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Solutes, Solvents, and Aqueous Solutions of Water

SECTION 4 - Types of Chemical Reactions and Solution Stoichiometry

Water as a Solvent

Solvent  =  the substance in a solution that "does the dissolving."

Water, as you might expect, is the most common solvent on Earth.

And solutions in which water is the dissolving medium are called aqueous solutions.

Virtually all of the chemistry that makes life possible occurs in an aqueous environment. 

Water is able to dissolve many different substances.

➞ ex:  the sugar you add to iced tea.

➞ ex:  the salt you add to a soup.

So...

How exactly does H2O dissolve a solute?

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How Does Water Dissolve a Substance?

Liquid H2O consists of a collection of H2O molecules.

And each water molecule is a bent molecule (V-shaped) with an H-O-H bond angle of 104.5°.

Water Acting as a Solvent

As seen in the picture above, the O-H bonds are covalent bonds, formed by unequal sharing of electrons.

The two bond dipoles have an additive effect and overall, water is a polar molecule.

➞  solute  =  the substance that "gets dissolved" (usually a solid).

➞  solvent  =  the substance that "does the dissolving" (usually H2O).

When a solid (solute) dissolves in water (solvent), the new "solute-solvent" interactions are replacing the former "solute-solute" interactions which had been holding the solid together.

ex:  H2O molecules interacting with the positive and negative ions of a salt.

Water Dissolving a Salt Examples

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Like Dissolves Like

➞  Most polar substances dissolve in water.

➞  Most nonpolar substances (i.e. fats, oils) do not dissolve in water.

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Strong and Weak Electrolytes

To discuss electrolytes and electrolytic solutions, we need to first consider what happens when a solute gets dissolved by a solvent.

solute  +  solvent  ➞  makes a solution

And a solution can be a strong, weak, or a nonelectrolyte.  Let's take a look...

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Aqueous Solutions can Conduct Electricity

Almost every textbook gives a "light bulb" example at this point 😊

1. Strong Electrolytes - solutions that conduct electricity very efficiently. Light bulb shines.

2. Weak Electrolytes - solutions that conduct electricity only sparingly. Light bulb glows dimly.

3. Nonelectrolytes - solutions that permit no current flow. They do not conduct electricity.

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In all 3 cases above, water is the solvent. So, in my next post on this topic, we'll see that: 

"Electrical conductivity depends on the solute."

We'll examine cases 1, 2, and 3 in detail in my 2nd blog entry from SECTION 4 - Types of Chemical Reactions and Solution Stoichiometry:

Strong, Weak, and Nonelectrolytes.

See you there!...