Chemistry
posted by Jake .
PreLab Questions
Data:
[mass of copper wire]
0.738 g
[standard solutions]
solution 1: 0.738 g of copper wire dissolved in 50.00 mL solution
solution 2: 1:2 dilution of solution 1
solution 3: 1:4 dilution of solution 1
[absorbance data at lambda(max)]
solution 1: 0.740
solution 2: 0.365
solution 3: 0.195
[least squares analysis of these data pieces]
slope: 49.458
yintercept: 0.0075
A brass sample of mass 0.643 g was dissolved to make 50.00 mL of solution, which was found to have an absorbance of 0.589 at lambda(max).
Questions:
1) Calculate the concentrations of the three standard solutions (in g/mL).
solution 1: 0.738 g / 50.00 mL = 0.0148 g/mL
solution 2: 0.0148 g/mL / 2 = 0.740 g/mL
solution 3: 0.740 g/mL / 2 = 0.370 g/mL
2) If the concentrations are in units of g/mL, what are the units for the slope?
If absorbance (A) is graphed against concentration (C) then, using the least squares method, the bestfit straight line through the data will be:
A = mC + b
m (slope) = delta y / delta x = delta A / delta C
A is dimensionless. C has units of g/mL. Therefore, the slope for the data presented above is 49.458 (g/mL)^(1).
3) What are the units for the yintercept?
The yintercept (b) is found when concentration is 0. This yield only a numerical value for A without any units.
Therefore, the yintercept for the data presented above is already correct as 0.0075.
4) Calculate the percent copper in the brass sample.
This is where I'm stuck. I have no idea how to use the absorbances of the various solutions to find the percent copper in the brass sample.
The only step I'm fairly certain about is:
% copper in brass = (mass of copper in brass sample) / (mass of brass sample) *100%
% copper in brass = (mass of copper in brass sample) / (0.643 g) *100%
Any feedback regarding my work for the first 3 questions and any help on the 4th question is greatly appreciated. Thanks in advance.

I assume you have drawn a graph to find the straight line. I also assume you have measured the absorbance of one or more of the brass samples. Using A from the unknown sample, look at the graph and convert A to C. C will be in g/mL. Use that to convert g/mL to grams of the sample, then calculate % Cu in the usual manner. There is insufficient data and/or explanation to comment on the other parts.
Respond to this Question
Similar Questions

Chemistry
In a laboratory, a student studies the absorption and transmission of light in order to analyze copper in brass and determine its percentage within the brass sample. He determines the amount of light absorbed by a sample by measuring … 
Chemistry 114
Write the balanced ionic equations for the following precipitations and complex forming reactions: a) AgNO3 solution + copper sulphate solution b) copper sulphate solution + lead nitrate solution c)CoCl2 solution + conc. HCl d) Zinc … 
Chemistry
An aqueous solution of copper (I) chloride is 15.7% by mass copper (I) chloride. Copper (I) is 35.8% by mass chlorine. If the solution has a density of 1.045 g/cm³, how many gallons of solution contain 2.3 kg of copper? 
Chemistry
An aqueous solution of copper (I) chloride is 15.7% by mass copper (I) chloride. Copper (I) is 35.8% by mass chlorine. If the solution has a density of 1.045 g/cm³, how many gallons of solution contain 2.3 kg of copper? 
Chemistry
An aqueous solution of copper (I) chloride is 15.7% by mass copper (I) chloride. Copper (I) is 35.8% by mass chlorine. If the solution has a density of 1.045 g/cm³, how many gallons of solution contain 2.3 kg of copper? 
Chemistry
An aqueous solution of copper (I) chloride is 15.7% by mass copper (I) chloride. Copper (I) is 35.8% by mass chlorine. If the solution has a density of 1.045 g/cm³, how many gallons of solution contain 2.3 kg of copper? 
chemistry university
A 179 mL solution of a copper complex with a molecular weight of 491.9 g mol1 was made. The absorbance of the solution at 638 nm wavelength was 0.376 using a 1 cm cuvette. It is known that this copper complex has a molar absorptivity … 
chem
A student based the analysis of Cu(II) in a sample on the formation of the blue complex [Cu(H2O)6]+2. A standard solution was made when 1.276g of pure copper wire (MM= 63.546g/mol) was weighed, dissolved in concentrated HNO3, and diluted … 
chemistry
You have been asked to do a dilution of a copper sulfate solution. The solution to be diluted is 2.88 M copper sulfate. What volume of the 2.88 M copper sulfate is required to make 250 mL of 1.03 M copper sulfate solution? 
Chemistry
1) If I add 10 grams of salt into 0.1 L of water, what is the molarity of the solution?