Calorimetry and the Enthalpies of Neutralization - Experiment

Purpose
 To demonstrate how to measure the energy changes associated with various   neutralization reactions, and how to measure the heat capacity of a calorimeter.


Acids and Bases

nAcid:  donates H+ ions to the aqueous solution in which it is dissolved

nBase: donates OH- ions to the aqueous solution or accepts H+ ions from the aqueous solution in which it is dissolved

nStrong acid: dissociates completely in aqueous solution

nStrong base: dissociates completely in aqueous solution

Neutralization Reactions

nStrong acids and strong bases react to produce a salt and water; a solution with an overall pH of 7 under ideal conditions (neutralization reaction):

HCl(aq) + KOH(aq) ® KCl(aq) + H2O(l) + heat

nNeutralization reactions are exothermic, thus liberating heat to the surroundings.

Calorimetry

nCalorimeters measure the heat associated with a chemical reaction.

nWe have to account for the heat transferred from the solution to the calorimeter so we can add it back in. For this reason we perform a calibration on the calorimeter prior to running the experiment on the acid / base reaction.

nHeat (q) is the transfer of energy between two objects; always from hot to cold. The amount of heat transferred depends on the mass of the object.

nTemperature reflects the random motion of particles in an object and is independent of mass.

nYou will be working with both heat and temperature today.

Procedure

nCalibrate your IC probe.

nCalibrate your calorimeter to find CCAL.

nUse the sample calculations on pp. 212 and 213 to help you with your calculations.

nDetermine the energy transfer involved with your neutralization reaction.

nUse the sample calculations on pp. 214 and 215 to help you with your calculations.

Safety Concerns – HCl (0.2N)

nIngestion Hazards:

nMay cause gastrointestinal disturbances

nEye Contact:

nMay cause irritation, redness and pain

Safety Concerns – HNO3 (1.0N)

nEye Contact:

nCorrosive.  Irritating and damaging to eyes.  Burns and permanent eye damage.

nSkin Contact:

nCorrosive.  Redness, pain and severe skin burns.  Ulcers may form and skin stains.

nInhalation:

nCorrosive.  Breathing difficulties can lead to pneumonia and pulmonary edema, which may be fatal.  Coughing, choking, irritation of nose, throat, and respiratory tract.

nIngestion:

nCorrosive.  Pain and burns of the mouth, throat, esophagus and gastrointestinal tract.  

Safety Concerns – NaOH (0.2N)

nWhy do you not want to inhale NaOH?

nRespiratory irritant

nWhy do you not want to drink NaOH?

nNaOH is corrosive!  Will cause burns all the way down.

nWhat happens when you get NaOH on your skin?

nSevere burns and scarring may occur.

nWhat happens when you get NaOH in your eyes?

nYou could go blind…and it hurts!

Safety Concerns – Potassium Hydroxide

nEye Contact:

nIrritant and corrosive.  Tearing, redness, pain and impaired vision

nSkin Contact:

nIrritant and corrosive.  Soreness, redness, destruction of skin

nInhalation:

nIrritant.  May cause serious burns.

nIngestion:

nToxic.  Corrosive to mucous membranes.  May cause perforation of the esophagus and stomach.  Abdominal pain, nausea, vomiting, general gastro-intestinal upset.

Waste

nAcid and base waste must be added together prior to disposal down the sink.  Flush with a lot of water.

Neutralized acid / base solutions may go down the sink.