Applications of Coordination Compounds

Transcript

0:00Introduction

Hello everyone! Let me start with a small puzzle. One platinum ion, two ammonia molecules and two chloride ions can join into two different compounds, with exactly the same formula. One of them is an anticancer drug, and the other is not. So which one, and why? Hold that question; we will answer it today, as we see where coordination compounds are used, from the lab to the hospital to the factory. Questions on these uses come up often in JEE, and they are quick marks. So, let's begin.

0:33In the lab: analysis with complexes

So, first, the laboratory. N i two plus: the small two plus up top is the charge on the nickel ion. The plus sign means we add dimethylglyoxime, and the arrow means gives, so we get a red precipitate. Okay? Next, copper, C u two plus. Add ammonia, N H three, the small three below counting the hydrogens, and you get a deep blue solution. Right? Iron, F e three plus, has two tests. With thiocyanate, SCN minus, it gives a blood red colour, and with ferrocyanide, Prussian blue. With me? Water hardness is measured by titration with N a two EDTA, the disodium salt of EDTA, right? One colon one on screen means it binds calcium, C a two plus, and magnesium, M g two plus, one ion each. Remember this for Example two.

1:29Metallurgy: extracting and purifying metals

Now, metallurgy. Silver and gold, written A g and A u, are leached, or dissolved out of their ores, as cyanide complexes. Read the first as: open square bracket, A g, C N in round brackets, two times, close bracket, with a minus charge up top. The gold complex is the same, with A u in place of A g. Okay? Then zinc is added, and the silver or gold is recovered as the metal. Simple, right? Nickel is purified by the Mond process. N i plus four C O gives N i, C O four, in square brackets, tetracarbonylnickel zero; the two half arrows mean it goes both ways. This complex is volatile: it vaporises easily. With me? It forms at three hundred and thirty to three hundred and fifty kelvin; the dash means to, and capital K is kelvin. At four hundred and fifty to four hundred and seventy kelvin, it decomposes to pure nickel. Got it?

2:32Biology: metals inside living things

Now, biology. Let me ask you this. Chlorophyll, the green pigment of leaves, which metal does it carry? Magnesium, M g, very good! Many students say iron, thinking of blood, and that is the trap. Iron, F e, is in haemoglobin, the red pigment of blood. Clear? Vitamin B twelve, the twelve written small below, is cyanocobalamin. Here is a topper's trick: cyano, cobal, amin, and cobal is for cobalt, C o, not iron. And carboxypeptidase A, an enzyme, has zinc, Z n. Got it?

3:13Medicine: cis-platin and chelation therapy

Now medicine, and our puzzle. The formula: P t, then N H three in round brackets, two times, then C l two, all in square brackets. Its two isomers are cis, with the chlorides adjacent, and trans, with them opposite. Which one is the anticancer drug? The cis isomer, yes, exactly! Cis-platin inhibits tumour growth, because only the cis form binds DNA in the way that is needed. Puzzle solved: same formula, different shape, different job. Okay? Next, metal poisoning. EDTA treats lead poisoning, D penicillamine removes excess copper, C u, and desferrioxamine B removes excess iron, F e. With me? This is chelation therapy: the chelating agent binds the metal ion and is excreted. Here is a common trap: EDTA and D penicillamine do not inhibit tumours; they treat metal poisoning. Clear?

4:15Catalysis: complexes in industry

Now industry, where complexes are catalysts. Wilkinson's catalyst is R h, C l, then P P h three in round brackets, three times, all in square brackets: rhodium with triphenylphosphine. It hydrogenates alkenes, adding hydrogen across the double bond. Okay? The Ziegler Natta catalyst is T i C l four with A l, C two H five in round brackets, three times, which is triethylaluminium. It polymerises alkenes. So, rhodium for Wilkinson's, titanium for Ziegler Natta. Got it?

4:50Photography and electroplating

Next, photography. Hypo fixes a film by dissolving the unexposed silver bromide, A g B r, as a complex ion: A g, S two O three in round brackets, two times, in square brackets, three minus. The full equation is our Example one. Okay? Now electroplating. To plate silver or gold, we use the cyanide complex, not a simple salt like silver nitrate, A g N O three. Why go to all that trouble? Because the complex keeps the free silver ions, A g plus, low and steady. So the metal deposits slowly, and the coating is smooth and even. Gold plating works the same way. Right?

5:34Example 1: reaction of hypo fixing a photographic film

Let's try Example one. Write the reaction by which hypo fixes a photographic film. Here is a hint: hypo is sodium thiosulfate. Pause the video and try it first. Done? Okay, let's check. Hypo is N a two S two O three. Silver is plus one, and each thiosulfate is minus two, so the complex has plus one, plus two times minus two, which equals minus three. So it needs three sodium ions, N a plus. With me? So, A g B r plus two N a two S two O three gives N a three, A g, S two O three two times, in square brackets, plus N a B r. Now count the sodium: two times two gives four. Three of them go into the complex, and the last one into sodium bromide. So it is balanced, and it takes two hypo, because each silver holds two thiosulfates.

6:33Example 2: water hardness in ppm CaCO3 by EDTA titration

Clear? Now a harder one, Example two. One hundred millilitres of hard water needs ten point zero millilitres of zero point zero one zero molar N a two EDTA; capital M means molar, moles per litre. Express the hardness as p p m, parts per million, of calcium carbonate, C a C O three. Pause the video and try it first. Done? Okay, let's check. First the moles of EDTA, written small n: ten millilitres is zero point zero one zero zero litres, times zero point zero one zero moles per litre, the raised minus one meaning per. That gives one point zero times ten to the power minus four moles. Okay? Now let me ask you this. How many moles of calcium and magnesium ions does this EDTA bind? The same, one point zero times ten to the power minus four moles, exactly! EDTA binds one to one, and M two plus stands for calcium or magnesium. Do not halve or double it; that is the trap. Right? Now count it all as calcium carbonate, at one hundred grams per mole. One point zero times ten to the power minus four, times one hundred, gives zero point zero one zero grams. That sits in one hundred millilitres of water, which is about one hundred grams. Got it? Parts per million means grams in a million grams of water. So zero point zero one zero over one hundred, times ten to the power six, gives one hundred. The hardness is one hundred p p m. See how fast that was?

8:16Quick revision: tests, metallurgy, biology, drugs, catalysts

So, quick revision. In the lab and in metallurgy: EDTA, one to one, for hardness, cyanide for silver and gold, and the Mond process for nickel. In the body: magnesium in chlorophyll, iron in haemoglobin, cobalt in vitamin B twelve, and zinc in carboxypeptidase A, an enzyme. In medicine, cis-platin, and chelation for poisoning; and for catalysts, rhodium in Wilkinson's, titanium in Ziegler Natta. Now go and try the practice problem on this page. All the best!