(MIDTERM) Biochemistry Lab - OCTOBER 3, 2025

A

The fundamental property defining lipids, according to the document, is their solubility in which type of solvent?

A. Organic (nonpolar) solvents

B. Polar solvents

C. Ionic solvents

D. Aqueous solvents

A

The principle of solubility, "like dissolves like," applied to nonpolar lipids means they will be soluble in which of the following?

A. Nonpolar solvents

B. Hydrophilic liquids

C. Water

D. Polar solvents

A

When a lipid is mixed with water, the expected result is that the lipid will be:

A. Insoluble (immiscible), forming two distinct layers or a cloudy suspension

B. Soluble, forming a clear solution

C. Neutralized, changing the pH

D. Hydrolyzed, breaking down immediately

A

What term is used to describe the property of lipids that makes them insoluble in water?

A. Hydrophobic

B. Isothermal

C. Hydrophilic

D. Emulsifying

A

Which of the following is often used as an intermediate solvent to emulsify a lipid before it dissolves fully in a nonpolar environment?

A. Ethanol

B. Chloroform

C. Water

D. Diethyl ether

D

A positive result for a lipid in a solubility test using a nonpolar solvent is the formation of a:

A. Cloudy suspension

B. Two distinct layers

C. Precipitate

D. Clear, homogeneous solution

D

Lipids are defined by their solubility, not by a specific functional group, unlike which other major biological molecules mentioned?

A. Nucleic acids and vitamins

B. Steroids and hormones

C. Minerals and enzymes

D. Carbohydrates and proteins

D

Which of the following nonpolar solvents listed in the document requires handling in a fume hood due to being volatile and flammable?

A. Water

B. Ethanol

C. Glycerol

D. Diethyl ether

D

What is the primary purpose of the Sudan IV or Sudan III staining test?

A. To measure the melting point of the lipid

B. To determine the degree of unsaturation

C. To break down the lipid using an acid

D. To visualize the presence of lipids under a microscope

D

Sudan IV and Sudan III are classified as fat-soluble dyes, also known by what specific term?

A. Chromophores

B. Metallochromes

C. Auxochromes

D. Lysochromes

C

A positive result for the Sudan staining test is when the lipids appear stained what color (depending on the specific dye)?

A. Blue or green

B. Black or brown

C. Red or orange

D. Yellow or purple

B

The Sudan staining test is described as a physical dissolution of the dye. This means it is a physical test as opposed to which other type of test mentioned in the notes?

A. A biological test

B. A chemical test

C. A qualitative test

D. A quantitative test

B

In the Sudan staining procedure, what is often created before staining in order to suspend small oil droplets in water?

A. A precipitate

B. An emulsion

C. A flocculate

D. A filtrate

B

Sudan dyes preferentially dissolve in which component of the sample?

A. Aqueous environment

B. Nonpolar lipid molecules

C. Polar carbohydrate chains

D. Protein backbone

D

The positive result of the Sudan stain confirms what about the biological sample?

A. That the sample is highly saturated

B. That a chemical reaction has occurred

C. The degree of unsaturation

D. The presence of a lipid

B

What chemical property of fats does the Iodine Test primarily differentiate?

A. Polarity and charge

B. Saturation and unsaturation

C. Molecular weight and size

D. pH and acidity

C

The key structural feature in fatty acid chains that reacts with iodine is the presence of:

A. Single C-C bonds

B. C=O (carbonyl) groups

C. Double bonds

D. Hydroxyl (OH) groups

B

What is the natural color of the iodine solution used as the reagent in the test?

A. Clear or colorless

B. Brown/yellowish-brown

C. Bright red

D. Deep purple

B

A positive result for unsaturation in the Iodine Test is indicated by what change in the reagent's color?

A. The brown color remains slow/no change

B. The brown color rapidly disappears

C. The solution turns a deep blue

D. A white precipitate forms

B

Why does the brown color of the iodine rapidly disappear in a positive test?

A. The iodine is boiled away by the reaction

B. The iodine is consumed by the chemical reaction with the double bonds

C. The iodine precipitates out of solution

D. The iodine reacts with the glycerol backbone

C

A negative result in the Iodine Test, indicating saturation, is characterized by:

A. The formation of a homogeneous solution

B. The rapid disappearance of the brown color

C. The brown color of the iodine remaining (slow/no change)

D. The solution changing to an orange color

C

The chemical reaction that occurs when iodine reacts across the double bonds is specifically called an:

A. Substitution reaction

B. Elimination reaction

C. Addition reaction

D. Hydrolysis reaction

B

Which type of fat, often liquid, is expected to give a positive result (unsaturation) in the Iodine Test?

A. Hard fats (solid, saturated)

B. Oils (liquid, unsaturated)

C. Soaps

D. Waxes

C

Which type of fat, often solid, is expected to give a negative result (saturation) in the Iodine Test?

A. Oils (liquid, unsaturated)

B. Waxes

C. Hard fats (solid, saturated)

D. Glycerides

D

The Iodine Test is key for characterizing the quality of fats by determining their degree of:

A. Polarity

B. Volatility

C. Purity

D. Unsaturation

C

Which test described in the document is considered a "true chemical reaction to determine a chemical property"?

A. Solubility Test with water

B. Sudan IV/III Staining

C. Iodine Test (Unsaturation)

D. Emulsification Test

C

Which test described in the document is considered a "physical dissolution of the dye to visualize the lipid"?

A. Iodine Test (Unsaturation)

B. pH Test

C. Sudan Staining

D. Solubility Test in Chloroform

C

Why must volatile solvents like Diethyl ether and Chloroform be handled in a fume hood?

A. To prevent rapid cooling of the solvents

B. To ensure accurate measurement of density

C. To prevent inhalation and fire hazards

D. To increase the rate of reaction

C

The overall objective of the experiment, Lipid Analysis, is to identify the presence and characteristics of lipids using what kind of tests?

A. Quantitative tests

B. Mass spectrometry tests

C. Qualitative tests

D. Titration tests

B

What term best describes a lipid forming two distinct layers when mixed with water?

A. Homogeneous

B. Immiscible

C. Hydrolyzed

D. Turbid