Water and Solutions

Water and Solutions

1. Water is the MOST important compound in living organisms!

2. It accounts for approximately 70% of a cell’s mass.

3. It covers about 70% of the world’s surface

1. Water is a polar molecule2. The bonds in a water molecule are

called polar covalent bonds3. It is this polarity that gives it some of

it’s unique characteristics

What makes water special?

4. Recall that covalent bonds involve atoms sharing electrons.

5. In the care of a “polar covalent bond” the electrons are not shared equally.

6. Electrons are more strongly attracted to the oxygen than the hydrogen.

7. This makes the oxygen side of the molecule slightly negative.

8. It also makes the hydrogen side of the molecule slightly positive.

“Polar opposites!”

Draw this

9. Polarity is the property of having two opposite poles (or ends).

9. Water is similar to a magnet. When the two oppositely charged sides of a water molecule are brought together they want to “stick” together the way magnets do. Opposites attract!

11. When a water molecule “sticks” to other water molecules it forms weak hydrogen bonds molecules around it.

-This stickiness creates surface tension in water.

12. Hydrogen bonds between water molecules hold them together

13. Hydrogen bonds are weak interactions

Water’s Properties1. Water’s properties can be attributed to

the fact that it is a polar molecule that forms hydrogen bonds with other water molecules around it.

2. Some of these special properties include…• Water’s ability to dissolve

polar substances• Water is the “universal

solvent”• Remember that like

dissolves like. Therefore, water dissolves other polar substances.

• Water cannot, however dissolve non-polar substances such as oil.

• Liquid water is most dense at 4 degrees C. Ice is less dense than liquid water.•Nutrients in water mix

due to changes in water density during spring and fall. Also, ice acts like an insulator in the winter.

•Water is adhesive• It forms hydrogen bonds with

molecules on other surfaces

• Water is cohesive•Water sticks to itself

That’s why a belly-smacker hurts!

Mixtures with Water1. Mixture = combination of two or more

substances where each substance retains its own characteristics and properties

2. Homogeneous mixtures = same throughout (ex. Air)

3. Solution is another name of homogeneous mixturea. solvent = dissolverb. solute = being dissolved

• Ex. Identify the solvent and the solute in chocolate milk.

4. Heterogeneous mixtures = appears different throughout

• ex. This cup of grains