2. What combination of physical and mechanical properties would be required for

Question

2. What combination of physical and mechanical properties would be required for the heat shield of the Space Shuttle? a. Low melting temperature and high density b. High melting temperature and low density c. Low stiffness and low density d. High stiffness and high density e. None of the above What material listed below would be a good candidate for the application described in Question #2? a. Covalently bonded material b. lonically bonded material c. Metallically bonded material d. Van der Waals bonded material e. None of the above 4. How many atoms are there in one gram of gold? (at. wt. = 196.97 grams/mole)

Explanation / Answer

2) answer is (B)

Since the temperature is high outside the space shuttle the shield should withstand that temperature therefore the shield material has melting point.

Density is low because less mass or weight is desirable for the space shuttle. High density will increase the weight of the space shuttle.

3) answer is (a)

Covalently bonded materials are best for lightweight and high melting point characteristics.Moreover they are poor conductor of heat.

3) 1 Mole contains 196.97 grams

1 gram will contain 1/196.97 moles

i.e. 1 gram will contain 0.005076 moles

1 Mole contains 6.022 × 10^23 atoms

0.005076 moles will contain 0.005076 × 6.022× 10^ 23 atoms

i.e. 0.005076 moles will contain 3.056 × 10^21 atoms

So, 1 gram contain 3.056×10^21 atoms

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