CHem 201 LAB Midterm

Lab 2, 3, 4, 5, 6

When a substance is pure, what are the characteristics of its melting point?

The range is high and narrow

When impurities are introduced into the substance, what happens to the melting point?

It widens and narrows

What is melting point depression?

an observable drop in MP

What is the eutectic point?

the specific temperature and composition where a liquid mixture solidifies into two distinct solid phase simultaneously

What can the eutectic point signify?

the lowest possible melting temperature

What is a mixed melting point used for?

to identify a compound in a mixed substance

If an MP depression occurs during a mixed melting point, what does this mean?

the substance is impure, therefore, cannot be the same substance

What amount of powder should be packed in the capillary tube?

1-2 mm

What does ‘d’ or ‘dec’ signify?

decomposition

What are electrostatic forces?

they occur between charged species, cations and anions, and are responsible for extremely high melting/boiling points of ionic compounds and metals

What does hydrogen bonding do the melting point?

increases it

What are the two uses of distillation?

separate/purify and determine/identify BP

What are the two components of a distillation and what are their respective boiling points?

component 1 has the lower boiling point

component 2 has the higher boiling point

When is simple distillation best?

boiling point differences greater than 100 degrees C

When is fractional distillation best?

boiling point differences less than 100 degrees C

What is different about fractional distillation?

it utilizes a fractionating column to provide reflux of the distillates

If an increase in barometric pressure occurs, what does this mean for the boiling point?

it increases as well

If an increase in barometric pressure occurs, what does this mean for the boiling point?

it decreases as well

What is the equation for Raoult’s Law? What does each component mean?

X_AP_A⁰ + X_BP_B⁰ = P_tot

X_A/B is mole fraction

P_A/B is partial pressure

What is the conversion for mmHg to atm?

760 mmHg = 1 atm

When a chemist ‘washes’ the ether layer with an aqueous solution, what types of compound might the chemistry try to remove from the ether layer?

inorganic salts 

What are the two layers present in liquid-liquid extractions?

Top layer: solvent with lower density (usually always the organic solvent bc it’s lighter than the aqueous layer)

Bottom layer: solvent with higher density