Illustrated Guide to Home Chemistry Experiments

144 DIY Science: Illustrated Guide to Home Chemistry Experiments

TABLE 7-3:

Determine concentration of a solution by visual colorimetry
(unknown solution): observed and calculated data

Item Data

A. initial mass of copper sulfate ____.____ g

B. interpolated mass-to-volume percentage

estimate _________%

C. mass of remaining copper sulfate

____.____ g

d. mass of copper sulfate sample (A–C)

____.____ g

E. actual mass-to-volume percentage ____.____%

f. percentage error

±___.___%

PII: RTA dETERNEmI THE CoNCENTRATIoN
of AN UNkNowN SoLUTIoN

1. 
   

   If you have not already done so, put on your splash
   goggles, gloves, and protective clothing.

   
   


2. 
   

   Use the 5.00 mL pipette to transfer 5.00 mL of distilled
   water into test tube #6.

   
   


3. 
   

   Place a weighing paper on the balance and tare the
   balance to read 0.00 g.

   
   


4. 
   

   Weigh out 2 to 3 g of copper sulfate and record the mass
   to 0.01 g on line A of Table 7-3.

   
   


5. 
   

   Using the spatula, transfer about one quarter of the
   copper sulfate to test tube #6, and swirl the test tube
   until all of the copper sulfate has dissolved.

   
   


6. 
   

   Compare the color of the solution in test tube #6
   against the colors of the solutions in test tubes #1
   through #5. You’ll find it easiest to get an accurate
   comparison if you place a well-lit sheet of white paper
   behind the test tubes.

   
   


7. 
   

   Estimate the concentration of the unknown solution in
   test tube #6 by judging how its color compares to the
   known sample solutions in test tubes #1 through #5.
   For example, you might judge that the color of your
   unknown solution is a bit more than halfway between
   the colors of test tubes # 3 and #4. By interpolation,
   estimate the mass-volume percentage of copper sulfate
   in test tube #6 as closely as possible, and enter that
   value on line B of Table 7-3.
   8. Weigh the remaining copper sulfate and record the mass
   to 0.01 g on line C of Table 7-3.
   9. Determine the mass of the copper sulfate sample that
   you dissolved in test tube #6 and enter the value to 0.01
   g on line D of Table 7-3.
   10. Calculate the actual mass-to-volume percentage for test
   tube #6, and enter that value on line E of Table 7-3.
   11. Calculate the percentage error and enter that value on
   line F of Table 7-3.