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Bölüm-2
60. How many atoms are present in a 75.0 cm sample of
plumber's solder, a lead-tin alloy containing 67% Pb
by mass and having a density of 9.4 g/cm³?
63. Medical experts generally believe a level of 30 µg Pb
per deciliter of blood poses a significant health risk
(1 dl 0.1 L). Express this level (a) in the unit mol.
Pb/L blood; (b) as the number of Pb atoms per milli-
liter blood.
64. During a severe episode of air pollution, the con-
centration of lead in the air was observed to be
3.01 µg Pb/m³. How many Pb atoms would be present
in a 0.500 L sample of this air (the approximate lung
capacity of a human adult)?
67. A solution was prepared by dissolving 2.50 g potas-
sium chlorate (a substance used in fireworks and
flares) in 100.0 mL water at 40 °C. When the solution
was cooled to 20 °C, its volume was still found to be
100.0 mL, but some of the potassium chlorate had
crystallized (deposited from the solution as a solid).
At 40 °C, the density of water is 0.9922 g/mL, and at
20 °C, the potassium chlorate solution had a density
of 1.0085 g/mL.
(a) Estimate, to two significant figures, the mass of
potassium perchlorate that crystallized.
(b) Why can't the answer in (a) be given more
precisely?