Synthesis and Characterization of Tin Iodide

Work by Brandon Lam, M15604

Synthesis and characterization of Tin(IV) Iodide 1 AIM OF EXPERIMENT The aim of the experiment is to prepare Tin(IV) iodide by redox reaction using Tin and Iodine. We characterize the product by melting point determination and calculate the yield of the reaction. Further characterization test are done to study the properties of Tin(IV) iodide.

2 INTRODUCTION Tin has atomic number 50 and can be recognized by its silvery-white, soft, malleable and metallic appearance. Tin has two oxidation states, +2 and the slightly more stable, +4. Tin is mined from Cassiterite, an ore containing the oxide form of tin. [1] Due to its many uses and applications, Tin has been mined excessively over the past decade, and soon its depleting primary source, cassiterite, would not be able to meet the world’s demand. One of its many uses include forming an alloy with lead to produce solder. Solder is commonly used for joining pipes and electrical circuits. Tin is also used for plating steel containers for food preservation. [1] Iodine is the 53rd element of the periodic table. It is a halogen bearing the appearance of a metallic lustrous grey in the solid phase and a violet gas in the gaseous phase. Sublimation of iodine occurs at standard pressure and room temperature due to its triple point being above 1 atm. Iodine has a low solubility in polar solvents like water, owing to its non-polar properties. However, it is easily solvated by non-polar solvents like hexane. Iodine adopts a variety of oxidation states, however only the oxidation state of -1 is of significance, being the form found in iodide salts and organoiodine compound. [2] Iodine plays an important role in our biological function, it is mainly stored in the thyroid gland, which has functions in synthesis of hormones for regulating body growth and temperature. Tin (IV) iodide is a tetrahedral covalent compound and its salt appears as a bright orange powder. It can dissolve in non-polar solvent and hydrolyse in water. It is used in reaction with phosphine for formation of halotin anions. [3] Otherwise, tin (IV) iodide has little to no real life applications.

3 CHEMICAL REACTION Sn (s)+2 I 2(s) C H 2 C l 2 Reflux Sn I 4 ( aq) →

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Work by Brandon Lam, M15604 The oxidation state of Sn changes from 0 in Sn to +4 in SnI 4, Sn is oxidized as a result. The oxidation state of I changes from 0 in I 2 to -1 in SnI4, I is reduced as a result. This is a redox reaction.

4 PROCEDURE 0.1190g of tin was shredded with scissors and added together with 0.4818g of iodine solid into a 25mL round bottom flask (RBF). 6mL of dichloromethane was measured out with a graduated cylinder and added to the RBF. A stir bar was added for stirring the solution. Reflux was set up by first connecting a water pump to the inlet of the condenser and rubber tubing out of the outlet. The RBF was securely clamped using a retort stand and the condenser was attached to the RBF using a keck clip. The water pump was turned on, pumping water at room temperature. The apparatus was lowered into a water bath set at 130°C with rotation at 1400rpm such that the content in the RBF is In line with the water bath level. Reflux was achieved and the mixture was refluxed for 30 minutes until the mixture turned brownishorange. Gravity filtration was used to filter the mixture into a 25mL RBF. The glass funnel used had a cotton plug to remove the excess solid from the filtrate. Attached the RBF to the adaptor head on the rotary evaporator and secured using a keck clip. Rotation was started and the RBF was lowered into a water bath of 55°C until the content level was aligned with the water bath level. Engaged the vacuum pump and the pressure decreased till a reading of 600 was achieved. The RBF was removed when all solvent was removed. The RBF (with the product) was weighed and the mass of product was calculated to be 0.549g. The purity of the product was determined using a melting point apparatus. The measured melting point range was 144°C – 146.1°C A further characterization test was done. Half a spatula of product was added to a dry test tube along with 2mL of analytical grade acetone. Following that, deionised water was added dropwise until no further changes was observed. All observation was recorded and will be discussed later. 5

RESULT

Theoretical Yield

n Sn=

n I2 =

mass 0.1190 = =0.001002 mol M r 118.71

mass 0.4818 = =0.001898 mol M r 253.80

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Work by Brandon Lam, M15604

Sn+ 2 I 2 C H 2 C l 2 Reflux Sn I 4 →

(workings for mole ratio in pen)

∴

The limiting reagent is I2 and the maximum moles of SnI4 formed is

0.00094917 mol

mass Sn I 4 =0.00094917 ×636.328=0.5945 g Percentage Yield & Melting Point

yield=

Actual yield 0.5490 = =92.3 Theoretical yield 0.5945

Theoretical melting point: 144.0°C Experimental melting point range: 144.0°C – 146.1°C Table of results: Percentage yield 92.3%

Melting point range (°C) 144.0 – 146.1

6 DISCUSSION Observations When CH2Cl2 in liquid phase is added to iodine solid, the solution turns purple as iodine is a non-polar molecule and thus dissolves in a solvent with similar polarity like dichloromethane (DCM). Tin is insoluble in DCM thus it remains as a solid at the bottom of the RBF. A reflux was set up for the maintenance of the reaction at a temperature higher than the boiling point of the solvent (DCM). This is also done so that the solvent is not lost to the atmosphere in the gaseous phase. The water pumped into the condenser was at room temperature. This was to ensure no condensation occurs at the cooling coils. The solvent used was DCM, not water, thus condensation will cause water droplets to form on the cooling coils, drip back into the RBF and contaminate the reaction mixture. Furthermore, from the characterization test, we see that the product reacts with water, so water should not be part of the reaction mixture. In order to increase the rate of reaction, the temperature of reaction must be moderately high. However, since DCM has a low boiling point (39.8°C), a reflux 3 | Page

Work by Brandon Lam, M15604 was set up so that the reaction could still take place at a high temperature. The reaction proceeded for around 30 minutes at 120°C. In the process, I2 and Sn is consumed as SnI4 is produced as the concentration of I 2 decreases and that of SnI4 increases. Consequently the reaction mixture turns from purple to brownishorange. The SnI4 dissolved in DCM takes the appearance of a brownish-orange solution. At the end of the reaction, black solid was observed at the bottom of the RBF. This black solid is the unreacted tin metal. This makes sense as iodine is the limiting reagent (as calculated above), leaving tin in excess. In order to remove the excess reactants, gravity filtration was used and the mixture in the RBF was pass through a cotton plug into a clean and dry RBF. After transferring the solution into the RBF, orange precipitate was observed to form on the walls of the RBF. This is probably due to the lower surrounding temperature which decreases the solubility of SnI 4 in DCM, causing its precipitation. Next, in order to purify the product, removal of the solvent is required. Therefore, we boil the product obtained from gravity filtration using the rotary evaporator. To quickly remove the solvent, a high temperature is needed, however, this may decompose the product. Thus the product is boiled under sub atmospheric pressure instead. At a lower pressure, a lower temperature is needed to boil the DCM away. After the DCM was removed, precipitation of SnI 4 crystals were observed, it appeared bright orange. The characterization test included adding half a spatula of the final product to 2mL of analytical grade acetone in a test tube. Acetone solvated the final product (SnI4 crystals), forming a dark brown solution. It may seem odd that acetone, a polar solvent, can solvate SnI4, a non-polar compound. But, acetone (CH3COCH3), has two non-polar and hydrophobic methyl groups, which help in the solute-solvent interactions between itself and SnI 4. Deionised water was added to the test tube, while agitating it continuously. The solution turned from dark brown to light brown then yellow as the concentration of SnI 4 decreases. Upon further addition of water, white precipitate formed. Tin(IV) hydroxide is the white precipitate and is formed as described by the equation below. [4]

OH ¿ 4 +4 HI Sn I 4 + 4 H 2 O → Sn ¿ Precaution and measures Some precautions were needed to prevent loss in percentage yield of the product. Weighing and addition of iodine solid was done after all required apparatus was properly set up in order to reduce the time it was left exposed as iodine solid has the ability to sublime under room temperature and pressure. Also, the heat setting on the heating unit was set to be slightly higher than the required temperature for reflux as heat may be lost to its surroundings, causing the temperature of reaction to be lower than the heat setting, lowering the rate of reaction. Experimental Flaws and improvement

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Work by Brandon Lam, M15604 Tin has two possible oxidation states, which makes the reaction between Tin and Iodine produce more than one product. The alternate reaction produces SnI 2 as described by the chemical equation below.

Sn+ I 2 C H 2 C l 2 Reflux Sn I 2 →

Although, the +4 oxidation state that tin takes is more stable, making SnI 4 the main product, the side reaction produces a significant amount of SnI 2. This affects the purity and yield of the final product. One way to reduce the alternate product is to use I2 in excess such that the side reaction is minimized and a larger yield of SnI4 can be obtained. Another method to improve on the purity of the final product is to perform recrystallization. This aids in removing the SnI2 and other impurities. SnI2 is polar, SnI4 is non-polar, and hence SnI2 is more soluble than SnI4 in CH2Cl2. By using the differing solubility of SnI2 and SnI4, we can separate both of the compound and isolate the latter. Finally, cotton plug used for gravity filtration absorbed a significant amount of filtrate. It is highly possible that cotton absorbs more filtrate than a simple filter paper, given its size and volume. Furthermore, cotton wool is fibrous and fluffy, there are multiple large air pockets that will allow contaminants to pass through, affecting the purity of the end product. An alternative method is to replace the cotton with filter paper, which has smaller pores and less absorbance.

7 CONCLUSION SnI4 was successfully synthesized using tin metal and iodine solid with a mass of 0.549g and 92.3% yield. The final product was reasonably pure as the melting point range, 144.0oC – 146.1oC is small with margin of error 2.1. Thus it can be concluded that the product, SnI4 was produced with high yield and moderate purity. SnI4 was also characterized for its hydrolysis reacction and some various properties.

8 POST-LAB QUESTIONS 1. SnI4 consist of four Sn-I bonds and each bond is polar covalent, with a dipole moment in each of them. Although each Sn-I bond has a dipole moment, because SnI4 has a tetrahedral symmetrical geometry, the dipoles cancel each other out. Thus SnI 4 is a non-polar molecule with no net dipole moment and has polar covalent bonding. SnI 4 has a relatively large Mr of 636.33g/mol, thus the London Dispersion Forces (LDF) between the molecules will be relatively strong. Consequently, a relatively high temperature is required to break the LDF interactions between the SnI 4 molecules, making the melting point of SnI4 relatively high. 2.

Sn I 4 ( s)+2 KI (aq)→ K 2 [Sn I 6 ]( aq)

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Work by Brandon Lam, M15604

9 REFERENCES [1]RSC.ORG,. TIN - ELEMENT INFORMATION, PROPERTIES AND USES | PERIODIC TABLE HTTP://WWW.RSC.ORG/PERIODIC-TABLE/ELEMENT/50/TIN (ACCESSED JUL 9, 2015). [2]RSC.ORG,. IODINE - ELEMENT INFORMATION, PROPERTIES AND USES | PERIODIC TABLE HTTP://WWW.RSC.ORG/PERIODIC-TABLE/ELEMENT/53/IODINE (ACCESSED JUL 9, 2015). [3] APOSTOLICO, L.; KOCIOK-KÖHN, G.; MOLLOY, K.; BLACKMAN, C.; CARMALT, C.; PARKIN, I. DALTON TRANS. 2009, 10486. [4] HYDROLYSIS OF SNI4 HTTPS://UK.ANSWERS.YAHOO.COM/QUESTION/INDEX? QID=20090119104630AAEBRK1 (ACCESSED JUL 13, 2015). [5] HARLANFALCONS.ORG,. SYNTHESIS OF TIN(IV) IODIDE AND COMPARISON OF REACTIVITY AMONG TIN(II) CHLORIDE, TIN (IV) CHLORIDE, AND TIN (IV IODIDE) HTTP://HARLANFALCONS.ORG/OURPAGES/AUTO/2010/10/13/45969889/AP_LAB%20REPORT %20EXAMPLE.DOC (ACCESSED JUL 13, 2015).

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