Enthalpy of Neutralization J. Smith M. Smith CHEM 1290-xx 10-31-06 TA
Purpose: The purpose of the experiment is to determine the calorimeter constant for the calorimeter holding a specific solution based on the data of heat lost and heat gained. The purpose is to also be able to determine the enthalpy of neutralization for the reaction of a strong acid (phosphoric acid) and a strong base (sodium hydroxide). Experimental: Materials: The materials needed for this lab included; 2 large beakers, a Calorimeter Styrofoam cup, computer, stirring rod, 2 thermometers, Logger Program, and Probes volumetric pipet. Sodium hydroxide (NaOH) (corrosive and toxic), and phosphoric acid (H3PO4) (corrosive and toxic) were used. Procedure:
The calorimeter was set up as shown in Figure 1 above. A Styrofoam cup was used to line the beaker. Cold distilled water (50 mL) was put into the cup along with a thermometer. Continue writing your procedure (what you actually did, not what you were supposed to do) in paragraph format. The list format below is to show an example of how to switch from directions in your lab manual to the formal lab report) 1. Set up the Calorimeter as in Figure 1. 2. Use Styrofoam cup as a liner in the beaker.
measure 50.0 ml cold distilled H2O in cup place thermometer inside
3. Place 50.0 ml distilled warm water (15-20 degrees above room temp.) in beaker 4. Measure and record initial temperature for both hot and cold for 2-3 minutes a. b. quickly lift lid and add hot water to the cold recover, stir and note mixing time
5. Record temperature every 30 seconds for 20 minutes or until temperature reaches its max. 6. Empty and dry all equipment 7. Place 50.0 ml NaOH in Styrofoam cup 8. Place 50.0 ml assigned acid (phosphorc acid) in beaker 9. Repeat steps 4-6 10. 11. Prepare computer apparatus Set the vertical axis for temperature and the horizontal for time
12. Connect one probe to CH1 and the other to CH2 13. Set up 2 large beakers a. hot bath should be at 35-40 degrees Celsius b. 2 nd bath at 0 degrees celcius
c. place thermometer and both probes in warm bath d. then record temp. and place in cold bath and record temp. e. do this for both probes 14. Calibrate program 15. Close window and select direct connect 16. Place Styrofoam cup in calorimeter a. Measure and transfer 50.0 ml NaOH to it 17. Place probe 1 and stirring rod in lid and
lower 18. Place probe 2 in beaker with acid 19. Click collect 20. Add acid to calorimeter a. stir continuously b. keep time like before c. stop collecting after constant cooling occurs 21. Fit appropriate lines to graph 22. Rinse and dry ALL equipment
Data: The following table represents the measured temperatures involving the warm and cold water measurements.
Discussion: Energy is never lost, but transferred. In many cases when substances react the energy is transferred into heat. The study of changes of heat as well as the transfer of energy into heat is known as thermochemistry. Thermochemistry can be easily studied with the use of calorimeters. These well insulated containers help observations to be more clear, easier to see and simpler to understand. The calorimeter represents the chemical system, the reactants are contained in the Styrofoam cup and the surroundings include the immediate air, thermometer and rod stirrer. In this lab the initial and final temperatures of the system were measured and the change in temperature was found by finding the difference of the two. When substances react in a calorimeter there is a change in enthalpies which also affects the temperature of the
solution. Enthalpy is the heat transferred whether it be from reactants to products or vise versa. If the energy, or in this case heat, is transferred to the products the reaction is said to be exothermic. If the heat is transferred...
References: 1 Chem. 1290 Laboratory Manual: Enthalpy of Neutralization. 2006. Thomson Brooks/Cole. Belmont, CA.
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