CHEM 2545 Midterm Labs 1-4 with
correct Answers 2023
What factors influence hazards of an acid? -
✔️Strength and concentration
Strong Acids Examples -
✔️Nitric acid (HNO3), Concentrated sulfuric acid (H2SO4), and concentrated
hydrochloric acid (HCl)
Weak Acids Examples -
✔️Acetic acid (vinegar), citric acid (fruits)
Strong Bases Examples -
✔️Sodium hydroxide (NaOH), Potassium Hydroxide (KOH)
Weak Bases Examples -
✔️Baking soda (NaHCO3), Ammonia (NH3)
_____ was a major ingredient in fingernail polish remover -
✔️Acetone
What modeled skin? -
✔️egg white and egg yolk
what modeled contact lenses? -
✔️polystyrene/styrofoam
what modeled metal jewelry? -
✔️aluminum foil
____ are a major component of skin and tend to be reactive with certain acids. -
✔️Sugars
physical property def. -
✔️one that can be observed without changing the identity of the pure substance
intensive property -
✔️independent of amount of sample used
extensive property -
✔️depend on amount present (mass and volume)
physical property ex -
✔️color, density, melting point, boiling point, solubility, molecular weight, refractive
index
boiling point -
✔️temperature where vapor pressure of liquid equals applied pressure of system
vaporization -
✔️change from liquid to vapor; endothermic (must add energy to system to increase
number of molecules in vapor phase)
What if the boiling/melting point differs from accepted values? -
✔️most likely impurity
Increase pressure..._____ b.p. -
✔️increase (exponential)
______ intermolecular forces = higher b.p. -
✔️stronger
, forces from weak to strong -
✔️vdw, dipole-dipole, h bond, and ionic
dipole-dipole forces are present in ... -
✔️polar molecules
acetone -
✔️(ch3)2c=o
ionic forces are present in many ... -
✔️salts
What occurs to b.p if two miscible liquids are mixed? -
✔️b.p. between two liquids depending on concentration of each in solution
density formula -
✔️D=m/v (g/mL or g/cm3)
Uses for refractive index -
✔️identify liquid and assess purity
closer RI measurement to accepted value = -
✔️more pure sample
Refractive index def -
✔️ratio of velocities (n=velocity of light in air/velocity of light in liquid = sin(angle of
incidence)/sin(angle of refraction))
What does a liquids RI depend on? -
✔️temperature and wavelength
melting point -
✔️temperature where molecules in a crystal gain necessary energy to overcome
forces holding them together and move freely
melting -
✔️similar to vaporization; endothermic
the presence of an impurity ____ m.p range. -
✔️widens
phases of melting point -
✔️1. first signs of change 2. first signs of liquid (T1) 3. formation of meniscus 4.
completely clear liquid (T2) T1-T2 = range
Steps for recrystallization -
✔️1. choose appropriate solvent 2. dissolve impure compound 3. decolorize
solution 4. remove suspended solids 5. recrystallize pure compound 6. collect, wash,
and dry crystals
best recrystallization solvent dissolves ____ amount desired solute at high temps.
and ____ amount at low. -
✔️large; minute
greater difference in solubility of solute at high/low temps -
✔️more efficient recrystallization
A good recrystallization solvent is... -
✔️inert, inexpensive, nontoxic, and easily removed (low b.p.)
how do you prevent oiling out? -
✔️bp below mp so solid does not melt in liquid and not dissolve
in recrystallization, too much solvent = -
✔️difficult for pure crystals to form
in recrystallization, too little solvent = -
correct Answers 2023
What factors influence hazards of an acid? -
✔️Strength and concentration
Strong Acids Examples -
✔️Nitric acid (HNO3), Concentrated sulfuric acid (H2SO4), and concentrated
hydrochloric acid (HCl)
Weak Acids Examples -
✔️Acetic acid (vinegar), citric acid (fruits)
Strong Bases Examples -
✔️Sodium hydroxide (NaOH), Potassium Hydroxide (KOH)
Weak Bases Examples -
✔️Baking soda (NaHCO3), Ammonia (NH3)
_____ was a major ingredient in fingernail polish remover -
✔️Acetone
What modeled skin? -
✔️egg white and egg yolk
what modeled contact lenses? -
✔️polystyrene/styrofoam
what modeled metal jewelry? -
✔️aluminum foil
____ are a major component of skin and tend to be reactive with certain acids. -
✔️Sugars
physical property def. -
✔️one that can be observed without changing the identity of the pure substance
intensive property -
✔️independent of amount of sample used
extensive property -
✔️depend on amount present (mass and volume)
physical property ex -
✔️color, density, melting point, boiling point, solubility, molecular weight, refractive
index
boiling point -
✔️temperature where vapor pressure of liquid equals applied pressure of system
vaporization -
✔️change from liquid to vapor; endothermic (must add energy to system to increase
number of molecules in vapor phase)
What if the boiling/melting point differs from accepted values? -
✔️most likely impurity
Increase pressure..._____ b.p. -
✔️increase (exponential)
______ intermolecular forces = higher b.p. -
✔️stronger
, forces from weak to strong -
✔️vdw, dipole-dipole, h bond, and ionic
dipole-dipole forces are present in ... -
✔️polar molecules
acetone -
✔️(ch3)2c=o
ionic forces are present in many ... -
✔️salts
What occurs to b.p if two miscible liquids are mixed? -
✔️b.p. between two liquids depending on concentration of each in solution
density formula -
✔️D=m/v (g/mL or g/cm3)
Uses for refractive index -
✔️identify liquid and assess purity
closer RI measurement to accepted value = -
✔️more pure sample
Refractive index def -
✔️ratio of velocities (n=velocity of light in air/velocity of light in liquid = sin(angle of
incidence)/sin(angle of refraction))
What does a liquids RI depend on? -
✔️temperature and wavelength
melting point -
✔️temperature where molecules in a crystal gain necessary energy to overcome
forces holding them together and move freely
melting -
✔️similar to vaporization; endothermic
the presence of an impurity ____ m.p range. -
✔️widens
phases of melting point -
✔️1. first signs of change 2. first signs of liquid (T1) 3. formation of meniscus 4.
completely clear liquid (T2) T1-T2 = range
Steps for recrystallization -
✔️1. choose appropriate solvent 2. dissolve impure compound 3. decolorize
solution 4. remove suspended solids 5. recrystallize pure compound 6. collect, wash,
and dry crystals
best recrystallization solvent dissolves ____ amount desired solute at high temps.
and ____ amount at low. -
✔️large; minute
greater difference in solubility of solute at high/low temps -
✔️more efficient recrystallization
A good recrystallization solvent is... -
✔️inert, inexpensive, nontoxic, and easily removed (low b.p.)
how do you prevent oiling out? -
✔️bp below mp so solid does not melt in liquid and not dissolve
in recrystallization, too much solvent = -
✔️difficult for pure crystals to form
in recrystallization, too little solvent = -
