Question

A student collected the following data to determine the specific heat of a metal sample.  50.0 g of metal were transferred from boiling water into a calorimeter containing 100 g of H₂O at 22.3^oC.  The temperature of the water rose to 23.5^oC.  Calculate the specific heat of the metal.

Enter your answer with 3 significant figures.

Based on the calculated specific heat, what is the most likely identity of the metal in the previous problem? Give your answer as the elemental symbol (e.g. sodium as Na)

QUESTION 12

Ethylene glycol is produced according to the following equation

                        C₂H₄O  +  H₂O  → HOCH₂CH₂OH

Use Hess’s law to obtain the enthalpy change in kJ for this reaction from the following enthalpy changes

2 C₂H₄O  +  5 O₂  → 4 CO₂  +  4 H₂O  ; ΔH = -2612.2 kJ

HOCH₂CH₂OH  + 5/2 O₂ → 2 CO₂  +  3 H₂O  ; ΔH = -1189.8 kJ

QUESTION 13

A student dissolved 10.5 g of NH₄Cl in 40 mL of water.  The temperature of the water changed from 22.5^oC to 5.1^oC.  Calculate the enthalpy of hydration of ammonium chloride in J/mol.   

QUESTION 14

A student completed the Kool-Aid Spectroscopy lab and obtained the following equation after plotting concentration vs. Absorbance.

y = 1.74 x  +  0.0096

What is the concentration of a sample with an absorbance of 0.44?

QUESTION 15

A galvanic cell is made using Pb(s)/Pb²⁺(1.0M) and Al(s)/Al³⁺(1.0M).   The cell gives a positive reading when Pb is the positive electrode. What is the correct cell notation for this system?

Enter Pb for lead electrode, Pb2+ for the lead solution, Al for the aluminun electrode and Al3+ for the aluminum solution.

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2 points   

QUESTION 16

What is the predicted cell potential in volts for the cell in the previous problem? Give an answer to two decimal places.

QUESTION 17

A Cu/Cu2+ electrolysis cell was used to determine Avogadro's Number. The copper cathode increased in mass by 0.049 grams after running the cell for 476 seconds at 0.47 amps. What experimental value for Avogadro's Number is determined from this data? The electron charge = 1.6x10^-19 C/e^-  Report your answer as _____x10²³ with 2 significant figures.

Answer 1

11) heat lost by metal = heat gained by water

m metal *S metal *DT1 = mwater*swater*DT1

DT2 = Tinitial - Tfinal = 100 - 23.5

DT2 = Tfinal - Tinitial = 23.5 - 22.3

50 * s*(100 - 23.5) = 100*4.184*(23.5-22.3)

smetal = specificheat of metal = 0.131 j/g.c

12)

( 2 C2H4O + 5 O2 ---> 4 CO2 + 4 H2O )*1/2

2 CO2 + 3 H2O ---> HOCH2CH2OH + 5/2 O2

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C2H4O + H2O → HOCH2CH2OH   DHrxn = (-2612.2*1/2)+1189.8 = -116.3 kj

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13) heat released (q) = m*s*DT

                      = 50.5*4.184*(22.5-5.1) = 3.68 kj

   no of mole of NH4Cl = 10.5/53.5 = 0.196 mole

enthalpy of hydration of ammonium chloride (DHhyd) = q/n

     = 3.68/0.196 = 18.77 kj/mol

    = 18770 j/mol