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Search for a liquid (solution or polymer) with a density of more than $\pu{1.35 g/cm3}$ and containing only elements with an atomic number less than 9. For example, a saturated solution of sugar in water is $\pu{1.35 g/cm3}$. There are liquids with high density (for example, sulfuric acid), but it contains sulfur with atomic number 16. Liquid polymers known to me have a density of less than $\pu{1.1 g/cm3}$ to $\pu{1.2 g/cm3}$.

Poutnik
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Vladimir Magidenko
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    Can you be more specific? By sugar you mean sucrose? Would honey be ok, or corn syrup? – Buck Thorn Jan 17 '24 at 09:23
  • corn syrup has the same density. I found one substance - nitroglycerin. but it's explosive – Vladimir Magidenko Jan 17 '24 at 09:28
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    Can you elaborate the intended purpose of the solution/liquid with a density greater than $\pu{1.3 g/cm3}$? E.g., trifluoroacetic acid, $\ce{C2HF3O2}$ would fit the requirement ($\rho = \pu{1.489 g/cm3}$ at $\pu{20 ^\circ{}C}$) though definitively requires some precaution to handle. – Buttonwood Jan 17 '24 at 09:33
  • this substance is needed as a sample for testing in CT. Ideally, this substance should be safe to use, inexpensive, transparent, odorless and have a density of more than 1.5. Perfluoropolyether CAS 69991-67-9 is almost suitable, but has too much fluorine and is slightly high in density. I have not found how to dilute it to obtain the desired density. – Vladimir Magidenko Jan 17 '24 at 11:28
  • The density of honey typically ranges between 1.38 and 1.45 kg/L at 20 °C.[43] (Wikipedia) . I assume traces of heavier elements would not matter. – Poutnik Jan 17 '24 at 14:45
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    65-68% HNO3 has density around 1.4 g/mL. 100% around 1.5. – Poutnik Jan 17 '24 at 15:43
  • If it doesn't need to be liquid at room temperature, PET should meet the requirement without even exceeding atomic number 8. – R.. GitHub STOP HELPING ICE Jan 18 '24 at 01:52

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If fully perfluorinated polyether polymers (such as Fomblin® PFPE Lubes from Solvay, density $\pu{1.88-1.90 g/cm3}$) are too dense or contain too much fluorine (how much fluorine is too much?) you might try a polyfluorinated polyether, for instance Galden-H (Density $\pu{1.65 - 1.67 g/cm3}$ from Solvay).

Buck Thorn
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  • I found the density of Galden in an MSDS from Canon (also other websites), not directly from Solvay or PubChem. – Buck Thorn Jan 17 '24 at 13:40
  • I need to get a liquid with an equivalent atomic number less than 7.5. I don’t want to burden you with formulas for calculating the equivalent atomic number, but approximately this is the arithmetic mean of the atomic numbers of the elements included in this substance. Florine-containing liquids suit my density, but have a somewhat high equivalent atomic weight. I need to dilute (dissolve) them with a low atomic number component. or... find another solution to the problem – Vladimir Magidenko Jan 18 '24 at 07:10
  • Computing the equivalent atomic number seems pretty trivial. Just guessing what it is gave me a number very close but perhaps slightly above 7.5 . Unfortunately perfluorinated compounds tend to be immiscible with anything else so finding a solvent to get the average AN of polyfluorinated polyether down does sound like a challenge. Maybe there is a solubility chart somewhere. – Buck Thorn Jan 18 '24 at 07:42
  • To my regret, as I understand it, this class of compounds dissolves (can serve as a solvent) only in fluorinated solvents and the previously proposed corn syrup does not dissolve in it; it matches my atomic number, but has a low density. Maybe there is another solution to this problem. (I'm not a chemistry expert). I will be grateful. – Vladimir Magidenko Jan 18 '24 at 09:50
  • You've set some tight constraints. Excluding fluorine doesn't make it any easier! – Buck Thorn Jan 18 '24 at 11:29
  • You may want to check this post: https://chemistry.stackexchange.com/questions/179885/what-liquid-mixture-has-largest-negative-excess-volume/179973#179973 – Buck Thorn Jan 18 '24 at 15:37