectly labeled graduated cylinder)
 Density of water depends on its____________.Temperature

Recall that the table in Appendix E gives you the density of H2O at various temperatures.
 Random uncertainty/errorRandom uncertainty/error affects the precision of your data by causing to scatter. It is caused by uncontrollable factors that are apart of all of your measurements.
 Experimental uncertainty/errorThe overall uncertainty of your measurements

Experimental uncertainty/error= (Random Uncertainty + Systematic Uncertainty)
 What affects the rate at which H2O cools?The container that the H2O is in
 BuretA buret is a vertical cylindrical device that has volumetric markings on it that allows the operator to add a fixed volume of a solvent

(in the measurement lab, recall that we used a buret to add 10mL of "cold" water to the cup of hot water, every 5 minutes.)
 How many sig figs can a measurement from the temperature probe have?4 sig figs
 T-coldTemperature of cold H2O
 T-finalTemp of H2O in cup after adding cold H2O
 How do you know many sig figs to include in a mass calculation?Mass must have the same amount of sig figs as volume
 gHmass of hot water
 gC mass of cold water
 deltaT-hot vs delta T-colddeltaT-hot= (T-hot)---(T-final)

deltaT-cold=(T-final)---(T-cold)
 Specific heat capacityThe amount of heat it takes to raise the temp of one gram of substance by one degree celsius
 Specific heat capacity of H2OThe specific heat capacity of water is a constant.
 Heat (q)The amount of heat energy (q) gained or lost by a substance is equal to the mass of the substance (m) multiplied by its specific heat capacity multiplied by the change in temperature (deltaT)

q= mass x specific heat capacity x deltaT
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