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Reactivity series
View on WikipediaIn chemistry, a reactivity series (or reactivity series of elements) is an empirical, calculated, and structurally analytical progression[1] of a series of metals, arranged by their "reactivity" from highest to lowest.[2][3][4] It is used to summarize information about the reactions of metals with acids and water, single displacement reactions and the extraction of metals from their ores.[5]
Table
[edit]| Metal | Ion | Reactivity | Extraction |
|---|---|---|---|
| Caesium Cs | Cs+ | reacts with cold water | Electrolysis (a.k.a. electrolytic refining) |
| Rubidium Rb | Rb+ | ||
| Potassium K | K+ | ||
| Sodium Na | Na+ | ||
| Lithium Li | Li+ | ||
| Barium Ba | Ba2+ | ||
| Strontium Sr | Sr2+ | ||
| Calcium Ca | Ca2+ | ||
| Magnesium Mg | Mg2+ | reacts very slowly with cold water, but rapidly in boiling water, and very vigorously with acids | |
| Beryllium Be | Be2+ | reacts with acids and steam | |
| Aluminium Al | Al3+ | ||
| Titanium Ti | Ti4+ | reacts with concentrated mineral acids | pyrometallurgical extraction using magnesium, or less commonly other alkali metals, hydrogen or calcium in the Kroll process |
| Manganese Mn | Mn2+ | reacts with acids; very poor reaction with steam | smelting with coke |
| Zinc Zn | Zn2+ | ||
| Chromium Cr | Cr3+ | aluminothermic reaction | |
| Iron Fe | Fe2+ | smelting with coke | |
| Cadmium Cd | Cd2+ | ||
| Cobalt Co | Co2+ | ||
| Nickel Ni | Ni2+ | ||
| Tin Sn | Sn2+ | ||
| Lead Pb | Pb2+ | ||
| Antimony Sb | Sb3+ | may react with some strong oxidizing acids | heat or physical extraction |
| Bismuth Bi | Bi3+ | ||
| Copper Cu | Cu2+ | reacts slowly with air | |
| Tungsten W | W3+[citation needed] | may react with some strong oxidizing acids | |
| Mercury Hg | Hg2+ | ||
| Silver Ag | Ag+ | ||
| Gold Au | Au3+[6][7] | ||
| Platinum Pt | Pt4+ |
Going from the bottom to the top of the table the metals:
- increase in reactivity;
- lose electrons (oxidize) more readily to form positive ions;
- corrode or tarnish more readily;
- require more energy (and different methods) to be isolated from their compounds;
- become stronger reducing agents (electron donors).
Defining reactions
[edit]There is no unique and fully consistent way to define the reactivity series, but it is common to use the three types of reaction listed below, many of which can be performed in a high-school laboratory (at least as demonstrations).[6]
Reaction with water and acids
[edit]The most reactive metals, such as sodium, will react with cold water to produce hydrogen and the metal hydroxide:
- 2 Na (s) + 2 H2O (l) → 2 NaOH (aq) + H2 (g)
Slightly less reactive metals, such as magnesium and zinc, do not react readily with cold water, but will react with steam to produce hydrogen and the metal oxide:
- Mg (s) + H2O (g) → MgO (s) + H2 (g)
Metals in the middle of the reactivity series, such as iron, will react with acids such as sulfuric acid (but not water at normal temperatures) to give hydrogen and a metal salt, such as iron(II) sulfate:
- Fe (s) + H2SO4 (aq) → FeSO4 (aq) + H2 (g)
There is some ambiguity at the borderlines between the groups. Magnesium, aluminium and zinc can react with water, but the reaction is usually very slow unless the metal samples are specially prepared to remove the surface passivation layer of oxide which protects the rest of the metal. Copper and silver will react with nitric acid; but because nitric acid is an oxidizing acid, the oxidizing agent is not the H+ ion as in normal acids, but the NO3− ion.
Comparison with standard electrode potentials
[edit]The reactivity series is sometimes quoted in the strict reverse order of standard electrode potentials, when it is also known as the "electrochemical series".[8]
The following list includes the metallic elements of the first six periods. It is mostly based on tables provided by NIST.[9][10] However, not all sources give the same values: there are some differences between the precise values given by NIST and the CRC Handbook of Chemistry and Physics. In the first six periods this does not make a difference to the relative order, but in the seventh period it does, so the seventh-period elements have been excluded. (In any case, the typical oxidation states for the most accessible seventh-period elements thorium and uranium are too high to allow a direct comparison.)[11]
Hydrogen has been included as a benchmark, although it is not a metal. Borderline germanium, antimony, and astatine have been included. Some other elements in the middle of the 4d and 5d rows have been omitted (Zr–Tc, Hf–Os) when their simple cations are too highly charged or of rather doubtful existence. Greyed-out rows indicate values based on estimation rather than experiment.
| Z | Sym | Element | Reaction | E° (V) |
|---|---|---|---|---|
| 3 | Li | lithium | Li+ + e− → Li | −3.04 |
| 55 | Cs | caesium | Cs+ + e− → Cs | −3.03 |
| 37 | Rb | rubidium | Rb+ + e− → Rb | −2.94 |
| 19 | K | potassium | K+ + e− → K | −2.94 |
| 56 | Ba | barium | Ba2+ + 2 e− → Ba | −2.91 |
| 38 | Sr | strontium | Sr2+ + 2 e− → Sr | −2.90 |
| 20 | Ca | calcium | Ca2+ + 2 e− → Ca | −2.87 |
| 11 | Na | sodium | Na+ + e− → Na | −2.71 |
| 57 | La | lanthanum | La3+ + 3 e− → La | −2.38 |
| 39 | Y | yttrium | Y3+ + 3 e− → Y | −2.38 |
| 12 | Mg | magnesium | Mg2+ + 2 e− → Mg | −2.36 |
| 59 | Pr | praseodymium | Pr3+ + 3 e− → Pr | −2.35 |
| 58 | Ce | cerium | Ce3+ + 3 e− → Ce | −2.34 |
| 68 | Er | erbium | Er3+ + 3 e− → Er | −2.33 |
| 67 | Ho | holmium | Ho3+ + 3 e− → Ho | −2.33 |
| 60 | Nd | neodymium | Nd3+ + 3 e− → Nd | −2.32 |
| 69 | Tm | thulium | Tm3+ + 3 e− → Tm | −2.32 |
| 62 | Sm | samarium | Sm3+ + 3 e− → Sm | −2.30 |
| 61 | Pm | promethium | Pm3+ + 3 e− → Pm | −2.30 |
| 66 | Dy | dysprosium | Dy3+ + 3 e− → Dy | −2.29 |
| 71 | Lu | lutetium | Lu3+ + 3 e− → Lu | −2.28 |
| 65 | Tb | terbium | Tb3+ + 3 e− → Tb | −2.28 |
| 64 | Gd | gadolinium | Gd3+ + 3 e− → Gd | −2.28 |
| 70 | Yb | ytterbium | Yb3+ + 3 e− → Yb | −2.19 |
| 21 | Sc | scandium | Sc3+ + 3 e− → Sc | −2.09 |
| 63 | Eu | europium | Eu3+ + 3 e− → Eu | −1.99 |
| 4 | Be | beryllium | Be2+ + 2 e− → Be | −1.97 |
| 13 | Al | aluminium | Al3+ + 3 e− → Al | −1.68 |
| 22 | Ti | titanium | Ti3+ + 3 e− → Ti | −1.37 |
| 25 | Mn | manganese | Mn2+ + 2 e− → Mn | −1.18 |
| 23 | V | vanadium | V2+ + 2 e− → V | −1.12 |
| 24 | Cr | chromium | Cr2+ + 2 e− → Cr | −0.89 |
| 30 | Zn | zinc | Zn2+ + 2 e− → Zn | −0.76 |
| 31 | Ga | gallium | Ga3+ + 3 e− → Ga | −0.55 |
| 26 | Fe | iron | Fe2+ + 2 e− → Fe | −0.44 |
| 48 | Cd | cadmium | Cd2+ + 2 e− → Cd | −0.40 |
| 49 | In | indium | In3+ + 3 e− → In | −0.34 |
| 81 | Tl | thallium | Tl+ + e− → Tl | −0.34 |
| 27 | Co | cobalt | Co2+ + 2 e− → Co | −0.28 |
| 28 | Ni | nickel | Ni2+ + 2 e− → Ni | −0.24 |
| 50 | Sn | tin | Sn2+ + 2 e− → Sn | −0.14 |
| 82 | Pb | lead | Pb2+ + 2 e− → Pb | −0.13 |
| 1 | H | hydrogen | 2 H+ + 2 e− → H2 | 0.00 |
| 32 | Ge | germanium | Ge2+ + 2 e− → Ge | +0.1 |
| 51 | Sb | antimony | Sb3+ + 3 e− → Sb | +0.15 |
| 83 | Bi | bismuth | Bi3+ + 3 e− → Bi | +0.31 |
| 29 | Cu | copper | Cu2+ + 2 e− → Cu | +0.34 |
| 84 | Po | polonium | Po2+ + 2 e− → Po | +0.6 |
| 44 | Ru | ruthenium | Ru3+ + 3 e− → Ru | +0.60 |
| 45 | Rh | rhodium | Rh3+ + 3 e− → Rh | +0.76 |
| 47 | Ag | silver | Ag+ + e− → Ag | +0.80 |
| 80 | Hg | mercury | Hg2+ + 2 e− → Hg | +0.85 |
| 46 | Pd | palladium | Pd2+ + 2 e− → Pd | +0.92 |
| 77 | Ir | iridium | Ir3+ + 3 e− → Ir | +1.0 |
| 85 | At | astatine | At+ + e− → At | +1.0 |
| 78 | Pt | platinum | Pt2+ + 2 e− → Pt | +1.18 |
| 79 | Au | gold | Au3+ + 3 e− → Au | +1.50 |
The positions of lithium and sodium are changed on such a series.
Standard electrode potentials offer a quantitative measure of the power of a reducing agent, rather than the qualitative considerations of other reactive series. However, they are only valid for standard conditions: in particular, they only apply to reactions in aqueous solution. Even with this proviso, the electrode potentials of lithium and sodium – and hence their positions in the electrochemical series – appear anomalous. The order of reactivity, as shown by the vigour of the reaction with water or the speed at which the metal surface tarnishes in air, appears to be
- Cs > K > Na > Li > alkaline earth metals,
i.e., alkali metals > alkaline earth metals,
the same as the reverse order of the (gas-phase) ionization energies. This is borne out by the extraction of metallic lithium by the electrolysis of a eutectic mixture of lithium chloride and potassium chloride: lithium metal is formed at the cathode, not potassium.[1]
Comparison with electronegativity values
[edit]
The image shows a periodic table extract with the electronegativity values of metals.[12]
Wulfsberg[13] distinguishes:
very electropositive metals with electronegativity values below 1.4
electropositive metals with values between 1.4 and 1.9; and
electronegative metals with values between 1.9 and 2.54.
From the image, the group 1–2 metals and the lanthanides and actinides are very electropositive to electropositive; the transition metals in groups 3 to 12 are very electropositive to electronegative; and the post-transition metals are electropositive to electronegative. The noble metals, inside the dashed border (as a subset of the transition metals) are very electronegative.
See also
[edit]- Reactivity (chemistry), which discusses the inconsistent way that the term "reactivity" is used in chemistry.
References
[edit]- ^ a b Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 82–87. ISBN 978-0-08-022057-4.
- ^ France, Colin (2008), The Reactivity Series of Metals
- ^ Briggs, J. G. R. (2005), Science in Focus, Chemistry for GCE 'O' Level, Pearson Education, p. 172
- ^ Lim Eng Wah (2005), Longman Pocket Study Guide 'O' Level Science-Chemistry, Pearson Education, p. 190
- ^ "Metal extraction and the reactivity series - The reactivity series of metals - GCSE Chemistry (Single Science) Revision - WJEC". BBC Bitesize. Retrieved 2023-03-24.
- ^ a b "Activity series". Archived from the original on 2019-05-07. Retrieved 2016-11-08.
- ^ Wulsberg, Gary (2000). Inorganic Chemistry. p. 294. ISBN 9781891389016.
- ^ "Periodic table poster". Archived from the original on 2022-02-24. Retrieved 2022-02-24.
{{cite web}}: CS1 maint: bot: original URL status unknown (link) by A. V. Kulsha and T. A. Kolevich gives:Li > Cs > Rb > K > Ba > Sr > Ca > Na > La > Y > Mg > Ce > Sc > Be > Al > Ti > Mn > V > Cr > Zn > Ga > Fe > Cd > In > Tl > Co > Ni > Sn > Pb > (H) > Sb > Bi > Cu > Po > Ru > Rh > Ag > Hg > Pd > Ir > Pt > Au
- ^ Standard Electrode Potentials and Temperature Coefficients in Water at 298.15 K, Steven G. Bratsch (NIST)
- ^ For antimony: Antimony - Physico-chemical properties - DACTARI
- ^ Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, Florida: CRC Press. ISBN 0-8493-0487-3.
- ^ Aylward, G; Findlay, T (2008). SI Chemical Data (6 ed.). Milton, Queensland: John Wiley & Sons. p. 126. ISBN 978-0-470-81638-7.
- ^ Wulfsberg, G (2018). Foundations of Inorganic Chemistry. Mill Valley: University Science Books. p. 319. ISBN 978-1-891389-95-5.
External links
[edit]Reactivity series
View on Grokipedia| Metal | Symbol | Common Ion |
|---|---|---|
| Potassium | K | K⁺ |
| Sodium | Na | Na⁺ |
| Calcium | Ca | Ca²⁺ |
| Magnesium | Mg | Mg²⁺ |
| Aluminium | Al | Al³⁺ |
| Zinc | Zn | Zn²⁺ |
| Iron | Fe | Fe²⁺ |
| Tin | Sn | Sn²⁺ |
| Lead | Pb | Pb²⁺ |
| Hydrogen | H | H⁺ |
| Copper | Cu | Cu²⁺ |
| Silver | Ag | Ag⁺ |
| Gold | Au | Au³⁺ |
Overview and Definition
Core Concept
The reactivity series is a qualitative ranking of common metals, arranged in a vertical list in decreasing order of their reactivity, based on their tendency to lose electrons and form positive ions during chemical reactions. It typically begins with the most reactive metal, potassium, and descends to the least reactive, gold, while including hydrogen as a reference point to compare metal reactivity with non-metals. This ordering reflects the relative ease with which these elements undergo oxidation, serving as a foundational tool in inorganic chemistry for understanding metal behavior.[5][6] The primary purpose of the reactivity series is to predict the outcomes of displacement reactions, where a more reactive element can liberate a less reactive one from its compounds in solution. For instance, zinc, positioned higher in the series than copper, readily displaces copper ions from copper sulfate solution to form zinc sulfate and deposit copper metal, demonstrating the directional nature of such reactions. Conversely, copper, being less reactive, cannot displace zinc from zinc compounds, highlighting the series' utility in forecasting reaction feasibility without quantitative calculations.[5] This qualitative framework correlates with quantitative indicators like standard electrode potentials, where metals with more negative reduction potentials exhibit greater reactivity and align with their position in the series. Educational resources often employ mnemonic aids to facilitate memorization of the order—potassium, sodium, calcium, magnesium, aluminum, zinc, iron, tin, lead, hydrogen, copper, silver, gold.[6]Historical Context
The concept of the reactivity series originated from early 18th-century observations of metal behaviors in chemical reactions. In 1772, Joseph Priestley conducted experiments repeating Henry Cavendish's work on metals dissolved in nitric acid, noting the production of different "airs" (gases) such as nitrous air from various metals, which highlighted qualitative differences in their reactivity with acids.[7] These findings laid initial groundwork for understanding relative metal reactivities through empirical observations rather than theoretical frameworks. The formalization of a structured series began in the early 19th century, spurred by advances in electrochemistry. Alessandro Volta's invention of the voltaic pile in 1800 provided a reliable source of electrical current, enabling systematic studies of metal interactions and influencing ideas about chemical affinity based on electrical properties.[8] Shortly thereafter, in 1800, Johann Wilhelm Ritter established the first electrochemical series by observing the order in which metals precipitate one another from solutions of their salts, such as zinc displacing copper, marking an early quantitative approach to reactivity ordering.[9] Further refinement came through Humphry Davy's electrolysis experiments in 1807–1808, where he isolated highly reactive alkali metals like potassium and sodium using Volta's battery, demonstrating their position at the top of the reactivity hierarchy and linking reactivity to electrochemical decomposition.[10] These 19th-century developments evolved into a more comprehensive tool by the 20th century, integrating qualitative observations with the electrochemical series based on standard electrode potentials for precise predictions.[8] By the mid-20th century, the reactivity series had become a standard educational aid in chemistry curricula worldwide for teaching metal reactivity patterns.Construction of the Series
Standard Table
The standard reactivity series lists metals in descending order of their reactivity, primarily determined by their observed ability to displace less reactive metals from compounds in displacement reactions, rather than relying on quantitative electrochemical data. This empirical ordering serves as a practical tool for predicting reaction outcomes in aqueous solutions. For instance, the top placements of alkali metals like potassium and sodium reflect their vigorous reactions with water, producing hydrogen gas and metal hydroxides.[11] The following table presents a canonical version of the series, adapted for clarity with reactivity levels categorized as high (typically react with cold water), medium (react with dilute acids but not cold water), and low (do not react appreciably with dilute acids). Hydrogen is included for reference, positioned between lead and copper.[11]| Metal/Symbol | Reactivity Level | Brief Notes |
|---|---|---|
| Potassium (K) | High | Most reactive; displaces all below it, including water. |
| Sodium (Na) | High | Highly reactive; reacts vigorously with water. |
| Lithium (Li) | High | Reacts with water but less vigorously than K or Na. |
| Calcium (Ca) | High | Reacts with cold water to form calcium hydroxide. |
| Magnesium (Mg) | Medium | Reacts slowly with cold water, readily with acids. |
| Aluminium (Al) | Medium | Reacts with acids; protected by oxide layer in air. |
| Zinc (Zn) | Medium | Displaces hydrogen from acids; used in galvanizing. |
| Iron (Fe) | Medium | Reacts with acids; prone to rusting in moist air. |
| Tin (Sn) | Medium | Weak reaction with acids; corrosion-resistant. |
| Lead (Pb) | Medium | Very slow reaction with acids; toxic heavy metal. |
| Hydrogen (H) | - | Reference point; non-metal for comparison. |
| Copper (Cu) | Low | Does not displace hydrogen from acids; reddish metal. |
| Silver (Ag) | Low | Unreactive; used in jewelry due to tarnish resistance. |
| Gold (Au) | Low | Least reactive; inert to most acids except aqua regia. |
Key Reactions for Ordering
The reactivity series of metals is primarily determined through experimental observations of their reactions with water (both cold and hot/steam), dilute acids, and in displacement scenarios, which provide a basis for ordering metals from most to least reactive.[1][13] The most reactive metals, particularly the alkali metals such as potassium (K), sodium (Na), and lithium (Li), react vigorously with cold water to produce hydrogen gas and the corresponding metal hydroxide. For instance, sodium reacts according to the equation: This reaction is highly exothermic, often igniting the hydrogen gas evolved, and demonstrates the high reactivity of these Group 1 metals, which readily lose their outer electron to form positive ions.[1][14] Less reactive alkali earth metals like calcium also react with cold water but more slowly, producing calcium hydroxide and hydrogen, while magnesium shows no visible reaction under cold conditions.[1] Metals lower in the series, such as magnesium, do not react appreciably with cold water but can react with steam or hot water to displace hydrogen and form the metal oxide. The reaction for magnesium with steam is: This observation places magnesium above metals like zinc or iron, which require even more forcing conditions or different reagents to react with water. Such experiments highlight the increasing stability of metal-water bonds as reactivity decreases down the series.[1][13] A key test for reactivity involves the reaction of metals with dilute acids, such as hydrochloric acid, where metals positioned above hydrogen in the series displace hydrogen gas to form a soluble metal salt. For example, zinc reacts with dilute hydrochloric acid as follows: The vigor of this reaction decreases down the series; highly reactive metals like magnesium produce rapid effervescence and heat, while less reactive ones like iron react slowly. Metals below hydrogen, such as copper, show no reaction, confirming their position relative to hydrogen. These acid reactions provide a reliable ordering for mid-series metals.[1][15] Displacement reactions further refine the series by showing that a more reactive metal can displace a less reactive one from its salt solution in aqueous media. For instance, iron displaces copper from copper(II) sulfate solution: This single displacement occurs because iron has a greater tendency to form ions than copper, leading to observable changes like color shifts and metal deposition. Experiments with pairs of metals systematically build the relative order, with no reaction indicating the displacing metal is less reactive.[1][16]Theoretical Foundations
Link to Electrode Potentials
The standard electrode potential, denoted as , quantifies the tendency of a species to gain electrons and undergo reduction in an electrochemical cell, measured relative to the standard hydrogen electrode (SHE) under standard conditions of 25°C, 1 M concentration, and 1 atm pressure. The SHE is assigned an value of 0 V for the half-reaction . A more positive indicates a greater propensity for reduction (acting as a stronger oxidizing agent), while a more negative signifies a stronger tendency for oxidation (acting as a better reducing agent). For metals, this is particularly relevant in their ionic forms, where reflects the ease with which the metal can lose electrons to form cations.[17] In the context of the reactivity series, the order of metals aligns closely with their standard reduction potentials, arranged from most reactive (most negative ) to least reactive (most positive ). For instance, lithium has an of -3.04 V for , indicating high reactivity as it readily oxidizes, whereas gold exhibits an of +1.50 V for , showing low reactivity due to its resistance to oxidation. Hydrogen serves as the reference point at 0 V, dividing the series into metals above it (more reactive, displace H₂ from acids) and below it (less reactive). This correlation stems from the half-cell reduction reaction for metals: The position in the reactivity series is determined by the ease of the reverse oxidation process, , where a more negative corresponds to a more spontaneous oxidation and thus higher reactivity.[18][6] While the reactivity series provides a qualitative ordering based on observed displacement reactions, standard electrode potentials offer a quantitative measure that underpins this arrangement, allowing prediction of reaction spontaneity via the cell potential . However, electrode potentials focus on thermodynamic feasibility and do not account for kinetic barriers, such as activation energies or overpotentials, which can prevent reactions from occurring at appreciable rates despite favorable values. Thus, the series remains a simplified tool, while potentials enable more precise electrochemical analysis.[17][19]Influence of Electronegativity
Electronegativity, as defined on the Pauling scale, quantifies an atom's tendency to attract shared electrons in a chemical bond, with values typically ranging from about 0.7 to 4.0 for elements. In the context of metals, lower electronegativity indicates a weaker hold on valence electrons, correlating with greater ease in losing those electrons to form cations and thus higher reactivity.[20] This trend is evident across the reactivity series, where alkali metals at the top exhibit notably low electronegativities—for instance, lithium at 0.98 and cesium at 0.79—enabling rapid ionization and pronounced reactivity with substances like water or acids. In contrast, noble metals positioned lower in the series, such as gold with an electronegativity of 2.54, retain electrons more strongly, contributing to their chemical inertness under standard conditions.[21] The inverse relationship between electronegativity and metal reactivity broadly underpins the ordering in the series, as metals with diminished electron attraction donate electrons more readily, aligning with observed displacement behaviors.[20] Nonetheless, electronegativity serves as an imperfect predictor, overlooking influences like successive ionization energies, which leads to deviations especially among transition metals where d-orbital effects dominate.[20] It remains particularly valuable for elucidating reactivity trends within periodic groups, such as the increasing reactivity down the alkali metal group due to progressively lower electronegativities.[20] This concept complements interpretations based on standard electrode potentials by highlighting underlying atomic electron affinities.[20]Practical Applications
Predicting Displacement Reactions
The reactivity series serves as a predictive tool for single displacement reactions in aqueous solutions, where a more reactive metal can displace a less reactive metal from the solution of its salt. According to this principle, a metal positioned higher in the series will replace one lower in the series in a compound, while the reverse reaction does not occur due to differences in reactivity.[13][5] This rule stems from the relative tendencies of metals to lose electrons, enabling straightforward forecasting of reaction outcomes without performing experiments.[22] A classic example is the displacement of silver by magnesium: when magnesium is added to a silver nitrate solution, the reaction proceeds as producing solid silver and magnesium nitrate, as magnesium ranks higher in the reactivity series than silver.[23] In contrast, iron, which is below magnesium but above silver, cannot displace magnesium from magnesium chloride solution, resulting in no observable reaction.[24] These examples illustrate the series' utility in anticipating whether a displacement will occur based solely on the metals' positions.[5] Hydrogen's placement in the reactivity series extends predictions to reactions with acids: metals above hydrogen can displace it from dilute acids to form hydrogen gas, whereas those below cannot.[22] For instance, copper, positioned below hydrogen, shows no reaction with hydrochloric acid (Cu + 2HCl → no reaction), as copper lacks the reactivity to liberate hydrogen.[25] A practical illustration is observed in a mixture of aluminium (Al), iron (Fe), and copper (Cu) treated with excess dilute hydrochloric acid, where Al and Fe react to produce hydrogen gas and soluble metal chlorides (AlCl₃ and FeCl₂), leaving Cu as the undissolved solid residue.[15][26] This aspect highlights the series' role in distinguishing reactive from noble metals in acidic environments.[5] The reactivity series also enables quantitative predictions of product volumes in such reactions. For example, when 2.00 g of magnesium reacts completely with excess dilute acid at 20.0°C and 100000 Pa according to the equation Mg + 2H⁺ → Mg²⁺ + H₂, the volume of hydrogen gas produced is 2.00 dm³ (2.00 L). This result follows from stoichiometric calculation: the molar mass of magnesium is 24 g/mol, giving 2.00 / 24 = 0.0833 mol of Mg and thus 0.0833 mol of H₂; at RTP (room temperature and pressure, commonly taken as 20°C and 100000 Pa in educational contexts), the molar volume of an ideal gas is 24 dm³/mol, yielding 0.0833 × 24 = 2.00 dm³. This example shows how the series supports not only qualitative predictions of reaction occurrence but also quantitative assessments of product amounts in acid displacement reactions. In education, the reactivity series underpins laboratory experiments designed to verify and reinforce these predictions, such as microscale displacement tests using spotting tiles to observe reactions between metals and salt solutions.[13] These activities help students develop an intuitive understanding of reactivity trends through direct observation, often incorporating word equations and formative assessments like reactivity series strips.[22]Uses in Metallurgy and Industry
In metallurgy, the reactivity series guides the selection of reduction methods for extracting metals from their ores, ensuring efficient industrial processes. For extraction purposes, carbon is included in an extended reactivity series, positioned between aluminum and zinc; metals below carbon, such as iron, can be extracted through thermal reduction using carbon or carbon monoxide in a blast furnace. Here, iron(III) oxide reacts with carbon monoxide to produce molten iron and carbon dioxide:This approach leverages the relative positions in the series, where carbon acts as a reducing agent capable of displacing iron from its oxide, making it a cornerstone of steel production worldwide.[27] For more reactive metals above carbon, like aluminum, carbon reduction is ineffective due to aluminum's higher affinity for oxygen, necessitating electrolytic methods. The Hall-Héroult process dissolves aluminum oxide in molten cryolite and uses electrolysis to reduce it at the cathode:
This energy-intensive technique, operating at around 950°C, accounts for nearly all primary aluminum production and highlights how the series dictates the shift from chemical to electrochemical extraction for highly reactive metals.[28][27] The reactivity series also informs corrosion prevention in industrial settings, particularly through cathodic protection using sacrificial anodes. Zinc, being more reactive than iron, is commonly applied as a coating or anode on steel structures like ship hulls, where it corrodes preferentially:
This galvanic action supplies electrons to prevent iron oxidation, extending the lifespan of marine and infrastructure assets in corrosive environments.[27] In alloy design, the series aids metallurgists in tailoring material stability for challenging conditions, such as acidic soils where reactive components may corrode faster. By combining metals of differing reactivities, alloys like certain aluminum-magnesium series achieve enhanced resistance to localized attack, optimizing performance in agricultural or environmental applications.[29]
