Chemical lesson 10 - studentsomshanticollege.com · Chemistry Module 1- Lesson 10 6 Chlorophyll is another porphyrin chelate. In chlorophyll, the metal at the centre of the chelate

Chemistry Module 1- Lesson 10

1

Chemical lesson 10

Study guide - Notes – Questions

This final week we look at chelates plus some revision topics.

Your weekly program. Develop your own method by all means but this will get you going.

Read the notes attached here. All questions and the final assessment are based on what is in the notes.

Read the chapter sections in the reading section ( the text has much greater detail than what you are expected to know) especially look at diagrams and figures

At this stage not much will make sense but that is OK

With your text as reference and this study sheet go through the Power point presentation. Make notes where needed.

MANDATORY watch all of the embedded video links (you will need internet access to do this)

Optional - Listen to the audio file of a live lesson; be aware that there will be long pauses with not much going on at certain points.

Refine your notes / mind maps on the key concepts outlined in these weekly study sheets. Check your understanding

Now go through your homework questions and answer those

Your study resources

Textbook

Audio files of the actual lessons

Weekly study sheet

Power Point slides

YouTube links and YouTube as a general resource

College forum site

Molecule kit

Textbook reference Bettleheim Edition 9 – There are no reading from the text for this topic


2

Key Concepts to understand

Chelates what are they

Chelates their properties and importance

Review questions

Use the links in the power point presentation. Good sources for chemistry videos are Bozeman science http://www.bozemanscience.com/ Crash course chemistry – YouTube Socratic.org https://socratic.org/

http://www.bozemanscience.com/


3

Study Notes

Chelates Chelates you hear the phrase or word often in nutrition and about fertiliser products for growing plants. But what really is a chelate?

A basic definition of a chelate is any metal that is attached to an anion (negatively charged group) by two or more attachment sites. Another way of saying this - a compound having a ring structure that usually contains a metal ion held by two or more coordinate bonds.

The coordinate bond is a special form of covalent bond (Coordinate covalent) where an element donates electrons from its lone electron pair into an empty metal species orbital to form the bond. The ions or molecules surrounding the metal species are called ligands. Ligands are bound to the central atom by a coordinate covalent bond and are said to be coordinated to the atom.


4

The central atom or ion, which is usually metallic, is called the coordination centre.

Chelation describes a particular way that ions and molecules bind metal ions. Ligands are organic compounds, and are can be called chelants, chelators, chelating agents, or sequestering agents. Many essential biological chemicals are chelates. Chelates play an important role in oxygen transport and in photosynthesis. Furthermore, many biological catalysts (enzymes) are chelates. In addition to their significance in living organisms, chelates are also economically important, both as products in themselves and as agents in the production of other chemicals. Porphine is a chelating agent in that it forms bonds to a metal ion through nitrogen atoms. Each of the four nitrogen atoms in the centre of the molecule can form a bond to a metal ion.


5

Porphine is the simplest of a group of chelating agents called porphyrins. Porphyrins have a structure derived from porphine by replacing some of the hydrogen atoms around the outside with other groups of atoms.

porphine heme

One important porphyrin chelate is heme, the central component of haemoglobin, which carries oxygen through the blood from the lungs to the tissues. Heme contains a porphyrin chelating agent bonded to an iron(II) ion. Iron can form six bonds. Four of these bonds tie it to the porphyrin. One of iron's two remaining bonds holds an oxygen molecule as it is transported through the blood. The diagrams above and below show the structure of the porphine and heme molecules.


6

Chlorophyll is another porphyrin chelate. In chlorophyll, the metal at the centre of the chelate is a magnesium ion. Chlorophyll, which is responsible for the green colour of plant leaves, absorbs the light energy that is converted to chemical energy in the process of photosynthesis.


7


8

Another biologically significant chelate is vitamin B-12. It is the only vitamin that contains a metal, a cobalt (II) ion bonded to a porphyrin-like chelating agent. As far as is known, it is required in the diet of all higher animals. It is not synthesized by either higher plants or animals, but only by certain bacteria and moulds. These are the sources of the B-12 found in animal products. Because vitamin B-12 is not found in higher plants, vegetarians must take care to include in their diets foods or supplements that contain the vitamin.


9

Chelate uses Biochemistry and microbiology As already mentioned important biological chelating agents include the porphyrin rings in haemoglobin and chlorophyll. Many microbial species also produce molecules that serve as chelating agents. Geology Chemical weathering is attributed to organic chelating agents (e.g., peptides and sugars) that extract metal ions from minerals and rocks. Most metal complexes in the environment and in nature are bound in some form of chelate ring (e.g., with a humic acid or a protein). Thus, metal chelates are relevant to the mobilisation of metals in the soil, the uptake and the accumulation of metals into plants and microorganisms. Selective chelation of heavy metals is relevant to bioremediation (e.g. removal of isotopes from radioactive waste). Nutritional supplements In the 1960s, scientists developed the concept of chelating a metal ion prior to feeding the element to animals. They believed that this would create a neutral compound, protecting the mineral from being complexed with insoluble salts within the stomach, which would render the metal unavailable for absorption. Amino acids, being effective metal binders, were chosen as the prospective ligands, and research was conducted on the metal-amino acid combinations. The research supported that the metal-amino acid chelates were able to enhance mineral absorption. Synthetic Chelates Synthetic chelates have also been developed. An example of such synthetics is ethylenediaminetetraacetic acid (EDTA). EDTA is a versatile chelating agent. It can form four or six bonds with a metal ion, and it forms chelates with both transition-metal ions and main-group ions.

Heavy metal detoxification Chelation therapy is used to detoxify poisonous metal agents such as mercury, arsenic, and lead by converting them to a chemically inert form that can be excreted without further interaction with the body.


10

Although they can be beneficial in cases of heavy metal poisoning, chelating agents can also be dangerous. Use of disodium EDTA instead of calcium EDTA has resulted in fatalities due to hypocalcemia. As an antidote for lead poisoning, calcium disodium EDTA exchanges its chelated calcium for lead, and the resulting lead chelate is rapidly excreted in the urine. The calcium salt of EDTA, administered intravenously, is also used in the treatment of acute cadmium and iron poisoning Fertilizers Metal chelate compounds are common components of fertilizers to provide micronutrients. These micronutrients (manganese, iron, zinc, copper) are required for the overall health of the plants. Most fertilizers contain phosphate salts that, in the absence of chelating agents, typically convert these metal ions into insoluble solids that are of no nutritional value to the plants. House hold products EDTA is frequently used in soaps and detergents, because it forms complexes with calcium and magnesium ions. These ions are in hard water and interfere with the cleaning action of soaps and detergents. The EDTA binds to them, sequestering them and preventing their interference. Food EDTA is also used extensively as a stabilizing agent in the food industry. Food spoilage is often promoted by naturally-occurring enzymes that contain transition-metal ions. These enzymes catalyse the chemical reactions that occur during spoilage. EDTA deactivates these enzymes by removing the metal ions from them and forming stable chelates with them. It promotes colour retention in dried bananas, beans, chick peas, canned clams, pecan pie filling, frozen potatoes, and canned prawns. It improves flavour retention in canned carbonated beverages, salad dressings, mayonnaise, margarine, and sauces. It inhibits rancidity in salad dressings, mayonnaise, sauces, and sandwich spreads. EDTA salts are used in foods at levels ranging from 33 to 800 ppm. In other applications, EDTA dissolves the CaCO3 scale deposited from hard water without the use of corrosive acid. EDTA is used in the separation of the rare earth elements from each other. The rare earth elements have very similar chemical properties, but the stability of their EDTA complexes varies slightly. This slight variation allows EDTA to effectively separate rare-earth ions. EDTA is used as an anticoagulant for stored blood in blood banks; it prevents coagulation by sequestering the calcium ions required for clotting. .


11

Homework Questions

Q1 Outline three ways chelates are used in everyday life.

Q2 What two important biological processes are made possible by chelates? And what is the metal species involved in these processes?

Q3 What is a coordinate bond?

Q4 Give one definition of a chelate molecule

Q5 Define simply what a Ligand is?

Review Questions

Q6 Using the equation below answer the following questions

Q7 What is the molecular weight of C6H12O6? Q8 Is this equation balanced? Q9 What is the molar ratio between Co2 and O2? Q10 If you have five moles of C6H12O6 produced how many moles of H2O are needed for its formation? Q11 Explain what the phrase Oil RIG means in redox chemistry Q12 In the picture below, explain what is happening to the Zinc rod in redox terms


12

Q13 vIn the graph below what type of reaction is being depicted And what happens to the energy being liberated?

Q14 Using Le Chatelier’s principle predict the change expected in equilibrium for the following circumstances

system change result

CO2 + H2 → H2O(g) + CO a drying agent is added to

absorb H2O

H2(g) + I2(g) → 2HI(g) Some nitrogen gas is added


13

NaCl(s) + H2SO4(l) →

Na2SO4(s)+ HCl(g)

reaction is carried out in an

open container

H2O(l) → H2O(g) water evaporates from an

open container

HCN(aq) → H+(aq) + CN–(aq) the solution is diluted

AgCl(s) → Ag+(aq) + Cl–(aq) some NaCl is added to the

solution

N2 + 3 H2 → 2 NH3 a catalyst is added to speed

up this reaction

Q15 What is the property of water that allows insects to cross on its surface Q16 Explain the difference between pouring petrol and pouring water in terms of intermolecular forces


14

Documents

Chemical lesson 10 - studentsomshanticollege.com · Chemistry Module 1- Lesson 10 6 Chlorophyll is another porphyrin chelate. In chlorophyll, the metal at the centre of the chelate