Chemical reactions

Question 1

Chemical reaction

Answer 1

- Process leading to transformation of 
  one set of chemical substances to 
  anther.
- Reactants → Products
- Same nr. of atoms before and after 
  reaction. According to stoichiometry 
  oxidation nr./state doesn't change.
- Can be reversible. Proceed in both 
  forward and backward direction. Tend 
  towards a chemical equilibrium.

Question 2

Chemical Equilibrium

Answer 2

- It is the point at which both the 
  forward and the reverse reactions 
  take place at the same rate.
- Since the forward and reverse rates 
  are equal, the concentrations of the 
  reactants and products are constant 
  at equilibrium.

Question 3

Why is equilibrium referred to as dynamic equilibrium?

Answer 3

Because even though the concentrations are constant at equilibrium, the reaction is still happening.

Question 4

Equilibrium constant

Answer 4

-  We can define the equilibrium 
  constant Kc of a reaction (fixed 
  conditions of temperature and 
  pressure) as:
Kc: (C)^c (D)^d / (A)^a (B)^b
-  a, b, c and d: stoichiometric 
  coefficients
-  [A], [B], [C] and [D]: equilibrium
  concentration of the chemical species
- Pure solids and pure liquids, including 
  solvents, are not included in the 
  equilibrium expression.

Question 5

Acid Base Reactions

Answer 5

Acid: Proton donor (deduction -) #→#-
Base: Proton acceptor (adding +) #→#+
Conjugate base: product of the acid (#-)
Conjugate acid: product of the base (#+)
- In acidic molecules all the bonds are 
  covalent. But the bond X – H is polar 
  covalent and when the molecule is 
  dissolved in water, this bond behaves 
  as ionic, and the molecule dissociates 
  into X- and H+

Question 6

Amphoteric substance

Answer 6

Can act as both base and acid.

H2O

Question 7

Strong acid

Answer 7

Ionize completely in aqueous solutions.
No reverse reaction.
HCI : Hydrochloric acid
HBr : Hydrobromic acid
HI: Hydroiodic acid
H2SO4 : Sulfuric acid
HNO3 : Nitric acid

Question 8

Weak acid

Answer 8

Ionizes partially in aqueous solution.
Forward and reverse reaction. 
We can calculate constant for acidity:
Ka = (H+)(A-)/(AH)     AH ↔ H+ + A-
Big majority of acids, carboxylic acid.
F.ex. CH3COOH: Acetic acid.

Question 9

Strong Base

Answer 9

Ionize completely in water.
No reverse reaction.
NaOH
KOH
Ca(OH)2
Group 1A, 2A, hydroxide compounds.

Question 10

Weak bases

Answer 10

Ionize partially in water.
Reverse reaction.
B (aq) + H2O ↔ BH+(aq) + OH-(aq)
We can calculate constant of basicity:
Kb = (BH+)(OH-) / (B)
Water
Conjugate bases of strong acids.
neutral nitrogen containing compounds such as NH3, amines and pyridines.

Question 11

Measuring acidity

Answer 11

pH = - log [H+] → [H+] = 10-pH
pOH = - log [OH-] → [OH-] = 10-pOH
- If pH increases, H+ decrease and vice 
  versa.
pKa = -Log Ka
pKb = -Log Kb
[H+] x [OH-] = 10^14 and pH + pOH = 14
Ka x Kb = 10^14 and pKa + pKb = 14

Question 12

Buffer solutions

Answer 12

- A buffer is an aqueous solution that 
  resists changes in pH upon the 
  addition of an acid or a base.
- A buffer solution contains:
• a weak acid and a substantial amount 
  of its conjugate base (from a soluble 
  salt)
• a weak base and a substantial 
  amount of its conjugate acid (from a 
  soluble salt)

Question 13

Henderson – Hasselbach equation

Answer 13

The pH of any buffer is defined by this equation:
pH = pKa + log ([deprotonated] / [protonated]) ↔ 10^pH-pKa = [A-] / [AH]
Protonated: Molar concentration of acid/conjugated acid
Deprotonated: Molar concentration of base/conjugate base

Question 14

Henderson – Hasselbach equation for an acid

Answer 14

HA + H2O ↔ H3O+ + A-

pH = pKa + log ([A-] / [HA])

Question 15

Henderson – Hasselbach equation for a base

Answer 15

B + H2O ↔ BH+ + OH-
pOH = pKb + log ([BH+] / [B])
pH = pKa + log ([B] / [BH+])

Question 16

Buffers in blood

Answer 16

The most important way that the pH of the blood (7.4) is kept relatively constant is by buffers dissolved in the
blood:
- proteins (2/3 of total buffering in 
  blood)
- bicarbonate buffer
- phosphate buffer

Question 17

What other organs help enhance the homeostatic function of buffers?

Answer 17

• The kidneys remove H+
• The lungs provide a faster way to
  help control the pH of the blood by
  removing CO2.