semiheavy water

{{short description|Chemical compound}}

{{confused|Heavy water}}

{{Chembox

| Verifiedfields = changed

| verifiedrevid = 461766699

| Name = Semiheavy water

| ImageFileL1 = Semiheavy-water-3D-vdW.png

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| ImageSizeL1 = 150

| ImageNameL1 = Spacefill model of water

| ImageFileR1 = Semiheavy water.svg

| ImageSizeR1 = 100

| IUPACName = ({{sup|2}}H{{sub|1}})Water

| OtherNames = Deuterium hydrogen monoxide
Deuterium hydrogen oxide, Water-d{{sub|1}}, Water-d

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| Section1 = {{Chembox Identifiers

| CASNo =14940-63-7

| PubChem = 139859

| ChemSpiderID = 123344

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| ChEBI = 33806

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| Gmelin = 115

| SMILES = [2H]O

| StdInChI = 1S/H2O/h1H2/i/hD

| StdInChIKey = XLYOFNOQVPJJNP-DYCDLGHISA-N

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| Section2 = {{Chembox Properties

| Formula = H{{sup|2}}HO or HDO

| MolarMass = 19.0214 g mol{{sup|−1}}

| Appearance = Very pale blue, transparent liquid, very similar to regular water

| Density = 1.054 g cm{{sup|−3}}

| MeltingPtC = 3.81

| BoilingPtC = 100.74

| Solubility = miscible

| LogP = −0.65

| Viscosity =

| Dipole =

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| Section7 = {{Chembox Hazards

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Semiheavy water is the result of replacing one of the protium (normal hydrogen, {{sup|1}}H) in normal water with deuterium ({{sup|2}}H; or D).{{Cite journal| vauthors = Tashakor S |date=2016-09-28|title= Neutronic Investigation of Semi-Heavy Water Application in Hplwr New Flow Pattern |journal=CNL Nuclear Review|language=en|pages=1–5|doi=10.12943/CNR.2016.00019 |doi-access=free}} It exists whenever there is water with {{sup|1}}H and {{sup|2}}H in the mix. This is because hydrogen atoms ({{sup|1,2}}H) are rapidly exchanged between water molecules. Water with 50% {{sup|1}}H and 50% {{sup|2}}H, is about 50% H{{sup|2}}HO and 25% each of H{{sub|2}}O and {{sup|2}}H{{sub|2}}O, in dynamic equilibrium.{{cite journal | vauthors = Goncharuk VV, Kavitskaya AA, Romanyukina IY, Loboda OA | title = Revealing water's secrets: deuterium depleted water | journal = Chemistry Central Journal | volume = 7 | issue = 1 | pages = 103 | date = June 2013 | pmid = 23773696 | pmc = 3703265 | doi = 10.1186/1752-153X-7-103 | doi-access = free }}

In normal water, about 1 molecule in 3,200 is HDO ({{sup|1}}H{{sup|2}}HO) (one hydrogen in 6,400 is {{sup|2}}H). By comparison, heavy water D{{sub|2}}O or {{sup|2}}H{{sub|2}}O{{Cite web|url=https://www.britannica.com/science/heavy-water|title=Heavy water {{!}} chemical compound|website=Encyclopedia Britannica|language=en|access-date=2019-04-24}} occurs at a proportion of about 1 molecule in 41 million (i.e., 1 in 6,400{{sup|2}}). This makes semiheavy water far more common than "normal" heavy water.

The freezing point of semiheavy water is close to the freezing point of heavy water at 3.81°C compared to the 3.82°C of heavy water.