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2013. Version 4.1. Chemistry NCEA L2 2.2 Identify Ions. SJ. Gaze. Achievem ent Standard 91162. Carry out procedures to identify ions involves collecting primary data and using these observations to identify ions in a solution using a procedure provided.

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Gaze

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  1. 2013 Version 4.1 Chemistry NCEA L2 2.2 Identify Ions 2013 Chemistry NCEA L2 2.1 Identify Ions GZ SJ Gaze

  2. Achievement Standard 91162 • Carry out procedures to identify ions involves collecting primary data and using these observations to identify ions in a solution using a procedure provided. • Carry out procedures to justify the identification of ions also includes writing balanced equations for all the reactions where precipitates are formed. • Carry out procedures to comprehensively justify the identification of ions also includes interpreting observations by recognising the formation of complex ions and writing balanced equations for these reactions. • Identification of ions must be supported by experimental observations and identification of all precipitates formed. • Ions to be identified will be limited to: Ag+, Al3+, Ba2+, Cu2+, Fe2+, Fe3+, Mg2+, Pb2+, Na+, Zn2+, Cl–, CO32–, I–, NO3–, OH–, SO42–. (Na+ and NO3– are identified by a process of elimination.) • Complex ions may include [FeSCN]2+ and those formed when OH–(aq) or NH3(aq) react with cations listed above, such as [Ag(NH3)2]+, [Al(OH)4]–, [Pb(OH)4]2–, [Zn(OH)4]2–, [Zn(NH3)4]2+, [Cu(NH3)4]2+. 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  3. Key Concepts >Ions – Anions (-ve) and Cations (+ve) >Ionic solution equations – breaking compounds into their ions >Formal equations – adding reactants to get products >Forming precipitates (insoluble ionic compounds) >Solubility rules – which compounds are soluble or insoluble >Ionic equations - leaving out spectator ions, solubility grids. >Testing for ions based on whether they precipitate or not and what colour the precipitate is. >Flow charts to help testing >Reagents – chemicals to help bring about a reaction >Complex ions – ionic compounds with a charge >Practice testing for ions 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  4. Ions Ions are charged particles. Ions form when atoms gain or lose electrons. Ions are formed when an atom loses or gains electrons. Elements are most stable when the outer shell (valence shell) is full. Elements can lose or gain electrons when they react with other chemicals to form ions. 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  5. Anions and Cations Atoms that lose electrons form positively charged ions, or cations. Atoms that gain electrons form negatively charged ions, or anions. Cation(Cat) Anion (an Iron) + Metals lose electrons to form Cations. They have 1-3 electrons in their outside shell Non-Metals gain electrons to form Anions. They have 7-8 electrons in their outside shell.

  6. Anions and Cations Ions are atoms or groups of atoms with electrical charge. Elements are most stable when the outer shell (valence shell) is full. Elements can lose or gain electrons when they react with other chemicals to form ions. CationSodium (Na) Anion Chlorine (Cl) 17+ 11+ Sodium now becomes the sodium ion Na+ Chlorine now becomes the chlorine ion Cl-

  7. Ion Chart - Cations Positive ions (+ve) - Metals 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  8. Ion Chart - Anions Negative ions (-ve) – Non Metals 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  9. Ionic Compounds Some compounds are ionic compounds, since they are made up of cations and anions. The Anion (F) takes the electrons off the Cation (Li) so their outer shells have a stable 8 electrons each. Anions and Cations have a strong electrostatic attraction for each other so they bond together as a compound. Compounds are neutral substances. For ionic compounds, the charges of the positive ions are balanced by the charges of the negative ions. 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  10. Ions in solution The ions of the ionic compound are in an aqueous solution – dissolved in water. They are therefore free moving and available to form bonds with other ions Soluble -dissolves in water form a solution e.g. NaCl(s) → Na+(aq) + Cl-(aq) Solubility = 35g/100g Sparingly Soluble - slightly soluble e.g. Calcium hydroxide Solubility = 0.1 g/100g Insoluble extremely solubility e.g. Silver chloride Solubility = 0.0002 g/100g 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  11. Naming Chemical Formula Compounds are represented by chemical formulas. If the compound is formed between a Metal cation (+ve) and a Non-Metal anion (-ve), then the compound name joins the two names together with the metal name first. Sodium + hydroxide You will be given an ion chart with the formula of the ions but you will need to remember the names. 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  12. Ionic Solution equations Ionic compounds in solution break down into their ions. dissolving NaCl(s) Na+(aq) + Cl-(aq) Write ionic solution equations for the following • potassium hydroxide b. sodium nitrate • c. magnesium chloride d. copper sulfate • e. sodium carbonate f. aluminium nitrate 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  13. Precipitation reactions Two solutions of soluble compounds are mixed. A new combination of ions (+ and -) occurs which is an insoluble compound. The insoluble compound is called a precipitate.

  14. Solubility Rules Some ions will form precipitates and are insoluble. Other ions will not form precipitates and are soluble.

  15. Solubility Rules Some ions will form precipitates and are insoluble. Other ions will not form precipitates and are soluble. 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  16. Solubility Grids When adding one ionic solution to another we use a solubility grid to decide if a precipitate has formed or not. e.g. CaCl2(aq) + Na2CO3(aq) g ? The Na+ and the Cl- ions are dissolved in solution in the beginning and remain in solution at the end. They are not involved in the precipitation reaction so they are known as spectator ions. They do not need to be writen in the equations for the reactions. 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  17. Solubility For each ionic compound decide whether it is soluble or not. If insoluble, write the formula of the solid down. If soluble, write the formulae of the ions present in a solution of the compound. a. sodium chloride b. copper hydroxide c. ammonium nitrate d. barium sulfate e. potassium carbonate f. silver chloride g. sodium sulfate h. magnesium nitrate i. silver iodide j. aluminum hydroxide k. zinc nitrate l. copper (II) carbonate m. barium sulfate n. iron (III) chloride o. zinc hydroxide p. potassium chloride q. sodium bicarbonate r. sodium bromide s. iron (II) sulfate t. ammonium carbonate u. calcium carbonate v. aluminum oxide 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  18. Balancing Equations Balanced equations must have the same number of atoms on each side of the equation i.e. reactants and products. 2Na + 2H2O = 2NaOH + H2 H H O O H H H H Na Na Na Na O O H H 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  19. Equations CaCl2(aq) + Na2CO3(aq) CaCO3(s) + 2NaCl(aq) Use solubility grids and solubility rules to complete the following equations Write formal equations and ionic equations where a ppt reaction occurs. a. Ba(NO3)2 (aq) + Na2SO4(aq) b. Cu(NO3)2(aq) + NaOH(aq) c. AgNO3 (aq) + K2CO3(aq) d. Cu(NO3)2(aq) + MgCl2(aq) e. Ca(NO3)2(aq) + (NH4)2SO4(aq) f. KCl(aq) + AgNO3(aq) g. NH4OH(aq) + FeCl3(aq) h. CuSO4(aq) + NaOH(aq) i. AgNO3(aq) + KI(aq) 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  20. Testing for Ions 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  21. Separation of precipitates Filtering Centrifuging Decanting 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  22. Important reagents Ammonia / Ammonium Hydroxide solution Ammonia reacts with water in a reversible reaction NH3 (aq) + H2O(l)                      NH4+(aq) + OH-(aq) The same solution contains two reactants OH- and NH3 The OH-(aq) concentration is quite low, but is important in the reactions of ammonia solutions 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  23. Ion Equations Under each step of the flow chart that produces a precipitate the correct ionic equation will need to be written. Use your ion chart your solubillty rules and solubility grids For example Add 2 drops NaOH(aq). 1.No ppt. NH4+, Na+ Add 1 mL NaOH(aq) Heat. Test for gas with wet red litmus. ­- No reaction Na+ - turns litmus blue/smell of ammonia, (fishy)NH4+ NH4+ + OH-(g) NH3(g) + H2O 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  24. Ion Equations 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  25. Complex Ions A complex ion is a compound rather than an atom that has more or less total electrons than total protons – therefore a complex ion has a charge. A central metal atom bonded to a specific number of other molecules or ions. tetrahydroxyplumbate(II) [Pb(OH)4]2- tetrahydroxyzincate(II) [Zn(OH)4]2- tetrahydroxyaluminate(III) [Al(OH)4]- tetraamminezinc(II) [Zn(NH3)4]2+ tetraamminecopper(II) [Cu(NH3)4]2+ diamminesilver(I) [Ag(NH3)2]+ iron(III) thiocyanateFeSCN2+ 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  26. 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  27. Complex Ions tetrahydroxyplumbate(II) [Pb(OH)4]2- tetrahydroxyzincate(II) [Zn(OH)4]2- Step one – add NaOH Pb2+ + 2OH- Pb(OH)2 Step two – add excess NaOH Pb(OH)2 + 2OH- [Pb(OH)4]2- OH- OH- Pb2+ Pb2+ OH- OH- OH- OH- + OH- OH- 2013 Chemistry NCEA L2 2.1 Identify Ions GZ SJ SJ Gaze Gaze

  28. Complex Ions tetrahydroxyaluminate(III) [Al(OH)4]- Step one – add NaOH Al3+ + 3OH- Al(OH)3 Step two – add excess NaOH Al(OH)3 + OH- [Al(OH)4]- OH- OH- Al3+ Al3+ OH- OH- OH- OH- OH- + OH- 2013 Chemistry NCEA L2 2.1 Identify Ions GZ SJ SJ Gaze Gaze

  29. Complex Ions tetraamminezinc(II) [Zn(NH3)4]2+ tetraamminecopper(II) [Cu(NH3)4]2+ NH3 + H2O NH4+ + OH- Step one – add 2 drops NH3 Zn2+ + 2OH- Zn(OH)2 Step two – add excess NH3 Zn(OH)2 + 4NH3 [Zn(NH3)4]2++ 2OH- OH- OH- NH3 NH3 NH3 Zn2+ Zn2+ OH- OH- + NH3 NH3 NH3 NH3 NH3 2013 Chemistry NCEA L2 2.1 Identify Ions GZ SJ SJ Gaze Gaze

  30. Complex Ions diamminesilver(I) [Ag(NH3)2]+ NH3 + H2O NH4+ + OH- Step one – add 2 drops NH3 Ag+ + OH- AgOH Step two – add excess NH3 AgOH+ 2NH3 [Ag(NH3)2]++ OH- OH- NH3 Ag+ Ag+ OH- + NH3 NH3 NH3 2013 Chemistry NCEA L2 2.1 Identify Ions GZ SJ SJ Gaze Gaze

  31. Complex Ions iron(III) thiocyanate FeSCN2+ Step one – add KSCN Fe3+ + SCN- FeSCN2+ K+ K+ Fe3+ SCN- Fe3+ SCN- + 2013 Chemistry NCEA L2 2.1 Identify Ions GZ SJ SJ Gaze Gaze

  32. Assessment Task One Identify the cation present in solution A. It is either Ag+(aq) or Fe3+(aq) Ion present is Ag+(aq) 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  33. Assessment Task One Identify the cation present in solution A. It is either Fe2+(aq) or Fe3+(aq) Ion present is Fe3+(aq) 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  34. Assessment Task Two Identify the anion present in solution B. It is either NO3-(aq) or OH-(aq) Ion present is OH-(aq) 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  35. Assessment Task Two Identify the anion present in solution B. It is either NO3-(aq) or CO32-(aq) Ion present is CO32- 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  36. Assessment Task Three Solution C is an aqueous solution of a metal nitrate. Identify the cation present. Cation present is Zn2+(aq) 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  37. Assessment Task Three Solution C is an aqueous solution of a metal nitrate. Identify the cation present. 2013 Chemistry NCEA L2 2.1 Identify Ions GZ Cation present is Pb2+(aq)

  38. Assessment Task Four Solution D is an aqueous solution of a sodium salt. Identify the anion present. Anion present is I-(aq) 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  39. Assessment Task Four Solution D is an aqueous solution of a sodium salt. Identify the anion present. Anion present is CI-(aq) 2013 Chemistry NCEA L2 2.1 Identify Ions GZ

  40. Task Five Identify the anion and the cation present in solution E. Anion present is SO42- Cation present is Al3+

  41. Task six Identify the anion and the cation present in solution F. Anion present is NO3- Cation present is Cu2+

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