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 Article Contributor Expert 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 Staff Member Team R2R R2R Supporter R2R Excellence Award Partner Member 2018 Article Contributor Build Thread Contributor

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    Going with B
     
  3. hammysreef

    hammysreef Member

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    A
     
  4. IonicBond

    IonicBond Member

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    a heavy metal carbonate
     
  5. SDReefer

    SDReefer Active Member SDMA 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 Article Contributor Expert Contributor

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

    IslandLifeReef Active Member

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    D
     
  9. Scott Campbell

    Scott Campbell Active Member

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    Going with "A" as well.
     
  10. Scarybo

    Scarybo Active 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 Valuable Member R2R Supporter Article Contributor Build Thread 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 Which way do I go R2R Supporter R2R Excellence Award Partner Member 2018 Build Thread Contributor

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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 Reef Squad R2R Excellence Award Reef Tank 365 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 Valuable Member R2R Supporter Partner Member 2018 Build Thread Contributor

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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 Active 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 Article Contributor Expert 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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