Chapter 9: Fermentation

What is the purpose of the fermentation experiment?

To ferment sucrose using yeast and test for ethyl alcohol and residual sugar

What is fermentation?

Slow decomposition of organic substances by microorganisms through enzymes

What organisms carry out fermentation?

Yeast cells

What is the role of enzymes in fermentation?

They act as catalysts to speed up chemical reactions

What enzyme in yeast converts sucrose into glucose and fructose?

Invertase

What enzyme in yeast converts glucose into ethanol and CO₂?

Zymase

What is the function of Pasteur's salt solution?

Provides nitrogen and nutrients for yeast

Which sugars can yeast ferment?

Glucose, fructose, mannose, sucrose (after hydrolysis), maltose (after hydrolysis)

Which sugars cannot be fermented by yeast?

Lactose and galactose (difficult to ferment)

What is the chemical formula of sucrose?

C₁₂H₂₂O₁₁

What happens when sucrose is hydrolyzed?

It forms glucose and fructose (invert sugar)

Write the hydrolysis reaction of sucrose by invertase.

C₁₂H₂₂O₁₁ + H₂O → 2C₆H₁₂O₆

Write the fermentation reaction of glucose by zymase.

2C₆H₁₂O₆ → 4CH₃CH₂OH + 4CO₂

What gas is produced during fermentation?

Carbon dioxide (CO₂)

What observation indicates CO₂ formation?

Lime water becomes cloudy from CaCO₃

What is the reaction between lime water and CO₂?

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

What compound forms when lime water becomes cloudy?

Calcium carbonate (CaCO₃)

### *IODOFORM TEST (ETHANOL TEST)*

What is the purpose of the iodoform test?

To detect the presence of ethanol

What color is a positive iodoform test?

Yellow precipitate

What is the yellow precipitate formed in the iodoform test?

Iodoform (CHI₃)

Write the chemical equation for the iodoform test.

CH₃CH₂OH + 4I₂ + 6NaOH → CHI₃ + HCOONa + 5NaI + 5H₂O

What reagent provides iodine in the iodoform test?

I₂ in KI

What provides the alkaline medium in the iodoform test?

NaOH

What oxidized intermediate forms from ethanol during the test?

Acetaldehyde (CH₃CHO)

### *BENEDICT'S TEST (SUGAR TEST)*

What is the purpose of Benedict's test?

To check for the presence of reducing sugars

What color indicates a positive Benedict's test?

Brick red

What precipitate forms in a positive Benedict's test?

Cuprous oxide (Cu₂O)

What does a negative Benedict's test mean?

All sugar was fermented (complete fermentation)

Write the reaction for Benedict's test.

C₆H₁₂O₆ + Benedict's reagent → Cu₂O + oxidized sugar

What ions provide the blue color in Benedict's solution?

Copper(II) ions (Cu²⁺)

What does a brick-red precipitate indicate?

Presence of reducing sugar (glucose)

### *REACTION-FOCUSED EXTRA QUESTIONS*

What are the final organic products of fermentation?

Ethanol and carbon dioxide

Is fermentation aerobic or anaerobic?

Anaerobic

Why does yeast eventually stop fermenting?

Accumulation of alcohol or depletion of sugar

What type of reaction converts ethanol to iodoform?

Oxidation followed by substitution

Why is sucrose not directly fermented?

It must first be hydrolyzed by invertase

What happens to glucose during fermentation?

It is reduced and oxidized simultaneously (redox) to form ethanol and CO₂

What is the role of yeast in fermentation?

Acts as a biological catalyst using enzymes

Why does limewater turn cloudy?

CO₂ reacts to form CaCO₃

What is the purpose of heating during the iodoform test?

To speed up oxidation and precipitation

What happens to the color of iodine when ethanol is present?

It becomes lighter and forms a yellow precipitate

Why does Benedict's reagent turn from blue to red?

Cu²⁺ is reduced to Cu⁺ forming Cu₂O

What does incomplete fermentation indicate?

Remaining reducing sugars present

What happens to the sugar molecules during fermentation?

They undergo glycolysis then alcohol fermentation