USING ENGLISH TO REPORT
Chemistry lab report
2H+(aq) + 2e- --> H2(g)
The iron(II) ions also react with hydrogen ions and oxygen to produce iron(III) ions:
Corrosion
of Iron Experiment
Purpose
Observe the corrosion of iron and investigate conditions related to
corrosion.
Pre-Lab Discussion
Corrosion is a oxidation-reduction (redox) reaction in which a free
metal is oxidized, or “corroded,” by some oxidizing agent. In nature, the oxidizing agent is frequently
atmospheric oxygen dissolved in water.
Perhaps the most familiar example of corrosion is the rusting of
iron. In this reaction, free iron, Fe,
is oxidized to Fe2+ and Fe3+ ions. In the reduction half-reaction, oxygen, O2,
reacts with water to form OH- ions.
See Chemistry The Central Science (Brown, LeMay, Bursten, Murphy) pages
874 – 876 for a detailed description of the corrosion of iron.
The rusting of iron usually is considered to be a destructive change,
and considerable time and money are expended to prevent it. One method which you will observe in this
experiment, make use of a “sacrificial” metal.
If iron is placed in contact with a more active metal (one that is more
easily oxidized) the more active metal will be corroded instead of the
iron. Metals situated below iron on the
table of standard electrode potentials can function as sacrificial metals.
In this experiment, indicators will be used to signal the formation of Fe2+
ions and OH- ions as products of the corrosion of iron. One such indicator, the hexacyanoferrate(III)
ion, turns blue in the presence of Fe2+ ions. The other, phenolphthalein, turns pink in the
presence of OH- ions. This
experiment should help promote a better understanding of corrosion and of
oxidation-reduction reactions.
Pre-Lab Questions:
- What type of
reaction is the rusting of iron?
- Write out
the half-reactions, complete reaction, half-reaction voltages, and reaction
voltage for the production of rust in this experiment? Which is the anode and which is the
cathode?
- Define the
term “sacrificial” metal?
- Why is iron
rust considered destructive and copper rust is not destructive, but
beneficial and attractive? (What is
the difference in the properties of each?)
Equipment
Balance
Tirrill Burner or Hot Plate
Graduated cylinder, 100 mL
Beaker, 250 mL
Ring stand
Iron ring
Wire gauze
Glass stirring rod
Dropper pipet
Petri dishes (2)
Emery paper
Metric ruler
Safety goggles
Lab apron
Materials
0.1 M K3Fe(CN)6 [potassium hexacyanoferrate(III)]
Agar powder
1% phenolphthalein solution
Distilled water
Copper wire, 5 cm
Zinc strip, 5 cm
10d Iron nails (4)
Safety
Observe all general lab safety precautions. Always wear safety goggles and a lab apron
when working in the lab.
Procedure
1. Set up a ring stand,
ring, and wire gauze. Add 200 mL of
distilled water to the 250 mL beaker and heat to boiling. While the water is being heated, clean four
nails with steel wool or emery paper.
2. Using the balance,
measure out 2.00 g of agar powder. When
the water is boiling vigorously, put out the flame and slowly add the agar to
the water, stirring constantly. When the
agar has dissolved, add 10 drops of 0.1 M K3Fe(CN)6. Rinse the dropper and pipet and add five (5)
drops of phenolphthalein solution.
3. Place one bent iron
nail and one straight iron nail into one of the Petri dishes. Be sure the nails do not touch and are
positioned as shown in Figure 1.
Figure 1
4. Tightly wrap one of
the remaining nails with copper wire and the other with the zinc strip. Place these nails in the other Petri dish, as
shown in Figure 1.
5. When the agar solution
is cool enough, pour it into each Petri dish to a depth of 0.5 cm (make sure
the nails are completely covered).
6. Make and record
observations in the time remaining.
7. At the end of the lab
period, place the dishes in your drawer to be observed on the following day.
Observations and Data
(Write a complete description of what you see in each Petri
dish and for each nail)
Petri Dish (a):
Petri Dish (b):
Lab Report
A brief, but complete report is expected for this lab. Please include
the following:
The Introduction should be a
discussion of the corrosion of iron, including the half-reactions that occur at
the anode and cathode. Explain how a “sacrificial” metal works to prevent
corrosion of iron. Describe the experimental set-up, and explain the purpose of
the two indicators.
The Results should be a
drawing or picture and a complete description of the qualitative results.
(Where are the pink and blue regions?)
The Conclusion should be a
complete interpretation of the results
- What is the
significance of the pink and blue regions around each nail?
- What
conclusions can you draw from each nail?
Compare and contrast the two nails in the two dishes.
- Why did
corrosion occur at the blue sites in Dish (a)?
- What is the
whitish substance surrounding the zinc-wrapped nail in Dish (b)?
- Explain the
difference in corrosion between the two nails in Dish (b).
- What effect
does stressing the nail have on the corrosion of the nail?
- What other
metals could be used as sacrificial metals?
- Did the
experiment produce expected results?
- Are there
any suggestions for improvements?
Teaching
Notes
Equipment
Balance
Tirrill Burner or Hot Plate
Graduated cylinder, 100 mL
Beaker, 250 mL
Ring stand
Iron ring
Wire gauze
Glass stirring rod
Dropper pipet
Petri dishes (2 per student)
Emery paper
Metric ruler
Safety goggles
Lab apron
Materials
0.1 M K3Fe(CN)6 [potassium
hexacyanoferrate(III)] FW 329.26 g
[use 3.2926g / 100mL]
Agar powder
1% phenolphthalein solution
Distilled water
Copper wire, 5 cm
Zinc strip, 5 cm [Use electrode
strips cut]
10d Iron nails (4 per student)
Pre-Lab Questions:
- What type of reaction is the rusting of
iron?
Oxidation-reduction reaction.
- Write out the half-reactions, complete
reaction, half-reaction voltages, and reaction voltage for the production
of rust in this experiment? Which
is the anode and which is the cathode?
2 Fe(s) ® 2Fe2+(aq)
+ 4e- Eº=
0.44 V (Anode)
O2(g) + 2H2O(l) + 4e- ® 4OH-(aq) Eº= 0.41 V (Cathode)
2Fe(s) + O2(g) + 2H2O(l) ® 2Fe(OH)2(s) Eº=
0.85 V (white, green solid)
Further oxidation to red flakes:
More acidic water increases corrosion. If the pH is very low the hydrogen ions
will consume the electrons anyway, making hydrogen gas instead of water:2H+(aq) + 2e- --> H2(g)
The iron(II) ions also react with hydrogen ions and oxygen to produce iron(III) ions:
4Fe2+(aq) -->4Fe3+(aq) + 4e- E° = -0.77 v (Anode)
4e- + 4H+(aq) + O2(aq)
-->2H2O(l) E° = 0.815 v
(Cathode)
4Fe2+(aq) + 4H+(aq) + O2(aq) -->4Fe3+(aq)
+ 2H2O(l) E° = 0.145
v
The loose porous rust or Fe(OH)3 can slowly transform into a
crystallized form written as Fe2O3.H2O the
familiar red-brown stuff that is called "rust" forming tubercles.
4Fe(OH)2(s) + O2(g) ® 2Fe2O3·H2O(s) + 2 H2O(l)
- Define the term “sacrificial” metal?
A metal that is more easily oxidized.
Fe is above on the activity series (Zn, Al, Mg, Na, Ca, K)
- Why is iron rust considered destructive
and copper rust is not destructive, but beneficial and attractive? (What is the difference in the
properties of each?)
Iron rust does not bond to the base metal iron and is slightly water
soluble. Therefore, iron rust will rub
off the metal and expose more metal to oxidation. Copper rust adheres to the copper metal and
protects the copper from other oxidation.
Lab Report
The Introduction should be a
discussion of the corrosion of iron, including the half-reactions that occur at
the anode and cathode. Explain how a “sacrificial” metal works to prevent
corrosion of iron. Describe the experimental set-up, and explain the purpose of
the two indicators.
The Results should be a
drawing or picture and a complete description of the qualitative results.
(Where are the pink and blue regions?)
The Conclusion should be a
complete interpretation of the results
- What is the
significance of the pink and blue regions around each nail?
- What
conclusions can you draw from each nail?
Compare and contrast the two nails in the two dishes.
- Why did
corrosion occur at the blue sites in Dish (a)?
- What is the
whitish substance surrounding the zinc-wrapped nail in Dish (b)?
- Explain the
difference in corrosion between the two nails in Dish (b).
- What effect
does stressing the nail have on the corrosion of the nail?
- What other
metals could be used as sacrificial metals?
- Did the
experiment produce expected results?
- Are there
any suggestions for improvements?
hi hudia, Zinc is selected as an iron coating to prevent corrosion ?
BalasHapusCause Zinc is more than eassy to oksidation than iron so iron be reduction. So, Zinc as coating on Iron can prevent corrosion
HapusWhat is the benefit of the contents of laporang entitled "Corrosion of Iron Experiment"?
BalasHapusThanks for visit. The benefit is we know what causes the rusting and know how to prevent it. And than we know the reaction of corrosion as a chemical reaction.
HapusWhat Causes Corrosion and Corrosion Control????
BalasHapusCorrosion occurs because of the reaction between the metal and the substances around it. In rust, rust can occur because moist air (oxygen and water) corrodes (reacts) to the iron so that a new substance appears, reddish brown solids.
HapusHere are some ways you can do to prevent / slow down corrosion:
HapusPaint
Paint can prevent direct contact between iron and moist air so that it can slow corrosion. This method is usually done on doors, fences, iron pipes, and others.
Oil with oil
Oil-lubricating can prevent direct contact with water and moisture. This method is usually done on tools and machines.
Wrapped with plastic
This method is commonly used for example on a dish rack and bicycle basket.
Tin Plating
Tin plating is coating with tin. This method is usually done on tin packaging because tin is an anti-rust metal.
Galvanisai
Galvanizing is coating with zinc. This is done because zinc is also an anti-rust metal. For example on: electric poles or telephone poles, water papa, and fences.
Cromium Plating
Cromium Plating is coating using chromium. Just like zinc, chromium can provide protection against corrosion even if there is a broken chromium layer. This way is usually done on bikes and bumper cars.
What is the function of 1% phenolphthalein solution?
BalasHapusThanks for visit. To know what is the factor of corrosion. One of them is acid. As we know fenolflatein is indicator for PH
HapusAs we know iron and gold belong to a metal group, so why iron can rust while gold does not rust?
BalasHapusThanks for visit. Cause iron more than reactive than gold. So iron easily to be oxidized than Aurum. Corrosion is a oxidation-reduction (redox) reaction in which a free metal is oxidized, or “corroded,” by some oxidizing agent.
HapusMention the elements that are difficult to experience corrosion.
BalasHapusAurum, platinum, silver, mercury, Copper, Bismuth. Cause in the volta line, they are the strong oxidator and difficult to rusting.
HapusWhat can be done to overcome corrosion? Explain.
BalasHapus
HapusChoosing the Right Metal
The type of corrosion is only half the story. It also depends on the steel you choose for a particular application.
Aluminum, for example, is a corrosion resistant material. This makes it ideal for applications that will be exposed to the elements.
In stainless steel, the corrosion resistance depends on the different types of metals used to create it. The most commonly used types of stainless, 304 and 316, are both corrosion resistant.
Carbon steel, however, is iron based and susceptible to corrosion. Adding a protective layer like a zinc coating or paint, helps to make it more corrosion resistant.
Surface Treatments
Coatings
Coatings include painting and plating. They are used to protect metals from environmental elements. They work by providing a protective layer of corrosion-resistant material between the steel and the damaging environment.
Anodization
Aluminum alloys are often anodized. Anodizing makes a material more resistant to weathering and corrosion and is commonly used on metal applications where the surface will be in constant contact with the elements.
Galvanization
Galvanized metal is coated with a thin layer of zinc to protect it against corrosion. The zinc oxidizes when it is exposed to air creating a protective coating on the metal surface.
For more tips on preventing corrosion or to find a metal that is the best fit for your application contact your local sales representative.
Mention metal that is easily oxidized and difficult to oxidize?
BalasHapusThe metal so easily to oxidized is Lithium cause it so reactive. And the metal so difficult to oxidized is Aurum (gold). It cause Aurum is the strongest oxidator.
Hapuswhy you use Lab apron in the lab?
BalasHapus
HapusWear lab coats that fit properly. Lab coats are available in a variety of sizes. Some lab coat services also offer custom sizes (e.g., extra long sleeves, tall, or woman’s fit). Lab coats should fasten close to the collar to provide optimal protection.
Lab coats should be worn fully buttoned or snapped with sleeves down.
Wear lab coats only when in the lab or work area. Remove lab coats when leaving the lab/work area to go home, to lunch, to the restroom, or meetings in conference rooms, etc.
What type of reaction is the rusting of iron
BalasHapusType half-reaction, with oxygen, O2, reacts with water to form OH- ions.
Hapus