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Unformatted text preview: Experiment 3
Qualitative Chemical Analysis Qualitative Analysis
What are solutions A-E? What AYou will identify what these chemicals are You based on:
how they react how or don’t react with one another or don’ 1 2 Two-Part Lab
Part 1: Mix eleven known solutions and Part record the results of the reactions Part 2: Mix your five unknowns and compare Part the results with what you saw in Part One. What are we looking for?
Precipitates. Precipitates. (See the solubility table in Appendix 2 and in these slides)
Don’t expect to see any acid-base action. Don’ acidWrite chemical equations for all of the reactions Write that form a precipitate. 3 4 Be Exact!
The more accurately you record your The observations, the easier it will be to identify your unknowns. The Known Solutions
Acids: H2SO4 HNO3 Acids: Bases: NaOH Na2S Na3PO4 Bases: Salts: NaCl Ba(NO3)2 AgNO3 Fe(NO3)3 Salts: Fe(NO Ni(NO3)2 K2CrO4 All solutions are 0.10M or 0.20 M. All 5 6 1 Naming Formula Units (metals + nonmetals)
Compounds formed by the bonding of Compounds metal with nonmetals are held together by electrostatic forces. That is, they form ions of different charges.
1. Metals form positive charges by losing electrons – cations. cations. 2. Nonmetals form negative charges by gaining electrons – anions. anions.
7 The Periodic Table
+1 +2 +3 -3 -2 -1 Group IA metals lose 1 electron Group 2A metals lose 2 electrons Group 3A metals lose 3 electrons Group 7A nonmetals gain 1 electron Group 6A nonmetals gain 2 electrons Group 5A nonmetals gain 3 electrons Group B transition metals 7 8 Naming Formula Units (metals + nonmetals)
Cations: positively charged atoms (metals) Group IA metals Group IIA metals Group IIIA metals +1 charge Li+ Na+ K+ Rb+ Cs+ +1 Li +2 charge Mg2+ Ca2+ Sr2+ Ba2+ +2 Mg +3 charge +3 Al3+ Ga3+ In3+ Al In Naming Formula Units (metals + nonmetals)
Anions: negatively charged atoms (nonmetals)
Group VIIA nonmetals Group VIA nonmetals Group VA nonmetals −1 charge F− Cl− Br− I− −2 charge O2– S 2– Se 2– Te 2– −3 charge N3– P3– As3– Sb3– 9 10 10 9 10 Naming Formula Units (metals + nonmetals)
Examples: Examples: Sodium + fluorine Na0 → Na+ + 1e− NaF F0 + 1e− 1e → F−
11 Naming Formula Units (metals + nonmetals)
1. If a cation: take the name of the element: cation:
sodium 2. If an anion: the name of the element with the 2.
ide ending: fluorine fluorine NaF fluoride fluoride sodium fluoride sodium 12 11 12 2 Naming Formula Units (metals + nonmetals)
Metals and Nonmetals may have unequal Metals charges: Mg2+ and N3To balance, cross the charges. Mg2+ N3magnesium nitride Naming Formula Units (metals + nonmetals)
Magnesium + sulfur Potassium + oxygen Calcium + bromine Aluminum + nitrogen Barium + nitrogen
13 Mg2+ + S2– 2K+ + O2– Ca2+ + 2Br– Al3+ + N3– 3Ba2+ + 2N3– 2Al3+ + 3O2– MgS K 2O CaBr2 AlN Ba3N2 Al2O3 Magnesium sulfide Potassium oxide Calcium bromide Aluminum nitride Barium nitride Aluminum oxide 14
13 Aluminum + oxygen Naming Formula Units (metals + nonmetals)
Transition metals and oxidation states: (There Transition are more than one possible positive charge on some transition metals) To name the salts with more than one possible To charge, we need to determine the charge of the cation and name the salt in such a way that we know which oxidation state the cation has. Transition Metals Oxidation States ● = possible common oxidation states ○ = rare oxidation states
16 15 15 Naming Formula Units (metals + nonmetals) Naming Formula Units (metals + nonmetals)
MnCl2 the overall charge on the formula unit must the equal zero. Chlorine as an anion is always −1. Therefore:
x −1 (this is the oxidation state of chloride) Most common oxidation states of metals and nonmetals in salts. E.g. although nickel has two common oxidation states, it is mostly Ni2+. Therefore, nickel is often named without its oxidation state in parenthesis. 17 17 MnCl2 = 0 x + 2(−1) = 0 x = +2 Manganese must have a +2 charge to balance the anions Manganese (II) chloride. Manganese 18 18 3 Naming Formula Units (metals + nonmetals)
MnCl3 the overall charge on the formula unit must the equal zero. Chlorine as an anion is always −1. Therefore:
x −1 (this is the oxidation state of chloride) Naming Formula Units (metals + nonmetals)
Examples: Examples: FeO iron(II) oxide iron(II) SnCl2 tin(II) chloride tin(II) PbF2 lead(II) fluoride lead(II) Cu2S copper(I) sulfide copper(I)
19 MnCl3 = 0 x + 3(−1) = 0 x = +3 Manganese must have a +3 charge to balance the anions Manganese (III) chloride. Manganese
19 Fe2O3 iron(III) oxide iron(III) vs. SnCl4 tin(IV) chloride tin(IV) vs. PbF4 lead(IV) fluoride lead(IV) vs. CuS copper(II) sulfide copper(II)
20 vs. 20 Naming Formula Units (metals + nonmetals)
Exceptions you should know! Silver always + 1, zinc always + 2 1, Silver + oxygen Ag2O silver oxide Ag Zinc + iodine ZnI2 zinc iodide ZnI zinc Polyatomic Ions
Polyatomic Ions: groups of charged molecules Polyatomic that act as a cation or anion. They form salts as though they were a single They cation or anion. 21 22 21 22 Polyatomic Ions
Some common polyatomic ions. There is a more complete list on Blackboard. 2. NO2− (nitrite ion) acts as a −1 anion 3. NO3− (nitrate ion) acts as a −1 anion 4. OH− (hydroxide ion) acts as a −1 anion 5. SO32− (sulfite ion) acts as a −2 anion 5. 6. SO42− (sulfate ion) acts as a −2 anion 6. 7. CO32− (carbonate ion) acts as a −2 anion 8. PO43− (phosphate ion) acts as a −3 anion 9. CH3COO– (acetate ion) acts as a –1 anion 10. MnO4− (permanganate ion) acts as a −1 anion 11. CrO42– (chromate ion) acts as a – 2 anion 12. Cr2O72– (dichromate ion) acts as a – 2 anion Polyatomic Ions anion All behave as a -1
ClO− hypochlorite ClO2− chlorite ClO3− ClO4−
23 1. NH4+ (ammonium ion) acts as a +1 cation chlorate perchlorate 24 23 24 4 Naming Salts with Polyatomic Ions
1. 2. 3. 4. 5.
Sodium + hydroxide ion = NaOH; sodium hydroxide NaOH; Ammonium ion + sulfur = (NH4)2S; ammonium sulfide Barium + sulfate ion = BaSO4; barium sulfate Calcium + phosphate ion = Ca3(PO4)2; calcium phosphate Aluminum + hypochlorite ion = Al(ClO)3; aluminum hypochlorite 6. Potassium + carbonate ion = K2CO3; potassium carbonate 7. Magnesium + nitrite ion = Mg(NO2)2; magnesium nitrite 8. Sodium + acetate ion = NaCH3COO; sodium acetate There is a nomenclature (naming) worksheet and answer key posted on Blackboard.
25 Naming Salts with Polyatomic Ions
Copper(II) hydroxide = Cu2+ + OH– = Cu(OH)2 Copper(II) Silver nitrate = Ag+ + NO3– = AgNO3 Silver Iron(III) sulfate = Fe3+ + SO42– = Fe2(SO4)3 Iron(III) Zinc perchlorate = Zn2+ + ClO4– = Zn(ClO4)2 Zinc Lead(II) carbonate = Pb2+ + CO32– = PbCO3 Lead(II) Tin(IV) nitrite = Sn4+ + NO2– = Sn(NO2)4 Tin(IV) NO Cobalt(III) sulfite = Co3+ + SO32– = Co2(SO3)3 Cobalt(III) 26 25 Reactions in Aqueous Solution
Reactions is solutions can be represented by three chemical equations leading to the driving force of the reactions. 1. The molecular (formula unit) equation is the molecular balanced chemical equation with states of the reactants and products. HCl(aq) + AgNO3(aq) → AgCl(s) + HNO3(aq) AgCl(s) HCl(aq) Reactions in Aqueous Solution
2. The complete (or total) ionic. The state of the reactants complete
and products in aqueous solution.
[H+(aq)+ Cl–(aq)] + [Ag+(aq)+ NO3–(aq)] → AgCl(s)+ H+(aq)+ NO3–(aq) [Ag (aq) (s) (aq) (aq) (the reaction solution) The complete ionic equation allows us to identify spectator ions. Spectator ions are the ions that do not participate in the reaction
27 28 Reactions in Aqueous Solution
3. Cross out spectator ions
H+(aq)+ Cl–(aq)+ Ag+(aq) + NO3–(aq) →AgCl(s) + H+(aq) + NO3–(aq) (s) (aq) (aq) (aq) Reactions in Aqueous Solution
1. NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s) (aq) (s) 2. Ba(Cl)2(aq)+ 2AgCH3COO(aq) → Ba(CH3COO)2(aq) + 2AgCl(s) 3. NH4Cl(aq) + AgClO3(aq) → NH4ClO3(aq) + AgCl(s) (s)
All of these reactions have the same net ionic equation: Ag+(aq) + Cl–(aq) → AgCl(s) (s) (aq) This leaves us with a net ionic equation: The driving net force of the reaction is the formation of a solid. Ag+(aq) + Cl–(aq) → AgCl(s) (s) (aq) 29 29 30 5 Reactions in Aqueous Solution
The net ionic equation describes the chemical The 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? How Solubility of Salts
All compounds containing alkali metals and All ammonium ion are soluble in dilute solutions. (Group IA metals)
Li+ Na+ K+ Rb+ Cs+ NH4+ All compounds containing nitrate, chlorate, All perchlorate, and acetate are soluble in dilute perchlorate, solutions.
NO3– ClO3– ClO4– CH3COO–
31 32 Solubility of Salts
All compounds containing PO43− CO32− or All SO32− are insoluble, except those that contain insoluble, alkali metals or NH4+. All compounds containing OH− or S2−are All insoluble, except Group I and NH4+and some insoluble, group II metals.
When in doubt, Ag+ Pb2+ and Hg2+ compounds When tend to be insoluble. Solubility Chart A copy of this chart is available on Blackboard.
33 34 The Experiment
Create a matrix of reactions in the microwell plate Create similar to the one in the lab manual. Use only 2 drops of each reactant. Use DO NOT touch the tips of the dropper bottles to the DO solutions in the microwell plate in order to prevent contamination. Empty your used microwell plates into the plastic tray Empty in the hood. Rinse the plates into the tray, then stack them in the Rinse hood.
Four reactions will turn cloudy even though no solid Four should be formed. Na2S + acid (H2SO4 & HNO3) Na Na2S + Ba(NO3)2 Na Ba(NO3)2 + NaOH Ba(NO These precipitates are due to unavoidable trace These contaminants in the solutions (polysulfides in Na2S (polysulfides and carbonate ion in NaOH). NaOH).
36 6 Lab Write-up
Your TA will write five combinations of possible reactions that occurred in this experiment. a) If the combination of compounds react:
Write the complete chemical equation with phases in parenthesis. Write Write the net equation. Write The five combinations
1. 2. 3. 4. 5.
AgNO3 (aq) + NaCl (aq) (aq) Ba(NO3)2 (aq) + H2SO4 (aq) Fe(NO3)3 (aq) + NaOH (aq) Na3PO4 (aq) + Ba(NO3)2 (aq) Fe(NO3)3(aq) + Ba(NO3)2 (aq) Eg. NH4Cl (aq) + Hg2(NO3)2 (aq) Eg. Complete: 2 NH4Cl (aq) + Hg2(NO3)2 (aq) → Hg2Cl2 (s) + 2 NH4(NO3) (aq) Complete: Net: Hg22+ (aq) + 2 Cl– (aq) →Hg2Cl2 (s) b) If the combination does not react: b)
Write NR after the arrow Write Eg. NH4Cl (aq) + NaOH (aq) → NR Eg.
37 38 Next Week
Quiz 3: Make sure you can name ionic compounds if Quiz given the formula, and can write formula if given the name. (practice naming using the worksheet on Blackboard). Also know some general solubility rules. (The ones Also provided in these slides) You will not need a calculator for next week’s quiz. You week’ Quiz 2 39 40 7 ...
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This note was uploaded on 03/17/2010 for the course CH 204 taught by Professor Leytner during the Spring '08 term at University of Texas at Austin.
- Spring '08