Heat of Solution Lab - Needham Public Schools解決方案實(shí)驗(yàn)室尼達(dá)姆公立學(xué)校熱

1、.Heat of Solution (Dissolving) LabName _Date _ Period _Purpose: To measure the enthalpy/heat flow as different solutes dissolve in solution and determine the molar heat of solution.Materials: goggles and aprongraduated cylinderdistilled waterfoam cup calorimeterthermometerbalancestirring rodNH4NO3Ca

2、Cl2Procedure: 1. Put on goggles and lab apron. Measure 100.0 mL of water at room temperature and pour it into the foam calorimeter cup. Record the mass of the water by recalling that the density of water is 1g/mL. Record the temperature of the water in the data table to the nearest 0.1°C. Do no

3、t remove thermometer from the cup, but be careful that it does not tip over. Using your laboratory balance, measure out 8-10 grams of ammonium nitrate on a plastic tray. Record the mass to the nearest 0.001 g. Without removing the thermometer from the cup, shake the NH4NO3 from the paper into the wa

4、ter and stir gently with the stirring rod until the solid is dissolved. CAUTION: Both of the solutions in the lab are irritating to the skin. Avoid contact with them.2. Make sure that the bulb of the thermometer is fully immersed in the liquid. If the temperature rises, record the highest temperatur

5、e reached. If the temperature falls, record the lowest temperature reached.3. Dispose of the solution by pouring it down the drain, followed by plenty of water. Rinse the cup, dry and return it and the thermometer to the lab bench. 4. Repeat steps 2-5 using calcium chloride.Observations:Data TableSo

6、luteSolute Mass (g)Mass of Water (g)Mass of Solution (g)Initial T (°C)Final T (°C)(+/-) DT (°C)Exothermic or EndothermicNH4NO3CaCl2Calculations for Molar Enthalpy (repeat for each solute: NH4NO3 and CaCl2)1. Calculate the change in temperature. DT = Tf - Ti 2. Calculate the heat absor

7、bed or released by the solution. The specific heat of water is 4.184J/g°C.qsurroundings = (mass of the solution) x (DT of the water) x (specific heat of the water)3. How much heat was released/absorbed (circle one) from/into the reaction? (qreaction = -qsurroundings)qreaction = 4. Using the per

8、iodic table, calculate the molar mass of the solute.5. How many moles of the solute were used in the reaction (grams à moles)?6. Calculate the molar heat of solution (DH) in (+/-) kJ/mol for the solute from the formula:H = Molar heat of solution = kJ / mol7. Calculate the percent error of your

9、experimental value. The accepted value for DH for NH4NO3 is +25.7 kJ/mol.The accepted value for DH for CaCl2 is 81.3 kJ/mol.Critical Thinking: Analysis and Conclusions1. When sodium chloride dissolves in water, the ions dissociate. The equation for this reaction is NaCl(s) ® Na+(aq) + Cl-(aq) W

10、rite similar ionic equations to show the dissociation in water of each of the solutes used in the investigation._2. Which reaction was exothermic? Which was endothermic? _3. Rewrite each of the ionic equations from Question 1 showing the molar heat of solution as a reactant or a product. _4. When th

11、e reactants get colder in an endothermic reaction, what has happened to the heat energy?_energy transformation_5. Is the change in enthalpy positive or negative for an exothermic reaction? Explain. _6. Suggest two uses for these solution reactions in sports injuries or camping. _7. Which solids from this investigation could be used in each of your answers in th