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MidTrm-PrepQs

# MidTrm-PrepQs - CHAPTER 2 Q1 How many grams are there in a...

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CHAPTER 2 Q1- How many grams are there in a one amu of a material? A1- In order to determine the number of grams in one amu of material, appropriate manipulation of the amu/atom, g/mol, and atom/mol relationships is all that is necessary, as # g/amu = 1 mol 6.023 x 10 23 atoms 1 g/mol 1 amu/atom = 1.66 x 10 -24 g/amu Q2- Show the electron configuration for Fe 3+ , Cu + , and S 2- A2- Fe 3+ - 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 Cu + - 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 S 2- - 1s 2 2s 2 2p 6 3s 2 3p 6 Q3. Why water expands on freezing? A3. The geometry of the H 2 O molecules, which are hydrogen bonded to one another, is more restricted in the solid phase than for the liquid. This results in a more open molecular structure in the solid, and a less dense solid phase. CHAPTER 3 Q1- What is the difference between a crystal structure and a crystal system? A1- A crystal structure is described by both the geometry of, and atomic arrangements within, the unit cell, whereas a crystal system is described only in terms of the unit cell geometry. For example, face-centered cubic and body-centered cubic are crystal structures that belong to the cubic crystal system. Q2- Show that the ideal c / a ratio for HCP is 1.633. A2- A sketch of one-third of an HCP unit cell is shown below. Consider the tetrahedron labeled as JKLM , which is reconstructed as

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The atom at point M is midway between the top and bottom faces of the unit cell--that is MH = c / 2. And, since atoms at points J , K , and M , all touch one another, JM = JK = 2R = a where R is the atomic radius. Furthermore, from triangle JHM , (JM ) 2 = ( JH ) 2 + ( MH ) 2 , or a 2 = (JH ) 2 + c 2 2 Now, we can determine the JH length by consideration of triangle JKL , which is an equilateral triangle, cos 30 ° = a/ 2 JH = 3 2 , and JH = a 3 Substituting this value for JH in the above expression yields a 2 = a 3 2 + c 2 2 = a 2 3 + c 2 4 and, solving for c / a c a = 8 3 = 1.633 Q3- Calculate the unit cell volume for Co which has an HCP crystal structure.
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MidTrm-PrepQs - CHAPTER 2 Q1 How many grams are there in a...

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