Purpose: To measure the heats of reaction for three related exothermic reactions and to verify Hess’s Law of Heat Summation.
NaOH(s) ( Na+(aq) + OH-(aq)ΔH = -10.6kcal/mol
NaOH(s) + H+(aq) + Cl-(aq) ( H2O + Na+(aq) + Cl-(aq) ΔH = -23.9kcal/mol Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) ( H2O + Na+(aq) + Cl-(aq)ΔH = -13.3kcal/mol
Background: Energy changes occur in all chemical reactions; energy is either absorbed or released. If energy is released in the form of heat, the reaction is called exothermic. If energy is absorbed, the reaction is called endothermic.
Materials: spatulasodium hydroxide pellets (NaOH)
1 Styrofoam cup1.0 M sodium hydroxide (NaOH)
1 100-mL graduated cylinder0.5M Hydrochloric acid (HCl)
1 400-mL beaker1.0 M hydrochloric acid (HCl)
1 50-mL beakerdistilled water
a. Measure 100mL of distilled water into a plastic-foam cup. Place the cup inside a 400mL beaker for support. This assembly, together with a thermometer, will serve as your calorimeter. b. Measure and record the mass of a 50mL beaker to the nearest 0.01g. CAUTION: NaOH is extremely corrosive. Using a spatula, add as close to 2.00g as possible of sodium hydroxide pellets to the beaker. Measure and record the combined mass of the beaker and sodium hydroxide to the nearest 0.01g. (Do this operation as quickly as possible to avoid error due to absorption of water by the NaOH.) c. Measure and record the temperature of the water in the foam cup to the nearest 0.5ºC. Add the NaOH pellets to the water in the calorimeter. Stir the mixture gently with the thermometer until all the solid has dissolved. CAUTION: Hold the thermometer with your hand at all times. Record the highest temperature reached during the reaction.
a. CAUTION: Low-concentration hydrochloric acid can irritate your skin. Measure...