Express

Bio l g y The Science of LIfe Wate

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Upon successful completion of this unit,

you will be able to do the following:

Draw a picture of a water molecule.

Identify the positive and negative end of a water molecule.

Explain why water molecules stick together.

List and describe the 3 properties of water.

Upon successful completion of this unit,

you will be able to do the following:

Use the following words in their correct context.

polar

water

solubility

inorganic compound

chemical formula

positive

negative

density

polarity

solute

solvent

universal solvent

H +

H +

O _

The chemical formula for water is H2O. That means that 1 oxygen atom is chemically bonded with 2 hydrogen atoms to make 1 water molecule.

H +

H +

O _ The 3 properties of water:

1. Polarity

3. Density

Water has a positive (+) and a negative (-) end.+ +-

Allows water to dissolve other substances.

How tightly a substance is

packed together

2. Solubility

Summary

• polarity

• solubility

• density

Water is extremely important to all living organisms.

The chemical formula for water is H2O, which means that 2 hydrogen atoms chemically bond with 1 oxygen atom to form water.

Water has 3 properties that are important to all life:

2. Solubility is the ability of water to dissolve substances. Because of this, water is able to dissolve many substances. That is why water is called the universal solvent. Chemicals have to be dissolved in water before they can work within a cell. Other wise reactions such as cellular respiration and photosynthesis would not take place.

1. Water is a polar compound. Polarity means that water has a positive (+) and a negative (-) end. This allows water to attach to itself (opposite charges attract) and to other substances. The surface tension of water and the solubility of water are based on the polar property of water.

3. Density refers to how tightly a substance is packed together. In a dense compound, the atoms are tightly bunched together. In a less dense compound, the atoms are not tightly packed together. In most cases solids are more dense than liquids which are more dense than gases. Water is the exception. Ice is less dense than liquid water.

Test Yourself

Answer the following:

1. Without referring back to your notes, write and draw as much about water as you can remember.

2. How would you define density?

3. What is unusual about the density of water?

A. Polar compound

B. Inorganic compound

C. A compound that contains carbon atoms

D. A compound that does not contain carbon atoms

E. A compound that has a positive end and

a negative end

F. Carbohydrate

G. Water

H. Universal solvent

I. Tightly packed

J. Dissolve

_____ 1. organic compound

_____ 2. inorganic compound

_____ 3. density

_____ 4. water

_____ 5. polar

_____ 6. solubility

Matching

True or False

 _____ 1.  Water is composed of 2 parts hydrogen and 1 part oxygen.

_____ 2.  You are mostly made of water so that certain chemical reactions can take place inside your body.

_____ 3.  Water is the universal solvent.

_____ 4.  The chemical formula for water is HO2.

_____ 5. Water molecules contain carbon atoms.

_____ 6.  Water is an inorganic compound.

_____ 7.  Water is a polar compound.

_____ 8.  Water has a positive end and a negative end.

_____ 9.  When the negative end of one water molecule comes near the negative end of another water molecule, the molecules are attracted.

_____ 10. Solubility is the ability of water to dissolve a substance.

_____ 11. Ice floats because it is more dense than water.

_____ 12. Water is usually a solute.

1.  ____________________ substances have a (+) and (-) end.

2. The ability of water to dissolve another substance is called ______________.

3.  _____________________ is the universal solvent.

4.  d=m/v is the formula for _________________.

5.  Living things contain a lot of _______________.

6.  Water is a _______________ molecule.

7.  A ______________ molecule has a positive end and a negative end.

8. _________________ is the term that tells how tightly a

substance is packed together.

9.  The solvent always dissolves the __________________.

10. Cells must contain _____________ in order for cellular

respiration and photosynthesis to occur.

polar water solvent solute

solubility polarity density compound

Fill in the Blank – Words may be used more than once or not at all.

True or False

_____ 1.  Water is a polar molecule._____ 2.  Water is a molecule that has a positive end and a negative end._____ 3.   Polarity is how tightly a substance is packed together._____ 4.   Ice floats in liquid water.  _____ 5.  Water is good at dissolving other substances._____ 6.  Water is needed as a solute in your body._____ 7.  Plant and animal cells must contain water in order for cellular reactions to occur._____ 8. Density is the ability of water to dissolve many substances._____ 9. Water is the universal solvent._____ 10. A polar substance is always a solid._____ 11. The formula for water is 2HO2._____ 12. Density determines if a substance will float on water._____ 13. Ice is less dense than water._____ 14. Water molecules contain carbon atoms._____ 15. Opposite charges attract._____ 16. Water can stick to itself because of its polarity._____ 17. Density refers to the universal solvent._____ 18. The more dense a substance is, the greater the polarity._____ 19. A substance less dense than water floats on water.

Answer the following:

 1.  What is meant by the word polar when describing a water molecule?  2. Draw a picture of a water molecule. Show where the positive (+)

charge and the negative (-) charge is located.   3. Define solubility using the following terms: water, universal solvent, solvent, solute.    4. Explain how polarity helps water dissolve other polar substances. Use a drawing to support your explanation.

Try This One: If it is true that each cell must contain water, is it also true that water must surround each cell? Explain your answer.

Express

Bio l g y The Science of LIfe Wate

r