SCH3U
Date: ____________________
8.3: THE DISSOLVING PROCESS
Instructions: Read through pg.382-389 and answer the following questions in the space provided.
1. Why are sodium chloride crystals unaffected by the heat from a Bunsen burner, yet it can
readily dissolve in water at room temperature?
Water is highly polar. As the molecules approach the crystal, they reorient themselves because the negative (oxygen)
end of each molecule is attracted to a nearby positively charged sodium ion. Likewise, the positive (hydrogen) end is
attracted to the chloride ion.
2. Explain, with the aid of a diagram, why sodium crystals when placed in water remain
dissolved in the solution.
When a sodium chloride crystal is placed in water, water molecules are attracted to the sodium cations and chloride
anions. These attractions pull the ions away from the crystal. Once in solution, each ion is surrounded by a layer of water
molecules in a process called hydration.
3. What is meant by the term hydration?
hydration: the process in which ions are surrounded by water molecules
4. What is dissociation?
dissociation: the separation of individual ions from an ionic compound as it dissolves in water
5. For the following solid compounds, write the dissociation equations:
a) Calcium chloride, CaCl2
CaCl2(s) -> Ca^2+(aq) + 2 Cl^-(aq)
b) Ammonium nitrite, NH4NO2
NH4NO2 -> NH4^+ + NO2^-
c) Iron(III) hydroxide, Fe(OH)3
Fe(OH)3 -> Fe^3+ -> OH^-
d) Aluminum sulfate, Al2(SO4)3
Al2(SO4)3 -> 2Al^3+ + 3SO4^-2
6. Differentiate between the terms miscible and immiscible.
miscible: able to mix to form a solution; usually describing liquids that mix with each other in all proportions to form a
solution
immiscible: unable to mix to form a solution; usually describing liquids that do not readily mix
7. Why does ethanol readily dissolve in water?
Because of the presence of several polar O-H bonds
SCH3U
Date: ____________________
8. Why is it essential for glucose to dissolve readily in water, with respect to the human body?
Glucose is the most common energy-rich "fuel" used by body cells. Brain cells rely exclusively on glucose as a fuel. Since
these cells are not capable of storing glucose, they rely on the bloodstream to bring them a steady supply.
9. Why do hydrocarbons, like crude oil, remain on the surface of water? Why is this
advantageous?
Hydrocarbons, including those found in crude oil, are immiscible with water. Crude oil is generally
less dense than water, so much of it floats on the surface. This is an advantage during an oil spill.
10.Explain why a molecule, like hexane, will not mix well with water.
Hexane is non-polar, the only attractive forces between hydrocarbon molecules are London dispersion forces--the weakest of
all intermolecular attractions. However, since hydrocarbon molecules tend to be quite large and regular in shape, these
London forces hold the non-polar molecules together quite strongly. However, there are almost no attractive forces between
hydrocarbon molecules and water molecules.
11.What must happen in order for a solute to remain dissolved in a solvent?
Solutes dissolve when the attractive forces between the solute and solvent are stronger than the attractive forces within
either the solute or the solvent.
12.State the general solubility rule.
Solutes dissolve in solvents of similar polarity
13.Why does drinking milk reduce the “burning” sensation of capsaicin (found in chili pepper)?
The fat in milk and capsaicin are both nonpolar. Fat dissolves capsaicin off the tounge.
14.What is a surfactant? Provide a common example of a surfactant.
A surfactant is a substance that acts on the surface of a liquid, reducing the surface tension. Soaps and detergents are
the most familiar surfactants.
15.Briefly describe how detergents work.
A typical soap or detergent is a compound that dissociates in water to form two ions. The cation is usually sodium ion.
The anion is a long structure with a charged "head" and a long, non-polar hydrocarbon "tail"
SCH3U
Date: ____________________
16.What prevents the oil and grease in the washing machine from reattaching to the fabric?
Draw a diagram to assist your explanation.
The hydrophobic tails of the detergent ions bond to the grease globule while the hydrophilic ends are attracted to the
surrounding water molecules. As the grease is dislodged, it becomes coated with more detergent ions. This prevents oil
and grease from reattaching to the fabric.