An orange paint is colored by a mixture of red lead (Pb3O4) and school bus yello

Question

An   orange   paint   is   colored   by   a   mixture   of   red   lead   (Pb3O4)   and   school   bus   yellow  
(PbCrO4),   and   contains   16.18%   Pb   by   weight.  
  
a.       What   is   the   maximum   amount   (in   units   of   g)   that   you   could   put   into   a   swimming  
pool   (3m   x   5m   x   8m)   to   ensure   that   any   lead   leached   into   the   water   would   remain  
below   the   WHO   drinking   water   standard   for   lead   of   10   ppb?  
  
b.       If   the   paint   contains   2.32%   Cr   by   weight,   calculate   the   relative   ratio   of   Pb3O4   and  
PbCrO4.  

Explanation / Answer

a.Volume of tank=3*5*8=120m3

Mass of watre in tank= density*volume=1000*120

=1.2*105 kg

Mass of lead at conc 10 ppb=(1.2*105)*10/109

=0.0012kg

=1.2g

Let m be the mass of paint.

16.18% of m=1.2

m=1.2/0.1618=7.417g

b.Let us consider 100g of paint.

Mass of lead=16.18g

Moles of lead=16.18/207=0.07816moles

Mass of Cr=2.32g

Moles of Cr=2.32/52=0.0446

Moles of PbCrO4=moles of Cr=0.0446mol

Moles of Pb remaining=0.07816-0.0446=0.03356 mol

Moles of Pb3O4=0.03356/3=0.0112

Ratio: Moles of Pb3O4 /Moles of PbCrO4=0.0112/0.0446=0.2511

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.