Corrosion of copper and formation of verdigris

Introduction

"A color known as verdigris is green. It is very green by itself. And it is manufactured by alchemy, from copper and vinegar." -Cennino Cennini, Il Libro dell' Arte. [1]

On a recent visit to Liberty Islands in New York Harbor, United States of America, the tour guide took us to one of the most famous of the Seven Wonders of the World, The Statue of Liberty, built in 1886. The statue is made of sheets of copper, and lies amidst the Hudson Bay in the Atlantic Ocean. It was originally dark brown or blackish in color, but with time, the color changed to green. The reason for the color change was the corrosion of the copper metal taking place since 100's of years, and formation of verdigris. Verdigris can be formed artificially as well as naturally. Artificial verdigris formation is faster than natural verdigris formation, though naturally formed verdigris is far more beautiful and attractive to look at. Common places (other than the Statue Of Liberty, New York) where verdigris is formed are:

· Base of ships which have a copper plating

· Old copper and bronze coins

· Old paintings

This kindled my curiosity and I wanted to estimate and analyze a few factors when present in water, can lead to or aid in the formation of verdigris, as the Statue of Liberty is surrounded by water and has shown a great variation in color over the years.

Background to Verdigris

Verdigris is a green coating or patina formed when an alloy of copper, bronze or brass is weathered and exposed to the atmosphere or water over a long period of time. Verdigris or verte de Greece [2] acquired its name from its place of origin, that is Greece. In the Old French it was called verte grez. In the olden times, there were several ways of preparing verdigris. In the early nineteenth century, when researches in chemistry were growing, copper sulphate (CuSO4) was reacted with solutions of lead, barium or calcium acetate as insoluble precipitates were formed leaving copper acetate [Cu(CH3COO)2] in solution, and copper acetate being one of the many types of verdigris [3]. Right from 13th to the 19th century, European, Italian and German painters used verdigris pigments in their paintings, landscapes and drapery. The simple reason for this was the transparency, which looked like a glaze. The color of verdigris varies from shades of blue to shades of green. The simple composition of verdigris is copper carbonate (CuCO3) and copper hydroxide (Cu(OH)2), but if verdigris is being formed at the seashore or somewhere near the sea, it consists of copper chloride (CuCl2). The chloride ion is due the presence of Sodium Chloride (NaCl) in seawater.

CuSO4 + 2NaCl → CuCl2 + Na2SO4

If there is presence of acetic acid at the time of weathering, copper (II) acetate is formed.

Cu + 2CH3COOH → + Cu(CH3COO)2 + H2

On the basis of chemical composition, verdigris can be classified into 2 groups: basic and neutral verdigris. Basic verdigris is formed by the combination of air, water vapor, acetic acid vapor, and copper or copper alloy mix. It has a color of blue, or blue-green. Blue basic verdigris is often in the shape of fine needles, but simply basic verdigris occurs in solid lumps, showing no needle like texture. The chemical formula for basic verdigris can include all of the following:

[Cu(CH3COO2]2. Cu(OH)2. 5H2O (blue)

Cu (CH3COO)2. Cu(OH)2. 5H2O (blue)

Cu(CH3COO)2. [Cu(OH)2]2 (blue)

Cu(CH3COO)2. [Cu(OH)2]3. 2H2O (green) [4]

Neutral verdigris, also known as 'verde eterno', 'crystallized', 'distilled' or 'purified' verdigris is made up of is neutral copper acetate Cu(CH3COO)2.H20. This type of verdigris comprises of blue green crystals and they dissolve completely in water. The structure of this on the other hand is that of tabular crystals with rhombic and hexagonal faces, having distinct boundaries. The formation of verdigris is a slow process, which may take months and even years.

The presence of verdigris on copper or copper alloys is an indication of active corrosion taking place. One of the various types of corrosion, the type of which takes place in copper and its alloys is known as direct surface attack [6]. This takes place when the copper surface is directly exposed to oxygen in the air or water and causes etching of the metal, resulting in tarnishing of copper alloys. The various factors that cause corrosion are

§ pH of the water: pH is the measure of the acidity of a solution. An acidic solution causes water to show corrosive properties. If the pH of water is <8, the copper oxide (CuO) (that is formed on copper when pH is >8 and acts as a barrier) is dissolved exposing the metal to corrosion by water.

§ Oxygen content in water: the dissolved oxygen content in freshwater is up to 30%, and the rest 70% being nitrogen which is non-corrosive. The oxygen corrodes the metal by an electro chemical process of oxidation, making the metal thinner and weaker due to rust (oxide) formation. The rate of this reaction increases with an increase in pressure and temperature.

2 Cu(s) + O2(g) → 2 CuO(s)

§ Chemical composition of water: presence of salts, sulfates, suspended solids such as sand, sediments, bacteria aid in corrosion. Different chemicals have a different effect on corrosion.

§ Dissimilar metals leading to galvanic corrosion: Galvanic corrosion is also known as electrolysis an takes place when different metals come in contact with one and other. When in contact, one of the metals tends to give up electrons, thus eventually dissolving over a period of time. This corrosion is limited to the area of contact.

§ Water temperature: the rate of oxidation is higher at an increased temperature.

Background To Experiment

For my experiment, I used thin, 20cm long copper plates as copper, being a Transition metal and having an electronic configuration of [Ar] 3d10 4s1 has the ability of showing variable oxidation states, thus having a greater scope for reactions with different substances. The common oxidation states for copper are +1 that is less stable as compared to copper in the +2 oxidation states. Copper can also show a +3 and +4 oxidation state, but the same is rare. The different chemicals present in natural water and their sources are:

§ Oxygen (dissolved oxygen): Oxygen is diffused from the atmosphere, a waste product of photosynthesis in aquatic plants and aeration (movement) of water from falls and rapids.

§ Carbon dioxide: Carbon Dioxide is produced in the atmosphere by the decay of organic matter, burning of fossil fuels, respiration in plants and animals. This enters the water through diffusion and is also known as the Carbon cycle:

CO2 (atmospheric) CO2 (dissolved)

CO2 (dissolved) + H2O(l) H2CO3(l). A weak acid is formed.

Carbon dioxide is generally present in water in the form of carbonates and bicarbonates.

§ Chlorides: Water contains about 2.9% out of 3.5% of dissolved Sodium Chloride (NaCl also known as table salt), the main source of which being inland lakes containing saline water.

§ Nitrates: Seepage from fertilized agricultural lands, domestic and industrial wastewater, refuses dumps, animal feedlots, sewage disposal systems, decaying plant debris.[7]

§ Bases: Sodium Hydroxide (NaOH): Infiltration of road salt due to flowing water, pollution due to sewage effluent, erosion of salt deposits and sodium containing rocks.

2Na(S) + 2H2O(l) → 2NaOH + H2

§ Acids: Acetic Acid (CH3COOH): excreted by acetic acid bacteria, called Acetobacter [8] found in food water, and soil.

Among all these factors that are present in natural water, I wanted to found out which of these factors aid most in the corrosion of copper and hence verdigris formation. With this in mind I decided to keep my research question as Which of the following factors – dissolved oxygen, dissolved carbon dioxide, dissolved salts and acidity in/of water aid most in the corrosion of copper, leading to verdigris formation.

Type I – Artificially prepared water/Water with different additives

1. Water without dissolved oxygen

2. De-oxygenated Water with excess of dissolved carbon dioxide (CO2)

3. Water with 2 grams Chloride (NaCl)

4. Water with 4 grams Chloride (NaCl)

5. Water with 6 grams Chloride (NaCl)

6. Water with 8 grams Chloride (NaCl)

7. Water with 10 grams Chloride (NaCl)

8. Water with 1 ml Acetic Acid (CH3COOH)

9. Water with 2 ml Acetic Acid

10. Water with 3 ml Acetic Acid

11. Water with 10 ml Acetic Acid

12. Water with 5 ml Sodium Hydroxide (NaOH)

13. Water with 10 ml Sodium Hydroxide (NaOH)

14. Water with 15 ml Sodium Hydroxide (NaOH)

Type II - Water from different sources

1. Tap water

2. De-ionized water

3. Bore-well water

4. Sea water

5. Water from the tank of a high rise building

Methodology

Type I – Artificially prepared water and Water with different additives

For sample 1: Water without oxygen

I took 1200ml of distilled water in a hard glass beaker and boiled it till it boiled completely and water began to vaporize. The beaker was kept covered to prevent atmospheric oxygen from getting dissolved and for the water to get cooled. After cooling, the water sample was tested using a water analysis kit for dissolved oxygen. Since dissolved oxygen was present, I boiled the water again and tested till the dissolved oxygen content in the water reached zero. As a precaution, 50 grams of Sodium Sulfite (Na2SO3) was added as it removes any traces of atmospheric oxygen that dissolves in the water (converting it into Sodium Sulphate). Once this was done, I immediately transferred the water into the specimen jar and cover the lid. I took a copper plate and scrubbed it properly using sand paper so as to remove any kind of atmospheric rust or oxide formed on it. The initial mass was recorded. The copper plate was placed into the jar and kept in a dry place under normal atmospheric conditions. At regular intervals (number of days), I removed the copper plate from the water using a pair of tongs and kept them in a dry place. I made sure to cover the specimen jar with the lid to prevent any oxygen from dissolving in the water. I dried the copper plate completely using a hair dryer, making sure no impurities passed on to the plate. The plate was weighed and mass recorded, after which the plate was inserted carefully into the specimen jar and covered immediately. At the last day when recording the mass, I weighed the dry plate. Next, I scrubbed the plate completely using sand paper and weighed it.

This mass when subtracted from the initial mass is the total corrosion and the total amount of verdigris formed (if any).

For sample 2: Deoxygenated water with excess of dissolved Carbon Dioxide

Using Calcium Carbonate (CaCO3) and 2 molar Hydrochloric acid (HCl), I added carbon dioxide to water. 50 grams of Sodium Sulfite (Na2SO3) was added to the water as it removes any traces of atmospheric oxygen that dissolves in the water (converting it into Sodium Sulphate). To a conical flask containing Calcium Carbonate, HCl was added. A delivery tube was attached to a stopper at the mouth of the flask. One end of the delivery tube was in the conical flask and one end dipped in the specimen jar so that all the gas (CO2) is transferred to the water. The same procedure was repeated with handling the copper plate as in the earlier experiment to test the level of corrosion and formation of verdigris (if any).

The equation for the formation of carbon dioxide using a carbonate is:

CaCO3 + 2HCl → CaCl2 + H2O + CO2 #

For sample 3, 4, 5, 6, 7: sodium chloride dissolved in water

I added 2, 4, 6, 8 and 10 grams of solid Sodium Chloride crystals respectively in different beakers containing 1000ml-distilled water. The solution was stirred well. The same procedure was repeated with handling the copper plate as in the earlier experiment to test the level of corrosion and formation of verdigris (if any).

For samples 8, 9, 10, 11: water with Acetic Acid

I added 1, 2, 3, and 10ml of Glacial Acetic Acid respectively in different beakers containing 1000ml tap water, after which I stir the solution well using a glass rod and made sure the grass rod is washed with water in the specimen jar itself after use so as to maintain the concentration of the acid. The pH of the solutions was recorded using a pH meter. The same procedure was repeated with handling the copper plate as in the earlier experiment to test the level of corrosion and formation of verdigris (if any).

For sample 12, 13, 14: Water with Sodium Hydroxide

I added 5, 10, and 15ml of 0.1 molar Sodium Hydroxide solution respectively in different beakers containing 1000ml tap water, and stirred well. The pH of the solutions was recorded using a pH meter. The same procedure was repeated with handling the copper plate as in the earlier experiment to test the level of corrosion and formation of verdigris (if any).

Type II - Water from different sources

For sample 1: Tap water

I collected 1000 ml of tap water in a beaker. Then I checked the dissolved oxygen (DO) content using the water analysis kit for Dissolved Oxygen. The water was immediately transferred into the specimen jar and the lid was closed so as to avoid dissolution of any more oxygen from the atmosphere. The same procedure was repeated with handling the copper plate as in the earlier experiment to test the formation of verdigris (if any).

For sample 2: de-ionized/distilled water

I collected the water sample in a specimen jar, to which I added 50 grams of Sodium Sulfite (Na2SO3) as it removes any traces of atmospheric oxygen that dissolves in the water (converting it into Sodium Sulphate). The same procedure was repeated with handling the copper plate as in the earlier experiment to test the formation of verdigris (if any).

For sample 3, 4, 5: bore well water, seawater, tank water

I collected about 1500ml of each water sample on the day the experiment is to be conducted, and using the water analysis kit for Dissolved Oxygen, Chloride, Phosphate and Nitrates, I checked the content of each in the 3 samples. The same procedure was repeated with handling the copper plate as in the earlier experiment to test the level of corrosion and formation of verdigris (if any).

Results

For Type I Samples

Water sample	Water without dissolved oxygen	Water with excess dissolved CO2
Change in mass	0.098 g	0.150 g

Mass of Sodium Chloride added	2 grams	4 grams	6 grams	8 grams	10 grams
Change in mass	0.003	0.005	0.003	0.014	0.020

Volume of sodium hydroxide	5 ml	10 ml	15 ml
Change in mass	0.097g	0.180g	0.376g

For type II Samples

Sample	Tap water	De – Ionized water
Change in mass	0.461 g	0.137 g

Water sample	Bore well water	Sea water	Tank water from a high rise building
Change in mass	0.131g	0.755g	0.088g

Conclusion and Analysis of Conclusion:

Type I – Artificially prepared water and Water with different additives

From the results obtained as shown in the above graph for type I samples, the factor that aids most in the formation of verdigris is the presence of acetate ions. Hydroxyl (OH-) ions are the second most important after which is Carbon Dioxide (CO2) and water without any dissolved oxygen and last is Sodium Chloride (NaCl).

Water with different amounts of Acetic Acid

Acetic acid reacts with copper to form copper acetate, a neutral form of verdigris. Commonly known as vinegar, it is sour in taste and corrodes the metal, forming a blue green patina, with the equation:

Cu+2 + 2CH3COOH → Cu(CH3COO)2 + 2H+

Acetic acid, a weak monoprotic acid reacts with copper and gets oxidized to copper acetate. It acts as a Bronsted Lowry acid, which is a proton donor, and donates H+ ions.

When the reaction takes place in water, hydrated copper acetate molecules are formed, because copper acetate is highly soluble in water.

Cu+2 + 2CH3COOH + H2O → Cu(CH3COO)2.H20

In the experiment, it is noticed that as the volume of acid increases, the concentration of acetic acid per mole of water increase, thus the total number of moles of acetic acid also increases and the pH of the water also increases. Thus there is more corrosion in the water sample with a greater volume of acid, resulting in more verdigris being formed.

Water with different volumes of Sodium Hydroxide

In the experiment it is noted, as the volume of the base in water increases, the number of moles of the base increases, thus increasing the concentration of the base. Hence we can see that there is maximum corrosion of the copper plate in the water sample with 15ml Sodium Hydroxide. The reaction is as follows:

Cu + 2NaOH → Cu(OH)2 + 2Na+

The net reaction is basically between copper and water molecules as sodium ions are left behind in the water.

Copper hydroxide is a green substance, and a simple form of verdigris. This process is slow and formation of verdigris takes time.

Water with excess carbon dioxide

Carbon dioxide reacts with water to form carbonic acid – a weak acid, which decreases the pH, making the solution more acidic.

CO2 (aq) + H2O (aq) → H2CO3 (aq)

In the above reaction, carbon dioxide is reduced.

The acid reacts with the copper plate, according to the equation:

H2CO3 (aq) + Cu(s) → CuCO3 (aq) + H2 (aq)

Copper is oxidized to Copper carbonate formed is blue green in color, and is the simplest form of verdigris formed. Carbonic acid on the other hand is reduced. Thus this is a redox reaction.

The rate of reaction is very slow, as carbonic acid is a weak acid and does not completely dissociate, thus attaining equilibrium would take a lot of time. In order to increase the rate of the reaction, addition of a base would be a good option as according to Le Chȃtelier's Principle, the base would react with the hydrogen ions to form water molecules, favoring the forward reaction.

Sodium Sulfite was added in order to absorb all the oxygen present in water before adding carbon dioxide to it. Sodium Sulfite reacted with carbon dioxide to produce sodium carbonate, a white precipitate of which could be seen at the base of the specimen jar.

Na2SO3 (s) + CO2(aq) → Na2CO3

Water without dissolved oxygen:

The trend observed in this sample is that initially, the weight of the copper plate increases, that is in the first one week; after which there is loss on the total mass.

The probable reasons for this could be that initially the verdigris or the rust formed was deposited on the copper plate, and with time they began to dissolve in water.

When copper reacts with water without any dissolved oxygen, the water obtained a yellowish tinge and the rest of the plate had a reddish color. Tiger like stripes appeared on the copper plate after drying, but of different colors. The H+ ions present in water corrode the copper plate. It has been proved in researches that oxygen free water can also lead to corrosion of copper as the hydrogen ions settle on the copper plate. Hence we can say that there is simply corrosion of the copper plate and no verdigris is formed.

[9]

Water with different amounts of Sodium Chloride:

Sodium Chloride reacts with copper to form Copper Chloride in the presence of water with the equation:

Cu(s) + 2NaCl(aq) + 2H2O(aq) → CuCl2(aq)+ H2(aq)+ 2NaOH(aq)

In the above reaction, copper is reduced, converting it to copper chloride, a blue green solution. In the process, water is also reduced to give Hydrogen gas, which is highly flammable.

The resulting solution formed will be highly alkaline as Sodium Hydroxide, a very strong base is formed which dissociated completely in water, with the equation:

NaOH(aq) → Na+(aq) + OH-(aq)

In this experiment, a trend of increase and then decrease in weight is observed. This could be due to dissolution of the copper chloride formed on the plate in water, and this is the reason why this water sample had a blue-green tinge. So on the final days, there was not mush color on the copper plate except a whitish coat, but the water was colored. The water sample with the maximum amount of Sodium Chloride had the maximum verdigris formed.

CuCl2(aq)+ 2H2O(aq) → Cu(OH)2(aq) + 2HCl (aq)

Thus, copper hydroxide that is formed is also responsible for the blue green color of the water.

Type II - Water from different sources

The maximum amount of verdigris is formed in seawater, after which is tap water, then de-ionized water, followed by bore well water, and least in tank water.

Tap water

When copper reacts with tap water, that reaction that occurs is:

2Cu(s) + H2O(l) + CO2(aq) + O2(aq) → Cu(OH)2(l) + CuCO3(l)

(Green) (Blue green)

The dissolved oxygen in the sample used by me was 13ppm. The copper plate initially showed no color change when in solution, but once it was removed, greenish colors appeared on dabbing it with a filter paper. This is because of the copper hydroxide and copper carbonate formed. The color of the copper became darker after a few days, since copper hydroxide gets oxidized to form copper oxide, also known as rust, which is black in color. The equation is represented as:

Cu(OH)2 (s) → CuO (s) + H2O (l)

(Green) (black)

Thus we can conclude that verdigris has been formed, as copper carbonate is a simple form of verdigris, and a green color is obtained.

De-ionized water

With de-ionized water, it is observed that the copper plate turns black in color. Since there is no carbon dioxide present, copper carbonate is not formed. De – ionized water, containing no mineral ions, is highly corrosive when exposed to copper. Thus the oxygen ions corrode copper to form rust, with the equation:

Cu(s) + O-(l) → CuO(s)

Thus there is simply rust formed, increasing the mass of the copper plate by 0.137g, corroding the metal, without formation of any kind of verdigris.

Bore well water, seawater, water from the tank of a high rise building:

All the 3 samples of water contain dissolved oxygen, which is one of the important factors aiding in the formation of verdigris. It was noticed that all the copper plates in all the 3 samples had become darker and the copper plate in tank water had pale spots. The main reason for this was the formation of copper oxide.

Initially copper reacts with oxygen to form black copper oxide with the equation:

2Cu(s) + O2 (l) → 2CuO(s)

The copper oxide reacts with water to form basic green copper hydroxide, a simple form of verdigris.

CuO (s) + H2O (l) → Cu(OH)2 (s)

Form all the 3 samples seawater has the maximum amount of dissolved oxygen, 8.55 ppm, thus maximum corrosion would take place in this sample as more copper oxide is formed. The presence of dissolved chloride helps in formation of copper chloride, another form of basic verdigris found near the sea.

Cu(s) + 2NaCl(aq) + 2H2O(aq) → CuCl2(aq)+ H2(aq)+ 2NaOH(aq)

The water sample of bore well water was hazy and dark due to the dissolved minerals and sand in the water. But with seawater, needle like green particles appeared at the base of the beaker and represents basic verdigris. The copper plate in this sample developed a reddish color after the first few days, which is a tarnish that appears when, copper reacts with gases (basically oxygen).

Though the quantity of dissolved oxygen in bore well water and tank water from a high-rise building is the same, there is more corrosion in bore well water, proving that simply oxygen is not responsible for corrosion. Bore well water contains salts and minerals which lie deep in the earth, being a prime cause of corrosion, which are not present in tank water as it is portable.

Evaluation

There were a few sources of error in the experimental procedure. The sample of water without any dissolved oxygen would have absorbed oxygen from the atmosphere when the lid of the specimen jar was opened to remove the copper plate. Not only in this sample but also the others, the chemical makeup, i.e., DO content, carbon dioxide content of the water may have changed due to dissolution of atmospheric oxygen and carbon dioxide. Because of this, there can be errors and changes in the readings. In addition, when the copper plate comes in contact with air, there would be some amount of corrosion as the atmospheric oxygen, carbon dioxide would be reacting with it, again leading to errors in the mass. Though Sodium Sulfite was added to a few solutions remove the dissolved oxygen from the atmosphere, it was not completely accurate and useful.

Suggestions for further research in this field:

After verdigris is formed, the composition of the verdigris can be tested, whether it is neutral, basic or of some other kind. In addition to this researches could also be carried to check whether the composition of verdigris depends on the factors, which lead to its formation or the concentration of additives in water.

BIBLIOGRAPHY

Hultquist, G., Szakálos, P., Graham, M. J., and Sproule, G. I., Detection Of Hydrogen In Corrosion Of Copper In Pure Water, NACE International, Texas.

Marcus, P., Dekker, Marcel., and Oudar, J., 1995, Corrosion mechanisms in theory and practice, Inc. New York, p. 436.

Edwards, M., Ferguson, J.L., and Reiber, S.H., 1994, 'On pitting corrosion of copper', Jnl. AWWA

Kuhn, Hermann, 1970, Verdigris and Copper Resinate (Studies in Conservation) The International Institute for Conservation of Historic and Artistic Works (IIC) © , p. 12 – 36.

Jones, H. Russell, 2001, Environmental Effects On Engineered Materials, Marcel Dekker, Inc., United States Of America.

Cennino D' Andrea Cennini, 1933, The Italian "Il Libro dell' Arte.", Translated by Daniel V. Thompson, Dover Publications, Inc., by Yale University Press, New York

Antonijevic, M. M., and Petrovic, M. B., 2007, Copper Corrosion Inhibitors. A review, International Journal Of Electrochemical Science, Serbia

The Native Elements Class"

http://www.galleries.com/minerals/elements/class.htm

(Accessed on 28th October 2009 )

APPENDIX

Calculation of amount of carbonate required for producing Carbon Dioxide gas in water.

CaCO3 + 2HCl → CaCl2 + H2O + CO2 #

m = 5gms n = 2x 0.05 n = 0.05moles

M = 100gms = 0.10moles

No of moles c = 2 M

= m/M v = n/c

= 0.05moles = 0.10/2

= 0.05 dm3

= 50 cm3

DATA COLLECTION TABLES

Type I – Artificially prepared water/Water with different additives

Samples 1, 2

	Water without dissolved oxygen	Water with carbon dioxide
Day 1 – initial	23.570 g	23.560 g
Day 8	23.614 g	23.632 g
Day 13	23.596 g	23.615 g
Day 15	23.561 g	23.575 g
Day 15 – final	23.472 g	23.410 g
Change in mass	0.098 g	0.150 g

Samples 3, 4, 5, 6, 7

	2 g of NaCl	4 g of NaCl	6 g of NaCl	8 g of NaCl	10 g of NaCl
Day 1 - initial	24.220 g	24.481 g	24.155 g	25.675 g	22.522 g
Day 9	24.292 g	24.555 g	24.230 g	25.761 g	22.577 g
Day 10	24.298 g	24.577 g	24.240 g	25.763 g	22.578 g
Day 13	24.306 g	24.566 g	24.231 g	25.742 g	22.507 g
Day 14	24.238 g	24.489 g	24.171 g	25.702 g	22.508 g
Day 15	24.219 g	24.567 g	24.244 g	25.775 g	22.585 g
Day 15- final	24.217 g	24.476 g	24.152 g	25.661 g	22.502 g
Change in mass	0.003 g	0 .005g	0.003 g	0.014 g	0.020g

Samples 8, 9, 10, 11 – acetic acid

	1 ml	2 ml	3 ml	10ml
pH	5.090	4.880	4.860	3.730
Day 1 – initial	24.029 g	23.787 g	23.186 g	23.750 g
Day 4	24.075 g	23.793 g	23.181 g	23.743 g
Day 16	24.043 g	23.693 g	23.120 g	23.657 g
Day 24	23.960 g	23.418 g	23.085 g	23.579 g
Day 24 – final	23.648 g	23.296 g	22.923 g	23.151 g
Change in mass	0.381 g	0.491 g	0.263 g	0.599 g

Samples 12, 13, 14 – sodium hydroxide

	5 ml	10ml	15ml
pH	8.900	9.310	9.480
Day 1 – initial	24.506 g	23.150 g	22.415 g
Day 3	24.567 g	23.173 g	22.451 g
Day 14	24.493 g	23.118 g	22.392 g
Day 14 - final	24.409 g	22.970 g	22.039 g
Change in mass	0.097 g	0.180 g	0.376 g

Type II - Water from different sources

Samples 1, 2

	Tap water (Dissolved oxygen = 13ppm)	De - ionized water
Day 1 – initial	30.913 g	24.770 g
Day 8	31.028 g	24.821 g
Day 13	30.914 g	24.820 g
Day 15	30.897 g	24.738 g
Day 15 – final	30.452 g	24.633 g
Change in mass	0.461 g	0.137 g

Samples 3, 4, 5

	Bore-well water	Sea water	Tank water
Day 1 – initial	24.040 g	25.190 g	23.951 g
Day 6	24.033 g	24.535 g	23.977 g
Day 7	24.005 g	24.565 g	23.968 g
Day 10	24.022 g	24.625 g	23.961 g
Day 15	23.975 g	24.538 g	23.899 g
Day 15 – final	23.909 g	24.435 g	23.863 g
Change in mass	0.131g	0.755 g	0.088 g
Dissolved oxygen (ppm)	7.8	8.55	7.8
Chloride content (ppm)	40	12300	20
Phosphate content (ppm)	NIL	NEGLIGIBLE	NEGLIGIBLE
Nitrate content (ppm)	NIL	NEGLIGIBLE	NEGLIGIBLE

[1] http://sca.livingpast.com/verd.html (accessed on 28th october.2009)

[2] Meaning "green of Greece"

[3] http://www.sewanee.edu/Chem/Chem&Art/Detail_Pages/Pigments/Verdigris (accessed on 25th october.2009)

[6] http://www.tpub.com/content/engine/14111/css/14111_80.htm (accessed on 5th November, 2009)

[7] http://www.idph.state.il.us/envhealth/factsheets/NitrateFS.htm (accessed on 5th November, 2009)

[8] http://www.britannica.com/EBchecked/topic/3262/Acetobacter(accessed on 6th November, 2009)

[9] DETECTION OF HYDROGEN IN CORROSION OF COPPER IN PURE WATER,

G. Hultquist and P. Szakálos (accessed on 31st October, 2009)