acid base equilibria Flashcards
(25 cards)
Properties of acid solutions
produces H+ ions in water taste sour corrode metals electrolytes react with bases to form a salt and water pH less than 7 turns blue litmus paper red
Properties of base solutions
produce OH+ ions in water taste bitter, chalky feel soapy, slippery electrolytes react with acids to form salts and water pH greater than 7 turns red litmus paper blue
Acid-base reactions
acids can be either strong or weak
a strong acid is a strong electrolyte
common strong acids
hydrochloric acid
nitric acid
sulfuric acid
common weak acids
methanoic acid
ethanoic acid
nitrous acid
acids react with metals
metal + acid –> salt + hydrogen
react with certain metals to produce hydrogen gas
acids react with carbonates
acid + carbonate –> salt + water + carbon dioxide
react with carbonates and bicarbonates to produce carbon dioxide gas
common bases
sodium hydroxide potassium hydroxide barium hydroxide magnesium hydroxide lithium hydroxide calcium hydroxide
Definition of acids
substances that when dissolved in water increase the concentration of H+ ions
Definition of bases
substances that when dissolved in water increase the concentration of OH- ions.
problem: some bases don’t have hydroxide ions
What is a Bronsted-Lowry acid?
proton donor
What is a Bronsted-Lowry base?
proton acceptor
H+ ion in water
a proton is just a hydrogen atom that has lost its electron
the interaction of a proton with water leads to the formation of the hydronium ion (H3O+)
chemists use H+ and H3O+ interchangeably to represent the same thing; namely the hydrated proton which is responsible for an aqueous acids properties
Non-aqueous reactions
HCl acts as the acid in this reaction and ammonia acts as a the base
an acid and a base always work together to transfer a proton
Kastle meyer test
phenolphthalein and hydrogen peroxide
haemoglobin acts as peroxidase - accelerates oxidation with peroxide
presumptive: potatoes and horseradish also give positive test
dissociation
strong acids completely dissociate in water. their conjugate bases have a very small tendency to accept protons in aqueous solution
weak acids only partially dissociate in aqueous solutions. they exist as a mixture of acid molecules and their constituent ions
pH scale
molar conc of H+ ions in aqueous solution is very small. we usually express [H+] in terms of pH
the pH scale is a way of expressing the strength of acids and bases
acidic and basic are two extremes that describe chemicals. similarly hot and cold are two extremes that describe temperature
mixing acids and bases can cancel out the extreme effects
pH
in neutral water the conc of H+ and OH- must be equal. their value is 10-7 moldm-3 at 25 degrees so that
Kw=10-7 x 10-7
= 10-14 mol2dm-6
How is pH defined for practical purposes?
pH= -log10[H+]
pH to concentration
10-pH
the other p scale
since acids and bases are the opposite of each other; we express the conc of OH- as pOH
pOH doesnt really exist but it is convinient for changing the bases to pH
pOH = -log[OH-]
pH + pOH = 14 at 25 degrees
pOH calculation
the OH- ion conc of a blood sample is 2.35 x 10-7 M what is pH of blood? pOH= -log[2.35 x 10-7] = -(-6.63) = 6.63 pH = 14-pOH = 14 - 6.63 =7.37
strong acids
strength of an acid dependent on the extent of ionisation
a strong acid is 100% dissociated in water
HCL + H20 –> H30+ + CL-
what is a strong base
a base that is completely dissociated in water
