WK04

• Tests for ions are simple because they can be done at room temperature (or little heat) and are quick.
• What is the reagent used to test for a carbonate ion?


  Acid, e.g. sulfuric (H2SO4).
• What is the formula of a carbonate ion?


  CO3^2-
• What is an example equation of a test for a carbonate ion?

  Na2CO3(aq) + H2SO4(aq) -----> Na2SO4(aq) + CO2(g) + H2O)l)
• What would you observe in a positive carbonate test?


  Bubbling/fizzing/effervescence.
• When is the carbonate test completed?


  First as carbonate reacts with Ag+ to produce AgCO3 which is a white precipitate. It also reacts with Ba2+ to form BaCO3 which is also a white precipitate so would give false positives for these tests.
• What is the formula of a sulfate ion?


  SO4^2-
• Sulfates are soluble except for lead, barium and calcium sulfate.
• Adding barium chloride to sulfate ions forms a white precipitate as the barium sulfate formed is insoluble.
• What is the reagent when testing for sulfate ions?


  Barium Chloride (BaCl2)
• What is an example equation of testing for sulfate?

  BaCl2(aq) + H2SO4(aq) -----> BaSO4(s) + 2HCl(aq)
• What is the ionic equation for testing for a sulfate?

  Ba2+(aq) + SO4^2-(aq) -----> BaSO4(s)
• What is the observation is sulfate is present?


  White precipitate will form.
• When should you do the sulfate test?


  Second as sulfate ions react with silver ions to form a white precipitate of Ag2SO4 which would be a false positive for the halide ion test.
• What is the reagent for testing for a halide?


  AgNO3(aq)
• What is the observation when AgNO3 is added to Cl-?


  White precipitate
• What is the observation when AgNO3 is added to Br-?


  Cream precipitate.
• What is the observation when AgNO3 is added to I-?


  Yellow Precipitate.
• Equation for when silver nitrate is added to Cl-?

  Ag+(aq) + Cl-(aq) -----> AgCl(s)
• Equation for when silver nitrate is added to Br-?

  Ag+(aq) + Br-(aq) -----> AgBr(s)
• Equation for when silver nitrate is added to I-?

  Ag+(aq) + I-(aq) -----> AgI(s)
• The colours of the silver halide precipitates are often difficult to distinguish between, therefore a further test is often carried out on the silver halide precipitate to confirm which halide is present.
• Why is a further test done to silver halide precipitates?


  Because the precipitate colours can be hard to distinguish between (white, cream, and yellow).
• What is the reagent for the solubility test on silver halides?


  Aqueous ammonia (dilute and concentrated).
• Add dilute aqueous ammonia solution followed by concentrates aqueous ammonia solution to the silver halide precipitates formed in the halide ion tests.
• AgCl will dissolve in dilute and concentrated ammonia.
• AgBr will not dissolve in dilute ammonia, but will dissolve in concentrated ammonia.
• AgI will not dissolved in dilute or concentrated ammonia.
• What is an alkali?


  A soluble base that releases OH- ions when in solution.
• An alkali is a soluble base that releases OH- ions when in solution.
• Molecular hydroxide ions, OH- are found in alkalis.
• Litmus paper or pH indicator solution is the simplest test for the presence of hydroxide ions.
• Red litmus paper turns blue in the presence of hydroxide ions.
• What is the test for an alkali?


  Red litmus paper will turn blue.
• What is the test for an acid?


  Blue litmus paper will turn red.
• Elemental hydrogen ions (protons), H+ are found in acids.
• An acid releases H+ ions in solution (proton donor).
• What is an acid?


  An acid is a substance that donates hydrogen ions (H+) in a chemical reaction.
• Litmus paper or pH indicator solution is the simplest test for the presence of protons (H+).
• Blue litmus paper turns red in the presence of protons (H+).