Question

Writing Balanced Molecular, Ionic, And Net Ionic Equations

Write Balanced Net-Ionic Equations for the following Reactions in Aqueous Solution:

1.      Copper metal (Cu_(s)) is immersed in an aqueous solution of silver nitrate (AgNO₃). The solution turns light blue and a silver coating appears on the copper.

2.      Dilute solutions of antimony(III) chloride and sodium sulfide are mixed to give a precipitate.

3.      Dilute solutions of silver nitrate and potassium iodide are combined and give a yellow precipitate.

4.      Dilute solutions of aluminum chloride and sodium hydroxide are mixed, giving a gelatinous precipitate.

5.      Dilute solutions of calcium chloride and sodium phosphate are combined to give a precipitate.

6.      Dilute solutions of nitric acid and sodium hydroxide are mixed, generating heat.

7.      Dilute solutions of sulfuric acid and sodium hydroxide are mixed, generating heat.

8.      A dilute solution of hydrochloric acid is poured over limestone (calcium carbonate) and a non-flammable, odorless gas is released as the rock dissolves.

9.      Dilute solutions of lead(II) nitrate and sodium chloride are combined and give a white precipitate.

10. Dilute solutions of barium chloride and sodium sulfate are combined to give a white insoluble precipitate.

Answer 1

Some important rules It is useful to remember some simple "rules" (really more like guidelines) to help in predicting reactions. For common compounds such as we see in general chemistry we can use the following rules: Nitrates (NO3-) are all soluble. Alkali metal (Li+, Na+, K+, Cs+, and Rb+) and ammonium (NH4+) salts are all soluble, with the exception of a few Lithium salts. Chloride, bromide, and iodide (Cl-, Br-, and I-) salts are generally soluble, except for the salts of silver, lead(II) and mercury(I) (Ag+, Pb2+ and Hg22+). Sulfates are soluble, except for the salts of barium {BaSO4}, lead(II) {PbSO4}, mercury(II) {HgSO4}, and calcium {CaSO4}. Most hydroxides are only slightly soluble (but see rule 2). Sulfides (S2-), carbonates (CO32-), phosphates (PO43-), and chromates (CrO42-) are only slightly soluble (but see rule 2).

1. Copper metal (Cu_(s)) is immersed in an aqueous solution of silver nitrate (AgNO₃). The solution turns light blue and a silver coating appears on the copper.

   1. First need to determine the species originally present and their formulae:
      Cu_(s), Ag⁺_(aq), NO₃^-_(aq), Cu²⁺_(aq), Ag_(s).

   2. From the description, silver metal is made, so we can write the unbalanced reaction:
      Cu_(s) + Ag⁺_(aq) + NO₃^-_(aq)$Rt_arrow.gif$ Cu²⁺_(aq) + NO₃^-_(aq) + Ag_(s)

   3. By inspection we see that the atoms are balanced, however charges are not. Balancing charge we get:
      Cu_(s) + 2 Ag⁺_(aq) + NO₃^-_(aq)$Rt_arrow.gif$ Cu²⁺_(aq) + NO₃^-_(aq) + 2 Ag_(s)

   4. Finally, canceling species present on both sides gives:
      Cu_(s) + 2 Ag⁺_(aq)$Rt_arrow.gif$ Cu²⁺_(aq) + 2 Ag_(s)

2. Dilute solutions of antimony(III) chloride and sodium sulfide are mixed to give a precipitate.

   1. First need to determine species originally present and their formulae:
      Sb³⁺_(aq), Cl^-_(aq), Na ⁺_(aq), S^2-_(aq).

   2. Since we know sodium chloride is soluble we can write the unbalanced reaction:
      Sb³⁺_(aq) + 3 Cl^-_(aq) + Na ⁺_(aq)+ S^2-_(aq)$Rt_arrow.gif$ 3 Cl^-_(aq) + Na ⁺_(aq) + Sb₂S_3(s)

   3. By inspection we see that the atoms are not balanced, we need to add one antimony and two sulfides on the left:
      2 Sb³⁺_(aq) + 3 Cl^-_(aq) + Na ⁺_(aq)+ 3 S^2-_(aq)$Rt_arrow.gif$ 3 Cl^-_(aq) + Na ⁺_(aq) + Sb₂S_3(s)

   4. Finally, canceling species present on both sides gives:
      2 Sb³⁺_(aq) + 3 S^2-_(aq)$Rt_arrow.gif$ Sb₂S_3(s)

3. Dilute solutions of silver nitrate and potassium iodide are combined and give a yellow precipitate.

   1. We know that potassium nitrate is soluble (there are no insoluble nitrates nor potassium salts), so the precipitate must be silver iodide:

   2. Ag⁺_(aq) + NO₃^-_(aq) + K ⁺_(aq) + I^-_(aq)$Rt_arrow.gif$ K ⁺_(aq) + NO₃^-_(aq)+ AgI_(s)

   3. Ag⁺_(aq) + I^-_(aq)$Rt_arrow.gif$ AgI_(s)

4. Dilute solutions of aluminum chloride and sodium hydroxide are mixed, giving a gelatinous precipitate.

   1. We know that sodium chloride is soluble, so the precipitate must be aluminum hydroxide:

   2. Al³⁺_(aq) + 3 Cl^-_(aq) + Na ⁺_(aq) + OH^-_(aq)$Rt_arrow.gif$ 3 Cl^-_(aq) + Na ⁺_(aq) + Al(OH)_3(s)

   3. Al³⁺_(aq) + 3 OH^-_(aq)$Rt_arrow.gif$ Al(OH)_3(s)

5. Dilute solutions of calcium chloride and sodium phosphate are combined to give a precipitate.

   1. We know that sodium chloride is soluble, so the precipitate must be calcium phosphate:

   2. Ca²⁺_(aq) + 2 Cl^-_(aq) + 3 Na ⁺_(aq) + PO₄^3-_(aq)$Rt_arrow.gif$ 2 Cl^-_(aq) + 3 Na⁺_(aq) + Ca₃(PO₄)₂

   3. 3 Ca²⁺_(aq) + 2 PO₄^3-_(aq)$Rt_arrow.gif$ Ca₃(PO₄)₂

6. Dilute solutions of nitric acid and sodium hydroxide are mixed, generating heat.

   1. This is an acid-base reaction, so water will be formed.

   2. H⁺_(aq) + NO₃^-_(aq) + Na⁺_(aq) + OH^-_(aq)$Rt_arrow.gif$ NO₃^-_(aq) + Na⁺_(aq) + H₂O_(l)

   3. H⁺_(aq) + OH^-_(aq)$Rt_arrow.gif$ H₂O_(l)

7. Dilute solutions of sulfuric acid and sodium hydroxide are mixed, generating heat.

   1. This is an acid-base reaction, so water will be formed. Bisulfate is a weak acid.

   2. H⁺_(aq) + HSO₄^-_(aq) + Na⁺_(aq) + OH^-_(aq)$Rt_arrow.gif$ SO₄^2-_(aq) + Na⁺_(aq) + H₂O_(l)

   3. H⁺_(aq) + HSO₄^-_(aq) + 2 OH^-_(aq)$Rt_arrow.gif$ SO₄^2-_(aq) + 2 H₂O_(l)

8. A dilute solution of hydrochloric acid is poured over limestone (calcium carbonate) and a non-flammable, odorless gas is released as the rock dissolves.

   1. From the description, the most likely gas is carbon dioxide.

   2. H⁺_(aq) + Cl^-_(aq) + CaCO_3(s)$Rt_arrow.gif$ Ca²⁺_(aq) + Cl^-_(aq) + CO_2(g) + H₂O_(l)

   3. 2 H⁺_(aq) + CaCO_3(s)$Rt_arrow.gif$ Ca²⁺_(aq) + CO_2(g) + H₂O_(l)

9. Dilute solutions of lead(II) nitrate and sodium chloride are combined and give a white precipitate.

   1. We know that sodium nitrate is soluble (there are no insoluble nitrates nor sodium salts), so the precipitate must be lead chloride:

   2. Pb²⁺_(aq) + 2 NO₃^-_(aq) + Na⁺_(aq) + Cl^-_(aq)$Rt_arrow.gif$ Na⁺_(aq) + 2 NO₃^-_(aq + PbCl_2(s)

   3. Pb²⁺_(aq) + 2 Cl^-_(aq)$Rt_arrow.gif$ PbCl_2(s)

10. Dilute solutions of barium chloride and sodium sulfate are combined to give a white insoluble precipitate.

    1. We know that sodium chloride is soluble, so the precipitate must be barium sulfate:

    2. Ba²⁺_(aq) + 2 Cl^-_(aq) + 2 Na ⁺_(aq) + SO₄^2-_(aq)$Rt_arrow.gif$ 2 Cl^-_(aq) + 2 Na⁺_(aq) + BaSO₄

    3. Ba²⁺_(aq) + SO₄^2-_(aq)$Rt_arrow.gif$ BaSO₄

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