Water, Acids, PH, buffers & Bases- Week 3

Question 1

what is the structure of water

Answer 1

consists of two hydrogen atoms bonded by covalent bonds to the oxygen atom.
Because of the higher electronegativity of the oxygen atom, the bonds are polar covalent (polar bonds).

Question 2

explain why water is electronegative, what effect does it have on water

Answer 2

Oxygen is more electronegative than hydrogen- this leads to the polarity of water (polarity leads or facilitates the formation of hydrogen bonds)

Question 3

what is the van der waals radius

Answer 3

its the area around the orbit around the atom where repulsion starts to take place- no atoms can get close than that van der waals

Question 4

what are the characteristics of water

Answer 4

• Fairly high melting point
  -Fairly high boiling point
• High surface tension
  -its polar

Question 5

how many hydrogen bonds can 1 molecule of water form

Answer 5

4

Question 6

what is the amount of energy needed to break a hydrogen bond

Answer 6

20kj of energy

Question 7

whats the amount of energy needed to break a covalent bond

Answer 7

400kj of energy

Question 8

what are the components for forming a hydrogen bond

Answer 8

• need a covalent bond
  -need the covalent bond to be dipole (one component is electropositive & the other electronegative)
• other molecule needs to be a electronegative atom

Question 9

what are the 2 types of hydrogen bonds

Answer 9

weak & strong hydrogen bonds - they are characterised by the fact of the 3 components of the electropositive, electronegative, electropositive are on a straight line or not

Question 10

what are some examples of hydrogen bonds

Answer 10

• between the hydroxyl group of an alcohol and water
• between peptide groups in polypeptides
• between complementary bases of DNA
• between the carbonyl group of ketone and water

Question 11

give some examples of polar molecules

Answer 11

• Glucose
• Lactate
• Glycerol
• Glycine

Question 12

what does polar molecules mean

Answer 12

hydrophilic compounds- form hydrogen bonds so are soluble in water
* hydrophobic compounds are non-polar as they cant form hydrogen bonds

Question 13

Give an example of a Non-polar molecule

Answer 13

Typical wax

Question 14

Give 2 examples of Amphipathic molecules

Answer 14

• Phenylalanine
• Phosphatidylcholine(its a phospholipid found in the membrane)

Question 15

what does Amphipathic molecules mean

Answer 15

molecules which have both polar & Non-polar compounds

Question 16

give 4 Non-covalent reactions

Answer 16

1- hydrogen bonds
2- Ionic compounds
3- Hydrophobic reactions
4- Van der waals interactions
(this are all relatively weak compared to covalent bonding)

Question 17

explain how water is a solvent

Answer 17

when water is added it creates a HYDRATING SHELL around each ion, due to the dipolar nature of water
*can happen with sugar where the water interacts directly and creates hydrogen bonds with the sugar molecules

Question 18

give an example of water acting as a reactant- explain it

Answer 18

means that water being a part of reactions in cells, ATP + H2O = ADP + Pi, it breaks phosphodiester bonds- provides energy for another reaction or can provide a phosphate in the reaction

Question 19

why is water important for the regeneration of ATP

Answer 19

as water facilitates the transfer of both protons and electrons in the cell- called PROTON HOPPING (beneficial as its much quicker than diffusion of protons & electrons)

Question 20

define acid

Answer 20

its a substance that produces hydrogen ions, by dissociation

Question 21

whats the difference between strong & weak acids

Answer 21

Strong acids completely dissociate in water- produce H+
weak acids only partially dissociate in water, and an equilibrium is established

Question 22

how is Base defied

Answer 22

its a substance that can:
1) extract a proton (H+) from water, forming hydroxide ion (OH-)
2) produce a hydroxide ion directly by dissociation

Question 23

what effect will a strong base have on water, give an example of a strong base

Answer 23

it will dissociate completely in water- and will increase the PH of the solution
KOH(aq)—> K+ + OH-

Question 24

what happens when weak bases react with water

Answer 24

they only partially react with water to EXTRACT a proton (H+) & LEAVE a HYDROXIDE ION (OH-)- equilibrium reached

Question 25

how is the acidity of a solution measured

Answer 25

the PH, and measure by the molar concentration of hydroxonium ions (H3O)—> equivalent to Proton concentration

Question 26

what is the Handerson- Hasselbach equation (for PH)

Answer 26

PH = PKa + log(acid/base)
or
PH = PKa + log(proton acceptor/proton donor)

Question 27

what is the equation for PH

Answer 27

PH = -log10(H+)

Question 28

what are buffers

Answer 28

they are a mixture of weak acids and their conjugate Bases. They resist change in PH

Question 29

when is Buffering capacity lost

Answer 29

when the PH differs fome PKa by more than 1 PH unit

Question 30

why are Buffers important

Answer 30

The maintenance of intracellular Ph is vital to all cells:
- protein structure
- Enzyme- catalysed reactions have an optimal PH
-Solubility of polar molecules depends on H-bond donors and acceptors

Question 31

what is the blood plasma PH

Answer 31

PH 7.35-7.45
* physiological changes by + or- 0.3 PH units are extreme

Question 32

whats the Ph of internal fluid of all cells

Answer 32

PH 6.9-7.4

Question 33

what are the 3 buffer systems that maintain the physiological PH

Answer 33

• Histidne (amino acid)
• Carbonic acid system
• Dihydrogen Phosphate system