1. Class Notes 2-2
Water and Solutions

2. Part I – Polar Molecules
What is a substance in which the atoms are held together by a covalent bond?
MOLECULE

3. What is the name for a molecule in which the charges are distributed evenly?
NONPOLAR

4. Example of a nonpolar molecule
METHANE

5. Example of a nonpolar molecule
Diagram
METHANE

6. Example of a nonpolar molecule
Diagram
METHANE H C C H H H H

7. What is the name for a molecule where the charges are unevenly distributed?
POLAR

8. What is an example of a polar molecule from the text?
WATER

9. WATER
Number of protons in oxygen? 8 8 +

10. Number of electrons in the outer shell of oxygen?
WATER 6 8 + O

11. Number of protons in hydrogen?
WATER 1 1 + 8 + H O

12. WATER 1 Number of electrons in the outer shell of hydrogen? H O 8 1 +

13. What would make oxygen happy?
WATER
A full outer shell 1 + 8 + H O

14. Example of a polar molecule
What would make oxygen happy?
WATER
A full outer shell 1 + H 8 + O

15. Example of a polar molecule
What would make oxygen happy?
WATER
A full outer shell 1 + 1 + H H 8 + O

16. One eight OXYGEN How many protons does hydrogen Have?
How many protons does oxygen have?
eight
Which of these two atoms (Hydrogen or oxygen) would have a greater attraction for the electrons?
OXYGEN

17. The electrons are pulled closer to the oxygen atom
The electrons are pulled closer to the oxygen atom. What is the charge on the oxygen atom in a water molecule?
NEGATIVE O H H

18. The hydrogen atom has less pull on the electrons than oxygen.+ +
What is the charge on the hydrogen atom?
POSITIVE

19. Two reasons why molecules are polar1. 2.

20. Two reasons why molecules are polar1.
unequal charge O H H + +

21. Two reasons why molecules are polar1.
unequal charge O H H + + 2.
asymmetrical shape

22. Two reasons why molecules are polar
unequal charge O H H + +
asymmetrical shape C H
Symmetrical

23. Two reasons why molecules are polar
unequal charge O H H + +
asymmetrical shape
polar C H
Symmetrical O
Asymmetrical
Non-polar H H

24. Part II
What is the name for the bond between the positive end of one polar molecule and the negative end of another polar molecule?
hydrogen bond

25. O is a strong chemical bond
Which bond is weaker, the hydrogen bond or the covalent bond?
Hydrogen bond H O +
hydrogen bond
covalent bond
is a
strong chemical bond

26. Part III Characteristics water#1
What property of water results from its attraction to the ions in a salt?
solvent
Water dissolves the salt.

27. Many compounds dissolve in water.
A solution is formed when one substance dissolves in another.
A solution is a homogeneous mixture.
Solvents dissolve other substances.
Solutes dissolve in a solvent.
solution

28. Diagram:
Dissolves O H H + + +
Water Na Cl
Salt

29. Diagram: Water dissolves salt: O O O Na Cl O O OH O + H O + H O + Na + H O + Cl H O + H O +
The (–) O of water is attracted to the (+) Na
The (+ ) H of water is attracted to the (-) Cl

30. Cohesion Adhesion Characteristic #2 (and a hint for the lab)
What is the attraction of one water molecule for another water molecule?
Cohesion
What is the attraction of one water molecule
for another (non-water) molecule?
Adhesion

31. Cohesion diagram: One molecule is attracted to another molecule. O
polar
to another
molecule.
polar H O +

32. Four polar properties of water
good solvent (the "universal" solvent) 1. 2. 3. 4.
cohesion O
high boiling point (100 C)
expands when freezes

33. The Solubility Rule Polar is soluble in Nonpolar is soluble in
Like dissolves in
like

34. Some compounds form acids or bases.
An acid releases a hydrogen ion when it dissolves in water.
high H+ concentration
pH less than 7
more acidic
stomach acid pH between 1 and 3

35. A base removes hydrogen ions from a solution.
low H+ concentration
pH greater than 7
bile pH between 8 and 9
more basic

36. A neutral solution has a pH of 7.
pure water pH 7

37. End !