Density of solutions answers
The concentration of solutions is often conveniently described in terms of the solutions’ percentage
composition on a weight basis. For example, a 5% sodium chloride solution contains 5g of sodium
chloride in every 100g of solution (which corresponds to 5g of sodium chloride for every 95 g of water
present).
Prepare solutions of sodium chloride in distilled water consisting of the following percentage by weight:
5%,10%,15%,20%,25%. Prepare 25 g of each solution (you do not have to prepare 100g of each solution
to be able to use the percentage composition). Make the weight determination of solute and solvent to
the nearest milligram.
Using the method described earlier for samples of pure liquids, determine the density of each of your
sodium chloride solutions. Record the temperature of each solution while determining its density.
Construct a graph of the density of your solutions versus the percentage of NaCI the solution contains.
What sort of relationship exists between density and composition?
Use a handbook of chemical data to determine the true density of each of the solutions you prepared.
Calculate the error in each of the densities you determined.
What is the %NaCI density measured at 5,10,15,20 and 25? What is their %error for each?
%NaCI
5
10
15
20
25
Density measured
Temperature
23℃
22℃
23℃
23℃
23℃
Value
1.036g/ml
1.074g/ml
1.112g/ml
1.152g/ml
1.193g/ml
%error
Calculate the percentage by mass of each element present in the following compounds.
Magnesium oxide, MgO
Magnesium nitride, Mg3N2
Suppose 2.033g of magnesium is heated in air. What is the theoretical amount of magnesium oxide that
should be produced?
are you good with chemistry?
A compound containing only carbon and hydrogen is analyzed, and is found to contain 74.88% carbon
on a mass basis. Show how the empirical formula of the compound may be calculated.
If 1.000g of elemental carbon is heated in a stream of hydrogen gas, 1.335g of a compound containing
only carbon and hydrogen is produced. Show how the empirical formula of the compound may be
calculated.
On density determinations paper what did you get for %NaCI density measured 5-25? And what did you
get for the %error 5-25? I’m a bit behind everyone in class because I didn’t have a partner that day.
If you had not added water to remove any Mg3N2 that was present in your example, would your
experimental % Mg have been too high or too low? Show with a calculation how you arrived at your
answer.
Suppose a similar experiment was to be performed, in which you would heat a weighed sample of
calcium metal in a crucible (in place of magnesium).
Calculate the theoretical percentage of calcium in calcium oxide.
If a 1.358g sample of calcium metal was heated in oxygen, what mass of calcium oxide would be
produced?
Pre-lab
Write definitions/explanations of each of the following terms:
a. A hydrated salt
b. An anhydrous salt
Suppose 2.3754g of copper (II) sulfate pentahydrate is heated to drive off the water of
crystallization.
a. Calculate what mass of water would be expected to be released from the salt.
b. Calculate what mass of anhydrous salt will remain.
Pre-lab5
What is a precipitation reaction? Write balanced chemical equations for three examples of
precipitation reactions.
How are the Arrhenius and Bronsted-Lowry definitions of what constitutes an acid and what
constitutes a base similar? How do these definitions differ?
What is a coordination complex? Give two examples from your textbook of important
coordination complexes.
What is meant by a redox reaction? Give two examples, including balanced chemical equations,
of redox reactions. What is meant by a half-reaction for a redox reaction? For the two examples
of redox reactions that you have given, also write the half-reactions, indicating which is the
oxidation and which is the reduction.
Pre-lab6
What is a standard solution of acid or base?
Rather than titrating the active ingredient in an antacid tablet directly with a standard solution
of a strong acid in our buret, in this experiment we first dissolve the antacid tablet in a
measured excess of standard acid, and then titrate(with standard sodium hydroxide solution)
the portion of the acid that was not consumed by the tablet. Explain.
Some of the common bases used as the active ingredient in commercial antacid tablets are
listed below. Calculate the number of milliliters of 0.100 M HCI solution that could be
neutralized by 1.00g of each of these substances. Show your calculations at the bottom of this
page.
a.
b.
c.
d.
CaCo3
NaHCO3
Mg(OH)2
AL(OH)3
Pre-lab7
Write the balanced redox equation for the reaction of iron (II) ion with permanganate ion in
acidic solution.
Another common anaylsis for iron is titration of iron (II) with potassium dichromate,
K2CR2O7. Divide the following reaction into half-reactions, balance the half-reactions, and
combine the balanced half-reactions into the balanced overall equation for the reaction.
Fe^2++Cr2O7^2-+H+ -->Fe^3++H2O
Use a chemical dictionary, handbook, or encyclopedia to list several other uses of potassium
permanganate (other than in the analysis of iron samples as in this experiment).
If 26.23 mL of potassium permanganate solution is required to titrate 1.041 g of ferrous ammonium
sulfate hexahydrate, FeSO4(NH4)2SO46H2O, calculate the molarity of the KMnO4 solution.
If a 2.893-g sample of an unknown containing iron requires 28.45 mL of the permanganate solution
described in pre-laboratory question 3 to reach the endpoint, calculate the % Fe in the unknown.
Pre-lab8
What is the definition of the joule in terms of the basic SI units?
What does the specific heat capacity of a substance or material represent? What are the units of specific
heat capacity?
What does a calorimeter constant represent? What value for the calorimeter constant will be used in
this experiment for a “coffee cup” calorimeter?
If the temperature of 85.2g of water increases from 25.2 temperature to 37.6 temperature, how much
heat was absorbed by the water?
What is the enthalpy change for a reaction, and how does this differ from the experimental heat flow
measured for an experiment involving the reaction.
Use your textbook or a chemical encyclopedia to write a specific definition of the term salt.
What does it mean to say that an ion becomes hydrated when a salt is dissolved in water?
Pre-lab9
Define the following:
a. Limiting reactant
b. Stoichiometry
Magnesium metal reacts with chlorine gas to produce magnesium chloride, MgCI2.
a. Write the balanced chemical equation for the reaction.
b. If 5.00g magnesium is combined with 10.0g of chlorine, show by calculation which substance is
the limiting reactant, and calculate the theoretical yield of magnesium chloride for the reaction.
Describe how you would prepare exactly 500.mL of 1.0M NaOH solution from a 3.0 M stock
NaOH solution. Show all calculations.
Consider the following data table, which is similar to the data you will collect in this experiment.
Complete the entries in the table. On graph paper from the end of this manual, construct a
graph of the data,plotting the temperature change measured for each run versus the number of
moles of substance A used for the run. Use your graph to determine the stoichiometric ratio in
which substances A and B react. Explain your reasoning. Attach your graph to this report page.
Pre-lab10
Given the wavelengths and colors of the major mercury emission lines listed in the introduction
to this experiment, construct a graph (on a sheet of graph paper from the end of this manual)
that will approximate the spectrum to be determined. Lay out the horizontal axis of the graph in
terms of the wavelengths of the lines (in nanometers), and make the vertical axis about 2 inches
high to approximate the appearance of the lines to be measured. Using colored pens that
correspond to those colors listed, sketch in the emission lines. Compare your sketch of the
spectrum to the actual spectrum recorded. Attach your sketch to this page.
a. What are the approximate wavelengths (in nanometers) in the spectrum of visible sunlight
that correspond to the following colors?
Red,yellow,green,blue
b. What are the approximate frequencies (in Hertz,Hz) corresponding to the wavelengths you
have listed?
Red,yellow,green,blue
The spectral lines observed in the visible spectrum of hydrogen arise from transitions from
upper states back to the n=2 principle quantum level. Calculate the predicted wavelengths for
the spectral transitions of the hydrogen atom from the n=6 to n=2, for the n=5 to n=2, for the
n=4 to n=2, and for the n=3 to n=2 levels in atomic hydrogen.
Why is it not possible to so easily interpret the spectrum of a poly-electronic atom (such as
nitrogen in this experiment)?
Hi, do you think you would have time to help me after class on lab density determination?
I’m a bit behind on the lab and didn’t have a partner that day. I just need the density measured and the
error percentages I’ve got the temp and the values. I have lab on Tuesday and Thursdays. Or maybe you
can explain it to me on Monday.
molar mass CuSO4 * 5 H2O = 249.68 g/mol moles CuSO4 * 5 H2O = 2.3754 g / 249.68 =0.0095238 moles H2O lost
= 5 x 0.0095238=0.047619 mass H2O lost = 0.047619 x 18.02 g/mol=0.8581 g mass of anhydrous salt that would
remain = 2.3754 - 0.8581=1.5173 g - See more at:
http://qna.somee.com/threadView_20100928185732AA3OCLj.aspx#sthash.bKrL0B6D.dpuf
You have CuSO4 5H20
63.55g + 32.1g + 64g +10g +80g = 249.65g
H2O = 90g %composition is 90/249.65 = 36.05%
CuSO4 is 100% - 36.05% = 63.95%
2.375 X 0.6395 = 1.52g