Identifying Unknown Salts with Calorimetry

Written by Charisa

Abstract

The purpose of this lab is to identify the unknown salts using the change in temperature to calculate heat realeased. With the given “q” values for all three identiies of the unknowns, one can compare the calculated heat of the reaction to the given value to identify the salt. The unknowns chosen were unknown “C” for trials 1 and 2, and unknwon “A” for trials 3 and 4. The initial temperature was taken before the salt was added, and after the salt had dissolved for 10 minutes in 30 second intervals.

Procedure

Bluedoor. Endothermic Enthalpy – Calorimetry. Bluedoor Labs. 29 Oct. 2013. www.bluedoorlabs.com/online_manual

Data Unknown “C”

Trial 1– mass = 5.061g Trial 2–Mass – 5.033g

Trial 1 Temp Change = -0.4 Degrees C Trial 2 Temp Change = -0.6 Degrees C ____________________________________________________________________________________ Unknown “A”
Trial 3–mass = 5.023g Trial 4–mass = 5.016

Trial 3 temp Change = 7.9 Degrees C Trial 4 Temp Change = 7.9 Degrees C

Calculations

To calculate the heat released by reaction: Unknown A

q = m*C*(Change in temp) where:
m = average mass of salt in g + mass of water
C = specific heat of water (4.186J/g* C) *(Av. Change in temp

q = 85.047g* 4.186*(-.5) q = -178 J

Unknown C
q = 85.020g* (4.186J/g*c)*(7.9) q = 364J

To calculate Heat of SOlution

Based on the calculated q values and the chart of Heat of Solution, it can be determined that Unknown A LiCl

Based on the appearance, and left over values in the chart of the head of solution, it can be determined that unknown C is NaCl

Conclusion

In conclusion, this experiment was a success in showing the different amounts of heat released based on the type of salt added to the water. As the salt crystals dissolved in the water, it released energy from the bonds breaking, which contributed to the temperature raising based on what type of salt was added. Table salt only changed the temperature of the water slightly, while the LiCl caused the temperature of the water to jump, then slowly decrease. The overal temperature change was 7.9 degrees, versus a cooldown of .4 degrees for the NaCl. As far as errors are concerned, the measurements may have been taken before the salt was completely disolved, casuing the temperature to change. To combat this error, one might need to employ a different method of stirring to make sure everything is disolved.