Reef Chemistry Question of the Day #232 Black Deposits in Sand

Discussion in 'Reef Chemistry by Randy Holmes-Farley' started by Randy Holmes-Farley, Oct 6, 2017.

  1. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    Reef Chemistry Question of the Day #232

    A friend of yours shows you the underside of his aquarium, looking up at the bottom of his sand bed through the bottom glass from inside his stand. In one section, there is a lot of black coloration.

    What is that black most likely to be?

    A. A heavy metal sulfide
    B. A heavy metal carbonate
    C. Sodium sulfide
    D. Potassium sulfide


    Good luck!





















    .
     
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  2. jsker

    jsker Reefing is all about the adventure R2R Supporter R2R Excellence Award Reef Squad Leader Build Thread Contributor Article Contributor Partner Member 2018

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    Going with B
     
  3. hammysreef

    hammysreef Well-Known Member

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    A
     
  4. IonicBond

    IonicBond Member

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    a heavy metal carbonate
     
  5. SDReefer

    SDReefer Well-Known Member Build Thread Contributor

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    I'm going to guess A.
     
  6. spiraling

    spiraling Well-Known Member Build Thread Contributor

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    google says sulfides are colorless, so I'm going with B
     
  7. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    Don't believe everything you read online. :D
     
  8. IslandLifeReef

    IslandLifeReef Well-Known Member

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    D
     
  9. Scott Campbell

    Scott Campbell Well-Known Member

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    Going with "A" as well.
     
  10. Scarybo

    Scarybo Well-Known Member Partner Member 2018

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    A. And danger if it is disturbed in a closed environment. Rotten Eggs = danger (Had to edit my response. I selected C originally in error)
     
    Last edited: Oct 9, 2017
  11. Sierra_Bravo

    Sierra_Bravo Well-Known Member R2R Supporter Build Thread Contributor

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    That missing goby you never could find again...

    ...or "A"
     
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  12. Surfandturf

    Surfandturf Well-Known Member

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    I'm going to go D
     
  13. AllSignsPointToFish

    AllSignsPointToFish Well-Known Member R2R Supporter Article Contributor

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    Seeing as how C and D are soluble in water, I'm going to guess B. I don't know of any carbonate species offhand that are black.
     
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  14. siggy

    siggy Well-Known Member R2R Supporter Build Thread Contributor Partner Member 2018

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    Randy, when i ordered live live rock, the backside was completely coated with a soft black crust. I assumed it was dead organics (no flow or light) and required scrubbing and curing. IS there any correlation between the two? and if so then "guess" D
     
  15. Jason mack

    Jason mack Monti madness R2R Supporter R2R Excellence Award Reef Squad Build Thread Contributor

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    I’m gonna say D
     
  16. spiraling

    spiraling Well-Known Member Build Thread Contributor

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    how can anything from google be false :eek:

    with a little more google Potassium sulfide readily reacts with water and is rarely a solid, so in a fish tank I'm ruling that out. Sodium sulfide is colorless. I'm ruling out B because you hinted it was wrong. I did find that some metal sulfides are dark -such as a tarnish on silver. ;Bookworm

    A - final answer
     
  17. MnFish1

    MnFish1 Well-Known Member R2R Supporter Build Thread Contributor Partner Member 2018

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    I read an article that said this 'On the other hand, even though the S-- form is only a small fraction of the total, it is also very important as it is this form that precipitates with metals to form the black deposits characteristic of hydrogen sulfide formation in sediments.' so I pick

    A
     
  18. IslandLifeReef

    IslandLifeReef Well-Known Member

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    And the answer is????
     
  19. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    And the answer is...

    What is that black most likely to be?

    A. A heavy metal sulfide

    Hydrogen Sulfide and the Reef Aquarium by Randy Holmes-Farley - Reefkeeping.com
    http://reefkeeping.com/issues/2005-12/rhf/index.php

    Hydrogen sulfide produced in anoxic regions can produce several possible outcomes. One is to diffuse into more oxic (aerobic) regions, even into the water column itself, where it can be toxic to organisms. In the water column it can be oxidized to sulfate or other sulfur species (elemental sulfur (S), sulfite (SO3-) and others; Figure 1, right). Such oxidation reactions are catalyzed both by soluble metals such as iron and by light. Hydrogen sulfide also can combine with metals such as iron (Fe++) to precipitate as black iron sulfide (Figure 1 bottom; FeS and FeS2). This blackness is the telltale sign of hydrogen sulfide formation that can be seen in anoxic seawater sediments, although similar appearing black precipitates may be formed from other materials.
     
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