L03: Water, Solutions, & Concentration Terms Flashcards
As you know by know H2O is a polar molecule. What does that mean? Why is a water molecule polar?
H20 has an unequal sharing of e—. Due to this, the water molecule has a V - like shape.
What do the symbols δ+ and δ– mean and which area of a water molecule is δ+ and δ–? How do these regions of a water molecule interact with cations, anions, and molecules with partial positive or negative charge?
δ+ partial positive. δ- partial negative. In H20 molecules, hydrogen atoms carry a positive charge where as oxygen carries partial negative charge. δ+ region of one molecule can attract to δ- forming a physical bond.
What is Hydrogen bonding?
Attraction of H molecules opposite charges. Usually with around 4 neighboring water molecules. Form and reform continuously.
What are four emergent properties of liquid water?
- Cohesion & Adhesion
- Expands when frozen
- High heat capacity
- Dissolves & disassociates (solvent for a lot)
How are the processes of cohesion and adhesion similar and different from each other
Cohesion is H-bonding causing H2O molecules to ‘stick’ to one another. Adhesion is H20 molecules H-bonding with other molecules (that aren’t water). Both use H-bonding
How do cohesive and adhesive forces of liquid water contribute to water uptake in plants? What is transpiration and what role does it play in water uptake in plants?
They fight against gravity by adhering up the walls of roots and other molecules by cohesion. Transpiration, evaporation from plant tissues, is the ‘towboat’ to tug on the water pulling it in through the roots.
What does it mean when we say that water has a high specific heat capacity?
it must absorb a great quantity of heat (1 cal/g/°C) to raise its temperature
What is the difference between heat and temperature?
Heat= total kinetic energy of matter of a mass.
Temperature= average kinetic energy of matter
How is heat transferred from matter of different temperatures?
Heat transfer from warmer to cooler matter.
Why does the temperature of a beverage decrease when ice is added? By adding the ice, what happens to the capacity for specific heat?
a glass of tap water is at room temp, you add ice to it. Heat in 25° water is transferred to ice. The temp decreases because ice has little kinetic energy so average kinetic energy decreased. Capacity for heat goes up because you’re adding more mass.
Why does water have such a high specific heat capacity? How is water’s high specific heat capacity important to biota such as humans? How does the high specific heat capacity of water contribute to body temperature maintenance?
Impacts body temperature because body fluids are aqueous. Body fluids warm slowly because absorbed energy must first overwhelm H-bonds before temp/activity increases. It is important for a body to maintain a cool temperature (70° C). for it to function.
What is evaporation?
transforming liquid H2O → gaseous H2O
How does evaporative cooling work? Can you explain your answer based on the kinetic energy concept developed previously? What must we ingest to maintain evaporative cooling?
Humans use evaporative cooling via sweating to ↓ body temperature. You must ingest water and ions (Na+, K+, Ca2+) to replace what is lost through sweating. Sweating is the body’s way of lowering kinetic energy (body temp)
How does humidity impact evaporation rate and, thus, evaporative cooling? In what kind of environment would evaporative cooling work best?
Evaporative cooling works best in dry air: evaporation rate ↓ as air humidity ↑.
What is mass and volume and how are these related to density?
Mass is how heavy something is, volume tells you how big it is, and density is mass divided by volume.
At which temperature is water most dense? What happens to the density/volume of water (assuming a constant mass) change when its temperature is increased and decreased?
Water is most dense at 4 °C (1 g/ml). Its volume ↑ as it
warms (one reason sea level ↑). Its volume also ↑ when its
temperature ↓ below 4 °C approaching 0 °C as it freezes.
How do liquid and solid (ice) water compare in their density and volume (assuming a constant mass)? How does the changing nature of H-bonds contribute to these differences?
In liquid water, the action of forming/reforming H-bonds allows H2O molecules to condense like a crowd at party. In solid water, H-bonds stabilize forming a lattice. Doing so ↑ the volume (↓ density) of the water by ∼10%
What can happen to a cell when it freezes? Why does this happen? What must biota do to prevent this from happening when they live in cold environs where freezing is a hazard?
Living cells possess as much as 70% water by volume and
can rupture/die when frozen. Biota must adapt to the cold.
What is an aqueous solution? What is a solute? What is a solvent?
Aqueous solutions (aq.) are comprised of two things; a solute and water as a solvent. Your body fluids are aqueous ex;blood, urine, semen.
Solutes are smaller quantity of various molecules dissolved into solvent. Body fluids posses ions, proteins, acids, bases, etc.
A solvent is able to dissolve other substances.
What does concentration mean? What is the parts system for expressing concentration?
Concentration refers to how much solute is in aq. Parts: How many parts of solute in parts solution.Parts can be expressed in mass (m/m), volume (v/v), or both (m/v).
What is the overall salt concentration of human blood plasma?
137 to 142 mEq/L
What is the order of magnitude or value of the following concentration terms: %, ‰, ppm, ppb, and ppt?
(picture)
What is molarity? What is a mol? If you wanted to prepare a 1 M solution of a particular solute, how many mols of solute must you add to a 1-liter flask and bring the volume to 1-liter with solvent (water)?
Molarity (M):How many solute molecules (mols) found in 1 L of aq. First, calculate the molar mass of the solute by summing the mass of all atoms in the solute.
