Writing Equations for Chemical Reactions

Writing Equations - Writing Equations for Chemical Reactions How can you figure out what reaction if any will occur when you combine two(or more

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Writing Equations for Chemical Reactions How can you figure out what reaction, if any, will occur when you combine two (or more) substances? You may find the following process useful: Step 1. Write down formulas of all the species present in the mixture when the substances are combined but before any reaction has occurred. Example. Consider the combination of iron and copper metals, hydrochloric acid, sodium hydrogen sulfate and sodium cyanide. The following species are present: Fe Cu H + (aq) Na + (aq) Cl - (aq) SO 4 2- (aq) HSO 4 - (aq) CN - (aq) Step 2. Can any redox reactions occur? If so, write the appropriate net ionic equation(s). In this example Fe is an active metal and copper is an inactive metal. Thus Fe can be oxidized by the H + (aq) but Cu cannot. There is no other oxidizing agent present. Fe(s) + 2 H + (aq) Fe 2+ (aq) + H 2 (g) Step 3. Can any combination of cation and anion give a precipitate. If so, write the appropriate net ionic equation(s). In this example there is no combination that gives a precipitate. (But see later!) Step 4. Are there any acids present? Are there any bases present? If so, write appropriate net ionic equation(s). In this example both H + (aq) – a strong acid - and HSO 4 - (aq) – a weak acid - can behave as acids. CN - (aq) can behave as a (weak) base. The appropriate net ionic equations are: H + (aq) + CN - (aq) HCN(aq) HSO 4 - (aq) + CN - (aq) SO 4 2- (aq) + HCN(aq) Note: The Fe 2+ (aq) formed in the redox reaction can react with the CN - (aq) to give a precipitate. Fe 2+ (aq) + 2CN - (aq) Fe(CN) 2 (s)
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To be able to use this method you need to know: What kinds of things are strong acids and weak acids What kinds of things are strong bases and weak bases What metals are very active, active and inactive What salts are soluble and what are insoluble The following reaction types must be known. 1.
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This note was uploaded on 04/17/2008 for the course CHEM 001 taught by Professor Cairns during the Fall '08 term at Drake University .

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Writing Equations - Writing Equations for Chemical Reactions How can you figure out what reaction if any will occur when you combine two(or more

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