Content

Introduction Objective Theory Procedure Chemical Reaction Observation Result Bibliography

IntroductionNickel

Nickel was first isolated by the Swedish chemist Cronstedt in 1751. It is the twenty-second most abundant element and the seventh most abundant transitional metal with an atomic number of 28 in the periodic table with an atomic weight of 58.71. It has five naturally occurring isotopes. It is a tough, silvery-white heavy metal and is highly resistant to attack by air and water. It occurs in igneous rocks, as a free metal and together with iron; it is also a component of the earth core. Nickel also occurs in living organisms, mainly in plants.

Nickel is hard, malleable, and ductile metal. It is of the iron group and it takes on a high polish. It is a fairly good conductor of heat and electricity. In its familiar compounds nickel is bivalent, although it assumes other valences. It also forms a number of complex compounds. Most nickel compounds are blue or green. Nickel dissolves slowly in dilute acids but, like iron, becomes passive when treated with nitric acid. Finely divided nickel adsorbs hydrogen.

Applications

The major use of nickel is in the preparation of alloys. Nickel alloys are characterized by strength, ductility, and resistance to corrosion and heat. About 65 % of the nickel consumed in the Western World is used to make stainless steel, whose composition can vary but is typically iron with around 18% chromium and 8% nickel. 12 % of all the nickel consumed goes into super alloys. The remaining 23% of consumption is

divided between alloy steels, rechargeable batteries, catalysts and other chemicals, coinage, foundry products, and plating.

Nickel is easy to work and can be drawn into wire. It resist corrosion even at high temperatures and for this reason it is used in gas turbines and rocket engines. Monel is an alloy of nickel and copper (e.g. 70% nickel, 30% copper with traces of iron, manganese and silicon), which is not only hard but can resist corrosion by sea water, so that it is ideal for propeller shaft in boats and desalination plants.

Humans use nickel for many different applications. The most common application of nickel is the use as an ingredient of steal and other metal products. It can be found in common metal products such as jewelry.

Occurance

Most nickel on Earth is inaccessible because it is locked away in the planet's iron-nickel molten core, which is 10 % nickel. The total amount of nickel dissolved in the sea has been calculated to be around 8 billion tons. Organic matter has a strong ability to absorb the metal that is why coal and oil contain considerable amounts. The nickel content in soil can be as low as 0.2 ppm or as high as 450 ppm in some clay and loamy soils. The average is around 20 ppm. Nickel occurs in some beans where it is an essential component of some enzymes. Another relatively rich source of nickel is tea which has 7.6 mg/kg of dried leaves.

Effects of nickel on health

Foodstuffs naturally contain small amounts of nickel. Chocolate and fats are known to contain severely high quantities. Nickel uptake will boost when people eat large quantities of vegetables from polluted soils. Plants are known to accumulate nickel and as a result the nickel uptake from vegetables will be eminent. Smokers have a higher nickel uptake through their lungs. Finally, nickel can be found in detergents.

Humans may be exposed to nickel by breathing air, drinking water, eating food or smoking cigarettes. Skin contact with nickel-contaminated soil or water may also result in nickel exposure. In small quantities nickel is essential, but when the uptake is too high it can be a danger to human health.

An uptake of too large quantities of nickel has the following consequences:

- Higher chances of development of lung cancer, nose cancer, larynx cancer and prostate cancer

- Sickness and dizziness after exposure to nickel gas

- Lung embolism

- Respiratory failure

- Birth defects

- Asthma and chronic bronchitis

- Allergic reactions such as skin rashes, mainly from jewelry

- Heart disorders

Nickel fumes are respiratory irritants and may cause pneumonitis. Exposure to nickel and its compounds may result in the development of a dermatitis known as “nickel itch” in sensitized individuals. The first symptom is usually itching, which occurs up to 7 days before skin eruption occurs. The primary skin eruption is erythematous, or follicular, which may be followed by skin ulceration. Nickel sensitivity, once acquired, appears to persist indefinitely.

Carcinogenicity- Nickel and certain nickel compounds have been listed by the National Toxicology Program (NTP) as being reasonably anticipated to be carcinogens. The International Agency for Research on Cancer (IARC) has listed nickel compounds within group 1 (there is

sufficient evidence for carcinogenicity in humans) and nickel within group 2B (agents which are possibly carcinogenic to humans). OSHA does not regulate nickel as a carcinogen. Nickel is on the ACGIH Notice of Intended Changes as a Category A1, confirmed human carcinogen.

Effects of nickel on the environment

Nickel is released into the air by power plants and trash incinerators. It will than settle to the ground or fall down after reactions with raindrops. It usually takes a long time for nickel to be removed from air. Nickel can also end up in surface water when it is a part of wastewater streams.

The larger part of all nickel compounds that are released to the environment will adsorb to sediment or soil particles and become immobile as a result. In acidic ground however, nickel is bound to become more mobile and it will often rinse out to the groundwater.

We do know that high nickel concentrations on sandy soils can clearly damage plants and high nickel concentrations in surface waters can diminish the growth rates of algae. Micro organisms can also suffer from growth decline due to the presence of nickel, but they usually develop resistance to nickel after a while.

For animals nickel is an essential foodstuff in small amounts. But nickel is not only favorable as an essential element; it can also be dangerous when the maximum tolerable amounts are exceeded. This can cause various kinds of cancer on different sites within the bodies of animals, mainly of those that live near refineries.

Nickel is not known to accumulate in plants or animals. As a result nickel will not bio magnify up the food chain.

Objective

The aim of this project is to determine Nickel content in chocolates.

MATERIAL Required

Test tube Dilute Hydrocloric acid Ammonium chloride Ammonium hydroxide Dimethyl Glyoxime Spatula Wash bottle

TheoryThere are many types of locally made toffees and chocolates available in the market at a cheaper price than known brands. Out of these, only 60–70% have food labels listing ingredients on the wrappers. The most common ingredients listed are sugar, liquid glucose, milk solids, cocoa solids, hydrogenated vegetable oil (HVO), vegetable fats, malt extract, soya solids, permitted emulsifier, salts, buffering agents, permitted stabilizer, sodium bicarbonate, cocoa butter, wheat flour, edible starches, vegetable oil, added flavour, soya lecithin, yeast and flour improvers, etc. Out of the above mentioned ingredients, milk solids, cocoa solids, cocoa butter, hydrogenated vegetable oil, vegetable fats, permitted emulsifier, buffering agents and permitted stabilizer may be the source of nickel, lead and cadmium contamination.Toxicity of nickelNickel in chocolates made the news headlines in the early 1990s. Nickel in various types of chocolates and toffees was reported by Selavpathy and Sarala Devi (1995) with a range of 0.15–3.55 mg/g with a mean of 0.88 mg/g. Nickel is the main known contaminant resulting from themanufacturing process of chocolate, when its hardening is done by hydrogenation of unsaturated

fats using nickel as catalyst. Cocoa butter is another important ingredient which may contain high concentrations of nickel (Selavpathy and Sarala Devi, 1995). Some other pathways for nickel to toffees are raw materials, their processing and canning for transportation and storage in nickel containers (Melsallam, 1987). Nickel at trace amount may be beneficial as an activator of some enzyme systems (Underwood, 1977). At higher levels, it accumulates in the lungs and may causebronchial haemorrhage. Other symptoms include nausea, weakness, dizziness, etc (Nielson, 1977).However, nickel compounds are not currently regarded as either human or animal carcinogens (WHO, 1984), but the possibility that Ni can act as a promoter has been reported (WHO, 1991).

This work has been done in view of the toxic effects of these heavy metals and their presence in chocolates, which can be deleterious to children. The present study reports concentration of lead, nickel and cadmium in the chocolates and candies available in suburban areas of Mumbai, India. Sample preparation and analysis A total of 69 different brands of chocolates and candies were procured from the different suburban areas of Mumbai. Two different batches of the same brand of chocolates packed on different dates were purchased to observe the variation in the elemental contamination levels of the products. All the chemicals used were AR grade. Standard stock solutions were prepared from lead nitrate (Pb(NO3)2) for lead, from nickel sulphate for nickel,

and from cadmium sulphate for cadmium, dissolved in nitric acid. These stock solutions were standardized with the primary standard Certified Reference Material (Hay V-10). Demineralized water from Millipore Elix-3 was used for all dilutions and preparation of solutions.After weighing (milk and cocoa based 5 g and sugar based 10 g) the chocolates were taken for wet digestion with mixture of nitric acid (HNO3) and perchloric acid (HClO4) in the ratio 3:1 for decomposition. After gentle heating for 16 h, colourless solution was obtained which was evaporated to near dryness. On completion of digestion and adequate cooling of residues, solutions were made up to 10 mLwith 0.04 mol/Lnitric acid. All the chocolates/candies samples were processed and digested in triplicate. The variation among the elemental content in these replicates was within78%. One blank was always prepared with each batch. Quality assurance oftrace metals analysis was done by analysing Certified Reference Material (CRM) Hay V-10, supplied by Analytical Quality Control Services (AQCS), International Atomic Energy Agency (IAEA). The results agree within 77% of the certified values (Table 1).

The determination of elemental concentrations by Atomic Absorption Spectrophotometer model GBC (Avanta PM) in all the digested solutions was made in triplicate and percentage of relative standard deviation (%RSD) in the concentrations of analytical replicates was 72%. Allthe measurements were made under optimization of the parameters mentioned in Table 2.

The range and arithmetic mean concentrations of cadmium, nickel and lead in the different types of chocolates and candies are given in Table 3 as averages of three replicates of the individual chocolates/candies.

From a preliminary survey of a small group of children, it was found that cocoa-based chocolates are their first choice and that they eat daily 2–3 chocolates. The weight of chocolates varies from 4 to 40 g, but the majority of the chocolates weight about 20 g. As chocolates are not a regular food item, ingestion rate of 20 g/day is taken for all the metal intake estimation in this study.Chocolates were divided into three categories, namely cocoa- , milk- and sugar-based candies, on the basis of their ingredients and labelling name. The range and average concentrations of lead, nickel and cadmium in all three types of chocolates are given in Table 3.Lead has been a well-known contaminant in all types of food items from the early phase of food industrialization in different parts of the world. A possible association between increased lead content in blood and reduced intelligence quotient has been substantiated and a lower threshold could not be set (FAO/WHO, 1993). Thus, the nickel intake from chocolate can be considered as less harmful. Processing of

chocolates is done in steel containers from which nickel contamination is possible in addition to the contamination from the catalyst used in preparation of the HVO. ConclusionsThe concentrations of all analysed elements were highest in the cocoa-based chocolates followed by milk-based and sugar- and fruit flavour-based chocolates. The higher concentration of these elements in the chocolates is due mainly to their higher contents in the raw materials suchas cocoa beans, cocoa solids, and cocoa butter. The daily intake of cocoa-based chocolates must be reduced to keep the PTWI for lead and cadmium within the prescribed limits. Raw materials having lower content of these elements should be used to decrease the concentrations of these metals in chocolates.

ARTICLE IN PRESS

Procedurev Take a small piece of the chocolate and crush it into fine powder. Put it into a test tube and

add prerare its original solution and a little hydrochloric acid .v To the solutions obtained, add ammonium chloride and ammonium hydroxide.v Now take a little amount of the solution and pass hydrogen sulphide gas through it using kipp's apparatus . Formation of a black colour indicates the presence of group four cations.v Now to the filtrate, add small amount of dimethyl glyxime. If a rose red coloured precipitate is obtained in a scarlet red solution, then presence of Nickel (Ni2+) i s confirmed.

Chemical reaction

OBSERVATIONS

S.NO. Name of chocolate Inference 1. Dairy milk Nickel absent

2. Melody Nickel present

3. 5 star Nickel absent

4. Munch Nickel absent

5. Bar one Nickel absent

Result

Nickel is found in melody.

Bibliography

1. Comprehensive practical chemistry 2.