08pAcidinjuices

08pAcidinjuices - Click to edit Master subtitle style Acid...

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Unformatted text preview: Click to edit Master subtitle style Acid Content of Beverages A titration exercise SUSB - 010 Last Update: 2/2/10 07:11:05 AM How can we characterize the acidity of a natural mixture of unknown acids? What do chemists mean when they talk about acids being strong or weak? ? QUESTIONS ? What is a quantitative measure of the strength of an acid? How do we conduct titrations and what can we learn from them? Concepts: Strong/Weak Acids Acid Dissociation / Ka Concentration Titration Titration curve Equivalence point End point Indicator Mole Relationships Polyprotic acids Total available acid pH & pKa Logarithms Techniques: pH Measurement Apparatus: Buret pH Meter Cylinder Titration MOLES, LITERS & CONCENTRATION UNITS In the lab, we generally measure volumes in mL and weights in mg or, at most, small numbers of grams . We never use even close to 1 kg , 1 mole or 1 Liter of anything. To avoid having to write many quantities with negative exponents, or lots of zer s after the decimal point, data sheets often ask for: volumes in m L (= 1 / 1000 liter) and molar quantitites in m mol (= 1 / 1000 mol) & For molar concentrations , the notation M (molar) has the same numerical value in mol / L E.g., 6 M HCl has 6 mmol of HCl in 1 mL, also 1.0 m mol of NaOH weighs 40 m g and, for atomic weights: the atomic weight of carbon is 12 m g / m mol as it has in m mol / m L Background Strong and Weak Acids (and bases ) Acids and bases can be characterized by the extent to which they dissociate in solution STRONG Fully Dissociated WEAK Partially Dissociated A QUANTITATIVE measure of the strength or weakness of an acid ( or base ) is the DISSOCIATION CONSTANT , Ka For the reaction HA Ï H+ + A- we define an acid dissociation constant, Ka [ H+ ] [ A- ] Ka = ------------- [ HA ] TITRATION A reaction conducted by the slow addition of a precisely measured volume of a reagent solution (usually from a buret) to an amount of a substance until a SIGNAL indicates that the reaction between reagent and substance is complete SIGNAL is often a COLOR CHANGE , but it may be an observable change in another property. If the reaction itself does not produce a SIGNAL when the desired point in the reaction is reached, an INDICATOR may be added to produce an observable change ....
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This note was uploaded on 02/01/2010 for the course CHE 133 taught by Professor Robertschneider during the Winter '08 term at SUNY Stony Brook.

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08pAcidinjuices - Click to edit Master subtitle style Acid...

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