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SamusGG
#1 Sep 12 2010 12:24pm
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Hi, guy. I've got some more chemistry questions if youd like to help! If you could explain any of them, that'd help too, thanks :)

1. A hydrogen-filled balloon was ignited and 2.00 g of hydrogen reacted with 16.0 g of oxygen.
How many grams of water vapor were formed? (Assume that water vapor is the only product.)



2. The mass ratio of sodium to fluorine in sodium fluoride is 1.21:1. A sample of sodium fluoride produced 28.2 g of sodium upon decomposition. How much fluorine (in grams) was formed?



3. An automobile gasoline tank holds 20 kg of gasoline. When the gasoline burns, 86 kg of oxygen is consumed and carbon dioxide and water are produced. What is the total combined mass of carbon dioxide and water that is produced?



4. A helium nucleus has two protons and two neutrons. How many electrons would it take to equal the mass of a helium nucleus? (Express your answer using two significant figures.)



5. Silver has only two naturally occurring isotopes. The mass of silver-107 is 106.9051 amu and the mass of silver-109 is 108.9048 amu.
Use the atomic mass of silver to calculate the relative abundance of silver-107. Use the atomic mass of silver to calculate the relative abundance of silver-109.



6. A solution of ammonia and water contains 1.40×10^25 water molecules and 7.00×10^24 ammonia molecules. How many total hydrogen atoms are in this solution?



7. 1 mol of sand grains would cover the state of Texas to several feet. Estimate how many feet by assuming that the sand grains are roughly cube-shaped, each one with an edge length of 0.10 mm . Texas has a land area of 268,601 square miles.



8. If your body develops a charge of -10 (microcoulombs), how many excess electrons has it acquired? (Express your answer using two significant figures)
What is their collective mass? (Express your answer using two significant figures)



9. How many electrons are necessary to produce a charge of -1.1 C? (Express your answer using two significant figures)
What is the mass of this many electrons? (Express your answer using two significant figures)


10. (density of neutron d= 4.0 x 10^14 g/cmcubed) Assuming that a neutron star has the same density as a neutron, calculate the mass in kg of a small piece of a neutron star the size of a spherical pebble with a radius of 0.16 mm. (Express your answer using two significant figures)


11. Factor completely
3x(x – 2)^-5 – 3x^2(x – 2)^-6
Gurby
#2 Sep 12 2010 12:49pm
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1. 18g (2 moles of H + 1 mole of O = 1 mole of H2O, which is 18g/mol)
2. 28.2/1.21 = 23.07g (or in moles: 28.2g Na is 2.564 moles, and 2.564 moles of F wheighs 23.07g)

4. nucleus wheighs 6.695*10^-27 kg which is 7349.67 electrons (2 significant figures as in 7.4*10^3?)
5. 106.9051x + 108.9048(1-x) = 107.8682 --> .99107x + 1.0096(1-x) = 1 --> 0.0096 - 0.01853x = 0 --> x = 0.518 for 107 and 48.2% for 109
6. 2 H per H2O, 3 H per NH3 gives 4.9*10^25 Hs
7. 268.601 mi² = 695.673396 km² or 695,373,396 m². to cover that with sand molecules (each with an area of 10^-8 m²) you'd need 6.95673 * 10^16 molecules. in one mole there are 6.022141 * 10^23 molecules however, so you can do it 8.657 * 10^6 times over. at a height of 1 * 10^-4 mm per molecule that gives a total height of 865.6563 m which is 2840.08 feet.
8. 10*10^-6 / 1.602176 * 10^-19 = 6.2 * 10^13 electrons with a mass of 5.7 * 10^-17 kg.

This post was edited by Gurby on Sep 12 2010 01:16pm
Gurby
#3 Sep 12 2010 01:26pm
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9. 6.9 * 10^18 electrons, they wheigh 6.3 * 10^-12 kg.
10. volume = 6.702 * 10^-2 cm³, wheight = 2.7 * 10^10 kg.

e:

Quote (QQL @ 12 Sep 2010 20:28)
3.  106 kg


that would be my guess as well

This post was edited by Gurby on Sep 12 2010 01:30pm
QQL
#4 Sep 12 2010 01:28pm
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3. 106 kg

11. Factor completely
3x(x – 2)^-5 – 3x^2(x – 2)^-6

lol how is this chem

This post was edited by QQL on Sep 12 2010 01:36pm
tim78
#5 Sep 12 2010 01:40pm
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Quote (QQL @ Sep 12 2010 03:28pm)
3.  106 kg

11. Factor completely
3x(x – 2)^-5 – 3x^2(x – 2)^-6

lol how is this chem


the x stands for ecstasy and the ^ is the advanced symbol for yield.
and a constant number is the # for molecule polarity strength.
SamusGG
#6 Sep 12 2010 03:08pm
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thanks a lot gurby!! and qql

yeah that last one is from my precalc class lol, decided to toss it in. thanks a lot guys :)
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