Lab Procedures and Techniques
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Transcript of Lab Procedures and Techniques
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Lab Procedures and Techniques
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Calorimetry
• Calorimetry is used to determine the heat released or absorbed in a chemical reaction. A calorimeter can determine the heat of a solution reaction at constant pressure
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Techniques:
• Use a double Styrofoam cup with a plastic top and hole for the thermometer
• Determine the change in temperature accurately
• Measure solution volumes precisely• Start with a dry calorimeter
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Formulas
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Information to know about calorimetry:
• Heat capacity (C) = the amount of heat needed to raise the temperature of an object by one degree Celsius or Kelvin, J/°C or J/K.
• The heat capacity of 1 mol of a substance is called its molar heat capacity (Joules per mole per degree) J/mol°C or J/molK.
• Specific heat, c, also known as specific heat capacity, is defined as the amount of heat necessary to raise the temperature of 1.00 g of a substance by one degree. Units are (joules per gram per degree), J/g°C or J/gK.
• You often use the specific heat capacity in analyzing gathered data then convert to molar heat capacity.
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Assumptions often made during calorimetry:
• (Be able to answer error analysis questions about each assumption below)
• The density of dilute solutions is the same for water. D= 1.0 g/mL
• The specific heat of the solutions is the same as that for water. c = 4.184 J/goC
• The solutions react in their Stoichiometric amounts.
• There is no loss of heat to the surroundings.
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The energy change associated with the process in which a solute dissolves in a solvent is called the Heat of Solution.
• This energy change is the net result of two processes, the energy required to break the solute-solute bonds, called the crystal lattice energy, and the energy released when the solute particles bond with the solvent molecules, called the heat of hydration.
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Heat of Solution
• Calculate the number of moles of your assigned solid dissolved in each of your trials.
)/()(molegramssofsoluteFormulamas
gramsteMassofsoluuteMolesofsol
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Step One
• Change in energy of the water, • Δq1 = total mass of material x specific
heat (4.18 joules/gC) x Δt
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If they give you a calorimeter constant
• Calculate the energy absorbed or released by the calorimeter from the calorimeter constant obtained in an earlier experiment and the change in the temperature of the water. Where
• Change in energy of the calorimeter, Δq2 = calorimeter constant x Δt
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Total Heat
• Calculate the total energy absorbed or released by the solution process from the sum of the change in energy of the water plus the change in energy of the calorimeter,
• Total energy, Δqt = Δq1 (Aqueous Solution) + Δq2 (calorimeter)
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• Calculate the heat of solution from the number of moles of salt dissolved (Q1) and the amount of heat liberated or absorbed when the salt dissolves (Q2c).
• Convert this value from joules/mol to kilojoules/mole. NOTE: 1000 joules = 1
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Calculating Molar Heat of Reaction
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Titration
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Technique
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Technique continued
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Calculation based on Stoichiometry
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Calculations
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Example Titration Curve
Equivalence Point
One-half the equivalence point
Point at which pKa = pH
4.8
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Gravimetric Analysis
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Chloride Analysis
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Determining Molar Mass
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Using Freezing Point Depression
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Data
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Graphical Data
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Using Titration
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MW of Volatile Liquid
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Spectrometric Analysis
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