Base your answers to questions 66 through 69 on the information below and on your knowledge of chemistry.

     Stamping an identification number into the steel frame of a bicycle compresses the crystal structure of the metal. If the number is filed off, there are scientific ways to reveal the number.

     One method is to apply aqueous copper(II) chloride to the number area. The Cu²⁺ ions react with some iron atoms in the steel frame, producing copper atoms that show the pattern of the number. The ionic equation below represents this reaction.

Fe(s) +Cu²⁺(aq) → Fe2(aq) + Cu(s)

    Another method is to apply hydrochloric acid to the number area. The acid reacts with the iron, producing bubbles of hydrogen gas. The bubbles form faster where the metal was compressed, so the number becomes visible. The equation below represents this reaction.

2HCl(aq) +  Fe(s) → FeCl₂(aq) +  H₂(g)

66 Explain why the Fe atoms in the bicycle frame react with the Cu²⁺ ions. [1]

67 Determine the number of moles of hydrogen gas produced when 0.001 mole of HCl(aq) reacts completely with the iron metal. [1]

68 Write a balanced half-reaction equation for the reduction of the hydrogen ions to hydrogen gas. [1]

69 Describe one change in the HCl(aq) that will increase the rate at which hydrogen bubbles are produced when the acid is applied to the steel frame. [1]