Go ahead and try again, there are tips and answers on the next page. 1. Write a balanced chemical equation for the combination of phosphoric acid (aq) plus calcium carbonate(s), one product is a solid. 2. Write balanced complete and net ionic equations for the combination of silver acetate (aq) plus iron(III) chloride (aq), one product is a solid 3. Calculate the volume (in L) of a 5.00 M stock solution of HCl that is needed to prepare 300.0 mL of 0.250 M HCl solution. 4. A 25.00 mL sample of aqueous oxalic acid is titrated to its endpoint, requiring 37.45 mL of 0.1100 M NaOH. Calculate the molarity of the acid. (hint: the oxalate anion is C2O42–) 5. Calculate the pH of a 1.98  10–4 M solution of nitric acid. _______________________ (show equation or work) 6. For the reaction below, identify the oxidation states of nitrogen in the reactants and products, the substance being reduced, the oxidizing agent, and the reducing agent. Elemental oxidation states (fill in): N ____ in NO3– –
Cu(s) + 2NO3
+
2+
(aq) + 4H (aq)  Cu (aq) + 2NO2(g) + 2H2O(l) Substance being reduced _____________ Oxidizing agent _________________ Reducing agent _______________________ N ____ in NO2 1. Write a balanced chemical equation for the combination of phosphoric acid (aq) plus calcium carbonate(s), one product is a solid. 2H3PO4(aq) + 3CaCO3(s) → 3H2O(l) + 2CO2(g) + Ca3(PO4)2(s) We used phosphate compounds in three consecutive labs. Writing the formula for phosphoric acid should not have been difficult. The worked example of net ionic reactions on page 168 involves phosphate. Page 174 is entirely about the reaction of a bicarbonate salt with an acid, complete with illustrations. Read the book, and look at the pretty pictures. Check this page out to determine the correct products. There is a table on page 175 with more information, and there is a worked example with sodium carbonate plus an acid on page 175. Bonus tip! When writing chemical formulas, only use parentheses around polyatomic ions if there are subscripts present. NaNO3 is correct, but not Na(NO3). 2. Write balanced complete and net ionic equations for the combination of silver acetate (aq) plus iron(III) chloride (aq), one product is a solid. 3AgC2H3O2(aq) + FeCl3(aq) → 3AgCl(s) + Fe(C2H3O2)3(aq) Ag+ + Cl– → AgCl(s) or 3Ag+ + 3Cl– → 3AgCl(s) although the first is preferred On page 168, acetate is one of the ions used in a worked example for net ionic equations. There is a picture on page 160, and an example mental model of the precipitate that forms in this reaction. Bonus tip! Don’t transfer subscripts from reactants to products. Bonus tip #2!! A formula like CaCl2 means that there one Ca2+ and two Cl– ions are present, written like this: Ca2+ + 2Cl– It doesn’t mean Cl22– or Cl2– or anything else. It simply means two chloride ions, like two nitrate ions would be 2NO3–. 3. Calculate the volume (in L) of a 5.00 M stock solution of HCl that is needed to prepare 300.0 mL of 0.250 M HCl solution. (0.0150 L) Bonus tip! Most students did fine, but make sure to label the values in your equations. Bonus tip #2!! Don’t forget significant figures. 4. A 25.00 mL sample of aqueous oxalic acid is titrated to its endpoint, requiring 37.45 mL of 0.1100 M NaOH. Calculate the molarity of the acid. (hint: the oxalate anion is C2O42–) (0.08239 M) Bonus tip! Writing the formula of an acid should be easy if you know the formula and charge of the anion. See page 169 (Table 4.2) or page 104. Bonus tip #2!! When acids are titrated, all of the acid protons (the H’s in the beginning of the formula) will react with OH– to make water. Example 4.14 on page 172 works out an acid‐base titration problem. 5. Calculate the pH of a 1.98  10–4 M solution of nitric acid. ________3.70_______________ see class notes. (show equation or work) 6. For the reaction below, identify the oxidation states of nitrogen in the reactants and products, the substance being reduced, the oxidizing agent, and the reducing agent. Elemental oxidation states (fill in): N __5__ in NO3– –
Cu(s) + 2NO3
N __4__ in NO2 +
2+
(aq) + 4H (aq)  Cu (aq) + 2NO2(g) + 2H2O(l) Substance being reduced _______N in NO3–____(N OK)__ Oxidizing agent ______ N in NO3–____(N OK)_______ Reducing agent __________Cu(s)_____(Cu OK)________ Page 178 goes through assigning oxidation states, one example is sulfate (similar to nitrate). The reducing agent reduces another substance. It must be oxidized. See page 180. The oxidizing agent grabs electrons to oxidize another substance. If it is gaining electrons, it must be reduced.