Chem 160 Lab Final Questions With Complete Solutions
A 7.218 g sample of hydrated CoCl2 is heated. After heating,
the sample weighs 3.939 g.
a. How much water was lost in the process?
b. How much anhydrous salt (CoCl2) is left behind?
c. What is the formula of the hydrate? Correct Answers a.
3.279 g or 0.1821 mol
b. 3.939 g or 0.03034 mol
c. CoCl2 6H2O
A monoprotic acid weighed 0.631 g and required 0.0131 mol of
OH- ions to titrate it. What is its molar mass? Correct Answers
48.2 g/mol
a sample of an unknown metal is placed in a graduated cylinder
containing water. The mass of the sample is 9.752g and its water
displacement is 3.25 mL. What is its density? Correct Answers
3.001 g/ml
A student measured 14.7 cm for "d" (see the illustration in the
procedure). Calculate the mercury-equivalent of this water-level
difference (in mm of Hg). Correct Answers 10.8 mm Hg
A student measures the density of a liquid to be 0.9992 g/ml. If
the true value of the liquid is 0.9874 g.ml, what should the
student report as his %error? Correct Answers 1.181%
A substance is known to have a molar extinction (ε) coefficient
of 18,300 mL·cm-1·mg-1 at its wavelength of maximum
absorption. The absorption of a solution containing this
,substance in a 1-cm sample cell was found to be 0.327 at this
same wavelength. Determine the concentration of the solution.
Correct Answers IDK HOW TO SOLVE FOR C CAUSE IDK
B with A =ebc
a= 0.327, e = 18,300,
accuracy Correct Answers % error
how close your answers are to the target
As you may have noticed, barium sulfate tends to settle at the
bottom of the solution. In addition, once barium sulfate forms in
solution, the particles begin to coalesce (clump together). Millie
the general chemistry student made all of her standard solutions
at the beginning of lab and let them sit before she measured their
turbidity. What kind of error would this settling and clumping of
barium sulfate introduce (i.e. systematic or random)? Explain
your answer. Correct Answers It would be a systemic error
since she didn't follow directions and let her product settle for all
of her solutions
Assume you have access to a balance that can accurately weigh
a sample to the nearest ±0.0001 g. If you used this balance to
obtain the mass of the zinc washers in Part 1, would your results
be more accurate than if you used a balance that was only
accurate to the nearest ±0.001 g? Why or why not? Correct
Answers Yes, because overall your numbers would average out
closer to the expected value
Ava the accident-prone chemistry student accidentally burned
herself when she touched a hot beaker. What should she do?
, Correct Answers Run the burn under cold water, tell her
teacher, and wear gloves next time
By using the general equation for dilution of a fixed amount of
solute, (M1)·(V1) = (M2)·(V2), where M represents
concentration and V represents volume, how much of a solution
of 0.0949 M sodium sulfate would be needed to prepare 10.0
mL of 0.00238 M sodium sulfate? Correct Answers V1= .251
mL
Cale the chemist also performed this lab and when he made his
unknown, he did not mix the solution well and the solution in
the bottom of the flask appeared a darker blue than the solution
at the top of the flask. How would this affect his calculation if he
used the lighter-colored part of solution to determine the mass%
aspartame (i.e. would it be higher, lower, or unchanged)?
Thoroughly explain your answer. Correct Answers It would
have been a lower mass% since the amount wasn't mixed. The
larger amount of aspartame would not have have been measured
since it was at the bottom
Cathy the chemist measures the mass of an empty 50-mL beaker
to be 24.278 g. She then pipets 25.00 mL of an unknown liquid
into the beaker and measures the mass of the beaker + liquid to
be 48.829 g. Based on this data, what should Cathy report the
density of the liquid to be? Correct Answers 0.9820 g/ml
Clarissa the chemist did not heat her salt sample long enough to
drive off all of the hydrated water. Would her calculated number
of water molecules be higher or lower than it should be? Explain
your reasoning. Correct Answers Her water molecules would
A 7.218 g sample of hydrated CoCl2 is heated. After heating,
the sample weighs 3.939 g.
a. How much water was lost in the process?
b. How much anhydrous salt (CoCl2) is left behind?
c. What is the formula of the hydrate? Correct Answers a.
3.279 g or 0.1821 mol
b. 3.939 g or 0.03034 mol
c. CoCl2 6H2O
A monoprotic acid weighed 0.631 g and required 0.0131 mol of
OH- ions to titrate it. What is its molar mass? Correct Answers
48.2 g/mol
a sample of an unknown metal is placed in a graduated cylinder
containing water. The mass of the sample is 9.752g and its water
displacement is 3.25 mL. What is its density? Correct Answers
3.001 g/ml
A student measured 14.7 cm for "d" (see the illustration in the
procedure). Calculate the mercury-equivalent of this water-level
difference (in mm of Hg). Correct Answers 10.8 mm Hg
A student measures the density of a liquid to be 0.9992 g/ml. If
the true value of the liquid is 0.9874 g.ml, what should the
student report as his %error? Correct Answers 1.181%
A substance is known to have a molar extinction (ε) coefficient
of 18,300 mL·cm-1·mg-1 at its wavelength of maximum
absorption. The absorption of a solution containing this
,substance in a 1-cm sample cell was found to be 0.327 at this
same wavelength. Determine the concentration of the solution.
Correct Answers IDK HOW TO SOLVE FOR C CAUSE IDK
B with A =ebc
a= 0.327, e = 18,300,
accuracy Correct Answers % error
how close your answers are to the target
As you may have noticed, barium sulfate tends to settle at the
bottom of the solution. In addition, once barium sulfate forms in
solution, the particles begin to coalesce (clump together). Millie
the general chemistry student made all of her standard solutions
at the beginning of lab and let them sit before she measured their
turbidity. What kind of error would this settling and clumping of
barium sulfate introduce (i.e. systematic or random)? Explain
your answer. Correct Answers It would be a systemic error
since she didn't follow directions and let her product settle for all
of her solutions
Assume you have access to a balance that can accurately weigh
a sample to the nearest ±0.0001 g. If you used this balance to
obtain the mass of the zinc washers in Part 1, would your results
be more accurate than if you used a balance that was only
accurate to the nearest ±0.001 g? Why or why not? Correct
Answers Yes, because overall your numbers would average out
closer to the expected value
Ava the accident-prone chemistry student accidentally burned
herself when she touched a hot beaker. What should she do?
, Correct Answers Run the burn under cold water, tell her
teacher, and wear gloves next time
By using the general equation for dilution of a fixed amount of
solute, (M1)·(V1) = (M2)·(V2), where M represents
concentration and V represents volume, how much of a solution
of 0.0949 M sodium sulfate would be needed to prepare 10.0
mL of 0.00238 M sodium sulfate? Correct Answers V1= .251
mL
Cale the chemist also performed this lab and when he made his
unknown, he did not mix the solution well and the solution in
the bottom of the flask appeared a darker blue than the solution
at the top of the flask. How would this affect his calculation if he
used the lighter-colored part of solution to determine the mass%
aspartame (i.e. would it be higher, lower, or unchanged)?
Thoroughly explain your answer. Correct Answers It would
have been a lower mass% since the amount wasn't mixed. The
larger amount of aspartame would not have have been measured
since it was at the bottom
Cathy the chemist measures the mass of an empty 50-mL beaker
to be 24.278 g. She then pipets 25.00 mL of an unknown liquid
into the beaker and measures the mass of the beaker + liquid to
be 48.829 g. Based on this data, what should Cathy report the
density of the liquid to be? Correct Answers 0.9820 g/ml
Clarissa the chemist did not heat her salt sample long enough to
drive off all of the hydrated water. Would her calculated number
of water molecules be higher or lower than it should be? Explain
your reasoning. Correct Answers Her water molecules would
