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PhyChem II Lab Practicum II
Terms in this set (88)
a measured amount of a solution of unknown concentration is added to a known volume of a second solution until the reaction between them is just complete
What are the chemical principles of a titration?
a known volume of both solutions are mixed until a signal alerts the titrator that the reaction has reached a certain level of completion, typically near the stoichiometric equivalence of the reactants
a substance that ca interact with both polar and nonpolar substances having both polar and nonpolar structural features
How many decimal places does a biuret provide?
two (ex: 41.00)
a substance that can act as both an acid and a base
Why is a chemical indicator used in an acid-base titration?
it alerts the titator that he reaction has reached a certain level of completion, typically near the stoichiometric equivalence of the acid and base
a highly purified solid compound used to check the concentration of the known solution in a titration
What are the characteristics of a primary standard?
-obtainable with high purity
-allows for precise and reproducible determination of the unknown concentration of a solute in a solution
What is the equation for molarity?
M=(mol/L) or M=(mmol/mL)
What is the equation used for titrations?
MaVa = MbVb
Ma: moles of acid
Va: volume of acid
Mb: moles of base
Vb: volume of base
What is the equation used for back titrations?
mmol = M(mmol/mL) x V(mL)
What happens when a small amount of KHP is lost when transferring it to the collection Earlenmeyer flask after weighing?
the concentration of base will be overestimated because less KHP will be present than what was measured and a smaller volume of base will be needed to neutralize it
What happens when a small amount of water were added to the solid KHP to fully dissolve it before adding the base?
there is no effect because adding water to the KHP will not alter the amount of it that is present
What happens when the tip of the buret is washed with a wash bottle while dispensing the base before the end point and that rinse is allowed to enter the collecting flask?
there will be no effect because any volume of base dispensed before reaching the end point must be accounted for and added to the collection Erlenmeyer flask
What happens when a few extra drops of base are added to the Erlenmeyer flask when approaching the end point and the phenolphtalein turns bright pink?
there will be a higher volume of base which will underestimate the concentration of base
What happens when a small amount of water is added to the antacid solution before adding the standardized NaOH solution?
there is no effect because this will dilute the acidic solution but will not change the total amount of acid that is present, which is what the titration aims to determine
By what factors does the acidity of a solution change for every unit change in pH?
a factor/power of 10
What are the physiological functions of HCl in the stomach?
-denaturation/unraveling of dietary proteins
-activation of gastric digestive enzymes
-partial digestion of foodstuffs
-controlling microbial growth
type 1 diabetes
lack of insulin production
type 2 diabetes
improper/deficient response to insulin
What are the common signs and symptoms of diabetes mellitus?
-poor wound healing
What are normal fasting blood glucose levels?
What are the blood glucose levels of a diabetic?
pre-diabetes: 101-125 mg/dL
diabetes: >126 mg/dL
What are the blood glucose levels in hypoglycemeia?
What two functional groups must a carbohydrate contain?
aldehyde or ketone
What classifies a reducing sugar as such?
the presence of aldehyde or ketone that can isomeize to an aldehyde o a hemiacetal
What happens to Benedict's reagent in the presence of reducing sugars?
it gets reduced as the aldehyde is oxidized to a carboxylic acid
-Cu(II) becomes Cu(I)
What is the reactive ingredient in Benedict's reagent that is involved in a redox reaction?
What color change does a "positive" Benedict's test always produce?
a change of color from light blue to orange-red
Which mono- or disaccharides should have a negative Benedict's test result?
sucrose because it s a non-reducing sugar, due to the anomeric carbons of both glucose and fructose being bonded to eachother, displaying no hemiacetal
What produces a positive clinitest?
sugars that have an aldehyde or hemiacetal functional groups, but can also react with other reducing agents, such as vitamin C or other drugs and their metabolites
What produces a negative clinitest?
confirms the absence of sugars with an aldehyde or hemiacetal, or other reducing agents
What is the signifigance of a sample dispaying a passthrough with the Clinitest?
there is a high amount of other reducing agents but appears to give a negative result
What is the implication of a newborn's urine displaying a positive Clinitest and negative Glucose Strip test?
there is no glucose present but there may be other reducing sugars, such as galactose, which can lead to galactosemia and eventually galactosuria
What would be observed with Lugol's iodine and Benedict's tests after the complete hydrolysis of starch?
negative (-) Lugol's iodine test and positive (+) Benedict's test
What would be observed with Lugol's iodine and Benedict's tests after the incomplete hydrolysis of starch?
positive (+) Lugol's iodine test and positive (+) Benedict's test
What is an example of a sugar that give a positive Benedict's test and a negative glucose dipstick test?
any aldose other than glucose or ketose that can isomerize to an aldose under the reaction conditions of the Benedict's test, including galactose or fructose
Why would galactose and fructose give a positive Benedict's test and a negative glucose dipstick test?
-the Cu(II) in the Benedict's reagent cannot discriminate between aldoses, since it reacts with any aldehyde
-glucose dipstick has glucose oxidase, an enzyme that specifically reacts with glucose only, so all other sugars will yield a negative result
What effect does urine being left out for a while have on the glucose disptick test?
as glucose is consumed through oxidation, its concentration goes down, eventually falling below the threshold of the detection of the test, so if it is not analyzed promptly, a sample that may have contained glucose will test negative if the glucose levels have fallen below the threshold
What class of functional group does a peptide bond belong to?
Chemically, what happens when a protein is digested in the GI tract?
peptide bonds in proteins undergo hydrolysis to yield . individual amino acids
Why does milk turn sour and curdle over time?
microbial metabolism of lactose produces lactic acid, which over time lowers the pH and causes denaturation of proteins in milk
Why do eggs turn white when cooked?
the heat of the cooking process denatures the proteins that make up the egg whites
What amino acids in proteins account for the sulfur content of foods?
cysteine and methionine
What causes a positive Biuret test?
two or more peptide bonds
What color does a positive Biuret test produce?
What causes a positive xanthoproteic test?
benzene ring with an amino or OH- group present
What color does a positive xanthoproteic test produce?
What causes a positive lead acetate test?
sulfur-contining amino acids
What color does a positive lead acetate test produce?
What does it mean if a substance has more charge on a TLC plate?
it has more affinity for the stationary phase
What does it mean if a substance has less charge on a TLC plate?
it has less affinity for the stationary phase
What does it mean if a substance has a low affinity for the solvent on a TLC plate?
it will move the least
What does it mean if a substance has a high affinity for the solvent on a TLC plate?
it will move the most
What does it mean if a substance is more polar on a TLC plate?
it will have a low migration
What does it mean if a substance is less polar on a TLC plate?
it will have a high migration
What does it mean if a substance has a large Rf value?
it will move further and will have less polarity/charge
What does it mean if a substance has a small Rf value?
it will move less and will have more polarity/charge
How can one determine the identity of an unknown amino acid in a TLC experiment?
by comparing the Rf of the unknown with that of the known samples
How can Rf value be determined?
(sample distance)/(solvent distance)
the pH at which the net charge is zero
migration of charged particles under the influence of an electric field
What is the purpose of the buffer solution in electrophoresis?
it maintains a constant pH throughout the electrophoresis medium to ensure the amino acids or proteins acquire a charge hat enables them to migrate toward one of the electrodes
Which way do cations (+) migrate during electrophoresis?
toward the cathode (-)
Which way do anions (-) migrate during electrophoresis?
toward the anode (+)
What factors/characteristics influence the separation of proteins by electrophoresis and the intensity of the bands observed?
-charge and size influence the rate of migration
-a larger charge will have a faster migration and a large size will have a slower migration
-amount of protein determines the intensity of the bands
What is the main function of enzymes?
they catalyze chemical reactions providing an alternative pathway for the substances to interact that has a lower activation energy, making the reaction faster
Why are enzymes needed only in small amounts?
they are regenerated as they act
What is a generally accepted model of enzyme action?
E+S <-> E-S <-> E-P <-> E+P
Is the model of enzyme action reversible?
What are the factors that affect the catalytic action of enzymes?
-oxidizing and reducing agents
-the binding of substances within and outside of the active site
Is it true that enzyme activity generally increases with increasing energy?
enzymes become denatured with heat, so there is a specific temperature at which it is optimal to work
What does specificity refer to with regards to enzymes?
the ability to differentiate between substrates and non-substates, based on structural features
constant rate occuring at high substrate concentration when all avaliable enzymes are saturated with the substrate
directly proportional to substrate concentration occuring at a low substrate concntration when enzymes are avaliable and more substrate producs a higher rate of reaction
Which enzymes can be used to diagnose liver disease?
ALT: liver specific
AST: heart and liver
these enzymes function to metabolize amino acids
Which enzymes can be used to diagnose pancreatic disease?
amylase: hydolyzes glycosidic bonds of dietray starches
lipase: hydrolyzes ester bonds on triglycerides
How can the presence of starch be detected?
using iodine solution, which turns dark-blue-black in the presence
Which body fluid serves as a source of amylase?
saliva and pancreatic fluid
At which temperature is the activity of amylase at its maximum?
37 degrees celcius because this is physiological temperature at which most enzymes within the body functions
What is the function of transaminase enzymes?
they trasfer amino groups between amino acid and alpha-keto group
What are the reactants and products of AST?
aspatate + alpha-ketoglutarate <-> oxaloacetate + glutamate
What are the reactants and products of ALT?
alanine + alpha-ketoglutarate <-> pyruvate + glutamate
Why must hemolysis be avoided when preparing a sample of AST?
RBCs contain AST and if lysed, they can release into the assay, causing an increase n the enzymatic activity of the sample that can be interpreted as falsley elevated
What is the reagent used to generate a colored product during the colormetric determination of AST activity?
What is the name of the colored product used during the colormetric determination of AST activity?
What is the conversion factor between SF and IU?
1 SF/mL = 0.48 IU/L
Which enzymes can be used to diagnose a myocardial infarction?
-CPK: peaks within 1-2 days, falls within 2-3 days
-AST: peaks within 2-3 days, falls within 5-7 days
-LDH: peaks within 5-7 days, falls within 7-10 days (with this, LDH2>LDH1 initially, but within a few days, LDH2<LDH1)
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