143_Lecture5_to_post

143_Lecture5_to_post - Be sure to bring a food sample for...

Info iconThis preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon
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 to cover all of it next week so I will spend part of lecture on it. Don’t forget in class quiz Oc-16. Don’t forget a lab report is required for this weeks lab it is due next week at the start of class. Late lab reports can’t be accepted---sorry
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Acid Content of Beverages A titration exercise SUSB - 010
Background image of page 2
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?
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Concepts: Strong/Weak Acids Acid Dissociation / K a Concentration Titration Titration curve Equivalence point End point Indicator Mole Relationships Polyprotic acids Total available acid pH & pK a Logarithms Techniques: pH Measurement Apparatus: Buret pH Meter Titration
Background image of page 4
MOLES, LITERS & CONCENTRATION UNITS In the lab, we generally measure volumes in mL and weights in mg or, at most, in small numbers of grams . We virtually never come close to using 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 volumes in mL (= 1 / 1000 liter) and molar quantitites in mmol (= 1 / 1000 mol) & weights in mg (= 1 / 1000 g)
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
For molar concentrations , the notation M (molar) has the same numerical value in mol / L For example 6 M HCl has 6 moles of HCl in 1 L, 6 M HCl has 6 m moles of HCl in 1 m L AND 1.0 m mol of NaOH weighs 40mg And the atomic weight of carbon is 12 m mol Which is the same as 12 grams per mole as it has in m mol / m L
Background image of page 6
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 ) Note there is never really free H + , Since it reacts with water to form H 3 O + . BUT We will use H + as a shorthand notation. WEAK Partially Dissociated
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Acetic Acid ( CH 3 COOH), is a WEAK acid in water CH 3 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
Background image of page 8
A QUANTITATIVE measure of the strength or weakness of an acid ( or base ) is the DISSOCIATION CONSTANT , K a For the reaction HA H + + A - we define an acid dissociation constant, K a [ H + ] [ A - ] K a = ------------------ [ HA ] LARGE K a ( >> 1) STRONG ACID SMALL K a ( << 1) WEAK ACID DISSOCIATION CONSTANTS
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
When applied to acids and bases, the words “ strong ” and weak ” refer to their extent of dissociation A True B False
Background image of page 10
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
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 12
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 45

143_Lecture5_to_post - Be sure to bring a food sample for...

This preview shows document pages 1 - 12. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online