Covalent and Ionic Compounds PDF

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Summary

This lab report investigates covalent and ionic compounds using experimental data to prove the qualities of each. This lab report includes a work cited page and charts and tables where needed....

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Covalent and Ionic Compounds SCH3U February 21, 2017 Purpose: The purpose of this lab is to investigate the qualities of ionic and covalent bonds in order to determine the bond type of the substance NaCl and guar gum. Materials: Gloves 2x test tubes 2x test tube stoppers 2x watch glasses 2x 250mL beaker Scoopula Crucible cover Clay triangle Test tube rack Flint lighter

Bunsen burner Heat resistant pad Retort stand Retort rod Ring clamp Electrical conductor light Sodium Chloride Guar Gum Water Cyclohexane

Procedure: 1) Put on gloves 2) Obtain a mL of sodium chloride on one watch glass and a mL of guar gum on another watch glass. For each solid, note whether it has a distinctive odour. 3) Rub a small sample of each solid between fingers. Note the relative hardness of the solids. Check by attempting to crush a few crystals of each solid with a scoopula. 4) (Refer to appendix A for set-up) Place a few crystals of sodium chloride and guar gum adjacent on an inverted crucible cover. Place the crucible cover on the clay triangle which is supported by the ring clamp attached to a retort stand. Work over a heat resistant pad. Heat the crucible cover gently until one of the two substances melts. Note which substance melts. 5) Add cyclohexane (a nonpolar solvent) to a clean, dry test tube to a height of 3 cm. Add a few crystals of sodium chloride to test tube and stopper test tube. Shake. Note whether the crystals were soluble. Dispose of mixture in the organic waste container. 6) Repeat step 5 using guar gum in place of sodium chloride. 7) Add water (a polar solvent) to a clean, dry test tube to a height of 3cm. Add a few crystals of sodium chloride to test tube and stopper test tube. Shake. Note whether the crystals were soluble. Dispose of mixture in organic waste container. 8) Repeat step 7 using guar gum in place of sodium chloride. 9) Fill two 250 mL beakers with 100 mL of water each. Using the scoopula, add one scoop of guar gum to one, and one scoop of sodium chloride to the other. Mix. 10) Using the electrical conductor light, test the electrical conductivity of each mixture. Note the degree of brightness emitted. 11) Dispose of any NaCl in the garbage, guar gum in the organic waste.

Observations: Table 1: Observations and Conclusions Substance

Before Change

Fusibility

Solubility in Cyclohexan e

Solubility in Water

Conductivity

Guar Gum

No odour, fine solid powder, white, soft

Not fusible. Substance burns and turns black when heated, but remains as a powder

Mixture is not soluble, creates cloudy water, particles can be seen floating in mixture

Guar gum expands in water, is not soluble

Guar gum is not conductive

Sodium Chloride

No odour, solid crystals, opaque, white, hard

Not fusible at a low heat, remains the same

Sodium chloride crystals sink to bottom of cyclohexane, is not soluble in this mixture

Sodium chloride is soluble in water. After mixing, water is clear with no visible crystals or precipitate

Sodium chloride in water is very conductive, instantly produces bright light

Conclusions: 1) a) If a solid has a distinctive odour, i.e. is volatile, the ions/molecules of the solid must be able to easily leave its surface. Keeping that in mind, are the molecules in covalent compounds or the ions in ionic compounds held together by the strongest forces of attraction? The ions in an ionic bond are more strongly held together than the molecules in covalent bond. This is because ionic bonds have the highest difference of electronegativity, meaning the one of the atoms paired in the bond is positive due to losing (an) electron(s), and the other atom in the bond is negative due to gaining (an) electron(s). Covalent compounds are not held together as strongly, as their difference of EN is not as large, meaning they have a similar charge and therefore not as strong of an attraction to each other. b) On the basis of your answer to 1 a), explain the results of the hardness and fusibility tests. As concluded in question 1 a), it is clear that ionic bonds are more tightly built than covalent bonds. NaCl is an ionic bond, therefore more strongly built than guar gum, which

explains why the sodium chloride crystals were very hard, and did not fuse together at the heat used in the experiment (NaCl melts at 801℃). Guar gum is a covalent bond, and its molecules are more easily moved from its surface. That is why guar gum quickly burned under the heat of the Bunsen burner, and was also softer than the sodium chloride. 2) Explain the results of all four of the solubility tests Sodium chloride is an ionic compound, as the difference of electronegativity of Na and Cl is 2.1, putting this substance right in the ionic range. In the lab, the sodium chloride dissolved in water, a polar solvent. This is because, since water has a slightly negative and a slightly positive side to each molecule, this attracted the positive sodium atom and the negative chlorine atom. The attraction was stronger than the attraction the water has to itself, therefore water molecules moved to surround the chlorine and sodium. When sodium chloride was placed in cyclohexane, the NaCl did not dissolve, and it was concluded that NaCl is not soluble in cyclohexane. This is because cyclohexane is a non-polar solvent, and the charge on each of the molecules is equal on both sides. Since the charge is equal, the attracting force between the cyclohexane and sodium chloride was not stronger than the attraction between cyclohexane and itself. The result of this is NaCl staying in crystal form, unchanged and visible. Guar gum is a covalent bond, proved by the results of this lab. Guar gum proved to be not soluble with water, as rather than dissolve, it expanded. Because of guar gum not dissolving in the water, it is evident that guar gum is a non-polar covalent substance, meaning the water molecules are more attracted to each other than they are to the guar gum. The guar gum expanded in the water as a result of hydration, meaning the guar gum absorbed the water. Guar gum is proven to be a nonpolar covalent bond, so when it was put in cyclohexane, a nonpolar solvent, the guar gum did not dissolve because the cyclohexane was more attracted to itself than it was to the guar gum. The particles of guar gum floated in the mixture in its prior form. 3) Explain the results of both electrical conductivity tests NaCl is a ionic bond. When put in water, the polar molecules of the water become more attracted to the positive sodium and negative chlorine atoms than itself, and moves to surround the Cl atom and Na atom. This destroys the rigid bonding of the ionic compound NaCl and allows the ions to move freely, also allowing them to conduct electricity, because of the positive sodium atoms being attracted to the negative side of the electrical conductor light, and the negative chlorine atoms being attracted to the positive side of the electrical conductor light. Guar gum is a nonpolar covalent bond, and when put in water, it does not change form. When the electrical conductor light was put in the solution of water and guar gum, the light did not turn on because there were no freely floating negative and positive charged particles. Question: A chemist was investigating a white solid which she knew was either camphor (C H O) or calcium chloride (CaCl ). She tested the solid and found that it had a distinctive odour, was soft, melted easily and was soluble in cyclohexane but not water. What must have been the identity of the solid? Explain your answer. The solid must have been camphor. This is because camphor is a covalent bond, and covalent bonds do not dissolve in water, and the molecules of covalent bonds are more easily able to leave its surface. In the investigation, the substance had a distinct odour, a sign the molecules are able to easily leave its surface, the substance also was soft, showing it was not

as tightly constructed as an ionic compound, and it did not dissolve water. It is known as a fact that ionic compounds are soluble in water.

Works Cited O'Leary, D. (2000). Sodium Chloride. Retrieved February 23, 2017, from https://www.ucc.ie/academic/chem/dolchem/html/comp/nacl.html Mudgil, D., Barak, S., & Khatkar, B. S. (2014, March). Guar gum: processing, properties and food applications—A Review. Retrieved February 23, 2017, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3931889/...