:Water-reactive substances
{{Disputed|date=September 2024}}
{{Short description|Substances that readily reacts with water}}
Water-reactive substances{{cite web |url=http://www.ilpi.com/msds/ref/waterreactive.html |title=The MSDS HyperGlossary: Metal Reactive |publisher=Interactive Learning Paradigms Incorporated |access-date=2007-05-10}} are those that spontaneously undergo a chemical reaction with water, often noted as generating flammable gas.{{Cite web |title=Shipping dangerous goods |url=https://www.gov.uk/shipping-dangerous-goods/what-are-dangerous-goods |access-date=2024-09-25 |website=GOV.UK |language=en}} Some are highly reducing in nature.Raymond, Chang (2010). Chemistry (PDF) (tenth ed.). Americas, New York: McGraw-Hill. pp.897-898. {{ISBN|0077274318}}. Retrieved 27 February 2018. Notable examples include alkali metals, lithium through caesium, and alkaline earth metals, magnesium through barium.
Some water-reactive substances are also pyrophoric, like organometallics and sulfuric acid. The use of acid-resistant gloves and face shield is recommended for safe handling; fume hoods are another effective control of such substances.{{cite web|last1=The University of Iowa|title=Reactive Chemicals|url=https://ehs.research.uiowa.edu/108-reactive-chemicals|website=Environmental Health & Safety|access-date=2 March 2018|archive-date=3 March 2018|archive-url=https://web.archive.org/web/20180303050527/https://ehs.research.uiowa.edu/108-reactive-chemicals|url-status=dead}}
Water-reactive substances are classified as R2 under the UN classification system and as Hazard 4.3 by the United States Department of Transportation. In an NFPA 704 fire diamond's white square, and in similar contexts, they are denoted as "W". The classification of substances as water-reactive is largely a consideration for the safety of firefighting and transportation operations.{{Cite book |last=Gallant |first=Brian J. |url=https://onlinelibrary.wiley.com/doi/book/10.1002/0470007257 |title=Hazardous Waste Operations and Emergency Response Manual |date=2006-01-13 |publisher=Wiley |isbn=978-0-471-68400-8 |edition=1 |pages=48–49 |language=en |doi=10.1002/0470007257}}
All chemicals that react vigorously with water or liberate toxic gas when in contact with water are recognized for their hazardous nature in the "Approved Supply List",{{cite journal|last1=Quinn|first1=D. J.|last2=Davies|first2=P. A.|title=MODELLING RELEASES OF WATER REACTIVE CHEMICALS|journal=Symposium Series|date=2003|volume=149|url=https://www.icheme.org/communities/subject_groups/safety%20and%20loss%20prevention/resources/hazards%20archive/~/media/Documents/Subject%20Groups/Safety_Loss_Prevention/Hazards%20Archive/XVII/XVII-Paper-41.pdf|access-date=25 February 2018|archive-date=26 February 2018|archive-url=https://web.archive.org/web/20180226033906/https://www.icheme.org/communities/subject_groups/safety%20and%20loss%20prevention/resources/hazards%20archive/~/media/Documents/Subject%20Groups/Safety_Loss_Prevention/Hazards%20Archive/XVII/XVII-Paper-41.pdf|url-status=dead}} or the list of substances covered by the international legislation on major hazards{{cite book|last1=Kapias|first1=T|last2=Griffiths|first2=RF|title=REACTPOOL: A new model for accidental releases of water-reactive chemicals|date=2001|publisher=Crown|isbn=0-7176-1995-8|url=http://www.hse.gov.uk/research/crr_pdf/2001/crr01331.pdf|access-date=25 February 2018}} many of which are commonly used in manufacturing processes.
Alkali metals
{{main|Alkali metals}}
File:Periodieksysteemmaardaneffeietsanders-kolom1.svg
File:Reaction of Sodium and Water.webm
File:Potassium metal in water.webm
The alkali metals (Li, Na, K, Rb, Cs, and Fr) are the most reactive metals in the periodic table - they all react vigorously or even explosively with cold water, resulting in the displacement of hydrogen.
The Group 1 metal (M) is oxidised to its metal ions, and water is reduced to hydrogen gas (H2) and hydroxide ion (OH−), giving a general equation of:
:2 M(s) + 2 H2O(l) ⟶ 2 M+(aq) + 2 OH−(aq) + H2(g) {{cite web|last1=Landas|first1=Trevor|title=Reactions of Main Group Elements with Water|url=https://chem.libretexts.org/Core/Inorganic_Chemistry/Descriptive_Chemistry/Main_Group_Reactions/Reactions_of_Main_Group_Elements_with_Water|website=Chemistry LibreTexts|date=2 October 2013 |access-date=9 February 2017}}
The Group 1 metals or alkali metals become more reactive as their number of energy levels inceases.
Alkaline earth metals
{{main|Alkaline earth metals}}
File:Periodieksysteemmaardaneffeietsanders-kolom2.svg
The alkaline earth metals (Be, Mg, Ca, Sr, Ba, and Ra) are the second most reactive metals in the periodic table, and, like the Group 1 metals, have increasing reactivity with increasing numbers of energy levels. Beryllium (Be) is the only alkaline earth metal that does not react with water, though it reacts with steam if it is heated to high enough temperatures.{{cite web |title=Reactions of Group 2 Elements with Water |url=https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/1_s-Block_Elements/Group__2_Elements%3A_The_Alkaline_Earth_Metals/1Group_2%3A_Chemical_Reactions_of_Alkali_Earth_Metals/Reactions_of_Group_2_Elements_with_Water |website=Chemistry LibreTexts |access-date=21 March 2025}} Additionally, beryllium has a resistant outer oxide layer that lowers its reactivity at lower temperatures.
Magnesium shows insignificant reaction with water, but burns vigorously with steam or water vapor to produce white magnesium oxide and hydrogen gas:{{Cite web |title=The reaction of magnesium with steam |url=https://edu.rsc.org/exhibition-chemistry/the-reaction-of-magnesium-with-steam/4012602.article |access-date=2024-05-11 |website=RSC Education |language=en}}
:Mg(s) + H2O(g) ⟶ MgO(s) + H2(g)
Magnesium has a mild reaction with cold water. The reaction is short-lived because the magnesium hydroxide layer formed on the magnesium is almost insoluble in water and prevents further reaction.
A metal reacting with cold water will produce a metal hydroxide and hydrogen gas. However, if a metal reacts with steam, like magnesium, metal oxide is produced as a result of metal hydroxides splitting upon heating.{{cite web|last1=Clark|first1=Jim|title=Reactions of the Group 2 Elements with Water|url=https://www.chemguide.co.uk/inorganic/group2/reacth2o.html|website=ChemGuide|access-date=16 February 2018}}
The hydroxides of calcium, strontium and barium are only slightly water-soluble but produce sufficient hydroxide ions to make the environment basic, giving a general equation of:
:M(s) + 2 H2O(l) ⟶ M(OH)2(aq) + H2(g){{cite web|last1=Landas|first1=Trevor|title=Reactions of Main Group Elements with Water|url=https://chem.libretexts.org/Core/Inorganic_Chemistry/Descriptive_Chemistry/Main_Group_Reactions/Reactions_of_Main_Group_Elements_with_Water|website=Chemistry LibreTexts|date=2 October 2013 |access-date=16 February 2018}}
Radium reacts similarly to the rest of the alkaline earth metals (other than magnesium), forming radium hydroxide and hydrogen gas.{{Cite report |url=https://www.osti.gov/biblio/4560824 |title=THE RADIOCHEMISTRY OF RADIUM |last1=Salutsky |first1=M. L. |last2=Kirby |first2=H. W. |date=1964-12-01 |publisher=Mound Lab., Miamisburg, Ohio (Grace (W.R.) and Co., Clarksville, Md. Washington Research Center) |issue=NAS-NS-3057 |page=4 |osti=4560824 |language=English}} Notably, radium hydroxide is the most soluble out of all alkaline earth hydroxide species.{{Cite journal |last1=Brown |first1=Paul L. |last2=Matyskin |first2=Artem V. |last3=Ekberg |first3=Christian |date=2022-06-27 |title=The aqueous chemistry of radium |journal=Radiochimica Acta |language=en |volume=110 |issue=6–9 |pages=505–513 |doi=10.1515/ract-2021-1141 |issn=0033-8230|doi-access=free }}
Reactivity series of metals
| class="wikitable" | ||
| Order of reactivity | Metal | Reactions with water or steam |
|---|---|---|
| Most reactive | potassium (K) | Very vigorous reaction with cold water |
| Second most reactive | sodium (Na) | Vigorous reaction with cold water |
| Third most reactive | calcium (Ca) | Less vigorous reaction with cold water |
| Least reactive | magnesium (Mg) | Slow reaction with cold water, vigorous with hot water |
- If metals react with cold water, hydroxides are produced.
- If metals react with steam, oxides are formed.
Hydrogen is always produced when a metal reacts with cold water or steam.{{cite book|last1=Gallagher|first1=RoseMarie|last2=Ingram|first2=Paul|title=Chemistry IGCSE Revision Guide|date=2009|publisher=Oxford University Press|location=Great Clarendon Street, Oxford OX2 6DP|pages=114–115}}
Halogens
Halogens are so named due to their potential to form salts, and form many simple strong acids with hydrogen. Out of the four stable halogens, only fluorine and chlorine have reduction potentials higher than that of oxygen, allowing them to form hydrofluoric acid and hydrochloric acid directly through reaction with water.{{Cite web |date=June 30, 2023 |title=Reactions of Main Group Elements with Halogens |url=https://chem.libretexts.org/@go/page/603 |website=Chemistry LibreTexts}} The reaction of fluorine with water is especially hazardous, as an addition of fluorine gas to cold water will produce hydrofluoric acid, oxygen gas, and ozone.{{Cite journal |last=Cady |first=George Hamilton |date=February 1935 |title=Reaction of Fluorine with Water and with Hydroxides |url=https://pubs.acs.org/doi/abs/10.1021/ja01305a006 |journal=Journal of the American Chemical Society |language=en |volume=57 |issue=2 |pages=246–249 |doi=10.1021/ja01305a006 |issn=0002-7863|url-access=subscription }} However, the reaction is fairly slow.{{Cite web |title=Fluoride Salts, Soluble {{!}} CAMEO Chemicals {{!}} NOAA |url=https://cameochemicals.noaa.gov/react/48 |access-date=2024-02-05 |website=cameochemicals.noaa.gov}}