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13 Dec 2019

Suppose you have a copper nitrate solid. You are not sure, however, if the solid is copper (I) nitrate, CuNO3, or copper (II) nitrate, Cu(NO3)2. You dissolve a 0.1015 gram sample of this solid in water and nitric acid and then dilute it to a final volume of 100. mL. You treat a sample of this solution with ammonia and then measure the absorbance of the resulting blue-violet solution. By comparing the absorbance of this solution to that of standard copper solutions you determine the concentration of Cu2+ to be 5.41 x 10-3 M. Use this information (and the hints below) to find the mole ratio of Cu : NO3 and determine the chemical formula for the original copper nitrate sample.1) Determine the total number of moles of Cu present in the original solid sample knowing that the solid was dissolved in enough water to make 100 mL of solution. Remember the molarity of this solution was experimentally determined using spectroscopy. 2) Calculate the mass of copper present in the original solid sample.3) Calculate the mass of nitrate ions present in the original solid sample of copper nitrate by mass difference.4) Determine the moles of NO3 present in the solid sample.5) Determine the Cu:NO3 mole ratio and figure out the chemical formula of the compound.Please label each part so I know what work goes with which part of the question.

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Lelia Lubowitz
Lelia LubowitzLv2
17 Dec 2019

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Related questions


You weigh out a piece of copper wire (AW=63.546):
Weight of copper standard....................0.2437 g
Dissolve it in a slight excess of concentrated nitric acid. Add tothe solution the required amount of concentrated ammonia. Transferthis quantitatively to a 100 mL volumetric flask, dilute to volume,and mix thoroughly.
10.00 mL of this is pipetted into a 100 mL volumetric flask, therequired amount of concentrated ammonia is added and diluted tovolume. This is Standard 1.
Standard 2 is made by pipetting 20 mL of the original solution intoa 100 mL volumetric flask, adding the required amount of ammonia,NH3, and diluting to volume.
Using the same cuvet for all measurements, the following %T's wereobtained at 625 nm:
Blank 101.3 %
Standard 1 61.0 %
Standard 2 35.5 %

Next:
You pipetted 10 mL of UNKNOWN into a 100 mL volumetric flask. Therequired amount of ammonia was added and the mixture diluted tovolume. The %T of this solution was measured at 625 nm, using thesame spectrometer and cuvet as for the standards.
%T unknown.................... 21.4 %
CALCULATE
a) The absorbance of Standard 1 ______________
b) The absorbance of Standard 2 ______________
c) The molarity of Cu in Standard 1 ______________ M
d) The molarity of Cu in Standard 2 ______________ M
e) Ratio: absorbance/molarity Std 1 ______________
f) Ratio: absorbance/molarity Std 2 ______________
g) Average ratio of absorbance/molarity ______________
h) Absorbance of unknown solution ______________
Concentration of copper in unknown...
i) solution as measured in cuvet ______________ M
j) in original solution ______________ M
k) in original solution ______________ w/V%

Finally:
You are given a solid UNKNOWN, containing copper, weighing........0.7937 g.
You dissolve this in concentrated Nitric Acid, HNO3, transferquantitatively to a 100 mL volumetric flask, add the requiredamount of Ammonia, NH3, dilute to volume and mix thoroughly.
This resulting solution is too concentrated and the resulting %Tmeasured in the same cuvet and spectrometer as before gave littleor no transmission (<10%). br="">You are told topipet.................... 16.00 mL
into a 100 mL volumetric flask, add the required amount of ammonia,dilute to volume and mix.
Spectroscopic measurement of this solution gave %T... 35.6 %
CALCULATE:
l) Absorbance of the dilutedsolution....................._____________________
m) The copper concentration in the dilutedsolution...._____________________ M
n) The copper concentration in the originalsolution..._____________________ M
o) The Per Cent copper in the original solidUNKNOWN..._____________________ % Cu

You weigh out a piece of copper wire (AW=63.546):
Weight of copper standard....................0.2437 g
Dissolve it in a slight excess of concentrated nitric acid. Add tothe solution the required amount of concentrated ammonia. Transferthis quantitatively to a 100 mL volumetric flask, dilute to volume,and mix thoroughly.
10.00 mL of this is pipetted into a 100 mL volumetric flask, therequired amount of concentrated ammonia is added and diluted tovolume. This is Standard 1.
Standard 2 is made by pipetting 20 mL of the original solution intoa 100 mL volumetric flask, adding the required amount of ammonia,NH3, and diluting to volume.
Using the same cuvet for all measurements, the following %T's wereobtained at 625 nm:
Blank 101.3 %
Standard 1 61.0 %
Standard 2 35.5 %

Next:
You pipetted 10 mL of UNKNOWN into a 100 mL volumetric flask. Therequired amount of ammonia was added and the mixture diluted tovolume. The %T of this solution was measured at 625 nm, using thesame spectrometer and cuvet as for the standards.
%T unknown.................... 21.4 %
CALCULATE
a) The absorbance of Standard 1 ______________
b) The absorbance of Standard 2 ______________
c) The molarity of Cu in Standard 1 ______________ M
d) The molarity of Cu in Standard 2 ______________ M
e) Ratio: absorbance/molarity Std 1 ______________
f) Ratio: absorbance/molarity Std 2 ______________
g) Average ratio of absorbance/molarity ______________
h) Absorbance of unknown solution ______________
Concentration of copper in unknown...
i) solution as measured in cuvet ______________ M
j) in original solution ______________ M
k) in original solution ______________ w/V%

Finally:
You are given a solid UNKNOWN, containing copper, weighing........0.7937 g.
You dissolve this in concentrated Nitric Acid, HNO3, transferquantitatively to a 100 mL volumetric flask, add the requiredamount of Ammonia, NH3, dilute to volume and mix thoroughly.
This resulting solution is too concentrated and the resulting %Tmeasured in the same cuvet and spectrometer as before gave littleor no transmission (<10%). br="">You are told topipet.................... 16.00 mL
into a 100 mL volumetric flask, add the required amount of ammonia,dilute to volume and mix.
Spectroscopic measurement of this solution gave %T... 35.6 %
CALCULATE:
l) Absorbance of the dilutedsolution....................._____________________
m) The copper concentration in the dilutedsolution...._____________________ M
n) The copper concentration in the originalsolution..._____________________ M
o) The Per Cent copper in the original solidUNKNOWN..._____________________ % Cu

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