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Physical Science:

Dr. Sunil Karna

Section 9.4 Examples

Example 9.4.1.

Why carbon dioxide solution is acidic?
Solution.
When carbon dioxide \((CO_2)\) dissolves in water \((H_2O)\text{,}\) it forms carbonic acid \((H_2CO_3)\) through the following reaction:
\begin{equation*} CO_2 + H_2O ⇌ H_2CO_3 \end{equation*}
Carbonic acid is a weak acid that dissociates in water to release hydrogen ions \((H^+)\) and bicarbonate ions \((HCO_3^-)\text{:}\)
\begin{equation*} H_2CO_3 ⇌ H^+ + HCO_3^- \end{equation*}
The hydrogen ions that are released make the solution acidic, as they increase the concentration of positively charged ions in the solution. This decrease in pH is due to the increase in hydrogen ion concentration and is therefore considered to be an acidic solution.

Example 9.4.2.

Why ammonia solution is basic (or alkaline)?
Solution.
Ammonia \((NH_3)\) is a weak base, and when it dissolves in water, it produces hydroxide ions \((OH^-)\) through the following reaction:
\begin{equation*} NH_3 + H_2O ⇌ NH_4^+ + OH^- \end{equation*}
The hydroxide ions make the solution alkaline or basic, as they increase the concentration of negatively charged ions in the solution. This increase in pH is due to the presence of hydroxide ions, which makes the solution more basic.

Example 9.4.3.

What is a crystalline solid?
  1. A solid that has a regular arrangement of particles.
  2. A solid that has an irregular arrangement of particles.
  3. Both a and b
  4. None of the above
Solution.
a.

Example 9.4.4.

What is true regarding amorphous solids?
  1. These solids have short-range order.
  2. These solids are not organized in a definite lattice pattern.
  3. Glasses are an example of amorphous solids.
  4. All of the above
Solution.
d.

Example 9.4.5.

A polar molecule can attract
  1. only ions.
  2. only other polar molecules.
  3. only other nonpolar molecules.
  4. All of the above.
Solution.
d.

Example 9.4.6.

What does "like dissolves like" mean?
  1. polar solvents dissolve in polar solutes.
  2. non-polar solvents dissolve in polar solutes.
  3. polar solutes dissolve in polar solvents.
  4. non-polar solutes dissolve in polar solvents.
Solution.
c.

Example 9.4.7.

Ice is an example of
  1. a covalent solid.
  2. an ionic solid.
  3. a metallic solid.
  4. a molecular solid.
Solution.
d.

Example 9.4.8.

Diamondis an example of
  1. a covalent solid.
  2. an ionic solid.
  3. a metallic solid.
  4. a molecular solid.
Solution.
a.

Example 9.4.9.

A saturated solution is a solution that
  1. contains the maximum amount of solute.
  2. contains polar molecules.
  3. contains the maximum amount of solvent.
  4. None of the above.
Solution.
a.
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