Is Fe2+ + 2e- = Fe an oxidation or reduction

The unit cell for cr2o3 has hexagonal symmetry with lattice parameters a = 0.4961 nm and c = 1.360 nm. If the density of this ma

IRINA_888 [86]

To calculate the packing factor, first calculate the area and volume of unit cell.

Area is calculated as:

$A=6R^{2}\sqrt{3}$

Here, R is radius and is related to a as follows:

$R=\frac{a}{2}$

Putting the value in expression for area,

$A=6(\frac{a}{2})^{2}\sqrt{3}=1.5a^{2}\sqrt{3}$

The value of a is 0.4961 nm

Since, $1 nm=10^{-7}cm$

Thus, $0.4961 nm=4.961\times 10^{-8} cm$

Putting the value,

$Area=1.5(4.961\times 10^{-8}cm)^{2}\sqrt{3}=6.39\times 10^{-15}cm^{2}$

Now, volume can be calculated as follows:

$V=Area\times c$

The value of c is 1.360 nm or $1.360\times 10^{-7} cm$

Putting the value,

$V=(6.39\times 10^{-15}cm^{2})\times (1.360\times 10^{-7} cm)=8.7\times 10^{-22}cm^{3}$

now, number of atom in unit cell can be calculated by using the following formula:

$n=\frac{\rho N_{A}V_{c}}{A}$

Here, A is atomic mass of $Cr_{2}O_{3}$ is 151.99 g/mol.

Putting all the values,

$n=\frac{(5.22 g/cm^{3})(6.023\times 10^{23} mol^{-1})(8.7\times 10^{-22}cm^{3})}{(151.99 g/mol)}\approx 18$

Thus, there will be 18 $Cr_{2}O_{3}$ units in 1 unit cell.

Since, there are 2 Cr atoms and 3 oxygen atoms thus, units of chromium and oxygen will be 2×18=36 and 3×18=54 respectively.

The atomic radii of $Cr^{3+}$ and $O^{2-}$ is 62 pm and 140 pm respectively.

Converting them into cm:

$1 pm=10^{-10}cm$

Thus,

$r_{Cr^{3+}}=6.2\times 10^{-9}cm$

and,

$r_{O^{2-}}=1.4\times 10^{-8}cm$

Volume of sphere will be sum of volume of total number of cations and anions thus,

$V_{S}=V_{Cr^{3+}}+V_{O^{2-}}$

Since, volume of sphere is $V=\frac{4}{3}\pi r^{3}$ ,

$V_{S}=36\left ( \frac{4}{3}\pi (r_{Cr^{3+})^{3}} \right )+54\left ( \frac{4}{3}\pi (r_{O^{2-})^{3}} \right )$

Putting the values,

$V_{S}=36\left ( \frac{4}{3}(3.14) (6.2\times 10^{-9} cm)^{3}} \right )+54\left ( \frac{4}{3}(3.14) (1.4\times 10^{-8} cm)^{3}} \right )=6.6\times 10^{-22}\times 10^{-8}cm^{3}$

The atomic packing factor is ratio of volume of sphere and volume of crystal, thus,

$packing factor=\frac{V_{S}}{V_{C}}=\frac{6.6\times 10^{-22}cm^{3}}{8.7\times 10^{-22}cm^{3}}=0.758$

Thus, atomic packing factor is 0.758.

6 0

3 years ago

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PLEASE ANSWER ASAP What does a ball falling through the air have?

max2010maxim [7]

Answer:

Kinetic energy because it has motion, Potential energy bc there is still more distance to fall and heat energy bc there is heat from friction.

Explanation:

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3 years ago

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The smallest unit of an element

Sliva [168]

The smallest unit of an element that retains the chemical and physical properties of an element is an Atom.

8 0

3 years ago

Why are elements with high electron affinities also the most electronegative?

melamori03 [73]

Explanation:

Electron affinity is the energy released in adding an electron to a neutral atom in the gas phase. This is a measure of the readiness of an atom to gain an electron. When an atom gains an electron readily, it has a high electron affinity.

The electronegativity is a property that combines the ability of its atom to lose and gain electrons.
It is expressed as a number that describes the relative tendency with which the atoms of the element attracts valence electrons in a chemical bond.

Therefore , we see that an atom with a high electronegativity will have a very high affinity to gain electrons. It will want to attract electrons by all means to itself.

Learn more:

Electronegativity brainly.com/question/11932624

#learnwithBrainly

7 0

4 years ago

Define the term half-life and illustrate it with an example.

drek231 [11]

Answer:

The half-life is defined as, the substance which are radioactive in the nature and it is charactertics constant. It basically measured the duration or time, when the quantity of the substance are reduced by the half with decay consequences. This process is defined the term half-life.

For example - The life of the medical are basically referred to the half life of the biological to drugs and other reactions in the body of human.

6 0

3 years ago