Classification of Chemical Substances

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Metals will SSE electrons to form actions (positively charged) and non-metals can gain electrons to form anions (negatively charged); these oppositely charged ions attract each other and form an ionic compound Because the attraction of the ions is so strong, ionic compounds are always solid at room temperature and usually crystalline with high melting and boiling points. They usually are soluble in water and form solutions that will conduct electricity because free ions are formed in solution.

They will also conduct electricity when melted and are usually insoluble in organic liquids. In molecular compounds, the toms share valence electrons and are said to be joined by covalent bonds. Molecular compounds can be gases, liquids or low-melting, boiling points and densities than ionic compounds and many are insoluble in water but soluble in organic liquids. They do not conduct electricity when melted or dissolved. Metallic bonding is a special type of bonding found in samples of pure metals or alloys (mixtures of metals).

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In a metal the nucleus and core electrons (I. E actions) are surrounded by a “sea” of valence electrons. Since the valence electrons are free to roam over the entire sample (they are described as localized), metals are good conductors of electricity in the solid state. Metals are typically lustrous (shiny), flexible, malleable and ductile In this experiment we will identify and classify’ the unknown substances into their types. Also we will investigate their melting point and solubility in different solvents.

Experimental Procedure About 1 gram of each of unknown substances was taken and placed in 6 test tubes. Test tubes were labeled according to the number of substance tested. 2 ml of polar organic solvent was added to each of unknown samples and the mixture was stirred, the reaction was observed and results were corded. Test tubes were thoroughly cleaned and the procedure was repeated two more times using non-polar organic solvent and water. Substances dissolved in water were checked on electrical resistance using a device called ohm meter.

Each solution was poured into beaker one by one and diluted by distilled water. Electrodes were immersed into the diluted solution and the electrical resistance was measured in ohms. For the third part of experiment 2 coins, rubber washer, 2 unknown substances in powder form and ohm meter were needed. The rubber washer was placed on the coin and the hole in the rubber was fully filled with powder f one of unknown substances. Another coin was placed on a top of the washer. Coins were compressed and electrodes were made to touch coins from both sides.

Results were recorded. Results 1) Solubility and Conductance of solutions Substance No. Melting point Solubility Electrical Resistance, k Electrical Conductivity H2O Monopoly Organic Polar COCA poorly soluble Insoluble 150 weak >COCA Poorly soluble wee k 100-300 co Soluble 90 -coca 20 VI >socio 7 Classification of unknown substances: Molecular Molecular Ionic Ionic Unknown compounds: AAA and B: Both compounds are soluble in water and polar solvent, but insoluble in inorganic solvent. Have poor electro conductivity.

Discussion After all experiments were performed we had to assign our unknown substances according to their physical properties, such as solubility, conductivity and melting point to one of four categories: ionic, molecular, macromolecular and metallic by comparing experimental results with theoretical characteristics of these substances. Results for melting point of unknown substances were given to us before the practical. The unknown substance number 1 had low melting point and did not dissolve either in water or polar organic solvent. But it was slightly soluble in a on-polar organic solvent.

As it did not dissolve in water it was assumed not to conduct electricity at all. These characteristics are suitable for molecular substance with a non-polar structure. The second substance had a relatively high melting point of COCA but was only slightly soluble either in water or polar organic solvent. It did not react with non-polar organic solvent and was classified as a weak conductor. This substance can be determined as a molecular-ionic, because its physical properties satisfy two categories at the same time. The third substance had the same characteristics as in the previous one.

It had a high melting point and it was also slightly soluble in water and polar organic solvent. Furthermore, it had a very low conductivity. These properties prove that this compound is molecular-ionic. The compound number 4 had a low melting point and was soluble in water. However, this compound is a very weak electrical conductor. As it dissolves in polar water it can be assumed to be polar molecular compound as it satisfies all properties of this category. 5th unknown compound had a relatively high melting point of COCA and was soluble in water; these characteristics fully satisfy ionic compounds.

However, despite the relatively low electrical resistance, which is the lowest among last 5 unknown compounds discussed, it is still very high. This property relates to molecular substances. Consequently, unknown number 5, similar to 2nd and 3rd substances, satisfies two categories of chemical substances and is assumed to be molecular-ionic compound. The unknown number 6 had the lowest resistance: only 5 k, meaning that this compound is a relatively good electrical conductor. Moreover, it had a high melting point and was soluble in water, but did not react with organic elevens.

These properties show us that this compound is ionic. We could not obtain results for electrical resistively of solids. It was probably due to the error in ohm meter device, which showed no numbers. We could not say that the resistively for these two unknowns is zero, because zero resistance means an extremely high conductivity of the material superconductivity, therefore we say that ohm meters were out of order. Another mistake which should be avoided when working with ohm meters is when you immersing electrodes in a solution you should thoroughly check if here are no drops of the solution which was checked just before another.

If there are some drops of the solution which was checked just beforehand it is necessary to rinse the electrodes with distilled water in order to make them clean. During experiment on solubility it was essential to thoroughly clean test tubes when changing the type of solvent. For example, if water was left on the inner walls of the test tubes, this would possibly lead to the wrong results when checking solubility of unknown substances in organic solvent. Conclusion Several properties of the substances were investigated, to find out to which localization type each of the unknown substances refer.

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