It reacts with bases like sodium hydroxide to form sodium tetrahydroxoaluminate.
Silicon dioxide also known as silica is similar to the aluminium oxide. It does not react with water due to the inability to dissolve in water. Silicon dioxide is made up of a giant structure due to extensive network of covalent bonds in the crystalline lattice structure that extends to infinity. The solubility of a substance is related to the similarity in bond strength in the solvent and the solute (water and silicon dioxide in this case). The extensive network of covalent bonds is much stronger than the water-water interactions (hydrogen bonds). Therefore silicon dioxide cannot be hydrated by water molecules which means that water cannot break down the giant crystal lattice structure of the macromolecule silicon dioxide to form aqueous ions. However, silicon dioxide does react with bases like sodium hydroxide but only when it is hot and concentrated to form sodium silicate.
Phosphorus(V) oxide reacts vigorously with water to produce phosphoric acid. The reaction is also an exothermic reaction which will generates much heat. Phosphoric acid is a strong acid with a pKa of 2.148.
Chlorine(I) oxide, reacts with water to some extent to yield hypochlorous acid. The reaction is reversible which indicates that the hypochlorous acid yielded is a moderately weak acid with a pKa of 7.53. Its anion formed is not stable and readily reclaims hydrogen to revert back to acid.
The hypochlorous acid formed will slowly decomposed into hydrochloric acid and oxygen gas in the presence of sunlight.
2HOCl 2HCl + O2
The structure of period 3 oxides is determined by the difference in electronegativity between each element in period 3 and the oxygen element. The electronegativity increases across period 3. Oxygen is more electronegative than any of the elements in period 3. Thus, the difference in electronegativity becomes smaller and smaller across the period 3. When the difference becomes smaller, the bonding becomes weaker. Thus, the trend of the structure is from giant ionic to giant covalent and finally small and simple covalent. The bonding is from ionic bonds in metal elements to covalent bonds in non-metal elements. Firstly, the structure of both sodium oxide and magnesium oxide is giant ionic structure. Both intermolecular and intramolecular bonding in the first two oxides is ionic bond. Thus, both oxides have high boiling and melting point due to the strong attraction between ions. These two oxides do not conduct electricity in solid state as there is no free ion movement but they do when in molten or aqueous state. Aluminium oxide is similar to both sodium oxide and magnesium oxide. The only difference is that it has covalent characteristic. Silicon dioxide has a giant covalent structure. There are covalent bonds between molecules. It has high melting and boiling points due to the extraordinary high amounts of covalent bonds. This is because many molecules of silicon dioxide are joined together to form a giant lattice. It does not conduct electricity in any state as the ions are not free to move around. As for phosphorus pentoxide and chlorine(VII) oxide, they have simple covalent structure. Both of them have low melting and boiling points due to the weak intermolecular forces which is Van Der Waals’ forces. They do not conduct electricity as well in any state as there is no mobile charge carrier.
With increasing atomic number, the oxides of period 3 elements changes from strongly basic nature on the left hand side to strongly acidic nature on the right. This trend is for the oxides in which the element in period 3 has the highest oxidation state. Ionic/metallic oxides like sodium oxide and magnesium oxide are mostly basic in nature. The basicity is account on the oxide ion, O2- which cannot exist alone in the aqueous solution. They tend to attack and form a bond with the partial positive hydrogen in a water molecule and subsequently releasing hydroxide ion. Also, the greater the degree of ionic character of the metal oxide, the more basic it is. Sodium oxide is the strongest base among all the oxides in period 3 as it contains the most oxide ions. The sequence is from forming metal hydroxide and dissociate into metal ions and hydroxide ions. As mentioned above, the basicity of the oxides decreases across the period. Thus, magnesium oxide is less basic than sodium oxide. This is because in the case of magnesium oxide, the free oxide ions are less than that of sodium oxide as more energy is required to break the attraction between 2+ and 2- than the sodium oxide case which is 1+ and 2-. Aluminium oxide situated at the middle portion is amphoteric and can acts as acid or base. Going from left to right, the acidity of oxides of elements in period 3 increases. The non-metal oxides on the other hand are usually characterized by polar covalent bond rather than the ionic bonds of metal oxides. In aqueous non-metal oxide solution, the partial negative oxygen atom from a water molecule will attack and form a bond with the partial positive non-metal atom from the non-metal oxide. At the same time, the oxygen atom in non-metal oxide forms a bond with hydrogen atom in water molecule. The breaking of water molecule forms an oxoacid which then splits into corresponding anion and hydronium ions. Silicon, the element next to aluminium has a weakly acidic oxide. Phosphorous pentoxide, P4O10 has a higher acidity than silicon dioxide while chlorine(VII) oxide, Cl2O7 has the highest acidity among all the oxides of period 3.
There are some precautions in this experiment. Firstly, when handling chemicals like phosphorus(V) oxide and sodium peroxide, extra care must be given. This is because phosphorus(V) oxide is an irritant which is also corrosive. If come in contact, it irritates eyes and skin as well as our lungs when inhaled. Sodium peroxide which is a powerful oxidant is also corrosive in nature. Physical contact will these chemicals should be avoided. Rubber gloves are worn all the time when handling these chemicals. Secondly, when mixing chemicals into distilled water, the boiling tubes should be placed on the tabletop and away from the eyes. Gas may evolve when mixing chemicals. These gas might irritate eyes and causes damage to lungs if inhaled. Next, when chemicals are dissolve in distilled water, the products formed is corrosive especially for sodium peroxide and phosphorus pentoxide. Direct handle should be avoided to prevent injury.
