Topic 3: properties of water, pH, acid/base

Question 1

Describe the bonding in water molecule

Answer 1

• Polar molecule = opposite charges on opposite ends = O more electronegative
• Polarity = H-bonds form = properties of water
• H-bond forms between -ve O on 1 water and +ve H on another

Question 2

What are the 4 properties of water?

Answer 2

1) Cohesion
2) Temperature moderation
3) Evaporative cooling
4) Versatile solvent

Question 3

Describe cohesion

Answer 3

• Related to adhesion + surface tension
• Helps pull water up plant vessels
• Transport in plants = adhesion of water molecules to plant cell wall due to H-bonds = transfer H2O against gravity + cohesion of molecules helps them stick together
• Surface tension = how hard it is to break surface of liquid = H2O has high compared to other liquids due to H-bonds

Question 4

Describe temperature moderation

Answer 4

1) Absorbing heat from air that is warmer
3) Releasing stored heat to cooler air
- Heat passes from warmer to cooler

Question 5

Define specific heat

Answer 5

• Amount of heat needed to be absorbed/lost for 1 gram of substance to change temp by 1ºC
• Water = high SH = resist changes in temp
• Water SH = 1 cal/g/ºC

Question 6

Why does water have a high SH?

Answer 6

• Due to H-bond
• Heat absorbed when H-bond break
• Heat released when H-bond form

Question 7

Describe evaporative cooling

Answer 7

• Heat of vaporization = quantity of heat liquid must absorb for 1 gram of it to convert to gas
• Water = high HOV due to H-bond
• Due to high HOV = water great coolant = cool surfaces when heat escapes
• Body temp constant via sweat

Question 8

How does ice insulate bodies of water?

Answer 8

• Ice = solid = less dense than liquid water = floats = insulates water under
• Life can exist under frozen surface
• Less dense = H-bonds in ice more ordered than in water

Question 9

Describe versatility as a solvent

Answer 9

• Due to polarity
• Form H-bond easily = form aqueous solutions
• Different regions of polar H2O = interact with ionic compound = dissolve
• Solvent = dissolving agent = H2O
• Solute = dissolved substance

Question 10

Define hydrophilic

Answer 10

• Affinity for H2O
• Polar solution + ionic molecules

Question 11

Define hydrophobic

Answer 11

• No affinity for H2O
• Non-polar solution + non-ionic molecules

Question 12

Explain the dissociation of water

Answer 12

• H2O dissociated = hydronium ions + hydroxide ions
• Acid = increased concentration H+
• Bases = reduce H+ concentration or release OH-
• H+/OH- equal in H2O
• Most biological fluids = pH 6-8
• Acidic = donates H+ to aqueous solutions
• Basic = Donate OH- / accept H+ in aqueous solutions

Question 13

Define buffer

Answer 13

• Substance that minimizes changes in concentration of H+/OH- ions in solution
• Acid-base pair that reversibly combine with hydrogen ions