Exercises and Case studies

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Chapter: Essentials of Inorganic Chemistry : Transition Metals and d-Block Meta Chemistry

1. Silver nitrate solution 2. Ferrous sulfate tablets 3. Zinc sulfate eye drops


Exercises

 

1. What is the oxidation state of the central metal atom in the following complexes?

(a)        [Au(CN)4]

(b)       [V(CO)6]

(c)        [Fe(H2O)6]2+

(d)       [PdCl6]2−

 

2. What is the charge of a complex formed by

(a)        Co2+ and 3C2O42−

(b)       Pt4+ and 3H2O and 3Br

(c)        Au+ and 2CN

 

3. Draw the energy diagrams displaying the d-orbital splitting for the low and high-spin complexes of the following examples assuming the formation of an octahedral complex:

(a)        Fe3+

(b)       Zn2+

(c)        Cu2+

(d)       Cr3+

(e)        Cr2+

 

4. Predict the geometry of the following complexes:

(a)        Zn(NH3)4

(b)       [Mn(OH2)6]2+

(c)        Ag(NH3)2+

 

Case studies

 

1. Silver nitrate solution

Your pharmaceutical analysis company has been contacted by an important client and asked to analyse a batch containing silver nitrate (AgNO3) solution for topical use. The description of your brief states that you are supposed to analyse the API in these solutions following standard quality assurance guidelines.

Typical analysis methods used for quality purposes are based on titration reactions. A certain amount of solution is diluted and treated with nitric acid and ammonium iron(III) sulfate. The solution is then titrated with ammonium thiocyanate [30].

(a)    Research the type of titration described. Describe the chemical structure of any reagents involved in the analysis.

(b)   Formulate the relevant chemical equations. What is the role of ammonium iron(III) sulfate?

(c)    The package states that each the solution contains 10% silver nitrate. A volume containing 50 mg of silver nitrate is diluted with water and 2 ml of nitric acid and 2 ml of ammonium iron(III) sulfate solution are added. The solution is then titrated with 0.02 M ammonium thiocyanate solution until a red colour appears.

(d)   For each titration, the following volume of ammonium thiocyanate solution has been used:

14.5 ml 14.8 ml 15.0 ml

(e)    Calculate the amount of AgNO3 present in your sample. Express your answer in grams and moles.

(e)    Critically discuss your result in context with the stated value for the API.

 

(f)     Research the typically accepted error margins.

 

2. Ferrous sulfate tablets

Your pharmaceutical analysis company has been contacted by an important client and asked to analyse a batch of tablets containing dried ferrous sulfate (FeSO4) tablets. The description of your brief states that you are supposed to analyse the API in these tablets following standard quality assurance guidelines.

Typical analysis methods used for quality purposes are based on titration reactions. A certain amount of ferrous sulfate tablets are crushed and dissolved. The solution is then titrated with cerium(IV)sulfate under acidic conditions using ferroin as the indicator British Pharmacopoeia.

(a)    Research the type of titration described. Describe the chemical structure of any reagents involved in the analysis.

(b)   Formulate the relevant chemical equations.

(c)    The package states that each tablet contains 200 mg ferrous sulfate. The weight of 20 tablets has been determined to be 6.24 g. A certain amount of powder containing 0.5 g of dried ferrous sulfate is dissolved in water and sulfuric acid, and ferroin is added as an indicator. The solution is then titrated with 0.1 M ammonium cerium(IV)sulfate solution [30].

For each titration, the following volume of ammonium cerium(IV)sulfate solution has been used:

32.5 ml 33.3 ml 32.9 ml

Calculate the amount of FeSO4 present in your sample. Express your answer in grams and moles.

(d)    Critically discuss your result in context with the stated value for the API.

(e)     Research the typically accepted error margins.

 

3. Zinc sulfate eye drops

Zinc sulfate solution has been traditionally used as an astringent and a mild antiseptic. Nowadays, its use is limited. Your pharmaceutical analysis company has been contacted by an important client and asked to analyse a batch of eye drops containing zinc sulfate (ZnSO4). The description of your brief states that you are supposed to analyse the API in these tablets following standard quality assurance guidelines.

Typical analysis methods used for quality purposes are based on titration reactions. A certain volume of the eye drops is diluted and typically titrated with ammonium edetate using morbant black as indicator [30].

(a)    Research the type of titration described. Describe the chemical structure of any reagents involved in the analysis. You might want to familiarise yourself with the concept of chelation (see Chapter 11).

(b)    Formulate the relevant chemical equations.

(c)     The package states that each sterile solution contains 0.25% w/v of zinc sulfate heptahydrate. For the titration, 5 ml of the zinc sulfate solution is diluted and an ammonia buffer is added to achieve pH 10.9. This solution is titrated with 0.01 M disodium edetate and mordant black as indicator [30].

For each titration, the following volume of edetate solution has been used:

5.0 ml 4.6 ml 4.3 ml

Calculate the amount of ZnSO4 present in your sample. Express your answer in grams and moles.

(d)    Critically discuss your result in context with the stated value for the API.

(e)     Research the typically accepted error margins.

 

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