Paint is generally 25% pigment, with the rest being solvent, resin, and other ad
ID: 491340 • Letter: P
Question
Paint is generally 25% pigment, with the rest being solvent, resin, and other additives. If you determine that 45% of the pigment in a mixed white paint is lead(II) carbonate, what mass of lead(II) carbonate is there in an 80 g tube of paint? A good qualitative test for titanium(IV) oxide is that when the compound reacts with hydrogen peroxide and sulfuric acid, the solution turns orange-red. What information would you need to know to use this test to determine how much titanium(IV) oxide is in a paint with this pigment? What instrument would you need? The currently preferred method of identifying cations in paint is a handheld X-ray fluorescence (XRF) analyzer that uses a beam of light to evaluate the surface of a painting. Explain why this method might be better for paintings than the type of tests done in lab.Explanation / Answer
(8)
Paint contains 25% pigment, so 80 g paint contains 20 g pigment.
Pigment contains 45% lead carbonate, so 20 g pigment contains 9 g lead carbonate.
(9)
Titration expermient needs to be performed where determination of end point is done. The apparatus needed for this includes a burette, a flask, an indicator dye.
(10)
The reason is that the laboratory methods for qualitative determination do not give good results if the analyte is present in extremely low concentrations. The XRF analyzer technique is more sensitive than the lab tests.
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