Chapter 2-2 PROPERTIES OF WATER

THE WATER MOLECULE Water is the most abundant compound in most living things; that’s why, to understand the chemical make up of the water structure is very important. What kinds of bonds join the atoms in a water molecule? Covalent bonds Are the hydrogen atoms bonded to each other? No, each is bonded to the oxygen atom

Why is the hydrogen end of the molecule positive and the oxygen end negative? In a water molecule, the electrons are shared unequally. At any moment, there is a greater probability of finding the shared electrons near the oxygen atom than near the hydrogen atoms.

The polarity of water molecules Water is made of oxygen and hydrogen. Oxygen has 8 protons while H only has 1 proton. Therefore, electrons are more attracted to oxygen than hydrogen. So electrons are shared with oxygen and not between the 2 hydrogen atoms This gives water molecule the bent shape Because O is slightly more negative (more electrons are shared with it) and H is slightly positive (less electrons are shared with it) – both are not even in electron distribution. Uneven electron distribution = polarity

Hydrogen bonds Hydrogen bonds- is an attraction between the hydrogen atom on one water molecule and the oxygen atom on another water molecule. A single water molecule can make four hydrogen bonds at the same time. Cohesion = attraction between molecules of the same substance ex. water with water Adhesion = attraction between molecules of different substances ex. water with glass

Solutions and Suspensions Mixture = material composed of two or more elements or compounds that are physically mixed together but not chemically together Example: salt and pepper a mixture Mixtures with water solutions suspensions

Mixture

Solutions Solution = mixture of two or more substances in which the molecules of the substances are evenly distributed Example: salt is evenly distributed in water = salt water Solute = substance that is dissolved in a solvent to make a solution ex: salt Solvent = substance in which a solute is dissolved to form a solution ex. water

Suspensions Suspension = mixture of water and non dissolved materials Example: tea leaves in hot water

Acids, Bases, and pH pH scale = measurement system used to indicate the concentration of hydrogen ions (H+) in solution; ranges from 0 to 14 Acid = compound that forms hydrogen ions (H+) in solution Base = compound that produces hydroxide ions (OH-) in solution Buffer = weak acid or base that can react with strong acids and bases to help prevent sudden changes in pH

Questions: 1.Use the structure of a water molecule to explain why it is polar.

2. Compare acidic and basic solutions of their H+ and OH- ion concentration.

3. What is a difference between a solution and a suspension?

4. What does pH measure? The pH scale measures the concentration of H- ions in a solution.

5. How are cohesion and adhesion similar? Different?

6. The strong acid hydrogen fluoride (HF) can be dissolved in pure water. Will the pH of the solution be greater or less than 7.0?

7. Page 41 Figure 2-7 shows the hydrogen bonds that form between water molecules. Why are water molecules attracted to one another?