Ansley Bonus Ch. 7-8 (Surface Tension Lab, Chromatography Lab, Water Video)
Why does ice float?
- lighter than liquid form - molecules slow down when cold - water actually expands when cold - less dense than liquid state
experimental results showing that the surface tension of water is greater than that of 2-propanol
- more drops of water fit on the penny - water evaporated slower
How is artificial snow made for ski slopes?
- snow max process - freeze dried bacteria added to mixture
name three of water's unusual characteristics
- universal solvent - liquid when it's makeup forms a gas - can be liquid, solid, or gas
What does 80 proof mean?
40% alcohol
What causes surface tension?
Water molecules at the surface of a liquid experience an unbalanced attraction between their hydrogen atoms. As a result, water molecules at the surface tend to be drawn inward.
When does the meniscus of a liquid in a glass tube curve downward?
When the liquid is more attracted to the sides of the glass than it is to itself
How is bacteria removed from drinking water?
disinfection with chlorine
How does water dissolve NaCl?
due to polarity and ability to form hydrogen bonds
(beginning of water video questions) Water reacts with carbon dioxide to form ________, the food of plants.
glucose
What type of substances dissolve in water?
ionic
Which liquid has the weaker intermolecular forces of attraction?
isopropanol
which liquid evaporates more quickly?
isopropanol
if the substances to be separated are polar, the developing solvent should be _____________. Likewise, non-polar substances would require ______________ solvents.
less polar, slightly polar
What is chromatography?
most useful method of separating organic compounds for identification or purification
How does our water supply get contaminated?
not properly treated, from industry and human waste
Why are water molecules polar?
oxygen has a stronger attraction for electrons
What effect does the addition of soap or detergent have on the surface tension of water?
reduces water's surface tension
Why has water been given its nickname?
so many things can dissolve in it
What is an eluent?
solvent which carries the materials to be separated through the absorbent
Why are fewer drops of water able to stay on the penny after alcohol is dropped on it even though the penny is dried off?
some alcohol residue is left on the penny, reducing water's surface tension
Which three-dimensional shape has the smallest surface area to volume ratio?
sphere
(beginning of chromatography questions) knowing that the solvent is quite polar, what can you infer about the relative polarities of the various dies?
the molecules that have a polarity closest to the polarity of the eluent are the most soluble and will move up the plate the fastest
How are contaminants removed from drinking water?
trapping them with chemicals and filtering them out with hard coal and sand
Water is unique. It is called the _____________
universal solvent
Since surface tension is a result of intermolecular forces of attraction, which liquid has the greater intermolecular forces of attraction?
water
Which liquid, water or 2-propanol, has a greater surface tension?
water
Why are some substances unable to dissolve in water?
water has polar molecules while others are nonpolar
Why is the volume of water that can stay on the penny greater than the volume of 2-propanol?
water is more polar, making it have a stronger cohesion/surface tension
explain in terms of intermolecular forces of attraction why the cohesive forces between water molecules are greater than the cohesive forces between 2-propanol molecules
water is polar, making opposite charges attract. this means the intermolecular forces are stronger. isopropanol is non-polar, so the intermolecular forces are weaker.
If a liquid evaporates quickly, are the forces of attraction between its molecules strong or weak?
weak
What are hydrogen bonds?
weak bond between two molecules