1 CH204 Potions Class Fall 2008 Professor Severus Snape Last Week in the Potions Laboratory Separated mixtures based on differing physical and chemical properties Used Excel to calculate average, standard deviation, and weight percents Q-test in action! Buchner filtering “”‘‘’"'..: .. Experiment 3 Qualitative Chemical Analysis2 “Quant” vs “Qual” Quantitative – how much is there? Qualitative – what is it? You will identify the chemical identities of 5 unknown solutions based on how they react (or don’t react!) with one another. Previous Years Gorgon’s blood Liquid gold Vitreous humor of a blind mule 2008 Acids Bases Inorganic salts Two-Part Lab • Part 1: Mix eleven known solutions and record the results of the reactions • Part 2: Mix your five unknowns and compare the results with what you saw in Part One.3 Be Exact! The more accurately you record your observations, the easier it will be to identify your unknowns. *Explosions *Supernatural creatures *Rashes, mutations, transformations What are we looking for? ^ What are we looking for? Precipitates. (See the solubility table in Appendix 2.) Don’t expect to see any acid-base action. Write chemical equations for all of the reactions that form a precipitate. really /\4 The Known Solutions Acids: HCl H 2 SO 4 HNO 3 Bases: NaOH Na 2 S Na 3 PO 4 Salts: Ba(NO 3 ) 2 AgNO 3 K 2 CrO 4 Fe(NO 3 ) 3 Ni(NO 3 ) 2 All solutions are 0.10 or 0.20 M. Naming Ionic Compounds If the cation forms only one kind of ion, name the cation, then the anion. Don’t use prefixes like mono- or di-, just name the ions. BaCl 2 – barium chloride K 2 CO 3 – potassium carbonate Al(NO 3 ) 3 – aluminum nitrate Naming Ionic Compounds If the cation can form more than one kind of ion, put the positive charge in Roman numerals: Sn(NO 3 ) 2 – tin (II) nitrate Sn(NO 3 ) 4 – tin (IV) nitrate FeO – iron (II) oxide Fe 2 O 3 – iron (III) oxide5 Naming Ionic Compounds Monatomic anions: -ide ending Cl – – chloride O 2– – oxide S 2– – sulfide Polyatomic anions: learn the names! OH – – hydroxide PO 4 3– – phosphate SO 4 2– – sulfate See the table on page A-5 of the lab manual Riddle me this What do you get when you cross hydrochloric acid with silver nitrate? Balanced Chemical Equation HCl + AgNO 3 AgCl + HNO 3 Add the physical states of each compound HCl(aq) + AgNO 3 (aq) AgCl(s) + HNO 3 (aq) This is called a molecular equation. Let’s Get Real HCl(aq) + AgNO 3 (aq) AgCl(s) + HNO 3 (aq) Write aqueous compounds as individual ions: H + (aq) + Cl – (aq) + Ag + (aq) + NO 3 – (aq) AgCl(s) + H + (aq) + NO 3 – (aq) This is a total ionic equation. Lots of spectator ions.6 Time to Clean House Cross out spectator ions H + (aq) + Cl – (aq) + Ag + (aq) + NO 3 – (aq) AgCl(s) + H + (aq) + NO 3 – (aq) This leaves us with a Net Ionic Equation Ag + (aq) + Cl – (aq) AgCl(s) The Net Ionic Equation NaCl(aq) + AgNO 3 (aq) NaNO 3 (aq) + AgCl(s) Ba(Cl) 2 (aq) + 2AgCH 3 COO(aq) Ba(CH 3 COO) 2 (aq) + 2AgCl(s) NH 4 Cl(aq) + AgClO 3 (aq) NH 4 ClO 3 (aq) + AgCl(s) All of these reactions have the same net ionic equation: Ag + (aq) + Cl – (aq) AgCl(s) Simple is Good • The net ionic equation describes the chemical reaction that occurs, and does not include any ions that do not take part in the reaction, even though those ions are present in solution. • How do we know which ions will react and which ones won’t?7 Some Quick Solubility Rules * All compounds containing alkali metals and ammonium ion are soluble.Li + Na + K + Rb + Cs + NH 4 + * All compounds containing nitrate, chlorate, perchlorate, and acetate are soluble. NO 3 – ClO 3 – ClO 4 – CH 3 COO – Some Quick INsolubility Rules * All compounds containing PO 4 3- CO 3 2- or SO 3 2- are insoluble, except those that contain alkali metals or NH 4 + . * All compounds containing OH - or S 2- are insoluble, except Group I and NH 4 + And some group II metals. * When in doubt, Ag + Pb 2+ and Hg compounds tend to be insoluble. In the Potions Laboratory * Create an array of reactions in the microwell plate similar to the one in the lab manual. * Use only 2 drops of each reactant. * DO NOT touch the tips of the dropper bottles to the solutions in the microwell plate or you will die a most painful death.8 Vile, hideous fluids! Empty your used microwell plates into the disgusting plastic tray in the hood. Rinse the plates into the tray, then stack them in the hood. Lab Report Molecular Equations for 15 precipitation reactions. Net Ionic Equations for 15 precipitation reactions. 15 + 15 is 30 equations altogether. Warning! Dark Magic! Five reactions will turn cloudy even though no solid should be formed. Na 2 S + acid Na 2 S + Ba(NO 3 ) 2 Ba(NO 3 ) 2 + NaOH These precipitates are due to unavoidable trace contaminants in the solutions (polysulfides in Na 2 S and carbonate ion in NaOH).9 Simple lab, monster write-up The report and post-lab for this experiment take a lot of time! Andwer post-lab question 2 using only the reagents used in this experiment or your ta will mark them wrong! Post-lab question 4 should refer to question 3, not question 2. Next Week Experiment 4: Acid-Base titration Pre-Lab question 1: the answer is NOT 71! Final Exam, Part 2 * You will need a calculator every week (except next week). * Make sure you know your section number and your TA’s name!
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