Trends Across Period 3 Oxides and Chlorides

Aim

The aim of this experiment was to identify critically the trend in the chemical properties of elements and compounds of period 3. The students were required to specifically study how the chemical properties of the oxides and chlorides of period 3 elements relate to each other and how the elements in this period react with water and oxygen. In the same regard, the experiment was aimed at enabling the students to understand the trends in the chemical reactivity of these compounds and elements.

Introduction

The understanding of the periodic table is paramount in studying chemistry. This understanding, therefore, requires keen observation of the reactions involving the many elements in the periodic table. This understanding however becomes incomprehensible, especially the theoretical part of these reactions.

Apparatus list

1. eye protection
2. test tube rack
3. six test tubes
4. indicator papers
5. spatula
6. 10ml measuring cylinder
7. Access to a fumes chamber
8. Source of heat

Chemical list

Samples of oxides of:

• sodium oxide
• magnesium oxide
• aluminum oxide
• silicon oxide
• phosphorous oxide
• sulphur dioxide
• distilled water

Sample of chlorides of:

• sodium chloride (NaCl)
• magnesium chloride (MgCl₂)
• aluminum chloride (AlCl₃)
• silicon chloride (SiCl₄)
• phosphorous chloride (PCl₅ )

Samples of elements of period 3:

• Method/procedure

Reactions of period 3 oxides

1. A small amount of each sample of the oxide was taken into a test tube using a spatula and about 2ml of distilled water was added.
2. A small piece of indicator paper was placed in the test tube.
3. The procedure was repeated for all the other oxides.
4. The physical states and the pH of the solutions were determined and recorded in a table.

Reaction of period 3 chlorides

1. A small amount of each sample of the chloride was taken into a test tube using a spatula and about 2ml of distilled water was added.
2. A small piece of indicator paper was placed in the test tube.
3. The procedure was repeated for all the other chlorides.
4. The physical states and the pH of the solutions obtained were determined and recorded in a table.

Reaction of period 3 elements with water

1. A small portion of each element was placed in a glass beaker containing distilled water.
2. The observation was made and the pH of the resulting solutions was determined by use of indicator paper.

Reaction of period 3 elements with oxygen

1. The element was placed in a spatula and heated in a flame.
2. The observation was made. The resulting compound was placed in a beaker of water and the pH of the resulting solution was determined.

Precautions

The students were required to have eye protection goggles as some of the oxides are in powder form and can be quite damaging if they get into the eyes. It was also required that the students should wear closed shoes and laboratory coats to avoid skin contact with the chemicals.

Observations

Trends in the oxides of period 3 elements

Trends in the chlorides of period 3 elements

Reaction of period 3 elements with water

Reaction of period 3 elements with oxygen

Analysis/ discussion

Sodium oxide, magnesium, oxide and aluminum oxide are the top oxides in this period. The outer electrons of these periods 3 elements have been used in making the bonds with oxygen. The structures of these oxides range from metallic to giant covalent and the last elements in this period have molecular oxides (Cremlyn 1996, p.78).

The metallic oxides, that is, sodium and magnesium dissolve readily in water to form acidic solutions. This is indicated by the use of the indicator paper which records the pH of the resulting solution. The oxide of aluminum despite being a metallic oxide is usually not soluble in water. It is however soluble in acidic solutions e.g. dilute hydrochloric acid as well as in basic solution e.g. sodium hydroxide. For this reason, the oxide of magnesium is said to be amphoteric. This means that it has both acidic and basic properties. It is henceforth given a pH value of 7 (Schimidt & Siebert 1973). On the other hand, the oxides of silica, phosphorus and sulphur are acidic. They dissolve in water to form acidic solutions of pH ranging from 5 to 2.

The chlorides of these elements vary in terms of their physical characteristics as well as their chemical attributes. Sodium chloride readily dissolves in water to give a solution with a pH value of 7 or in other words a neutral solution. This is due to the neutralization of the H+ by the Cl- ions and the Na+ by the OH- ions (Cremlyn 1996, p.78). Contrarily, the oxide of magnesium dissociates in water to give a solution with a pH value of about 6. Such a solution shows slightly basic characteristics. Chlorides of aluminum, silica and phosphorous dissolve in water to form acidic solutions. This is due to the presence of hydrogen ions after the hydrolysis of the compound by the polar water molecules (Schmidt & Siebert 1973).

Period 3 elements react with water to form hydroxides and hydrogen gas. Phosphorous and sulphur however do not react with water. They also burn in oxygen to form oxides. The hydroxides are basic. The metallic oxides are basic while those of silica, phosphorus and sulphur are acidic.

Conclusion

The students conducted the exercise with utmost precision ­and they were able to meet the required expectations and the aims and objectives of the practical.

Evaluation

From the results of this experiment, an evaluation would prove that the purpose of the practical helps a lot in integrating the understanding of theoretical approaches done in class. They do a very great extent expand the knowledge of the student as well as help the individuals in perceiving the information dispensed in class which at times seems very irrational and incomprehensive.

References

Cremlyn, J 1996, An Introduction to Organosulfur Chemistry, John Wiley and Sons, Chichester.

Schimidt, M& Siebert 1973, Comprehensive Inorganic Chemistry, Vol 2, Trotman-Dickenson, New York.