Exam 2


The compound aluminum bromide is a strong electrolyte. Write the reaction when aluminum bromide is put into water

A strong electrolyte dissociates completely into ions in aqueous solution. When aluminum bromide, a strong electrolyte, is put into water the cations and anions are surrounded by water molecules and the solid dissolves.


AlBr3(s) [image] Al3+(aq) + 3Br(aq)

We represent this state by the symbol “(aq)” to indicate that the ions are in aqueous solution.

The compound sodium hydrogen carbonate is a strong electrolyte. Write the reaction when sodium hydrogen carbonate is put into water:

A strong electrolyte dissociates completely into ions in aqueous solution. When sodium hydrogen carbonate, a strong electrolyte, is put into water the cations and anions are surrounded by water molecules and the solid dissolves.


NaHCO3(s) [image] Na+(aq) + HCO3(aq)

We represent this state by the symbol “(aq)” to indicate that the ions are in aqueous solution.

Solubility Rules for Some Ionic Compounds in Water

Soluble Ionic Compounds
1. All sodium (Na+), potassium (K+), and ammonium (NH4+) salts are SOLUBLE.
2. All nitrate (NO3), acetate (CH3CO2), chlorate (ClO3), and perchlorate (ClO4) salts are SOLUBLE.
3. All chloride (Cl), bromide (Br), and iodide (I) salts are SOLUBLE — EXCEPT those containing: lead, silver, or mercury (I) (Pb2+, Ag+, Hg22+) which are NOT soluble.
4. All sulfate (SO42-) salts are SOLUBLE — EXCEPT those containing: calcium, silver, mercury (I), strontium, barium, or lead (Ca2+, Ag+, Hg22+, Sr2+, Ba2+, Pb2+) which are NOT soluble.
Not Soluble Ionic Compounds
5. Hydroxide (OH) and oxide (O2-) compounds are NOT SOLUBLE — EXCEPT those containing: sodium, potassium, or barium (Na+, K+, Ba2+) which are soluble.
6. Sulfide (S2-) salts are NOT SOLUBLE — EXCEPT those containing: sodium, potassium, ammonium, or barium (Na+, K+, NH4+, Ba2+) which are soluble.
7. Carbonate (CO32-) and phosphate (PO43-) salts are NOT SOLUBLE — EXCEPT those containing: sodium, potassium, or ammonium (Na+, K+, NH4+) which are soluble.

Soluble compounds are defined as those that dissolve to the extent of 1 g or more per 100 g water.
NOT soluble compounds are further classified as:
-Slightly soluble, which dissolve to the extent of 0.01 g to 1 g per 100 g water.
-Difficultly soluble or Insoluble, for which less than 0.01 g per 100 g water will dissolve.

There are six strong acids I need to know… What are they?

 

HI H+(aq) + I(aq)
HBr H+(aq) + Br(aq)
HClO4 H+(aq) + ClO4(aq)
HCl H+(aq) + Cl(aq)
HClO3                     H+(aq) + ClO3(aq)
H2SO4 H+(aq) + HSO4(aq)  (HSO4 is a weak acid that 
                                  contributes additional protons)
HNO3 H+(aq) + NO3(aq)


The substance methylamine is a weak nitrogenous base like ammonia.

Write a net ionic equation to show how methylamine, CH3NH2, behaves as a base in water.

A nitrogenous base accepts a proton (H+) when it reacts with water.

In this case, CH3NH2 accepts a proton from H2O to form CH3NH3+ and OH.

[image]
CH3NH2 (aq) + H2O (l) [image] CH3NH3+ (aq) + OH (aq)

The double arrow in the equation indicates that the reaction does not go to completion.

Write the net ionic equation for the following molecular equation.

Zn

      (s) +

Ni(NO3)2

      (aq)

[image]Zn(NO3)2

      (aq) +

Ni

    (s)

When solid Zn metal is put into an aqueous solution of Ni(NO3)2, solid Ni metal and a solution of Zn(NO3)2 result.

Step 1: Start with the balanced molecular equation.Zn

      (s) +

Ni(NO3)2

      (aq)

[image]Zn(NO3)2

      (aq) +

Ni

    (s)

Note that (aq) means that the substance is both soluble and in aqueous solution. The solid metals are not soluble in water.

Step 2: Write the total ionic equation.Write the soluble ionic compounds in ionic form. In this case there are no insoluble ionic solids to be written in molecular form:Zn

      (s) +

Ni2+

      (aq) +

2 NO3

      (aq)

[image]Zn2+

      (aq) +

2 NO3

      (aq) +

Ni

    (s)

Step 3: Write the net ionic equation.Cross out “spectator ions”, ones that appear on both sides of the reaction (these ions do not participate in the chemistry), and rewrite the “net” reaction using the smallest possible coefficients.Zn

      (s) +

Ni2+

      (aq)

[image]Zn2+

      (aq) +

Ni

    (s)

Write a net ionic equation for the reaction that occurs when magnesium carbonate (s) and excess hydrobromic acid (aq) are combined.

When a solution of hydrobromic acid and magnesium carbonate (s) are combined, magnesium bromide, water and carbon dioxide gas are formed.

Step 1: Write the balanced “molecular” equation:
2HBr(aq) + MgCO3 (s) [image] MgBr2 (s) + H2O(l) + CO2(g)

Step 2: Carbon dioxide and water are written in molecular form. Consult the solubility and net ionic equation rules on the information page to determine which of the other substances will dissociate:

2HBr(aq) +   MgCO3 (s) [image]   MgBr2 (s) + H2O(l) + CO2(g)  
yes     no     yes      

Step 3: Dissociate all soluble salts, strong acids, and strong bases (except calcium hydroxide). Leave together all “not soluble” salts and weak acids or bases:
2H+(aq) + 2Br(aq) + MgCO3(s)[image] Mg2+(aq) + 2Br(aq) + H2O(l)  + CO2(g)

Step 4: Cross out “spectator ions” that appear on both sides of the reaction (these ions do not participate in the chemistry) and rewrite the “net” reaction using the smallest possible coefficients:
2H+(aq) + MgCO3(s)[image]Mg2+ (aq) + H2O(l) + CO2(g)

Write a net ionic equation for the reaction that occurs when excess hydrobromic acid (aq) and sodium sulfite (aq) are combined. Note: Sulfites follow the same solubility trends as sulfates.

When a solution of hydrobromic acid and sodium sulfite (aq) are combined, sodium bromide , water and sulfur dioxide gas are formed.

Step 1: Write the balanced “molecular” equation:
2 HBr(aq) + Na2SO3 (aq) [image] 2 NaBr(aq) + H2O(l) + SO2(g)

Step 2: Sulfur dioxide and water are written in molecular form. Consult the solubility and net ionic equation rules on the information page to determine which of the other substances will dissociate:

  2 HBr(aq) +   Na2SO3 (aq) [image]   2 NaBr(aq) + H2O(aq) + SO2(g)  
 
yes
   
yes
   
yes
     

Step 3: Dissociate all soluble salts, strong acids, and strong bases (except calcium hydroxide). Leave together all “not soluble” salts and weak acids or bases:
2H+(aq) + 2Br(aq) + 2(aq) + (aq) [image] 2Na+(aq) + 2Br(aq) + H2O(l) + SO2(g)

Step 4: Cross out “spectator ions” that appear on both sides of the reaction (these ions do not participate in the chemistry) and rewrite the “net” reaction using the smallest possible coefficients:
2H+(aq) + SO32-(aq) [image] H2O(l) + SO2(g)