Acid Reactions

• Acids react with some metals to produce salts and hydrogen
• A redox reaction is where reduction and oxidation happen in the same reaction
• Aqueous solutions of alkalis contain hydroxide ions (OH $^-$ )
• Acids produce hydrogen ions (H $^+$ ) in aqueous solutions
• The pH scale, from 0 to 14, is a measure of the acidity or alkalinity of a solution
• The pH can be measured using universal indicator or a pH probe
• A solution with pH 7 is neutral
• Aqueous solutions of acids have pH values of less than 7
• Aqueous solutions of alkalis have pH values greater than 7
• In neutralisation reactions between an acid and an alkali, hydrogen ions react with hydroxide ions to produce water

  H $^+$$_{(aq)}$ + OH$^-_{(aq)}$ $\rightarrow$ H$_2$O$_{(l)}$
• The pH scale

  A) Alkaline

  B) Neutral

  C) Acidic

  
• A strong acid is completely ionised in aqueous solution
• Examples of strong acids are hydrochloric, nitric and sulfuric acids
• A weak acid is only partially ionised in aqueous solution
• Examples of weak acids are ethanoic, citric and carbonic acids
• For a given concentration of aqueous solutions, the stronger an acid, the lower the pH
• As the pH decreases by one unit, the hydrogen ion concentration of the solution increases by a factor of 10
• pH will decrease when increasing an acid concentration weather it is a strong or weak acid
• A base is a substance that reacts with an acid to form a salt
• Insoluble metal hydroxides and metal oxides are bases
• acid + metal oxide $\rightarrow$ salt + water
• acid + metal hydroxide $\rightarrow$ salt + water
• hydrochloric acid + copper oxide $\rightarrow$ copper chloride + water 


  2HCl + CuO $\rightarrow$ CuCl$_2$ + H$_2$O
• hydrochloric acid + sodium hydroxide $\rightarrow$ sodium chloride + water 


  HCl + NaOH $\rightarrow$ NaCl + H$_2$O
• Metal carbonates are bases
• Metal carbonates react with acids to form salt, water and carbon doixide
• Metal oxides and metal hydroxides react with acids to form salts and water
• acid + metal carbonate $\rightarrow$ salt + water + carbon dioxide
• hydrochloric acid + sodium carbonate $\rightarrow$ sodium chloride + water + carbon dioxide 


  HCl + NaCO$_3$$\rightarrow$ NaCl + H$_2$O + CO$_2$
• Soluble salts can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates
• Salt solutions can be crystallised to produce solid salts
• To make a soluble salt from an insoluble base

  • The solid is added to the acid until no more reacts
  • The excess solid is filtered off to produce a solution of the salt
  • The solution is placed in a water bath to evaporate some of the water
  • The crystals will start to form and should be filtered out of the solution and left to dry