chapter-19 lecture-3

chapter-19 lecture-3 - Sample Problem PROBLEM: Preparing a...

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Sample Problem Preparing a Buffer PROBLEM: An environmental chemist needs a carbonate buffer of pH 10.00 to study the effects of the acid rain on limsetone-rich soils. How any grams of Na O ust she add to 1.5 L of freshly prepared many grams of Na 2 CO 3 must she add to 1.5 L of freshly prepared 0.20 M NaHCO 3 to make the buffer? K a of HCO 3 - is 4.7x10 -11 . PLAN: The K a and the conjugate acid-base pair are known. Convert pH to + find the number of moles of carbonate and convert to mass SOLUTION: [H 3 O ], find the number of moles of carbonate and convert to mass. HCO 3 - ( aq ) + H 2 O( l ) CO 3 2- ( aq ) + H 3 O + ( aq ) K = [CO 3 2- ][H 3 O + ] CO - [HCO 3 ] pH = 10.00; [H 3 O + ] = 1.0x10 -10 4.7x10 -11 = [CO 3 2- ](1.0x10 -10 ) 0.2 O = 0 094 [CO 3 2- ] = 0.094 M moles of Na 2 CO 3 = (1.5 L)(0.094 mols/L) = 0.14 105.99 g 19-17 = 15 g Na 2 CO 3 0.14 moles mol
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Acid-Base Titration Curves HIn ( aq ) + H 2 O( l ) In - ( aq ) + H 3 O + ( aq ) Indicator molecule is a weak acid: pH Colors and approximate pH range of some common acid-base indicators 19-18 Most acid-base indicators have a range of about 2 pH units
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The color change of the indicator bromthymol blue.
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chapter-19 lecture-3 - Sample Problem PROBLEM: Preparing a...

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