Electrolytes

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  • Created by: LBCW0502
  • Created on: 26-02-18 17:58
What is an electrolyte?
A substance that will dissociate into ions in solution and acquire the capacity to conduct electricity
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Describe simple test to determine the presence of electrolytes
Connect circuit to solution. If the light bulb is lit, then the solution contains electrolytes (higher concentration leads to a brighter light)
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Give examples of strong electrolytes
Sodium ions and chloride ions (NaCl - complete dissociation in water with the equilibrium shifted to the right)
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Give examples of weak electrolytes
Ethanoate ions, drugs (incomplete dissociation in water - equilibrium shifted to the left)
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What is the Arrhenius theory?
Acids are proton producers and bases are hydroxide producers
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What is the Bronsted-Lowry theory?
Acids are proton donors and bases are proton acceptors
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What is the Lewis theory?
Acids are electron acceptors and bases are electron donors
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Describe the conjugate acid base relationship
Strong acid (weak conjugate base), strong base (weak conjugate acid) - equilibrium e.g. water and hydrochloric acid
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Can water act as both as acid and base?
Yes - (proton donor/acceptor). Water acids ionisation process
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Can organic solvents aid the process of ionisation?
No - due to no water being present
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Describe the acid equilibria
Ka = [H3O+] [A-] / [HA] (in dilute solutions, water is considered to be in sufficient excess to be constant)
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How do you convert Ka to pKa?
pKa = -log Ka (the lower the pKa value, the stronger the acid and there is more dissociation)
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Describe the base equilibria
Kb = [OH-] / [BH+] / [B] (water considered to be excess/remains constant)
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How do you convert Kb to pKb?
pKb = -log Kb (the lower the pKb, the stronger the base and there is more dissociation)
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What is the ionisation of water?
Kw = [H3O+] [OH-] (water is in excess and remains constant)
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In pure water, are the hydrogen and hydroxide ions equal?
Yes
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Which expression shows the relationship between Ka and Kb?
Kw = Ka x Kb
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Do non-ionised molecules pass biological barriers easily?
Non-ionised molecules pass biological barriers easily. Ionised molecules don’t cross biological barriers easily (most components in drug molecule are ionisable molecules)
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Give examples of natural electrolytes
DNA and proteins
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Describe features of Sorensen's pH scale
Value of 10^-14 is always the product of the molar concentration of H3O+ and OH-. If acid is in pure water, the H3O+ ion concentration will be > 10^-7 (for base, the OH- concentration > 10^-7). Product of two must equal 10^-14 (equilibrium)
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What is pH?
The negative logarithm of the concentration of hydrogen ions (measure of H+ ions)
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Do organic solvents have pH values?
No - No hydronium ions produced. Organic molecules not ionised in water. pH relevant to water. Cannot deliver drugs in organic solvents e.g. hexane. Organic solvents toxic to the body Water based systems used
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Which expression can be derived from the Henderson-Hasselbalch equation for acids?
pKa = pH + log [HA]/[A-] (also see in textbooks Cu/Ci)
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Which expression can be derived from the Henderson-Hasselbalch equation for bases?
pKa = pH + log [BH+]/[B]
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Interpret the Henderson-Hasselbalch equation (solubility/graph) - acid?
If there is 50% ionisation, the pKa = pH. If there is >50% ionisation, the pKa < pH. If there is pH (learn graphs with examples)
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Interpret the Henderson-Hasselbalch equation (solubility/graph) - base?
If there is 50% ionisation, the pKa = pH. If there is >50% ionisation, the pKa > pH. If there is
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Give features of acid-base indicators
Weak acids or bases which will ionise in solution. Concentration of indicator doesn't affect reactants. Colour changes
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Give examples of common indicators
Thymol blue, methyl red, litmus, bromothymol blue, phenolphthalein
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Describe features of pH measurement
Electrochemical cell (glass electrode/solution/reference electrode). Nernst equation. System needs to be calibrated with known solutions/reproducible pH - buffer solutions. Glass membrane sensitive to pH. pH meter (electrode in solution to measure)
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Give examples of acid base applications
Control solubility in chemical reactions. Quantification of ionic substances. Drug delivery targeting. Biological regulation IV infusions (buffering)
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What is a neutralisation reaction?
The reaction of acid and base to produce a salt and water
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Describe features of titration
Analytical technique to determine the concentration of an acid or base. Using a standard solution to neutralised another solution with an unknown concentration. Biuret, flask, indicator (electrolyte in liquid system) - pH curve
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What are buffers?
Compounds or mixtures of compounds that by their presence in solution, resist changes in pH upon the addition of small amounts of acid or alkali
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Describe features of buffers
Stabilise a system by keeping the pH constant. Conjugate acid-base relationship. Acetic acid
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What is a buffer capacity?
The amount of acid or base that can be added before the pH of the solution changes significantly
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Give examples of common buffers
Phosphate, formic acid, acetic acid, citrate etc.
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Other cards in this set

Card 2

Front

Describe simple test to determine the presence of electrolytes

Back

Connect circuit to solution. If the light bulb is lit, then the solution contains electrolytes (higher concentration leads to a brighter light)

Card 3

Front

Give examples of strong electrolytes

Back

Preview of the front of card 3

Card 4

Front

Give examples of weak electrolytes

Back

Preview of the front of card 4

Card 5

Front

What is the Arrhenius theory?

Back

Preview of the front of card 5
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