CHEM 1B LAB FINAL EXAM QUESTIONS COMPLETE
WITH VERIFIED ANSWERS
/. Three methods of separating compounds - Answer-✅Filtration, sublimation,
evaporation
/.Filtration - Answer-✅the process that separates a solid from the liquid in a
heterogeneous mixture
/.Sublimation - Answer-✅A change directly from the solid to the gaseous state without
becoming liquid
/.Evaporation - Answer-✅Removing a liquid from a mixture by turning it into a gas.
/.Solve for the mass of a chemical in a container - Answer-✅[mass total] - [mass empty
dish] = [mass of chemical]
/.Fire diamond colors - Answer-✅Blue (health risk), Red (flammability), Yellow
(reactivity), white (other comments; ie reacts with water).
/.Hydrates - Answer-✅Compounds that contain water molecules as part of their
crystaline structure (ex: MgSO₄ ⋅ 7H₂O)
/.Lab three was called "hydration of an Epsom salt"... so what's anEpsom salt? -
Answer-✅A magnesium sulfate hydrate which can exist in a number of states ranging
from [MgSO₄ ⋅ H₂O] to [MgSO₄ ⋅ 9H₂O]
/.What was the objective of the third lab titled "hydration of an Epsom salt" - Answer-
✅To experimentally determine the number of water molecules per formula unit of
Epsom salt. We know Epsom salt is [MgSO₄ ⋅ XH₂O] and we're solving for X.
/.Limiting reagent - Answer-✅any reactant that is used up first in a chemical reaction; it
determines the amount of product that can be formed in the reaction
/.Theoretical yield - Answer-✅the maximum amount of product that can be produced
from a given amount of reactant
/.Actual Yield - Answer-✅the measured amount of a product obtained from a reaction
/.How do you calculate percent yield? - Answer-✅AY/TY x100%
, /.Solving for limiting reagent - Answer-✅Using molecular weights of the PT, convert
each of the reactants into moles. Now utilize the mole-to-mole ratios of each reactant to
the end product to convert to the amount which could be synthesized. Whichever
reactant produces less can be identified as the limiting reagent.
/.What does it mean if a chemical is available "in excess" when calculating limiting
reactants? - Answer-✅It is not the limiting reactant and can be treated as if an indefinite
amount exists.
/.Explain the procedure in lab four named "Limiting excess reagents" - Answer-✅Mix
together the chemicals benzaldehyde and acetone in a test tube. Mix with catylist
NaOh/Ethanol, which don't react with the chemicals but expedite their otherwise-slow
rate of reaction. The initial chemicals will react to form dibenzalacetone precipitate, a
solid, leaving a decent amount of liquid left over. Use a vacuum filtration system to
seperate the solid from the liquid. Take the now-seperated solid and heat in oven to
remove the last of the liquid.
/.In lab four, "limiting excess reagents" we synthesize dibenalacetone from
benzaldehyde and acteone and then mass the result. What's the importance of this
recorded mass? - Answer-✅We compare the result to the mathematically-calculated
theoretical yield. From this, we can calculate how effective our reaction was by solving
for the percent yield.
/.What is the objective of lab five, titled "titrations, accuracy and precision"? - Answer-
✅Determing the concentration of our NaOH solution through titration.
/.What is the purpose of a titration? - Answer-✅To use a solution of known concentration
to determine the concentration of another solution
/.What is molarity? - Answer-✅Moles/L
/.When completing a titration, what term will we use to describe concentration? -
Answer-✅Molarity
/.When measuring precisely from a burret, a curve (meniscus) appears at the top you're
trying to measure from. How do you know where to read your measurement from? -
Answer-✅Always read from the bottom of a meniscus
/.How do we find the volume of fluid used when dispensing fluid from a burret? -
Answer-✅The volume used is the difference between the final volume and initial
volume.
V.used = V.final - V.initial
/.In lab five, titled "titrations, accuracy and precision" we determine how many liters of
one reagent it took to trigger the die effect which stains everything pink. What was the
purpose of this? - Answer-✅If we know how many liters (V.used) it took to reach
WITH VERIFIED ANSWERS
/. Three methods of separating compounds - Answer-✅Filtration, sublimation,
evaporation
/.Filtration - Answer-✅the process that separates a solid from the liquid in a
heterogeneous mixture
/.Sublimation - Answer-✅A change directly from the solid to the gaseous state without
becoming liquid
/.Evaporation - Answer-✅Removing a liquid from a mixture by turning it into a gas.
/.Solve for the mass of a chemical in a container - Answer-✅[mass total] - [mass empty
dish] = [mass of chemical]
/.Fire diamond colors - Answer-✅Blue (health risk), Red (flammability), Yellow
(reactivity), white (other comments; ie reacts with water).
/.Hydrates - Answer-✅Compounds that contain water molecules as part of their
crystaline structure (ex: MgSO₄ ⋅ 7H₂O)
/.Lab three was called "hydration of an Epsom salt"... so what's anEpsom salt? -
Answer-✅A magnesium sulfate hydrate which can exist in a number of states ranging
from [MgSO₄ ⋅ H₂O] to [MgSO₄ ⋅ 9H₂O]
/.What was the objective of the third lab titled "hydration of an Epsom salt" - Answer-
✅To experimentally determine the number of water molecules per formula unit of
Epsom salt. We know Epsom salt is [MgSO₄ ⋅ XH₂O] and we're solving for X.
/.Limiting reagent - Answer-✅any reactant that is used up first in a chemical reaction; it
determines the amount of product that can be formed in the reaction
/.Theoretical yield - Answer-✅the maximum amount of product that can be produced
from a given amount of reactant
/.Actual Yield - Answer-✅the measured amount of a product obtained from a reaction
/.How do you calculate percent yield? - Answer-✅AY/TY x100%
, /.Solving for limiting reagent - Answer-✅Using molecular weights of the PT, convert
each of the reactants into moles. Now utilize the mole-to-mole ratios of each reactant to
the end product to convert to the amount which could be synthesized. Whichever
reactant produces less can be identified as the limiting reagent.
/.What does it mean if a chemical is available "in excess" when calculating limiting
reactants? - Answer-✅It is not the limiting reactant and can be treated as if an indefinite
amount exists.
/.Explain the procedure in lab four named "Limiting excess reagents" - Answer-✅Mix
together the chemicals benzaldehyde and acetone in a test tube. Mix with catylist
NaOh/Ethanol, which don't react with the chemicals but expedite their otherwise-slow
rate of reaction. The initial chemicals will react to form dibenzalacetone precipitate, a
solid, leaving a decent amount of liquid left over. Use a vacuum filtration system to
seperate the solid from the liquid. Take the now-seperated solid and heat in oven to
remove the last of the liquid.
/.In lab four, "limiting excess reagents" we synthesize dibenalacetone from
benzaldehyde and acteone and then mass the result. What's the importance of this
recorded mass? - Answer-✅We compare the result to the mathematically-calculated
theoretical yield. From this, we can calculate how effective our reaction was by solving
for the percent yield.
/.What is the objective of lab five, titled "titrations, accuracy and precision"? - Answer-
✅Determing the concentration of our NaOH solution through titration.
/.What is the purpose of a titration? - Answer-✅To use a solution of known concentration
to determine the concentration of another solution
/.What is molarity? - Answer-✅Moles/L
/.When completing a titration, what term will we use to describe concentration? -
Answer-✅Molarity
/.When measuring precisely from a burret, a curve (meniscus) appears at the top you're
trying to measure from. How do you know where to read your measurement from? -
Answer-✅Always read from the bottom of a meniscus
/.How do we find the volume of fluid used when dispensing fluid from a burret? -
Answer-✅The volume used is the difference between the final volume and initial
volume.
V.used = V.final - V.initial
/.In lab five, titled "titrations, accuracy and precision" we determine how many liters of
one reagent it took to trigger the die effect which stains everything pink. What was the
purpose of this? - Answer-✅If we know how many liters (V.used) it took to reach
