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I.E.S. Gabriela Mistral Leyre González López Oxyacids These are compounds with the following general formula: HaXbOc where X is a non metal with a positive oxidation number. X can also be a transition metal with a high oxidation number, such as Cr(+6), Mn(+6) or Mn(+7). H has an oxidation number of +1. O has an oxidation number of -2. How do we know the oxidation number of X? To know the oxidation number of X, remember that the addition of all the oxidation numbers must be 0. For example: H2SO4: (+1)∙2 + x + (-2)∙4=0 → x=+6 → S has an oxidation number of +6 How are they formed? They are obtained by adding one molecule of water to an oxide. For example, if we want to form the oxyacid of S in which it has an oxidation number of +6 we do the following steps: We form the oxide. S2O6 → SO3 We add a molecule of water (the molecule we obtain is simplified if necessary). SO3 + H2O → H2SO4 Let´s see another example. Let´s form the oxyacid of Cl in which this element has an oxidation number of +3: We form the oxide: Cl2O3 We add one molecule of water and in this case we will need to simplify: Cl2O3 + H2O → H2Cl2O4 → HClO2 How are they named? Root of X with suffixes and prefixes which indicate its oxidation number + “acid” The suffixes and prefixes used are: 1. If X has 1 oxidation number: -ic 2. If X has 2 oxidation numbers: -ous for the smallest -ic for the biggest 3. If X has 3 oxidation numbers: hypo- -ous for the smallest -ous for the middle one 4. If X has 4 oxidation numbers: hypo- -ous for the smallest -ous for the middle smallest one -ic for the middle biggest one per- -ic for the biggest -ic for the biggest En español: “ácido” + raíz de X con prefijos y sufijos que indican su estado de oxidación Los prefijos y sufijos a usar son: Si X tiene 1 estado de oxidación: -ico Si X tiene 2 estados de oxidación: -oso para el menor Si X tiene 3 estados de oxidación: hipo- -oso para el menor -ico para el mayor -oso para el mediano -ico para el mayor Si X tiene 4 estados de oxidación: hipo- -oso para el menor -oso para el mediano menor -ico para el mediano mayor per- -ico para el mayor Let´s see some examples: S has +2, +4 and +6 as oxidation numbers. In H2SO4, S has an oxidation number of +6 (the biggest), so H2SO4 is sulphuric acid (ácido sulfúrico). Cl has +1, +3, +5 and +7 as oxidation numbers. In HClO2, Cl has an oxidation number of +3 (the middle smallest one), so HClO2 is chlorous acid (ácido cloroso). In HBrO4, Br has an oxidation number of +7 (Br has 4 oxidation numbers and +7 is the biggest one), so HBrO4 is perbromic acid (ácido perbrómico). In HIO, I has an oxidation number of +1 (I has 4 oxidation numbers and +1 is the smallest one), so HIO is hypoiodous acid (ácido hipoyodoso). Exercises 1. Write the formula of the following oxyacids: a) perchloric acid b) sulphurous acid c) nitric acid d) nitrous acid e) carbonic acid f) chloric acid 2. Write the name of the following oxyacids: a) HBrO b) H2SeO3 c) HClO4 d) H2SO2 e) H2TeO4 f) HBrO3