6. Chemical Equations + Tests for Anions https://www.youtube.com/watch?v=X7ckfeRjjvI

Syllabus

Chemical Reaction In a chemical reaction, elements react together to form a new compound A new substance is always formed when a chemical reaction occurs

Evidence of a Reaction

Evidence of a Reaction Effervescence (gas) Colour change Temperature change Light given off Noise given off Precipitate formation

Balancing Chemical Equations Law of Conservation of Mass The total mass of the products of a chemical reaction is the same as the total mass of the reactants Law of Conservation of Matter Matter is neither created nor destroyed but merely changed from one form into another

Balancing Chemical Equations CH4 + O2 CO2 + H2O Left hand side of equation = right hand side of equation Left Right C atom 1 H atom 4 2 O atom 3

Balancing Chemical Equations 2 2 CH4 + O2 CO2 + H2O Left hand side of equation = right hand side of equation Left Right C atom 1 H atom 4 2 O atom 3

Balancing Chemical Equations 2 CH4 + O2 CO2 + H2O Left hand side of equation = right hand side of equation Left Right C atom 1 H atom 4 O atom 3

Tests for Anions in Aqueous Solution Ion= a charged atom or group of atoms Anion = a negative ion e.g.: Cl-, OH- Cation = a positive ion e.g.: Na+

Tests for Anions in Aqueous Solution Chloride Cl- Sulfate SO42- Sulfite SO32- Carbonate CO32- Hydrogen carbonate HCO3- Nitrate NO3- Phosphate PO4 3-

Tests for Anions in Aqueous Solution Chloride Sulfate Sulfite Carbonate Hydrogen carbonate Nitrate Phosphate

Tests for Anions in Aqueous Solution Qualitative Analysis The identification of constituents present in a substance

Tests for Anions in Aqueous Solution Test for Carbonate (CO32-) and Hydrogencarbonate (HCO3-) Dil HCl Effervescence observed: CO2 produced CO32- + 2H+ -> CO2 + H2O HCO3- + H+ -> CO2 + H2O Carbonate or hydrogencarbonate + dil HCl Bubbles!! Limewater

A solid material that settles out of solution Tests for Anions in Aqueous Solution Precipitate A solid material that settles out of solution Test for Carbonate (CO32-) and Hydrogencarbonate (HCO3-) To distinguish between carbonates and hydrogen carbonates Magnesium Sulphate (MgSO4) Carbonate: white precipitate formed Mg2+ + CO32- -> MgCO3 (insoluble) Hydrogen carbonate: no precipitate Mg2+ + 2HCO3- -> Mg(HCO3) Magnesium carbonate is insoluble in water Magnesium hydrogencarbonate is soluble in water

Tests for Anions in Aqueous Solution Test for Carbonate (CO32-) and Hydrogencarbonate (HCO3-) Fizzing: CO32- + 2H+ -> CO2 + H2O White precipitate: Mg2+ + CO32- -> MgCO3 ↓ Dil HCl MgSO4 CO32- Dil HCl Clear solution: Mg2+ + 2HCO3- -> Mg(HCO3)2 (sol) Fizzing: HCO3- + H+ -> CO2 + H2O MgSO4 HCO3-

Nitrate test also called the ‘Brown Ring’ Test Tests for Anions in Aqueous Solution Nitrate test also called the ‘Brown Ring’ Test Test for Nitrate (NO3-) Iron sulphate (FeSO4) Conc sulphuric acid (H2SO4): N.B: test tube tilted and H2SO4 added slowly down the side of the test tube so that 2 layers are formed Brown ring formed at the junction of the 2 layers

Tests for Anions in Aqueous Solution Test for Nitrate (NO3-) NO3- + FeSO4 Conc. H2SO4 2 layers Brown ring formed between the layers

A solid material that settles out of solution Tests for Anions in Aqueous Solution Precipitate A solid material that settles out of solution Test for Phosphate (PO43-) Ammonium molybdate: (NH4)2MoO4 Conc nitric acid (HNO3) Placed in warm water Yellow precipitate

Tests for Anions in Aqueous Solution Test for Phosphate (PO43-) PO43- + Ammonium molybdate Conc. HNO3 Place in warm water Yellow ppt

A solid material that settles out of solution Tests for Anions in Aqueous Solution Precipitate A solid material that settles out of solution Test for Chloride (Cl-) Silver nitrate (AgNO3) White precipitate formed: Ag+ + Cl- -> AgCl Silver Chloride Silver chloride is insoluble in water To confirm silver chloride: add dilute ammonia solution and cloudiness disappears

Tests for Anions in Aqueous Solution Test for Chloride (Cl-) Cl- + AgNO3 White ppt: AgCl

Tests for Anions in Aqueous Solution Test for Sulfate (SO42-) and Sulfite (SO32-) Barium Chloride (BaCl) White precipitate formed in both: Ba2+ + SO42- -> BaSO4 Ba2+ + SO32- -> BaSO3 Both barium sulfate and sulfite are insoluble in water Barium Sulfate Barium Sulfite

Tests for Anions in Aqueous Solution Test for Sulfate (SO42-) and Sulfite (SO32-) To distinguish between sulfate and sulphite ions: Dil HCl Sulfate: precipitate remains (no reaction ) BaSO4 + HCl -> no reaction Sulfite: precipitate dissolves (cleat solution) SO32- + 2H+ -> SO2 + H2O Barium Sulfate is insoluble in HCl Barium Sulfite is soluble in HCl

Tests for Anions in Aqueous Solution Test for Sulfate (SO42-) and Sulfite (SO32-) BaSO4 Dil HCl SO42- White ppt Ba2+ + SO42- -> BaSO4 ↓ No reaction (ppt remains): BaSO4 + HCl -> no reaction BaSO4 White ppt Ba2+ + SO32- -> BaSO3 ↓ Dil HCl Clear solution (ppt dissolves) SO32- + 2H+ -> SO2 + H2O SO32-

Outline 2 assumptions of daltons atomic theory Who discovered cathode rays How did Thompson discover the electron Describe the plum pudding model How was the nucleus discovered