Lab Exam 2

A titration is best defined as an analytical technique for determining the

concentration of a specific solute in a solution

What color is the indicator used in today's exercise in acidic solutions?

Colorless

The equivalence point of a titration is when the indicator changes color and alerts you to stop.

False

How will you determine that you are approaching the end point of a titration?

The solution will change color and then return to the original color within 30 seconds with stirring

What TWO kinds of chemical reactions takes place between KHP and NaOH?

neutralization

double replacement

Which of the following is NOT a common active ingredient in commercial antacid tablets?

acetaminophen

Neutralization of stomach acid with an antacid produces a salt.

True

TWO functions of Benedict's solution make it useful for clinical diagnoses.

• To react with sugars that can be oxidized

• To produce a color change that can be detected visually or colorimetrically

The term renal glucose threshold means

Blood glucose level above which glucose appears in the urine

A disease that can be diagnosed by an elevated level of a sugar other than glucose in the blood or urine is

galactosemia

Fatty acids are termed unsaturated if they are less likely to contribute to cardiovascular disease and obesity.

False

Saponification involves

• Hydrolysis of triglycerides using strong base

• Formation of a carboxylate salt

• Formation of a substance that allows emulsification

Soaps can lose their cleaning power in hard water due to precipitation of sodium salts of carboxylate ions.

False

two main functions of bile salts in the body.

Activation of enzymes that hydrolyze triglycerides

Emulsification of fats/oils in intestinal fluids

Benedict Reaction

Option C

Sucrose

• Comprise of alpha-D-glucose and beta-D-fructose molecule

• Alpha 1 → beta 2 glycosidic linkage

• Not a reducing sugar because the anomeric carbons of both sugars are forming an acetal

• Sweetener, sugarcane, preservative

D-Glucose

• Known as blood sugar since it’s transported by the blood to body tissues for energy requirements

• Other sugars are absorbed by the liver and converted to glucose

• Commonly used as sweetener, and baby foods

D-Fructose

• Most important ketohexose

• Known as levulose/fruit sugar due to being the sweetest monosaccharides and use as sweetener

Reducing Sugars

Simple sugars that can be oxidized if they have:

• Aldehyde

• Ketone that can be isomerized to aldehyde in solution

• Hemiacetal formed by reversible intramolecular condensation of an aldehyde and an alcohol

Benedict’s Reagent

• Contain copper II sulfate (CuSO₄)

• Blue color due to presence of hydrated copper II ions (Cu⁺²)

• Reducing sugar oxidized, and the Cu⁺² reduced to Cu⁺ forming bright orange-red copper I oxide (Cu₂O)

• Semiqualitatively test since color is related to the glucose concentration

• Test for reducing sugars

• A non-reducing sugar can give a positive Benedict’s test if it is first hydrolyzed into reducing sugars

Xanthoproteic Test

Amino acid will only test positive if the aromatic ring bears amino or hydroxyl groups

Albumin

The protein fraction that shows the largest, darkest band

Arrhenius Acid & Base

Only apply in aqueous solution, H+ & OH^- are involved

• Acid: provide H⁺ (proton) when dissolved in water (aqueous solution)

• Base: provide OH^- when dissolved in water (aqueous solution)

Bronsted-Lowry Acid & Base

Proton transferring, and apply to non-aqueous solution

• Acid: hydrogen-containing substance that donate H⁺ to another substance

• Base: any substance that can accept H⁺ from another substance

Lewis Acid & Base

Electron transferring, the most inclusive theory

• Acid: substance accepts a pair of electron

• Base: substance provides a pair of electron

• Ex: binding between a metal ion and ligand (molecule/ion that donates electron pairs to central method ion to form coordinate bond)

Hydrolysis

• Chemical reaction where a bond is broken by water

• May produce acidic or basic solution depending on the reaction

• Ex: NH₄ + H₂O → NH₃ + H₃O

Amphiprotic/Amphoteric

• A substance that can act as both acid or base depending on its reacting partner. Essential for life and biochemical reactions

• Ex: water, HCO₃^-, H₂PO₄^-

Buffer

• Consists of weak acid and weak conjugate base

• Buffer capacity: amount of acid (H+) or base (OH-) that can be absorbed without causing significant change in pH

Respiratory and Kidney Physiological

Respiratory Acidosis

• pH ↓

• PCO₂ ↑

• HCO₃⁻ ↑ (renal compensation, if chronic)

Respiratory Alkalosis

• pH ↑

• PCO₂ ↓

• HCO₃⁻ ↓ (renal compensation, if chronic)

Metabolic Acidosis

• pH ↓

• HCO₃⁻ ↓

• PCO₂ ↓ (respiratory compensation: hyperventilation)

Metabolic Alkalosis

• pH ↑

• HCO₃⁻ ↑

• PCO₂ ↑ (respiratory compensation: hypoventilation)

Titrant/Standard

• Is the base in the experiment, using buret to add drop-wise until endpoint is reached

• Known concentration and volume

Equivalence Point

• Theoretical point of completion

• M_a * V_a = M_b * V_b

• Can also be obtained using pH meter during titration, inflection point (steepest slope on the curve)

• mmol = M * V (unit is ml)

Endpoint

• Measured based on the presence of indication

• The difference between theoretical and actual is negligible, and refers to as indicator error

Back-Titration

• Adding excess titrant to analyte solution (initial titrant)

• React leftover titrant with second standard to calculate leftover titrant

• Find used titrant by subtracting initial with leftover, then calculate the analyte

• Useful when first titration is slow, or when analyte is non-soluble solid as in the case of antacid titration

Roles of HCl in Stomach

• Combine with precursor pepsinogen to activate pepsin enzyme

• Denature (unfold) proteins in order to efficiently promote degradation by enzymes

• Provide pH for pepsin to break down proteins molecules efficiently

Phenolthalein

• Color indication used in titration

• Colorless when <8.2, and pink if higher

• pH transition overlaps steep pH change near equivalence point

Glucose Reference Range

80-110 mg/dL

Diabetes Mellitus

• Metabolic disorder that lead to hyperglycemia

• Type I diabetes: destruction of beta cell of pancreas, little to no insulin production

• Type II diabetes: insulin resistance in the body even if there are adequate amounts

• Symptoms include excessive thirst, frequent urination, hunger, slow healing

Galactosemia

• Genetic disease in which enzyme for galactose is deficient

• Can result in mental retardation and permanent physical impairment

• Diagnosed by positive Clinitest and negative glucose test strip

Glucosaria

• Kidney cannot completely reabsorbed sugar, and so there are glucose in the urine

• Hormonal disorders such as Cushing’s syndrome, hyperthyroidism

• Fanconi’s syndrome: abnormal renal tubular reabsorption due to genetic defect or damage to kidneys by drugs or heavy metal

• Renal glycosuria: renal threshold for glucose to be extremely low

Clinitest Tablet

• Contains copper sulfate (CuSO₄), sodium carbonate (Na₂CO₃), sodium citrate, and sodium hydroxide

• Test for reducing sugars

• Negative result: blue

• Positive result: green, orange

Reagent Test Strips

• Contains glucose oxidase that specifically oxidizes glucose to gluconic acid and hydrogen peroxide

• Contains peroxidase to catalyze hydrogen peroxide to change the color

• Positive result: color change

• Negative: no color change

Lipids

• Low polarity, insoluble in water

• Soluble in nonpolar solvents such as membranes

• Triglycerides are the most abundant. Recommend 25-35% of TG intake

Chromatography

• Measure the middle point of the spot

• R_f factor: $\frac{spot}{solvent}$

Biuret Test

• Test positive when there are ≥ 2 peptides bonds

• The lone pair of nitrogen in peptide bonds form covalent bond with copper (II) ion to change color to purple

Lead Acetate Test

• Test for presence of sulfur-containing amino acids

• Positive: form insoluble black precipitate

Xanthoproteic Test

• Test for proteins that contain aromatic amino acids

• Positive in the formation of