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Equilibrium Cations & Anions

Equilibrium Cations & Anions.

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Equilibrium Cations & Anions

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  1. Equilibrium Cations & Anions http://www.google.com.au/imgres?q=cation+comic&hl=en&biw=1093&bih=538&tbm=isch&tbnid=dizwhswY7cumeM:&imgrefurl=http://www.rosschurchley.com/category/blog/comics/&docid=hHXbptgEtjAw5M&imgurl=http://rchurchley.files.wordpress.com/2010/11/115-cheshire-cation.png&w=585&h=640&ei=BCouT9HsDI_omAWxlc3cDw&zoom=1&iact=hc&vpx=96&vpy=133&dur=3207&hovh=235&hovw=215&tx=87&ty=114&sig=109607668085463456387&page=1&tbnh=143&tbnw=131&start=0&ndsp=10&ved=1t:429,r:0,s:0

  2. Today’s Lesson • Equilibrium • Start of Cations & Anions • Test/Exam Revision

  3. Equilibrium • Most chemical reactions are reversible. The method of making ammonia is reversible. • N2 (g) + 3H2 (g)  2NH3 (g) • The reactants in this reaction will be Nitrogen & Hydrogen • The product is ammonia. • When conditions change, the amount of product and reactants change

  4. Continued • Below explains equilibrium: • At the start of a reaction, some of the reactants produces the product. • After some time, the amount of product and reactants stabilizes. This means that the amount of product and reactants dues not change unless there is a change in condition (temp, pressure etc). • The chemical reaction is still occurring , but the same amount of product is being produced as the broken down into reactants. Thus it’s in equilibrium

  5. Simple Idea!! • When a reversible reaction is in equilibrium and you make a change, it will do what it can to oppose that change. • As such, sometimes making a change will actually do the opposite as you expected.

  6. Temperature • When you increase temperature, particles move faster which allows more collisions. Collisions help more reactions occur. • However, producing Ammonia is an exothermic reaction (hear producing). The breakdown of ammonia is endothermic (it takes in heat). • As such, when you add more heat ammonia will break down to oppose the change • You get a lower concentration of ammonia with a higher temperature, but more ammonia can be made due to an increase in the reaction rate.

  7. Pressure • Just like adding temperature, adding pressure will increase the amount of collisions. The particles are closer together so they are more likely to collide and cause a reaction. • Using a catalyst can also help increase the amount of ammonia produced. • Removing ammonia will also allow more ammonia to be produced as there will be more reactants than product.

  8. Remember – for reversible gas reactions: • If the forward reaction is: • exothermic and the temp increases the yield decreases • Endothermic and the temp increases then yield will increase • If there are fewer molecules of product than reactants in the equation: • Pressure increase means yield increase

  9. Choosing The Right Conditions • To improve yield we can: • Have high pressure • Have low temperature • Remove ammonia • To get a decent reaction rate • Raise temperature (compromise) • Use a catalyst

  10. Testing Gases • Oxygen is flammable, so can be tested glowing splint. • Hydrogen is flammable, so can be tested with a lighted splint • Carbon Dioxide can be tested in Lime water and will form a precipitate of Calcium Carbonate • Ammonia gas will turn wet blue litmus paper red (alkali)

  11. Cations • We will explore what happens to the following: • ammonium, copper(II), iron(II), iron(III) and zinc by means of aqueous sodium hydroxide and aqueous ammonia as appropriate

  12. Anions • we will explore what happens to the following: • carbonate by means of dilute acid and then limewater, • chloride by means of aqueous silver nitrate under acidic conditions, • nitrate by reduction with aluminium • sulfate by means of aqueous barium ions under acidic conditions

  13. Testing for Halide Ions • You can test for Halides in acidic conditions (normally Nitric Acid or Hydrochloric Acid) • They will form a precipitate with Silver Nitrate. • Chloride ions forms a white precipitate (need to know this one) • Bromide ions form a cream precipitate • Iodide ions for a yellow precipitate

  14. Testing Sulfate Ions • You test for Sulfate ions in acidic conditions (normally Hydrochloric acid) • Barium Sulfate is insoluble, so you adding Barium in acidic conditions will form Barium Sulfate if there is Sulfate present.

  15. Testing Metal Ions • Many metal ions will form precipitates under basic or alkali conditions. This normally means they are in Sodium Hydroxide. • Copper 2+ makes a pale blue precipitate (Copper (II) Hydroxide) • Iron 2+ makes a green precipitate (Iron (II) Hydroxide) • Iron 3+ makes a red-brown precipitate (Iron (III) Hydroxide)

  16. Carbonates • Adding Carbon Dioxide into lime water will turn it milky by making Calcium Carbonate • Adding an acid to this will reverse the reaction

  17. Ammonia Ions • Ammonia (NH4+) can be testing in Sodium Hydroxide which is lightly heated. • If it is present, Ammonium will turn into Ammonia and water. It will make a smelly gas (Ammonia) and turn red litmus blue

  18. Nitrate Ions • Sodium Hydroxide and Aluminium can be used to find Nitrate Ions. • Take a small amount of the solution with Al and Sodium Hydroxide. • Nitrate will form Ammonia and AlO2-

  19. Questions • Read Page 156-157 and answer Q 1-4 in your books.

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