Thickness of Zinc in Galvanized Iron
January 30, 2007
Zinc Thickness in Galvanized Iron
Pre-lab Questions:
1) What is meant by corrosion of metals?
2) What is galvanized metal?
3) How will the thickness of the zinc coating be determined in this experiment?
4) What precautions must be taken in performing this experiment and why?
Procedures:
1) Put on your goggles and lab apron. Determine the mass of a piece of galvanized iron and record in your data table.
2) Measure the length and width of the galvanized iron and record these values in your data table.
3) Put on gloves. Work in the fume hood. Place the galvanized iron in the 250ml beaker and cover with 30ml of 6.o molar HCl. (Caution HCl is highly corrosive and will give off hydrogen chloride gas!) When the rapid evolution of gas stops, add water to the beaker and then pour the liquid in the beaker into the waste container provided. Rinse the remaining metal with water and dry thoroughly.
4) Determine the mass of the remaining metal and record it.
5) Clean up your work area and wash your hands before leaving the laboratory.
Data Table:
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Mass of galvanized iron (g) |
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Mass of remaining iron (g) |
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Mass of zinc (g) |
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Length of metal strip (cm) |
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Width of metal strip (cm) |
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Calculations:
1) Find the area of the iron covered by zinc. (remember that the strip has two sides.)
2) Find the mass of the zinc coating.
3) Given the density of zinc as 7.14 g/cm3, find the volume of zinc.
4) Find the thickness of the zinc coating.
5) Given that the thickness of a zinc atom is 2.66X10-8 cm, find the thickness of the coating in atoms.
6) How many moles of zinc are in the coating?
Include in your conclusion:
1) The balanced equation for the reaction of zinc with hydrochloric acid.
2) How could you tell when the zinc fully reacted with the zinc coating?
3) Sources of error in the lab.
4) What does the thickness of the zinc coating tell you about the effectiveness of zinc in protecting iron?
5) Improvements to the lab?
Energy in Stoichiometry
January 10, 2007
Endothermic Vs. Exothermic Laboratory
Prelab Questions:
1) What is the difference between heat and temperature?
2) When the reactants get colder in an endothermic reaction, what happened to the heat?
3) On which side of a chemical equation would energy appear in an exothermic reaction? In an endothermic reaction?
Procedures:
1) Measure out 50ml of water at room temperature and pour it into the Styrofoam cups (two nestled together) Record the temperature of the water in data table. Do not remove the thermometer from the cup, but be careful that the cups do not tip over.
2) Using the balance measure out 4.00 grams of calcium chloride on to a piece of paper. (remember to include the weight of the paper in your weight.)
3) Pour the calcium chloride into the 50 ml of water and stir GENTLY!! With the thermometer. (Thermometers are breakable and cost $7.00)
4) If the temperature rises then record the highest temperature attained. If the temperature lowers, then record the lowest temperature attained.
5) Dispose of the solution by pouring it down the sink, followed by lots of water. Rinse and dry the upper cup.
6) Repeat steps 1-5, using ammonium nitrate as your solute.
7) Clean up your lab space when finished.
Data Table:
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Solute |
Mass (g) solute |
Mass (g) solution |
Initial Temperature T (Co) |
Final Temperature T (Co) |
Change in Temperature T (oC) |
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Calcium Chloride |
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Ammonium Nitrate |
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Calculations:
1) T is the change from initial to final temperature.
2) Find the total mass of the solution that changed temperature in both reactions and write the values in the data table
3) Calculate the energy (in joules) absorbed or released by the solution in each reaction. Use the absolute value of T in the following equation.
Energy = (mass) X ( T ) X ( specific heat of solution)
(The specific heat of solution is slightly different than that of pure water. Use 3.34 kJ/gCo for both solutions.)
4) Calculate the energy per gram of solute for each solution. (J/g)
5) Using the periodic table calculate the molar mass of each of the solutes.
6) Calculate the molar heat of solution for each solute using the formula molar heat of solution = (energy/gram) #4 X (gram / mole of solute) #5
7) Your instructor will give you the accepted values for these solutes. Use those to calculate the percent error of your experimental value, use the following equation.
% error = accepted value- experimental value/accepted value X 100%
Conclusion:
1) Suggest two uses for these solutions in sports injuries. Relate this experiment to real life.
2) What did you learn about solutions?
3) Which side of the balanced chemical equation would the energies from these solutions show up on? Include these equations in your conclusion.
4) Discuss the reason you have the experimental error you have. Any possible sources of error or what went right.
5) How would you reduce any of these experimental errors?
