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Discuss - Metal oxides are alkaline, non-metal oxides are acidic

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Discuss - Metal oxides are alkaline, non-metal oxides are acidic Moving across the periodic table from left to right will bring about a change in the nature of the element. Generally, there are trends in certain properties in the elements that we can spot, for instance boiling/melting points. Period three elements are from Sodium to Argon inclusive, and possess particular characteristics. All of the period 3 elements except argon and chlorine will combine with oxygen to form oxide molecules (Na2O, MgO, Al2O3, SiO2, P4O10, SO2 and SO3). How does their pH differ, and what is different about Al2O3? It is not just the properties of the period 3 elements that differ as we move across the periodic table; this movement also affects the properties of the oxides of said elements. These changes are a result of the transition from metal elements to non-metal elements. The oxides of sodium, magnesium and aluminium are all examples of the compounds formed by a metal combined to a non-metal. ...read more.


acid. This ionises, so the solution is acidic. P4O10 (s) + 6H2O (l) --> 4H3PO4 The H3PO4 (aq) ionises in stages, the first being: H3PO4 H+ (aq) + H2PO4- (aq) pH ~0-1 Sulphur dioxide is also fairly soluble in water, and reacts with it to give sulphuric acid. This partially dissociates producing H+ ions. This causes the acidity in the solution. SO2 (g) + H2O (l) --> H2SO3 (aq) H2SO3 (aq) H+ (aq) + HSO3- (aq) pH ~ 2-3 Sulphur trioxide reacts violently with water to produce sulphuric acid: SO3 (g) + H2O (l) --> H2SO4 (aq) --> H+ (aq) + HSO4- (aq) pH ~0-1 This overall pattern in reactivity of the period 3 oxides is that metal oxides will form alkaline solutions win water, whilst non-metal oxides will form acidic ones and those in the middle will not react. This behaviour can be explained by looking at the bonding and structure: * Sodium and magnesium oxides are composed of ions. ...read more.


--> Na2SiO3 (aq) + H2O (l) Due to the giant covalent lattice, silicon dioxide is very resistant to attack from bases. It will only react with a base given the conditions are right, using hot, concentrated hydroxide solution. SiO2 (s) + 2 OH - (aq) ? SiO3 2 - (aq) + H2O (l) Some of these reactions can be problematic. For instance, sulphur trioxide causes problems when reacting with water as it forms sulphuric acid (see above for equation). Were the SO3 to mix with rain water, it would form acid rain. This provides a number of environmental problems, such as, changing the pH of lakes and harming aquatic life, killing crops by changing pH of soil and ruining limestone buildings. I would mostly agree with the statement "Metal oxides are alkaline, non-metal oxides are acidic". Within period 3, the metal oxides react as an alkali whilst the non-metal oxides react as acidic. The only exception to this rule is aluminium oxide, which can act as both an acid and alkali depending on the conditions and the reactant and is referred to as amphoteric. Excluding this exception, the statement proves correct. ...read more.

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