4-3 General Types (Sections 7.6, 7.7) And you

1) Synthesis reaction elements come together to form solid (in general but exceptions occur) A + B → C or element + element → compound Use periodic table to determine charges of elements. Write product using criss-cross or balancing of charges to determine subscripts. Balance equation

Synthesis rxn. Demo Al(s) + I2(s) → http://www.youtube.com/watch?v=8TXjxhuycBU Now balance this puppy please 2 Al(s) + 3 I2(s) → 2 AlI3(g) You can see this is an example where a solid is not formed!!! AlI3(g)

Synthesis Practice 4 Na(s) + O2(g) → K(s) + S8(s) → Now balance them please   2 Na2O(s) 8 16 K2S(S)

2) Decomposition reaction Solid heated to form solid and gas (in general) C → A + B or compound → element + element Reactants will consist of just one compound. Write compound’s elements as the products. Remember the 7 diatomics! Balance the equation

Decomposition Demo NI3(s) → www.youtube.com/watch?v=DFfRqoIdArM Now please balance this puppy 2 NI3(S)  N2(g) + 3 I2(g) N2(g) + I2(g)

Decomposition practice HgO(s) → Now balance it please 2HgO (s)  2Hg (l) + O2 (g) H2O (l) → Products and balance please 2H2O (l)  2H2 (g) + O2 (g) Hg (l) + O2 (g)

3) Combustion reaction (my favorite) CxHy (or CxHyOz) + O2 → CO2 + H2O Rapid burning; one of the reactants will be O2. For hydrocarbons (compounds with C, H, and/or O), the products are: CO2 + H2O

Combustion Demo CH4(g) + O2(g) → http://www.youtube.com/watch?v=q5W2trP0PmU The Methane Mamba! Demo Balance please CO2 (g) + H2O (g)

Combustion Practice Recall the suggestion of starting with a 2 in front of the hydrocarbon, and reducing at the end if needed C2H4O2 (l) + O2 (g) → 2 C2H4O2 (l) + 4 O2 (g) → 4 CO2 (g) + 4 H2O (g) C2H4O2 (l) + 2 O2 (g) → 2 CO2 (g) + 2 H2O (g)

More combustion rxn. practice C2H2(g) + O2(g) → 2 C2H2(g) + 5 O2(g) → 4 CO2 (g) + 2 H2O (g) Starting with the 2 really helps on this one!

4) Single Replacement rxn. A + BC → AC + B or element + compound → compound + element Note: most take place in aqueous environment Recall the H.S. dance parallel Metals replace metals and nonmetals replace nonmetals. Replacement occurs only if the element is higher on the activity list than the element in the compound.

Activity list or metals K Ca Na Mg Al Zn Cr Fe Ni Sn (tin) Pb (lead) H Cu Hg Ag (silver) Pt Au (gold) So Li would replace K if K was in a compound

Activity list for non metals fluorine chlorine bromine Iodine (general trend – but Cl may be more active)  

Write the new compound with balanced charges and the individual element (is it diatomic?????). If the element is lower on the list then the element in the compound, no reaction occurs. Kind of a weird chemical hierarchy thing

Single replacement rxn. demo Al(s) + CuCl2(aq) → Demo in class 2 Al(s) + 3 CuCl2(aq) → 3 Cu (s) + 2 AlCl3 (aq) Note Al is higher = “more attractive” than Cu

Single replacement practice HCl(aq) + Zn(s) → 2 HCl(aq) + Zn(s) → ZnCl2 (aq) + H2 (g) MgCl2(aq) + Zn(s) → MgCl2(aq) + Zn(s) → No reaction !!!!! Cl2(aq) + CaBr2(aq) → Cl2(aq) + CaBr2(aq) → CaCl2 + Br2

5) Double replacement AB(aq) + CD(aq) → AD + CB compound + compound → compound + compound Takes place in an aqueous environment Metal pairs with nonmetal from other compound and vice versa. Write new products with charges balancing. Consult solubility chart to determine the insoluble compound (ppt). This chart, seen below, is also found on the inside back cover of your text and on page 170.

1. Most nitrate (NO3-) salts are soluble. 2. Most salts of Na+, K+, and NH4+ are soluble. 3. Most chloride salts are soluble. Notable exceptions are AgCl, PbCl2, and Hg2Cl2. 4. Most sulfate salts are soluble. Notable exceptions are BaSO4, PbSO4, and CaSO4. 5. Most hydroxide (OH-) compounds are only slightly soluble. The important exceptions are NaOH and KOH. Ba(OH)2 and Ca(OH)2 are only moderately soluble. 6. Most sulfide (S-2), carbonate (CO3-2), and phosphate (PO4-3) salts are only slightly soluble.   Note: slightly soluble and moderately soluble are, essentially, the same as “insoluble”.

Double replacement demo CuCl2(aq) + Na2CO3(aq) → http://www.youtube.com/watch?v=lEdAkBNNqSY CuCl2(aq) + Na2CO3(aq) → CuCO3(s) + 2NaCl(aq) Note: see the solubility chart to know what forms if you do observe a ppt.

Practice double replacement rxns. NaOH(aq) + FeCl3(aq) → 3NaOH(aq) + FeCl3(aq) → 3NaCl(aq) + Fe(OH)3 WOW that was FUN!!!!

Molecular, Complete Ionic, and Net Ionic Equations The full double replacement is also called the” molecular equation.” For example, the molecular equation from above is: 3NaOH(aq) + FeCl3(aq) → 3NaCl(aq) + Fe(OH)3(s)

Molecular, Complete Ionic, and Net Ionic Equations The full double replacement is also called the” molecular equation.” For example, the molecular equation from above is: 3NaOH(aq) + FeCl3(aq) → 3NaCl(aq) + Fe(OH)3(s) A variation of this equation is the “complete ionic equation”, where the (aq) compounds are broken into their respective ions: Like this:

3NaOH(aq) + FeCl3(aq) → 3NaCl(aq) + Fe(OH)3(s) 3Na+(aq) + 3OH-(aq) + Fe+3(aq) + 3Cl-(aq) → 3Na+(aq) + 3Cl-(aq) + Fe(OH)3(s) Note how the solid remains as a compound. This equation more accurately depicts what is happening in solution, since (aq) means that the ions a surrounded by water molecules (“hydrated”):

Cancel the redundant parts to find: 3OH-(aq) + Fe+3(aq) → Fe(OH)3(s) A final version of the molecular equation is the “net ionic equation.” Simply put, this form only shows the ions that form the solid: 3Na+(aq) + 3OH-(aq) + Fe+3(aq) + 3Cl-(aq) → 3Na+(aq) + 3Cl-(aq) + Fe(OH)3(s) Cancel the redundant parts to find: 3OH-(aq) + Fe+3(aq) → Fe(OH)3(s)

Practice: Na2SO4(aq) + BaCl2(aq) → Complete ionic: Net Ionic: Note: All equations, regardless of the variation, require the atoms and charges to balance and the phases of matter included Practice: Na2SO4(aq) + BaCl2(aq) → Na2SO4(aq) + BaCl2(aq) → 2NaCl(aq) + BaSO4(s) Complete ionic: 2Na+ + SO4-2 + Ba+2 + 2Cl-  2Na+ + 2Cl- + Ba SO4 (s) Net Ionic: SO4-2(aq) + Ba+2(aq)  BaSO4 (S) NOW that was FUN!!!!