1. Chapter 6.3
6.3: Water and Solutions

2. Learning Targets
I can explain the unique properties and structure of water molecules
I can explain how hydrogen ions and hydroxide ions affect the pH of a solution

3. Water and Solutions Water –
2 Hydrogen and 1 Oxygen atom are covalently bonded to form water
*Reminder: covalent bonds share electrons
The shared electrons are more attracted to the nucleus of the oxygen, making an uneven distribution of the electron
This means one end of the molecule is more positive and the other is more negative

4. Water and Solutions
Polar Molecule: the molecule has oppositely charged regions
Think: magnets

5. Water and Solutions
Hydrogen Bonds: a weak interaction involving a hydrogen atom and a fluorine, oxygen, or nitrogen atom
Results from a weak electrostatic attraction between charged regions of another molecule

6. Water and Solutions Properties of Water
Water is called the universal solvent because many substances dissolve in it
Liquid water becomes more dense as it cools, yet when it freezes ice is less dense than liquid water
Water is adhesive: it forms hydrogen bonds with molecules on other surfaces.
Water is cohesive: molecules of water are attracted to each other due to hydrogen bonds

7. Mixtures with Water
Mixture – two or more substances combined in which each substance retains its individual characteristics and properties
Homogenous: this is a mixture that has a uniform composition throughout
Also known as a solution
Solvent: substance in which another substance is dissolved
Solute: substance that is dissolved in the solvent

8. Heterogeneous Mixtures
Mixtures with Water
Heterogeneous Mixtures
These are mixtures in which the components remain distinct
Ex: Sand in Water

9. Acids and Bases
Acids – these are any substance that releases hydrogen ions when dissolved in water
The more hydrogen ions the more acidic the solution
Bases – these are substances that release hydroxide ions when dissolved in water
The more hydroxide ions in a solution the more basic

10. pH scale – measures how acidic or basic a solution is
pH and Buffers
pH scale – measures how acidic or basic a solution is
It measures the hydrogen ions in a solution
Acids have more hydrogen ions and because Bases have more hydroxide ions they have fewer hydrogen ions

11. Buffers
The majority of biological processes carried out by cells occur between pH 6.5 and 7.5
To maintain homeostasis it is important to control hydrogen ion levels
Buffers – are mixtures that can react with acids or bases to keep the pH within a particular range
Example: if you have an upset stomach you take an antacid. The antacid is a buffer that lowers the acidity within your stomach

12. Review Questions
A molecule that has oppositely charged regions is called what?
Hydrogen Bond
Polar Molecule
Mixture
Heterogenous Molecule

13. Review Questions
2. A substance in which another substance is dissolved is known as what?
a. Mixture
b. Solute
c. Solvent
d. Solution

14. Review Questions
3. Which of the following are any substances that release hydrogen ions when dissolved in water?
a. Acid
b. Base
c. Buffer
d. pH

15. Review Questions
Which of the following is a mixture that can react with acids or bases to keep the pH within a particular range?
a. pH
b. Buffer
c. Solution
d. Solvent