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lecture5topost - Be sure to bring a food sample for the...

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Be sure to bring a food sample for the lab. Don’t use MM’s since we used them last week We will talk about lab reports in class The lecture notes are for the acid in food lab. It is complicated material and we won’t have enough time
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Acid Content of Beverages Acid Content of Beverages A titration exercise SUSB - 010
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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?
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Concepts: Strong/Weak Acids Acid Dissociation / K Concentration Titration Titration curve Equivalence point End point Indicator Mole Relationships Polyprotic acids Total available acid pH & pK Logarithms Techniques: pH Measurement Apparatus: Buret pH Meter Titration
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In the lab, we generally measure volumes in mL and weights in mg or, at most, in small numbers of grams . We virtually never use even close to 1 mole or 1 Liter of anything. To avoid having to write many quantities with negative exponents, or lots of zeros after the decimal point, the data sheets often ask for: volumes in mL (= 1 / 1000 liter) and molar quantitites in mmol (= 1 / 1000 mol) & weights in mg (= 1 / 1000 g) 3.421 X 10 -2 L 0.002845 mol 34.21 mL 2.845 mmol 0.4257 g 425.7 mg
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For molar concentrations , the notation M (molar) has the same numerical value in mol / L E.g., 6 M HCl has 6 m mol of HCl in 1 m L, 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 m m
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Background 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 E.g., In water, HCl is a STRONG acid HCl (aq) H + (aq) + Cl - (aq) proceeds virtually to completion (no undissociated HCl ) + WEAK Partially Dissociated
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Acetic Acid ( CH 3 COOH), is a WEAK acid in water CH COOH (aq) CH 3 COO - (aq) + H + (aq) Lots of CH 3 COOH exists in UNDISSOCIATED form undissociated proceeds only slightly in the forward direction. dissociated
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A QUANTITATIVE measure of the strength or weakness of an acid ( or base ) is the a DISSOCIATION CONSTANTS DISSOCIATION CONSTANTS
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When applied to acids and bases, the words “ strong ” and weak ” refer to their extent of dissociation A True B False
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TITRATION TITRATION A reaction conducted by the slow addition of a precisely measured volume of a reagent solution (usually from a buret) to a precisely known 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.
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If the reaction itself does not produce a SIGNAL when the desired point in the reaction is reached, an INDICATOR
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This note was uploaded on 09/21/2009 for the course CHE 143 taught by Professor Raleigh during the Fall '09 term at SUNY Stony Brook.

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lecture5topost - Be sure to bring a food sample for the...

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