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Definition pH and pOH. Given pH, pOH, [H 3 O + ] or [OH¯], calculate the remaining values. Calculate Ka/Kb, given the pH or pOH and the concentration of a weak acid solution. Describe how an acid-base indicator works in terms of the colour shifts and Le Chatelier's Principle.
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Definition pH and pOH. • Given pH, pOH, [H3O+] or [OH¯], calculate the remaining values. • Calculate Ka/Kb, given the pH or pOH and the concentration of a weak acid solution. • Describe how an acid-base indicator works in terms of the colour shifts and Le Chatelier's Principle.
KW = [H+][OH¯] KW = 1.0 x 10-14 Acids / bases dissolve in water - increase [H+] / [OH-] and cause an equilibrium shift. Acidic - [H+] is greater than the [OH-] Basic - [OH-] is greater than [H+] H2O(l) H+(aq) + OH¯(aq)
Acidic - [H3O+] > [OH¯] Alkaline (basic) - [OH¯] > [H3O+] Neutral - [OH¯] = [H3O+] 1909 - Soren Sorensen developed a simplified system for the degree of acidity of a solution. pH - the potenz (power) of hydrogen - German potentia hydrogenii - Latin
Convenient way to express [H+] pH = -log [H+] Similarly, the concentration of hydroxide can be expressed as pOH: pOH = -log [OH-] pOH has its own scale – like pH – that runs from 0-14 for strength of bases.
[H+][OH-] = 1.0 x 10-14 pH + pOH = 14 Special case - pH can be read straight from the value of the [H+]. [H+] = 1.0 x 10-x then pH = x [OH-] = 1.0 x 10-x then pOH = x
Remember, in a neutral solution pH & pOH = 7 Acidic - pH < 7 Basic - pH > 7
Calculate the pH of an HCl solution whose concentration is 5.0 x 10-6 mol/L. remember strong acids are 100% dissociating: [HA]i = [H+]e = [A-]e pH = -log[H+] = -log(5.0 x 10-6 M) = -(-5.30) = 5.30
The pH of a solution is 3.25. Calculate the hydrogen ion concentration in the solution. [H3O+] = 10-pH Find the “10 x” button on your calculator. = 10-3.25 = 5.6 x 10-4 M ** also means: [OH-] = 10-pOH
The pH of a solution is 10.30, what is the hydroxide ion concentration? OR solved this way pOH = 14.00 - pH pOH = 14.00 - 10.30 = 3.70 [H+] = 10-pH [OH-] = KW [H+] [OH-] = 10-pOH = 10-3.70 = 2.0 x 10-4 mol/L
Mg(OH)2 (s) Mg2+(aq) + 2 OH-(aq) xi xf 2xf What is the pH of 5.0 x 10-5 M Mg(OH)2 solution? remember strong bases are 100% dissociating [OH-] = 2x = 2(5.0 x 10-5 M) = 1.0 x 10-4 M pOH = -log[OH-] = 4.00 pH = 14.00 - 4.00 = 10.00
YOUR ACID/BASE FORMULAE: • Kw = [H+][OH-] = 1.0 x 10-14 • The pH and pOH scales goes from 0 - 14. • pH = -log[H+] and[H+] = 10-pH • pOH = -log[OH-] and[OH-] = 10-pOH • pOH + pH =14
Measuring pH There are two ways to measure pH: pH Meters Indicators The [H+] inside the probe (reference electrode) is compared to [H+] outside the probe. Probe must be calibrated first. (inserted into known pH solution)
An indicator is a weak acid or base that undergoes a colour change when they gain or lose hydrogen ions. Natural pH indicators Beets, Blackcurrant juice, Blueberries , Carrots , Cherries , Curry Powder , Delphinium Petals , Geranium Petals , Grapes , Horse Chestnut Leaves , Hydrangea , Morning Glories , Onion , Pansy Petals , Petunia Petals , Poison Primrose , Poppy Petals , Purple Peonies , Rayhan Leaves , Red cabbage , Red Radish , Rhubarb , Rose Petals , Strawberries ,Tea , Thyme , Turmeric , Tulip Petals , Violet Petals
Phenolphthalein is a commonly used indicator. Weak acid is colourless and its conjugate base ion is bright pink.
Kw = [H+][OH-] = 1.0 x 10-14 • pH = -log[H+] and[H+] = 10-pH • pOH = -log[OH-] and[OH-] = 10-pOH • pOH + pH =14 • Indicators are weak acids or bases that change • colour in response to changing hydronium ion • concentrations.