1
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.
2
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! ?
Galvanized
Corroded
3
The most common corrosion reaction is the
rusting of iron in water 4 Fe 6 H2O 3 O2
lt--gt 4 Fe(OH)3
The oxidation portion of the reaction results in
the actual loss of metal Fe lt--gt Fe2 2 e-
Step one (OX)Fe2 lt--gt Fe3 e- Step two
(OX) Fe lt--gt Fe3 3 e- Overall Oxidation
half-reaction The reduction portion of the
reaction drives the process of corrosion O2 2
H20 4 e- lt--gt 4 OH- Reduction half-reaction
4
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
5
Anodic Protection
An anodic layer, such as chromium, nickel,
copper, or paint, allows corrosion to grow under
its layer when it is scratched.
Cathodic Protection
The steel is protected by the surrounding zinc
even if it is scratched.
6
How Does Zinc Protect The Underlying Iron Surface?
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.
http//www.videopediaworld.com/video/41136/Deconst
ruction-Building-a-House-Galvanizing-Nails 
7
The oxidation of zinc is more likely than the
oxidation of iron.


These potentials indicate the relative
thermodynamic tendency for the indicated
half-reaction to occur.
Zn lt--gt Zn2 2 e E 0.763 voltsFe lt--gt
Fe2 2 e E 0.409 volts
8
Zinc Coating Experiment
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.
Vernier Calipers
Outer diameter
Inner diameter
Height
https//www.youtube.com/watch?vZUNoWWw6V10
9
Zinc Coating Experiment
4. Weigh and record the mass of each washer to
the nearest 0.001 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.
10
Zinc Coating Experiment
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 ?
H2(g) ZnCl2 (aq)
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.
11
Zinc Coating Experiment

• 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.
• Dispose the washers in the used
• solids container.
• 16. Dispose the exhausted HCl in the
• liquid waste container.

12
Calculations
0

• Total Surface Area
• 2p(r02-ri2) 2pr0h 2prih
• where r radius ½ diameter

5 individual measurements for each washer

• 1. Volume of Zinc Coating Mass of Washer
  Reacted / Density of Zinc
• where dzinc7.14 g/cm3
• 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 1012 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.

13

Error Analysis of Accuracy Precision
AccurateThe average is accurate butnot precise.
PreciseThe average is precise but not accurate.
Accurate Precise The average is both accurate
and precise.
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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Determination of Accuracy
The accuracy can be determined by looking at the
difference between the expected (theoretical)
average and the experimental (observed) average.
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.
The Average or Mean Value (xbar)
? means sum
The average or mean of a set of numbers, Xi, 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.
15
The Standard Deviation
The standard deviation, a measure of the spread
of N values, Xi, about the average value, ?, a
measure of precision, is given by,
The standard deviation is used for large
populations, N 30.
Estimate of the Standard Deviation

If the number of values, N, is small, i.e., if N
lt 30, an estimate of the standard deviation, s,
is given by,
We will be using the Estimate of the Standard
Deviation because we have a small data set.
16
Confidence Limit
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 ?.
Students t-factors are given in tables for
different probabilities. (Note The table in
your book is on page 56.)
17
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
18
Graph 2
Graph 3
19
Hazards for Zinc Experiment
Reactant 3 M HCl is a corrosive strong acid.
(If spilled, NaHCO3 will be used to
neutralize.) Product Hydrogen gas is flammable.
Stockroom Information
Before Experiment Check Out 5 Zinc coated
washers 1 set of Vernier calipers 5 pieces of
filter paper 1 piece of Copper wire
After Experiment
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
Pour in Zinc Lab liquid waste carboy Used HCl
with Zn2 Rinsings Leftover HCl
20
Next Week - February 10-13
Read Determining the Empirical Formula of
Copper Chloride pp. 77-94. Read Dimensional
Analysis Sets 2 3 (pp. 24-28)
Turn-In 1.) Dimensional Analysis Sets 2 3
(all problems) 2.) Zinc pp. 65-75
(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