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blahhhhh12345678

How many molecules of H2O are there in 1.0 g of H2O?

  • one year ago
  • one year ago

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  1. dimensionx
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    in 1.0 grams of H2O. okay so.. You are given grams (mass). To go from mass to molecules, you have to convert: Mass -> Moles -> Molecules. To go from mass to moles, Divide by the molecular weight. To go from moles to molecules, multiply by 6.02 x 10^23.

    • one year ago
  2. abb0t
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    convert to moles. then use avogradro's number \(6.022 \times 10^{23}\frac{ atoms }{ mol }\)

    • one year ago
  3. blahhhhh12345678
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    I do not know how to do this ..

    • one year ago
  4. dimensionx
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    Sure you do ;) Let's take it step by step. You are given 1 gram of H2O, and need to divide this by the molecular weight. The molecular weight can be found by adding up all the individual masses of the atoms. How many atoms of Hydrogen are in H2O? How many atoms of Oxygen are in H2O? Multiply the number of atoms of Hydrogen by the atomic mass of hydrogen. Multiply the number of atoms of Oxygen by the atomic mass of oxygen. Add these two values together, what do you get?

    • one year ago
  5. blahhhhh12345678
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    2 atoms in Hydrogen and 1 atom of Oxygen. atomic mass of hydrogen is 1 2*1=1 atomic mass of oxygen is 15.9994 15.994*1=15.9994 Added together is 16.9994

    • one year ago
  6. Mertsj
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    Do you have it now? Or do you still need help?

    • one year ago
  7. blahhhhh12345678
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    I don't know if 16.9994 is the answer?

    • one year ago
  8. Mertsj
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    Hang on. I'll figure it out

    • one year ago
  9. blahhhhh12345678
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    Okay thank you

    • one year ago
  10. Mertsj
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    No. Obviously no. It's way too small.

    • one year ago
  11. blahhhhh12345678
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    I have no clue what I am doing

    • one year ago
  12. Mertsj
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    Do you know what a mole is?

    • one year ago
  13. blahhhhh12345678
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    Not really

    • one year ago
  14. Mertsj
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    That might be your trouble. A mole of any compound or element is the molecular weight in grams. So if you had a scale and wanted to weigh out a mole of water, you would weigh out 18 g because 2H=2, O = 16 and the molecular weight is 18

    • one year ago
  15. Mertsj
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    Do you understand that?

    • one year ago
  16. blahhhhh12345678
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    No, I am so sorry

    • one year ago
  17. Mertsj
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    Do you know how to find molecular weight?

    • one year ago
  18. blahhhhh12345678
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    I looked it up online

    • one year ago
  19. Mertsj
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    So I take that to be a yes?

    • one year ago
  20. Mertsj
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    Do you have a periodic table?

    • one year ago
  21. blahhhhh12345678
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    I looked up the weight online. and I do, yes

    • one year ago
  22. Mertsj
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    Find the molecular weight of HCl

    • one year ago
  23. blahhhhh12345678
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    36.46094

    • one year ago
  24. Mertsj
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    So a mole of HCl is 36.46094 grams.

    • one year ago
  25. Mertsj
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    Now here is the next important point: a mole of "stuff" has 6.023 x 10^23 molecules in it.

    • one year ago
  26. Mertsj
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    That's Avagadro's number. That is something you cannot reason out you have to learn it.

    • one year ago
  27. Mertsj
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    So lets say I have some carbon. A mole of carbon is 12 grams. I have 24 grams. How many moles is that?

    • one year ago
  28. blahhhhh12345678
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    12

    • one year ago
  29. blahhhhh12345678
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    2

    • one year ago
  30. Mertsj
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    Yes. Good. Now remember each mole is 6.023 x 10^23 molecules so how many molecules of carbon do I have?

    • one year ago
  31. blahhhhh12345678
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    I suppose I do not understand how 6.023 X 10^23 works because if there are 2 moles how exactly do I work that in?

    • one year ago
  32. dimensionx
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    If you have 1 mole of "stuff", you have exactly 6.023 x 10^23 molecules. If you have 2 moles of stuff, you would multiply Avogadro's number by 2.

    • one year ago
  33. Mertsj
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    Would you agree that 2 moles is twice as much as 1 mole and so I should multiply by 2?

    • one year ago
  34. dimensionx
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    ^

    • one year ago
  35. Mertsj
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    And \[2(6.023 \times 10^{23)}=12.046 \times 10^{23}\]

    • one year ago
  36. Mertsj
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    So that is the number of molecules in 2 moles of carbon.

    • one year ago
  37. Mertsj
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    Ok. dimensionx will help you now. Too many cooks.

    • one year ago
  38. blahhhhh12345678
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    so we aren't really solving the entire equation because when I did that I had a ginormous number

    • one year ago
  39. dimensionx
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    @Mertsj sorry didn't mean to tread on you xD blahhhh, We are taking it step-by-step ;)

    • one year ago
  40. dimensionx
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    So we know that we have 2 Hydrogens and 1 Oxygen. 2 x Hydrogen 1 x Oxygen 2 x (1) = 2 1 x (16) = 16 Total Molecular Weight = 18

    • one year ago
  41. dimensionx
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    Do you understand how I got this value?

    • one year ago
  42. blahhhhh12345678
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    yes.

    • one year ago
  43. Mertsj
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    So why isn't this problem done yet?

    • one year ago
  44. blahhhhh12345678
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    because I do know how to apply this... I am thinking at 18 is the answer. I am sorry It is just not clicking.

    • one year ago
  45. Mertsj
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    18 grams is 1 mole of water. How many moles is 9 grams of water?

    • one year ago
  46. blahhhhh12345678
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    .5

    • one year ago
  47. Mertsj
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    That would be 9/18 right?

    • one year ago
  48. blahhhhh12345678
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    yes

    • one year ago
  49. Mertsj
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    How many moles is 3 grams of water?

    • one year ago
  50. Mertsj
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    Just tell me the fraction.

    • one year ago
  51. blahhhhh12345678
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    50 g

    • one year ago
  52. Mertsj
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    3/18

    • one year ago
  53. Mertsj
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    I think I see a pattern here: I will draw it because I want you to see it too.

    • one year ago
  54. blahhhhh12345678
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    okay!

    • one year ago
  55. Mertsj
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    |dw:1364947152844:dw|

    • one year ago
  56. Mertsj
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    Do you see the pattern?

    • one year ago
  57. Mertsj
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    How many moles is 1 g water?

    • one year ago
  58. blahhhhh12345678
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    1/18

    • one year ago
  59. Mertsj
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    Very good.

    • one year ago
  60. Mertsj
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    Now we know we have 1/18 mole of water and each mole has 6.023 x 10^23 molecules. So we should multiply 1/18 by 6.023 x 10^23 to find how many molecules we have.

    • one year ago
  61. Mertsj
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    What do you get?

    • one year ago
  62. blahhhhh12345678
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    hang on

    • one year ago
  63. blahhhhh12345678
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    my calculator says 0

    • one year ago
  64. Mertsj
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    |dw:1364947644414:dw|

    • one year ago
  65. blahhhhh12345678
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    I am not getting those numbers..

    • one year ago
  66. Mertsj
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    Type 6.023 divided by 18 equals

    • one year ago
  67. Mertsj
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    Did you get .334611111111 ??

    • one year ago
  68. blahhhhh12345678
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    yes.

    • one year ago
  69. Mertsj
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    That has to be multiplied by 10^23 but that is WAAAAAAY to many zeros so we we just write it: \[.33461111 \times 10^{23}\]

    • one year ago
  70. Mertsj
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    However we have two problems. 1. That is too many significant digits 2. It is not in scientific notation.

    • one year ago
  71. Mertsj
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    So we will round it to .33 So now we have: \[.33 \times 10^{23}\]

    • one year ago
  72. Mertsj
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    But that is still not scientific notation so we will change the .33 to 3.3 but that means we have to change the exponent to 22: \[3.3 \times 10^{22}\]

    • one year ago
  73. blahhhhh12345678
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    Oh! that mas sense

    • one year ago
  74. blahhhhh12345678
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    makes*

    • one year ago
  75. Mertsj
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    Excellent. Now. You can do these problems without really understanding them if you know or can find the right conversion factors and just set it up so that the units turn out right. Do you care to see that?

    • one year ago
  76. blahhhhh12345678
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    Of course!

    • one year ago
  77. Mertsj
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    Start with what is given: 1 g water

    • one year ago
  78. Mertsj
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    \[1 gram water \times \frac{1 mole water}{18g water} \times \frac{6.023 x 10^{23}molecules}{1 mole water}\]

    • one year ago
  79. Mertsj
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    Notice how the units cancel just like numbers and you end up with the number of molecules which is just what the problem asked for.

    • one year ago
  80. Mertsj
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    So if the units come out right, you know you have the numbers right.

    • one year ago
  81. blahhhhh12345678
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    so that would translate to 1 x 18/18= 1 x 6.023x10^23/18?

    • one year ago
  82. Mertsj
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    yes. multiply all the numerators and divide by all the denominators.

    • one year ago
  83. Mertsj
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    But the powers of 10...just leave that til the end.

    • one year ago
  84. blahhhhh12345678
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    when I did that I got a massive number..since I already knew it 3.3x10^22 it made sense how do I figure it out when there is no decimal?

    • one year ago
  85. Mertsj
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    The exponent 22 means move the decimal point 22 places to the right. That's why we use scientific notation. Who wants to mess with all those zeros?

    • one year ago
  86. blahhhhh12345678
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    right, it is like I get it for a second then it all goes away. when I did it using the formula you gave canceling everything out I just got a massive number 334111111111...

    • one year ago
  87. blahhhhh12345678
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    33461*

    • one year ago
  88. Mertsj
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    Exactly. You can enter it into your calculator if you use the EE button to enter the exponent. At least that's the way it is on my calculator. I enter 6.023 EE23 and then it manages the exponents and scientific thing for me.

    • one year ago
  89. blahhhhh12345678
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    Oh I get it! .... so when it is a .xy number you move the decimal and it becomes x.y^22 instead of ^23. and if it turns out a x.y number it stays ^23?

    • one year ago
  90. Mertsj
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    Bingo!!

    • one year ago
  91. blahhhhh12345678
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    OH MY GOD YOU ARE POSITIVELY AMAZING AND YOU HAVE NO IDEA HOW MUCH I APPRECIATE YOUR TIME AND PATIENCE! In the future if I come across a problem like this I would like to run it by you so you check it? Or any other problems that threaten a brain aneurysm lol

    • one year ago
  92. Mertsj
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    Glad to be of service. Remember Jesus said, "Whoever would be great among you, let him be your servant."

    • one year ago
  93. blahhhhh12345678
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    Beautiful. I wouldn't want to call you a servant but, I love to learn from those who know more than I do.

    • one year ago
  94. Mertsj
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    Me too.

    • one year ago
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