Simple tests to understand chemical bonds

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Aim

The aim of this experiment was to practice general laboratory procedures,"mixing liquids and solids, measuring small changes in temperature as well as observing reactions and other changes."(Lane, 2009a)

Introduction

The principle of why liquids can be miscible which can be summarized as "like mixes with like"(Lister and Renshaw,2000: p118). When liquids meet other substance with similar bonds, they both produce shared intermolecular forces to mix together. However, some liquids are not miscible when they are mixed, because energy needs to be supplied to make attractions to form a mixture with different components.

Again Lister and Renshaw states (2000), liquids can mix with solids according to the similar rule "like dissolve like". Solids form the bonds can dissolve in the same type of solvent.

Sodium is a very reactive metal which must be handled with care, therefore sodium must be kept under oil to protect it from reacting with oxygen in the air.

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4Na(s) + O2(g) > 2Na2O(s)

Sodium also reacts with water, here acting as an acid,

2Na(s) + 2H2O(l) --> 2NaOH(aq) + H2(g)

The equation shows that sodium hydroxide is produced.(Lane, 2009b)

Methodology

Equipment

Ethanol: CH3CH2OH

Hexane: CH3CH2CH2CH2CH2CH3

Distilled Water

Potassium Carbonate (s): K2SO4

Copper Sulphate (s): CuSO4

Potassium (s): K

Small bottle of Sodium

Small bottle of Iodine (s)

3 pipettes (for 3 different liquids)

Large and small test tubes

A thermometer

A beaker

A conical flask

Tweezers

Method

The experiment was divided into 3 parts: mixing liquids; mixing liquids and solids, observing the reaction of sodium and potassium with water.

  1. Mixing liquids
  2. Firstly, with a thermometer to measure the temperature of the water in the beaker, then using the pipette, 1 cm3 water was put into a large test tube. Using another pipette 1 cm3 of ethanol was added into the tube. The tube was shaken gently and the temperature was measured again. And then keep as tube A for second part.

    1 cm3 water was put into a test tube using a pipette, and then using the pipette 1 cm3 of hexane was added into another tube. After shaking the tube gently and observing what happened, the temperature was measured, and then labeled as tube B.

    Next, using the pipette, 1 cm3 of hexane was poured into a test tube. Meanwhile, 1 cm3 of ethanol was poured into the tube. The tube was shaken gently and was observed and the temperature was measured. Another 1 cm3 of ethanol was poured into the tube and labeled as tube C.

  3. Mixing liquids and solids
  4. Initially, some potassium carbonate was placed into the tube A. The tube was shaken and observed.

    Secondly, 1 cm3 water was poured into a small test tube. 1 cm3 of hexane and ethanol were poured into 2 large test tubes. After using a spatula placed a small amount of copper sulphate into each tube, these tubes were shaken gently.

  5. Reaction of sodium and potassium with water
  6. 75 cm3 water was poured into the conical flask. Using the tweezers, a small piece of the sodium was put into the water. The experiment was repeated using potassium.

Discussion

Table 1 shows clearly that ethanol and water were miscible. However, two layers occurred in water and hexane as well as in hexane and ethanol, which meant that they did not mix. According to Lister and Renshaw (2000), ethanol and water mix together because both of them have hydrogen bonds. Moreover, Hexane and ethanol have weak van der Waals bonds, between the organic parts of each molecule. Nevertheless, these forces are weak and they separate, so hexane and ethanol do mix. However, in our experiment hexane and ethanol produced bilayer, which means they are not mix successfully. Besides, hexane and water cannot form a mixture, because the hexane molecule is not polarized permanently and can not form hydrogen bond. To mix them together requires large amount of energy to break hydrogen bonds, so water and hexane do not mix.(Lister and Renshaw, 2000)

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In addition, some solids can dissolve in some liquids which have the similar composition. Table 2 indicates clearly that copper sulphate dissolves in water while it did not dissolve in the hexane. It is stated by Lister and Renshaw (2000:119) that "ionic compounds can only dissolve well in polar liquids." Ionic bonds are present in copper sulphate. Water is a polar liquid also ionic, while hexane is a non-polar liquid. So the dissolution is reasonable. It also showed that iodine solution mixed with water, hexane and ethanol successfully. Iodine molecules can form van der Waals attractions and do dissolves poorly in polar solvents but well in non-polar solvents. (Lister and Renshaw, 2000).

The results show clearly that sodium reacts strongly with water. According to:

2Na(s) + 2H2O < 2NaOH(aq) + H2(g)

Strongly alkaline sodium hydroxide (caustic soda) and hydrogen gas are made as the products. During the process of releasing heat, hydrogen gas reacts strongly with the oxygen, so it can burn with an orange flame. (Lenntech, 2009)

Besides, potassium is more reactive than sodium, so it can react more strongly with water.

Possible errors may have arisen during the process of mixing. Firstly, the theory indicates that hexane can mix with ethanol. In fact, the result was different to the truth. Errors may have arisen from the given ethanol which contains water. Since water can not dissolve in the hexane, the layer occurred in our experiment. Secondly, It is not obvious to see that iodine dissolved in hexane successfully due to the colour change, which is a little different with the theory that iodine dissolves well in non-polar solvents. The discrepancy may be as a result of using the same pipette for adding water into a test tube. Hence, it might affect the hexane solution. Thirdly, we cannot see an orange flame during the test of reaction of sodium with water. It might stem from the purity and the mass of sodium. Thirdly, the equipment were not clean enough, which may cause the result not precise. A future experiment should use different pipettes to absorb different solution. In addition, it is good procedure to ensure the purity and mass of substance. Moreover, the equipment should be clean enough before doing any test.

Conclusion

Therefore it can be concluded that liquids can mix with liquids due to their similar

Intermolecular forces. Besides, liquids can mix with some solids which have the similar composition. ie:CuSO4 and water are ionic; I2 and hexane have van der waals attractions; water and ethanol have hydrogen bond polar attractions. The active metal can react strongly with water.

References

  • Lane, R (2009a) IFY Chemistry Handouts Week 4 Chemistry Practical Guangzhou IFY Center
  • Lane, R (2009b) IFY class discussions Week 4 Chemistry Practical Guangzhou IFY Center
  • Lenntech, 2009 [Online] Sodium (Na) and water Available at http://www.lenntech.com/periodic/water/sodium/sodium-and-water.htm (Access date 22/11/09)
  • Lister,T. and J. Renshaw (2000) Chemistry for Advanced Level (3rd edition). Cheltenham: Nelson Thornes Ltd