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Statistical Analysis of Zinc Coated Washers Purpose of the Experiment Determine how many centimeters of zinc and layers of zinc atoms are present on the surface of a galvanized steel washer.

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What is Corrosion? Natural process of deterioration of metals and alloys in a corrosive environment. Results in an actual decrease in the thickness or size of the original metallic structure. A poorly protected surface can be a big mistake - So dont compromise... Galvanize! Corroded Galvanized

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The most common corrosion reaction is the rusting of iron in water 4 Fe + 6 H 2 O + 3 O 2 4 Fe(OH) 3 The oxidation portion of the reaction results in the actual loss of metal Fe Fe e - Step one (OX) Fe +2 Fe +3 + e - Step two (OX) Fe Fe e - Overall Oxidation half-reaction The reduction portion of the reaction drives the process of corrosion O H e - 4 OH - Reduction half-reaction

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What is Galvanizing? The process of galvanizing consists of coating metals, such as iron, with a thin protective layer of zinc. The zinc layer provides protection to the metal from corrosion. Before & After Hot Dip Galvanizing

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The steel is protected by the surrounding zinc even if it is scratched. Cathodic Protection An anodic layer, such as chromium, nickel, copper, or paint, allows corrosion to grow under its layer when it is scratched. Anodic Protection

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Zinc coatings prevent corrosion of the protected metal by forming a barrier, and by acting as a sacrificial anode if this barrier is damaged. When exposed to the atmosphere, zinc reacts with oxygen to form zinc oxide, which further reacts with water molecules in the air to form zinc hydroxide. Finally zinc hydroxide reacts with carbon dioxide in the atmosphere to yield a thin, impermeable, tenacious and quite insoluble dull gray layer of zinc carbonate which adheres extremely well to the underlying zinc, so protecting it from further corrosion. How Does Zinc Protect The Underlying Iron Surface?

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These potentials indicate the relative thermodynamic tendency for the indicated half-reaction to occur. The oxidation of zinc is more likely than the oxidation of iron. * * Zn Zn e – E = –0.763 volts Fe Fe e – E = –0.409 volts

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1. Get 5 washers, filter paper & Vernier calipers from the stock room. 2. Keep washers in the same order during the experiment. This can be done by writing numbers on the filter paper. 3. Record on datasheet the inner and outer diameters and the height of each washer to the nearest 0.01 cm. Zinc Coating Experiment Outer diameter Inner diameter Height Vernier Calipers https://www.youtube.com/watch?v=ZUNoWWw6V10

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4. Weigh and record the mass of each washer to the nearest gram. (Making sure to weigh the washers on the same balance each time.) To Weigh: Place filter paper on the balance. Tare. (Set the balance to zero.) Place the washer on the filter paper. Record weight. Zinc Coating Experiment

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5. In an 100 ml beaker, get ~60 ml of 3M HCl. 6. Attach copper wire to one of the zinc washers. 7. Dip the washer in the beaker of HCl and observe the reaction. Zn (s) + 2 HCl H 2 (g) + ZnCl 2 (aq) Zinc Coating Experiment 8. Allow the reaction to continue until bubbling stops, approximately 90 sec. (The surface will change from shiny silver to a dull gray.) 9. Remove the washer from the acid and rinse with distilled water over a waste beaker.

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10. Use paper towel to dry the washer. 11. Place dried washer on corresponding filter paper. 12. Weigh the washer on the same balance used before. 13. Record the mass. 14. Repeat the same procedure for other washers. 15.Dispose the washers in the used solids container. 16. Dispose the exhausted HCl in the liquid waste container. Zinc Coating Experiment

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1. Volume of Zinc Coating = Mass of Washer Reacted / Density of Zinc where d zinc =7.14 g/cm 3 2. Total Surface Area of Zinc = Total Surface Area of Washer 3. Thickness of Zinc Coating = Volume of Zinc Coating / Total Surface Area of Zinc 4. Thickness of Zinc in Atoms, where Diameter of Zn atom = 268 pm, 1 m = pm 5. Error Analysis & Statistics: Find the Mean (Average), Standard Deviation and Confidence Interval (98%) for Volume, Surface Area and Thickness of Zinc in Atoms. Height of the washer, h D i : Inner diameter D o : Outer diameter Total Surface Area = 2 r 0 2 -r i 2 )+ 2 r 0 h + 2 r i h where r = radius = ½ diameter Calculations 5 individual measurements for each washer

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Accurate The average is accurate but not precise. Precise The average is precise but not accurate. Accurate & Precise The average is both accurate and precise. Error Analysis of Accuracy & Precision Systematic or Determinate Errors: Shifts in the measured values from the true values which reduces the accuracy of a result. (An example of a systematic error is misreading a graduated cylinder). Random or Indeterminate Errors: Shifts in the measured values from the true values which influences the precision or scatter of the result. (Examples of random errors might be the imprecision among multiple readings).

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Percent Error The percent error is the absolute value of the quantity of the theoretical value minus the observed value divided by the theoretical value and multiplied by one hundred. Determination of Accuracy The accuracy can be determined by looking at the difference between the expected (theoretical) average and the experimental (observed) average. The Average or Mean Value (x bar ) The average or mean of a set of numbers, X i, is found by adding the numbers and dividing by the number of values, N. Thus the average of 3, 5, 7, 3, and 5 = 23 / 5 or 4.6. Ʃ means sum

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*Estimate of the Standard Deviation The standard deviation, a measure of the spread of N values, X i, about the average value,, a measure of precision, is given by, The Standard Deviation If the number of values, N, is small, i.e., if N < 30, an estimate of the standard deviation, s, is given by, The standard deviation is used for large populations, N 30. *We will be using the Estimate of the Standard Deviation because we have a small data set.

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Confidence Limit Students t-factors are given in tables for different probabilities. (Note: The table in your book is on page 56.) where t is Students t-factor. At the 90 % confidence limit, 90 times out of 100 the true value will be within ±1.64 of the experimental results. The confidence limit defines an interval about the average that most likely contains.

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Graphs of the Volume, Surface Area and Thickness of Zinc in atoms. Page 75 #2: In Excel (or any program that will make graphs), make 3 column graphs where the washers and the average washer are listed on the x axis of all three. On the y axis of graph #1 show their volumes; on graph #2 their surface areas; and, on graph #3 their thicknesses. Do not forget to include units. Graph #1

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Graph #2 Graph #3

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Hazards for Zinc Experiment Reactant: 3 M HCl is a corrosive strong acid. (If spilled, NaHCO 3 will be used to neutralize.) Product: Hydrogen gas is flammable. Stockroom Information Before Experiment Check Out: 5 Zinc coated washers1 set of Vernier calipers* 5 pieces of filter paper1 piece of Copper wire* *Return to Stockroom: 1 set of Vernier calipers 1 piece of Copper wire Place in Used Solids bucket: 5 washers with Zinc coating removed 5 pieces of filter paper After Experiment: Pour in Zinc Lab liquid waste carboy: Used HCl with Zn 2+ & Rinsings Leftover HCl

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Next Week - February Read: Determining the Empirical Formula of Copper Chloride pp Read: Dimensional Analysis Sets #2 & #3 (pp ) Turn-In: 1.) Dimensional Analysis Sets #2 & #3 (all problems) 2.) Zinc pp (This includes the Post-Lab). Note: #2 (p 75) - You need to make 3 graphs! Monday Only - Extensions for February 10 Turn In: 1.) Dimensional Analysis Set #1 2.) Graphing Lab & Survey

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