SOLUTIONS 19.1

Chapter Nineteen: Solutions

19.1 Water

19.2 Solutions

19.3 Acids, Bases, and pH

Chapter 19.1 Learning Goals

Describe water in terms of its polarity.

Discuss properties of water related to hydrogen bonding.

Explain why water is a good solvent.

Investigation 19A

Key Question:What is a solubility curve?

Solubility Curve of KNO3

19.1 Water

We live on a watery planet. All life on Earth depends on this combination of hydrogen and oxygen atoms.

What are the properties of water that make it so valuable?

19.1 The shape of a water molecule

When two hydrogen atoms each share one electron with an oxygen atom, a neutral molecule is formed.

19.1 The shape of a water molecule

Because negative charges repel, the electrons pairs around the oxygen atom are located where they are the farthest apart.

This results in a geometric shape called a tetrahedron.

19.1 Water is a polar molecule

A water molecule has a negative end (pole) and a positive end.

A molecule (like water) with a charge separation is called a polar molecule.

19.1 Another polar moleculeAmmonia, NH3, is another polar molecule. With one lone pair and three bonding pairs of electrons.

This gives the ammonia molecule a pyramid shape.

19.1 Water is a polar moleculeMethane, CH4, is a

nonpolar molecule.

Since there are no lone pairs of electrons, the electrons are shared equally between atoms.

19.1 Hydrogen bondsA hydrogen bond is a bond between the hydrogen on one molecule to another atom on another molecule.

Hydrogen bonds are relatively weak so they constantly break and re-form.

19.1 Ice and hydrogen bondsFrozen water (or

ice) has an organized structure that resembles a honeycomb because each water molecule can form hydrogen bonds with four other water molecules.

19.1 Properties of waterWater has a high

specific heat value because of hydrogen bonds.

In order for water to boil, enough energy must be added to separate the hydrogen bonds.

19.1 Plants and hydrogen bonds

The attraction between water molecules helps water travel from roots to stems and leaves.

19.1 Water as a solvent

Water dissolves sodium chloride (salt) to form a solution of sodium (+) and chlorine (-) ions.

19.1 Water as a solvent

In general, like dissolves like: water dissolves

polar substances non-polar

solvents dissolve non-polar substances