Done by:

1. Asiah Bt. Abang Kassim
2. Elsabet Ellen Tze
3. Jonnathan Stephan
4. Melanie Ann Perera
5. Natasha Zainorin
6. Nur Farahana Halil
7. Nurul Najihah Khamil
8. Siti Nazliah Yusoff
9. Tharani Malar David
10. Yong Siok Chin

Transition Metal

In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings: It commonly refers to any element in the d-block of the periodic table, including zinc, cadmium and mercury. This corresponds to groups 3 to 12 on the periodic table, which are all metals. More strictly, IUPAC defines[1] a transition metal as "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." By this definition, zinc, cadmium, and mercury are excluded from the transition metals, as they have a d10 configuration. Only a few transient species of these elements that leave ions with a partly filled d subshell have been formed, and mercury(I) only occurs as Hg22+, which does not strictly form a lone ion with a partly filled subshell, and hence these three elements are inconsistent with the latter definition.[2] They do form ions with a 2+ oxidation state, but these retain the 4d10 configuration. Element 112 may also be excluded although its oxidation properties are unlikely to be observed due to its radioactive nature. This definition corresponds to groups 3 to 11 on the periodic table.

Problem 1

“Please help! I recently purchased a copper ring that has turned my finger green. It has been a few days and the green stain is still there. Can you please tell me why does the copper ring turn my skin green?”

Statement 2


“Please help!! My kettle is stained with brownish spots left by the water faucet. After adding vinegar into the kettle and let it boil after some time, its now giving out a golden brown goo. Can you please tell me why this is happening?”

Question 1 (For both Problem 1 and Statement 2)

The metals that caused coloured stains in the statements are all from the same type. Determine the type.

Answer:
The type of metal that caused the staining in both the problems is the transition metals. This is because both the staining were coloured. In the first problem, it was green in colour whereas in the second problem, the staining was a golden brown.

Question 2

What makes this type of metals form coloured stains?

Answers:

1) The copper ring is actually a metal ring coated with copper (golden in colour). Reactions such as oxidation made the layer of copper fall off, exposing the metal beneath to chemical reactions that can happen in open air. Three possible metals were found to be able to produce a green stain. The metals are Nickel, Iron, and Vanadium. Since rings are jewellery, the most common metal used in the production of them is Nickel. The green stain therefore is [Ni(H2O)6­]2. 2) The brown spots in the kettle are insoluble iron (III) oxide. It is the product of the oxidation of iron (II) in water.

Chemical equation: 6CH3COOH +Fe2O3 2Fe(CH3COO)3 + 3H2O Ionic equation: 4Fe2+ (aq) + 8HCO3 - (aq) + O2 (g) 2Fe2O3(s) + 8CO2(g) + 4H2O(l)

When vinegar (aqueous solution of acetic acid) was added to the water in the kettle and left to boil, Fe3+ (aq) was formed directly. Fe(s) + NO­3-(aq) + 4H+(aq) Fe3+(aq) + NO(g) + 2H2O(l) When an acidic solution of iron (III) is made more basic, a gelatinous red-brown precipitate (a hydrous oxide, Fe2O3.nH2O) is formed.

Additional:

What made the green stain remain even after a few days?

Answer: The metal Nickel had already been oxidised to its stable state and therefore can remain as it is for a number of days on the skin until it its scrubbed off thoroughly. This is because going across the 1st transition series, the +2 oxidation state become more stable compared to the +3 oxidation state. This means that this process becomes increasingly difficult: M2+ (aq) M2+ + e- This is because the 3rd electron removed is from the inner 3d subshell which is closer to the nucleus. As the nuclear charge increases across the series, the ionization energy also increases. Fe3+ is expected to be more stable than Fe2+ because the removal of an electron from Fe2+ forms the more stable Fe3+, where the 5d orbitals are all half filled. Fe2+([Ar]3d6) Fe3+([Ar]3d5)