وين السؤال هنا

2.


Use information on the endpapers of this book to calculate

the average density of the Earth. Where does the

value

fit among those listed in Tables 1.5 and 14.1? Look

up the density of a typical surface rock like granite in another

source and compare the density of the Earth to it.

3.


The standard kilogram is a platinum–iridium cylinder

39.0 mm in height and 39.0 mm in diameter. What is the

density of the material?

4.


A major motor company displays a die-cast model of its

fi

rst automobile, made from 9.35 kg of iron. To celebrate

its hundredth year in business, a worker will recast the

model in gold from the original dies. What mass of gold is

needed to make the new model?

5.



What mass of a material with density & is required to make

a hollow spherical ****l having inner radius

r 1 and outer

radius

r 2?

6.


Two spheres are cut from a certain uniform rock. One has

radius 4.50 cm. The mass of the other is

five times greater.

Find its radius.

7.


Calculate the mass of an atom of (a) helium,

(b) iron, and (c) lead. Give your answers in grams. The

atomic masses of these atoms are 4.00 u, 55.9 u, and 207 u,

respectively.

8.



The paragraph preceding Example 1.1 in the ****

mentions that the atomic mass of aluminum is

27.0u

$ 27.0 ! 1.66 ! 10"27 kg. Example 1.1 says that

27.0 g of aluminum contains 6.02

! 1023 atoms. (a) Prove

that each one of these two statements implies the other.

(b)

What If ? What if it’s not aluminum? Let M represent

the numerical value of the mass of one atom of any chemical

element in atomic mass units. Prove that

M grams of the

substance contains a particular number of atoms, the same

number for all elements. Calculate this number precisely

from the value for u quoted in the ****. The number of

atoms in

M grams of an element is called Avogadro’s number

N


A. The idea can be extended: Avogadro’s number of molecules

of a chemical compound has a mass of

M grams,

where

M atomic mass units is the mass of one molecule.

Avogadro

’s number of atoms or molecules is called one

mole,


symbolized as 1 mol. A periodic table of the elements,

as in Appendix C, and the chemical formula for a compound

contain enough information to

find the molar mass

of the compound. (c) Calculate the mass of one mole of

water, H

2O. (d) Find the molar mass of CO2.

9.


On your wedding day your lover gives you a gold ring of

mass 3.80 g. Fifty years later its mass is 3.35 g. On the average,

how many atoms were abraded from the ring during

each second of your marriage? The atomic mass of gold is

197 u.

10.


A small cube of iron is observed under a microscope. The

edge of the cube is 5.00

! 10"6 cm long. Find (a) the

mass of the cube and (b) the number of iron atoms in the

cube. The atomic mass of iron is 55.9 u, and its density is

7.86 g/cm

3.

11.



A structural I beam is made of steel. A view of its crosssection

and its dimensions are shown in Figure P1.11. The

density of the steel is 7.56

! 103 kg/m3. (a) What is the

mass of a section 1.50 m long? (b) Assume that the atoms

are predominantly iron, with atomic mass 55.9 u. How

many atoms are in this section?

15.0 cm

1.00 cm

1.00 cm

36.0 cm

Figure P1.11

12.



A child at the beach digs a hole in the sand and uses a pail

to

fill it with water having a mass of 1.20 kg. The mass of

one molecule of water is 18.0 u. (a) Find the number of

water molecules in this pail of water. (b) Suppose the

quantity of water on Earth is constant at 1.32

! 1021 kg.

How many of the water molecules in this pail of water are

likely to have been in an equal quantity of water that once

fi

lled one particular claw print left by a Tyrannosaur hunting

on a similar beach?