answers to exam 1

answers to exam 1 - Solutions 1 Solution: Do not get hung...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Solutions 1 Solution: Do not get hung up thinking “Hey, we never did one like this before!” Think in terms of relationships. To Find You need atoms moles and N A moles mass and atomic mass So the problem becomes more clear once you identify the relationships. atoms moles N A atoms grams atomic mass N A So now we know what we are looking for. We need the mass of the iron metal! Let’s see if we can find that from the density. Density has units g/cm 3 . For iron the density is 7. 9 g/cm 3 . How can we use this to get grams? Let the units guide you. To get the mass of iron metal it looks like we just need to multiply density by cm 3 which is a unit of volume. mass g 7. 9 g/cm 3 sphere volume cm 3 7. 9 g/cm 3 4 3 4.0 in 2 2.54 cm/in 3 4338. g Don’t forget the inch to cm conversion! Now that we have the mass we can find moles and atoms. We have already written the formula we need. atoms grams atomic mass N A 4338. g 55. 85 g/mol 6.022 10 23 atoms/mole 4. 678 10 25 atoms 2 Solution: The thin sheet looks like a cylinder that is 1 atom high. The volume is V r 2 h 1. 1 cm 3 where h is the diameter of the atom. We are asked to find the diameter of the thin sheet. d 2 2 h 1. 1 cm 3 The thickness of the thin metal sheet is equal to the diameter of the atom. h 2. 78 Å
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Solving the equation for the diameter of the metal sheet gives d 4 1. 1 cm 3 h 1/2 4 1. 1 cm 3 1 2. 78 Å 1 10 10 m 1m 100 cm 1/2 d 7098. cm Converting to meters gives d 7098. cm 100 cm 70. 98 m 3 Solution: 2AgNO 3 aq Na 2 SO 4 aq Ag 2 SO 4 s 2NaNO 3 aq 4 Solution: The mass listed in the periodic table is an average mass for all of the naturally occurring isotopes of each element. The mass of the isotopes depends mostly on the protons and neutrons. So although telluride has only 52 protons it must have heavier naturally occurring isotopes with more neutrons than the isotopes of iodine. Suppose, as an example, that 6 He atomic number 2 was the only stable isotope of He and 5 Li atomic number 3 was the only stable isotope of lithium. IF this were true, the element He would be heavier than Li. (In real life these are not the most stable isotopes for these elements.) 5 Solution: An amu is an extremely tiny unit of mass. A dime has a mass of about 2.2g The conversion factor between AMU and grams is Avogadros number so we expect a very
Background image of page 2
large number of AMU in a few grams of substance. 2.2 6.0 10 23 1.0 10 24 6 Solution: The result of the addition is Least significant digit 1. 234 .2 3 4 .1 0 1. 568 1.568 which should be rounded to the least significant digit (from the 0.10) to 1.57. Complete the rest of the calculation and round the number to the same number of significant figures as in the least significant number (5 has 1 sig fig so round to 1 place.) 1.085 is the calculator number and that gets rounded to 1 sig figs or 1.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/14/2011 for the course BIOL 1201 taught by Professor Wishtichusen during the Spring '07 term at LSU.

Page1 / 12

answers to exam 1 - Solutions 1 Solution: Do not get hung...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online