(Prelims) BioChem Lab #1

pH Indicator

A compound that changes color in solution over a narrow range of pH values, used to determine acidity or alkalinity.

Halochromic

A substance that changes color in response to a change in the pH of its environment.

Phenolphthalein

A chemical compound with the formula C₂₀H₁₄O₄ and is often written as "HIn" or "phph" in shorthand notation.

Phenolphthalein

A pH indicator used in acid-base titrations, colorless in acid and pink in base.

Methyl Orange

A pH indicator that changes from red in acid to yellow in base, often used in titrations of strong acids.

Litmus Paper

A natural dye mixture used as one of the oldest pH indicators, red in acid and blue in base.

Phenolphthalein

It belongs to the class of dyes known as phthalein dyes.

Phenolphthalein

pH 8.2 - 10.0

Litmus Paper

pH 4.5 - 8.3

Methyl Orange

pH 3.1 - 4.4

Common Ion Effect

Decrease in solubility of a salt when a solution already contains one of its ions.

Buffer Solutions

A solution of weak acid and conjugate base (or vice versa) that resists changes in pH when small amounts of acid or base are added.

- Maintains blood pH (7.35 - 7.45)

- Prevents Enzyme Denaturation

What are the biological importance of Buffer Solutions?

Denaturation

pH rises or lowers too much

Sodium Hydroxide (NaOH)

A strong alkali that is highly caustic, decomposes proteins, and can cause burns.

Iron (III) Chloride (FeCl₃)

A highly corrosive, acidic compound used in labs, dangerous if ingested.

Copper (II) Sulfate (CuSO₄)

An inorganic compound commonly in pentahydrate form, known as blue vitriol.

Sodium Chloride (NaCl)

Common salt, an ionic compound of sodium and chloride.

Magnesium Chloride (MgCl₂)

A highly soluble ionic salt, often extracted from seawater or brine.

Sodium Carbonate (Na₂CO₃)

Also known as washing soda or soda ash, a strong alkali salt historically derived from plant ashes.

Ammonium Chloride (NH₄Cl)

An acidic salt formed from HCl and NH₃, dissociates into NH₄⁺ and Cl⁻ in water.

Ammonium Hydroxide (NH₄OH)

A solution of ammonia in water, also called aqueous ammonia.

True

(True or False)

Buffer Solutions maintain blood pH

False.

pH indicators do not affect a solution's pH.

(True or False)

pH indicators affect a solution's pH

True

(True or False)

Litmus paper is one of the oldest indicators

True

(True or False)

The common ion effect results in more precipitation.

False.

pH 7 at 25°C

(True or False)

The body's neutral pH is 7 at 35°C

Phenolphthalein

Acid: Colorless

Base: Pink

What is the color of Phenolphthalein in;

Acid:

Base:

Methyl Orange

Acid: Red

Base: Yellow

What is the color of Methyl Orange in;

Acid:

Base:

Litmus Paper

Acid: Red

Base: Blue

What is the color of Litmus Paper in;

Acid:

Base: