Periodic Trends Across The Period 3 Oxides

Periodic trends across the period three oxides

Clare Smerdon
Access to Higher Education Science
08/04/2015
Julie Day

Periodic trends across the period three oxides

Objective

This experiment is intended to explore the relationship between the physical properties of the oxides of Period 3 elements (sodium to chlorine) and their structures. Argon is obviously omitted because it doesn't form an oxide.

Hypothesis

This experiment will be investigating the following properties of the oxides of group three;

A) State at room temperature
B) Appearance
C) Volatility
D) Conductivity of electricity of molten oxide
E) Solubility in water
F) pH of solution in water
G) Classification of oxide (acidic, basic or amphoteric)
H) Structure of oxide (simple molecular, giant molecular, giant ionic)
I) Reactions with hydrochloric acid and/or sodium hydroxide.

It is expected that some trends will appear across the period three oxides. Conductivity of electricity of molten oxide is likely to occur in the metal oxides as they have giant metallic structures which are capable of transferring delocalized electrons throughout their structure. This is not true of giant covalent structures and covalent bonds where all of their electrons are concerned with bonding, and therefore conductivity will not be a trait of non-metal elements in period three.

Another expected trend across the period is that the pH of the oxide solution will change from basic on the left of the group (especially alkali metals) to acidic on the right, once dissolved in water. This characteristic is then likely to affect the last of the properties being looked at, which is the reaction the oxide caused when exposed to hydrochloric acid and sodium hydroxide. The basic solutions should be neutralized by the addition of hydrochloric acid, and the acidic solution should be neutralized by the sodium hydroxide. Any metal oxide solution that have a relative amphoteric pH are likely to be acidified or made more alkaline.

Materials

Sodium Hydroxide
Magnesium oxide
Aluminum oxide
Silicone Dioxide
Phosphorus pentoxide
Sulphur dioxide
Chlorine oxide
Hydrochloric acid
Sodium Hydroxide
Distilled Water

Equipment

7x 25ml beakers
Spatula
Stirring Rod
Universal indicator
Four-terminal ohmmeter
Eye Protection
Laboratory coat
Latex Gloves

Procedure

1. Note the appearance of the period three oxide at room temperature. Fill a 25ml beaker with approximately 10mls of distilled water.
2. Take a small amount of the sample period three oxide using a spatula, and place it into the beaker. Use a stirring rod if necessary to dissolve the oxide. Note the volatility of the oxide.
3. Add a strip of universal indicator to the oxide solution and identify the pH of the solution. Write down the pH and whether the oxide is acidic, basic or amphoteric.
4. Take 5ml of the oxide solution and add 5ml of hydrochloric acid, note any changes in pH by testing with universal indicator.
5. Take 5ml of the oxide solution and add 5ml of sodium hydroxide, note any changes in pH by testing with universal indicator.
6. To test for conductivity, melt the sample and use the manufacturer’s guidelines on a four-terminal ohmmeter to test for electrical charge. This step was not possible in a classroom environment due to potential hazards.
7. Record the results.

Results

Please see attached results table.

Conclusion

The results of this experiment, as shown in the results table support the initial hypothesis.

Structure
The trend in structure is from the metallic oxides containing giant metallic structures on the left of the period via a giant covalent oxide (silicon dioxide and phosphorus pentoxide) in the middle to molecular oxides on the right.
Volatility
From period 1-5 the oxides were solid at room temperature whereas the period 6 and 7 oxides where gaseous. This caused an increase in volatility across the group. This can be explained through the structure of each oxide. The structures which are bound in giant bonding structures are far less inclined to break their strong ionic or covalent bonds intermolecular bonds to dissolve readily in the water. Conversely, the gaseous oxides contain only weak Vann Der Vaal’s intermolecular forces and are therefore much more able to dissolve in water rapidly.
Electrical conductivity
None of oxides used in this experiment conducts electricity in the solid state, but electrolysis is possible if they are molten. Only metallic elements are capable of conduction as the movement and discharge of delocalized electrons are essential for conduction to occur.
Solubility in water
All of the oxides used in this experiment are soluble in water, apart from one (aluminum oxide). This trait meant that the pH classification of this group three oxide in water was found to be amphoteric. pH Classification of Group 3 oxides
A distinct trend in pH was found in group three oxides. Sodium (alkali metal) hydroxide contributed to the production of the highest basic solution (pH), followed by Magnesium oxide (pH10). As mentioned above aluminum oxide was found to be insoluble in water and therefore the solution was found to be amphoteric. The non-metal element oxides appeared to contribute to production of acidic solutions with the lowest pH, with the Sulphur dioxide solution having a pH of 1.

Evaluation
Although this experiment did support the hypothesis and showed some trends in group three oxides, the results cannot be used to substantiate all trends in group three oxides, as only a limited number (seven) of oxides were evaluated. In order to get a better idea of trends through the group three oxides, a comprehensive experiment working through different compound oxides of each element would have to be carried out. Further investigation into traits of the group three oxides could involve, testing the melting and boiling points of the oxides, the ionization energies of the oxides, reactions under pressure or increased temperature could all help to determine trends which were not established from this experiment.