Week 3 - Water Flashcards
True or False: The hydrogen ion (also known as a ‘proton’) is hydrated and essentially exists minimally as H3O+ in aqueous solution
True: The actual structure of water is still a contentious issue but there is general agreement that the minimal structure for a hydrogen ion (H+) in aqueous (water) solution is as a hydronium ion (H3O+) which is formed by the proton ‘hopping’ from one water molecule to the other.
What is Osmosis?
The movement of a water molecule across a semipermiable membrane.
How does the ion-product of water, Kw, relate to the equilibrium constant, Keq, for the dissociation reaction of water?
Kw is found by multiplying Keq by the concentration of water
True or False: Hydrogen bonds are important in biochemistry because, although weak, they are numerous and can be made and broken relatively easily and rapidly
True
True or False: Water is excluded from cellular membranes and does not contribute to the stability of membrane structures
True
what is the pH of a 10-4 M solution of HCl?
4.0
True or False: Water has no effect on the structure of macromolecules?
False: Water influences both the structure and function of macromolecules
True or False: Oxygen has very good solubility in water and that is how oxygen can be transported easily in blood plasma in humans?
False: Oxygen and other biologically important gasses such as carbon dioxide and nitrogen are poorly soluble in water. Consequently, it a transport system such as haemoglobin is necessary to transport these gases in blood plasma.
Water derives most of its properties from what?
polarity and hydrogen-bonding capacity
Molecules that are both hydrophobic and hydrophilic are ________.
Amphipathic
Choose the incorrect statement about water:
A. pure water is always pH 7
B. pure water is neutral and has a concentration of H+ ions of 10-7M at 25°C
C. pure water can change pH when exposed to air
D. pure water has a pH of 7 at 25°C
E. water can have a pH that is not pH 7
A. pure water is always pH 7
The pH of water can change depending upon the temperature. Temperature affects the equilibrium constant Kw and hence the pH changes with changes in temperature. Water is pH 7 at 25°C. At 40°C its pH is 6.97. Water can have a pH that is not pH 7 and pure water can change pH when exposed to air. Both of these statements are due to carbon dioxide in the air. The carbon dioxide can dissolve in water creating dihydrogen carbonate which can then dissociate to give hydrogen carbonate and hydrogen ions. The increase in hydrogen ions then decreases pH
why do solutes diffuse more slowly in cytoplasm than in water?
Because the presence of many crowded molecules in the cytoplasm.
Compounds that ionize when dissolved in water are called ________.
Electrolytes
What is meant by the term Isotonicity?
Equal osmolarity inside the cell as outside the cell
