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blahhhhh12345678

  • 2 years ago

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

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  1. dimensionx
    • 2 years ago
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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.

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

  3. blahhhhh12345678
    • 2 years ago
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    I do not know how to do this ..

  4. dimensionx
    • 2 years ago
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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?

  5. blahhhhh12345678
    • 2 years ago
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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

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

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

  8. Mertsj
    • 2 years ago
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    Hang on. I'll figure it out

  9. blahhhhh12345678
    • 2 years ago
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    Okay thank you

  10. Mertsj
    • 2 years ago
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    No. Obviously no. It's way too small.

  11. blahhhhh12345678
    • 2 years ago
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    I have no clue what I am doing

  12. Mertsj
    • 2 years ago
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    Do you know what a mole is?

  13. blahhhhh12345678
    • 2 years ago
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    Not really

  14. Mertsj
    • 2 years ago
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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

  15. Mertsj
    • 2 years ago
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    Do you understand that?

  16. blahhhhh12345678
    • 2 years ago
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    No, I am so sorry

  17. Mertsj
    • 2 years ago
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    Do you know how to find molecular weight?

  18. blahhhhh12345678
    • 2 years ago
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    I looked it up online

  19. Mertsj
    • 2 years ago
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    So I take that to be a yes?

  20. Mertsj
    • 2 years ago
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    Do you have a periodic table?

  21. blahhhhh12345678
    • 2 years ago
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    I looked up the weight online. and I do, yes

  22. Mertsj
    • 2 years ago
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    Find the molecular weight of HCl

  23. blahhhhh12345678
    • 2 years ago
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    36.46094

  24. Mertsj
    • 2 years ago
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    So a mole of HCl is 36.46094 grams.

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

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

  27. Mertsj
    • 2 years ago
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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?

  28. blahhhhh12345678
    • 2 years ago
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    12

  29. blahhhhh12345678
    • 2 years ago
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    2

  30. Mertsj
    • 2 years ago
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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?

  31. blahhhhh12345678
    • 2 years ago
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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?

  32. dimensionx
    • 2 years ago
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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.

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

  34. dimensionx
    • 2 years ago
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    ^

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

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

  37. Mertsj
    • 2 years ago
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    Ok. dimensionx will help you now. Too many cooks.

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

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

  40. dimensionx
    • 2 years ago
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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

  41. dimensionx
    • 2 years ago
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    Do you understand how I got this value?

  42. blahhhhh12345678
    • 2 years ago
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    yes.

  43. Mertsj
    • 2 years ago
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    So why isn't this problem done yet?

  44. blahhhhh12345678
    • 2 years ago
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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.

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

  46. blahhhhh12345678
    • 2 years ago
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    .5

  47. Mertsj
    • 2 years ago
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    That would be 9/18 right?

  48. blahhhhh12345678
    • 2 years ago
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    yes

  49. Mertsj
    • 2 years ago
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    How many moles is 3 grams of water?

  50. Mertsj
    • 2 years ago
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    Just tell me the fraction.

  51. blahhhhh12345678
    • 2 years ago
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    50 g

  52. Mertsj
    • 2 years ago
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    3/18

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

  54. blahhhhh12345678
    • 2 years ago
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    okay!

  55. Mertsj
    • 2 years ago
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    |dw:1364947152844:dw|

  56. Mertsj
    • 2 years ago
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    Do you see the pattern?

  57. Mertsj
    • 2 years ago
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    How many moles is 1 g water?

  58. blahhhhh12345678
    • 2 years ago
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    1/18

  59. Mertsj
    • 2 years ago
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    Very good.

  60. Mertsj
    • 2 years ago
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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.

  61. Mertsj
    • 2 years ago
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    What do you get?

  62. blahhhhh12345678
    • 2 years ago
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    hang on

  63. blahhhhh12345678
    • 2 years ago
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    my calculator says 0

  64. Mertsj
    • 2 years ago
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    |dw:1364947644414:dw|

  65. blahhhhh12345678
    • 2 years ago
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    I am not getting those numbers..

  66. Mertsj
    • 2 years ago
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    Type 6.023 divided by 18 equals

  67. Mertsj
    • 2 years ago
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    Did you get .334611111111 ??

  68. blahhhhh12345678
    • 2 years ago
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    yes.

  69. Mertsj
    • 2 years ago
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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: \[.33461111 \times 10^{23}\]

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

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

  72. Mertsj
    • 2 years ago
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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: \[3.3 \times 10^{22}\]

  73. blahhhhh12345678
    • 2 years ago
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    Oh! that mas sense

  74. blahhhhh12345678
    • 2 years ago
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    makes*

  75. Mertsj
    • 2 years ago
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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?

  76. blahhhhh12345678
    • 2 years ago
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    Of course!

  77. Mertsj
    • 2 years ago
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    Start with what is given: 1 g water

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

  79. Mertsj
    • 2 years ago
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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.

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

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

  82. Mertsj
    • 2 years ago
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    yes. multiply all the numerators and divide by all the denominators.

  83. Mertsj
    • 2 years ago
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    But the powers of 10...just leave that til the end.

  84. blahhhhh12345678
    • 2 years ago
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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?

  85. Mertsj
    • 2 years ago
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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?

  86. blahhhhh12345678
    • 2 years ago
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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...

  87. blahhhhh12345678
    • 2 years ago
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    33461*

  88. Mertsj
    • 2 years ago
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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.

  89. blahhhhh12345678
    • 2 years ago
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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?

  90. Mertsj
    • 2 years ago
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    Bingo!!

  91. blahhhhh12345678
    • 2 years ago
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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

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

  93. blahhhhh12345678
    • 2 years ago
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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.

  94. Mertsj
    • 2 years ago
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    Me too.

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