Lab - Polar Nature of Water – Answer Sheet
IA.
“My cup runneth over” Observations -
2015
( Top of Cup )
Draw a sketch of the water surface above the cup:
Q1.
Describe what happens as you keep adding more drops of water: _______________________________
Q2.
Did the water pile up as much as you expected? ____
more? ____
less? ____
[Check
one.]
Q3.
What keeps the water from overflowing sooner? ________________________________
Q4.
What do you think caused the water to eventually overflow? _______________________
IB.
“Nickel Defense” Observations –
Q5.
Draw a sketch of the water surface above the nickel:
Q6.
Did the water pile up as much as you expected? ____
more? ____
less? ____
[Check
one.]
Q7.
What evidence do you have that the water is sticking to itself? ________________________________
Q8.
What do we call the property that allows water to stick to itself? _________________
Q9.
What evidence do you have that the water must be sticking to the nickel? ________________________
Q10. What do we call the property that allows water to stick to other things? __________________
IIA.
Floating Needle Observations -
Q11. Describe what the needle is doing: _____________________________________________________
Q12. How does the needle affect the shape of the water surface immediately around it? _________________
Q13. The needle is made of steel, which is denser than water. What do we call property of water that allows
heavy objects like the needle to float? _________________ ____________________
IIB.
Floating Needle Observations (after touching soapy toothpick to water):
Q14. When I touched the soapy toothpick to the water, ___________________________________________
Q15. If surface tension is pulling on the needle from both sides to start with, the detergent must __________
the surface tension on the side of the needle where the toothpick touched.
Q16. Does the detergent eventually break all of the surface tension? _________
How can you tell? _________________________________________
IIIA. “Take a Powder” - Baby Powder in Beaker observations Q17. Describe what happens to the baby powder when you sprinkle it on the water: _____________________
Q18. Did the dry toothpick break the surface tension? _____
IIIB. Baby Powder in Beaker and Soapy Toothpick observations –
Q19. Describe what happens to the powder when the toothpick with a drop of detergent is
touched to the center of the powdery surface layer: ______________________________
_____ Q20. The toothpick with the detergent drop ( a) did
_____ Q21. The powdery layer was:
or
b) did not ) break the surface tension.
a) pushed to the edge of the beaker by the detergent
b) pulled by the remaining surface tension at the edge of the water surface.
IV.
Wax Paper Experiment Observations Oil
Q22. Does the water droplet mix with the oil drop when you place it on top? _____
Q23. Describe what happens to the alcohol droplet when it is placed
alongside of the oil droplet? _______________________________
________________________ (should happen right away)
Water
Alcohol
Q24. Describe what happens to the water droplet (it may take several seconds):
__________________________________________________________
Oil
Q25. Can alcohol mix with oil? ______
Q26. The “squiggle” in the water occurs when the alcohol finally reaches the water droplet. The alcohol
V.
___________ the surface tension of the water droplet, causing it to run off to the side of the oil droplet.
“Magic Milk” Observations -
Q27. Milk contains many proteins and fats which attach to and are twisted into shape by surrounding polar
water molecules. What evidence do you see to indicate that some of these molecules are untwisting
when the drop of soap is added to the milk? ______________________________________________
VI.
3-D Molecular Water Model Observations:
Q28. When two water models roll around and bump into each other, they will _________ _____________.
Q29. a) Do the water models stick together while they’re moving? _____ b) when they stop moving? ____
____ Q30. Which parts of the two water models stick together?
a)
red to red
b)
white to white
c)
red to white
____
____
____
____
____
____
____
____
____
____
Q41.
Q42.
____
____
Q31. Molecules such as water that have positive and negative ends are called _________ molecules.
a) Ionic
b)
Polar
c)
Non-polar
Q32. Which is easier to break apart? a) two water models or b) hydrogen ion from oxygen ion
Q33. Which bond is stronger?
a) a hydrogen bond
or
b) a covalent bond
Q34. Will ethane form a hydrogen bond with water?
a) Yes or b) No
Q35. Is ethane:
a) a polar molecule
or
b) a non-polar molecule?
Q36. This “opposites attract” bond between positive & negative ions is called:
a) an ionic bond
b) a covalent bond
c) a hydrogen bond
Q37. Chloride ( Cl - ) ions must be: [ a) positively
or
b) negatively ] charged…
Q38. …because the Cl- ions are attracted to: [ a) the +
or
b) the - ] end of the H2O.
Q39. Sodium (Na+ ) ions must be: [ a) positively
or
b) negatively ] charged,
+
Q40. because the Na ions are attracted to: [ a) the + or
b) the - ] end of the H2O.
Does sodium chloride attach to the nonpolar (gray) ethane molecule? _______
Would sodium chloride dissolve as well in a nonpolar liquid as well as it does in water? ____
Q43. Because of its polar nature, water is the universal ______________: it can dissolve all ionic
and polar covalent compounds. (doesn’t work as well on nonpolar compounds like grease!)
a) solvent
b) solute
c) soldier
d) remote
Q44. The chemical formula for methanol is CH3 OH . Does water attach to:
a)
methanol’s CH3+ group
or
b)
methanol’s OH - group.
Q45. NaCl will interact with/stick to ethanol (C2H5OH). However, would ethanol molecules be able to
easily surround and “cage” the Na+ and Cl - ions in the way that water molecules can? _____