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Cells and corrosion

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15 diapositives · 825 Views · Feb 24, 2012

Cells and corrosion. AN ACTIVITY SERIES FOR METALS. REF 353. ■ With oxygen Li, Na, K, Ca and Ba react rapidly at room temperature, while Mg, Al, Zn and Fe react slowly (but burn vigorously if heated in air or oxygen), and Sn, Pb and Cu react slowly but only if they are heated.

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  1. Cells and corrosion

  2. AN ACTIVITY SERIES FOR METALS REF 353 ■ With oxygen Li, Na, K, Ca and Ba react rapidly at room temperature, while Mg, Al, Zn and Fe react slowly (but burn vigorously if heated in air or oxygen), and Sn, Pb and Cu react slowly but only if they are heated. ■ Li, Na, K, Ca and Ba react with water (to form hydrogen gas) while the other metals do not. ■ With dilute acids Mg, Al, Zn, Fe react readily, Pb and Sn react if the acid is hot and Cu, Ag, Pt and Au do not react at all. ■ In displacement reactions Zn will displace Fe, Cu and Ag from solutions of their cations but will not displace Mg; Fe will displace Cu and Ag (but not Mg or Zn), while Cu will only displace Ag

  3. The activity series is a listing of metals in order of decreasing reactivity, meaning decreasing ease of oxidation or decreasing ease of giving up electrons. K Na Li Ba Ca Mg Al Zn Fe Sn Pb (H) Cu Ag Pt Au This series can be used to decide: ■ whether a metal will react with dilute acid (yes, if it is to the left of hydrogen) ■ whether a metal will react with water (only if it is on the extreme left) ■ whether metal X will reduce the cation of metal Y (yes, if X is to the left of Y) ■ whether metal P is a stronger reducing agent than metal Q (yes, if P is to the left of Q) and conversely ■ whether metal L is a stronger oxidising agent than metal M (yes, if L is to the right of M).

  4. REFER TO THIS LIST select three metals which will displace: a lead from a solution of lead nitrate b iron from a solution of iron(II) sulfate Write balanced equations for these reactions. K Na Li Ba Ca Mg Al Zn Fe Sn Pb (H) Cu Ag Pt Au

  5. CHEMICAL REACTIONS PRODUCING ELECTRICITY

  6. A strip of copper metal is suspended in a beaker of copper sulphate solution, and a piece of zinc in a beaker of zinc nitrate solution. The two solutions are connected by a U-tube filled with a solution of potassium nitrate held in place by plugs of cotton wool (a strip of filter paper soaked in ammonium nitrate is often used) This U-tube which makes electrical contact between the two solutions is called a salt bridge; in order to make electrical contact it must contain some conducting substance such as a solution of potassium nitrate. CHEMICAL REACTIONS PRODUCING ELECTRICITY

  7. Copy Blank electrochemical cell showing two half cells

  8. anode cathode -2e- salt bridge +2e- Zn2+ Cu Cu2+ Zn At this point we should move these labels

  9. -2e- salt bridge Zn Cu +2e- Zn2+ Cu2+ anode cathode

  10. So what will happen here? Mg Ag Ag+ Mg2+ Please refer to the previous example. What electrical processes happen here. HINT Mg is the anode!

  11. So what will happen here? Mg Ag Ag+ Mg2+ some web links follow........

  12. http://tutors4you.com/electrochemicalcell.jpg http://tutors4you.com/electrochemicalcells.htm

  13. http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/imgche/cellelece.gifhttp://hyperphysics.phy-astr.gsu.edu/hbase/chemical/imgche/cellelece.gif

  14. http://z.about.com/d/chemistry/1/0/c/5/battery.gif http://chemistry.about.com/library/weekly/aa082003a.htm