Reactivity series Revision Notes

The reactivity series is a ranking of metals based on their tendency to lose electrons and form positive ions. This property determines how readily a metal reacts with other substances such as water, acids, and oxygen. Metals higher in the series react more vigorously, while those lower down are less reactive and often found in their native state in nature.

This series is essential for predicting the products of reactions involving metals and for understanding processes such as metal extraction, corrosion, and displacement reactions. Carbon and hydrogen are also included in the series to provide reference points for metal reactivity relative to these non-metals.

• Reactivity depends on how easily a metal loses electrons.
• Higher metals react more vigorously with water and acids.
• Carbon and hydrogen are included as benchmarks.

The reactivity series from most reactive to least reactive is: potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, and gold. Potassium is the most reactive metal listed, reacting explosively with water, while gold is the least reactive and does not easily form compounds.

Carbon is included between aluminium and zinc because it is used in metal extraction processes; metals above carbon are extracted by electrolysis, while those below can be extracted by reduction with carbon.

Knowing this order helps predict which metals will react with water or acids and which metals can displace others from their compounds.

• Potassium is the most reactive metal in the series.
• Gold is the least reactive and very resistant to corrosion.
• Carbon's position indicates its role in metal extraction.

Metals high in the series, such as potassium and sodium, react vigorously with cold water, producing hydroxides and hydrogen gas. For example, sodium reacts with cold water to form sodium hydroxide and hydrogen: 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g).

Calcium reacts with cold water less vigorously, while magnesium reacts slowly with cold water but more readily with steam, producing magnesium oxide and hydrogen gas.

Metals like zinc and iron react with dilute acids, releasing hydrogen gas and forming salts, but copper, silver, and gold do not react with dilute acids under normal conditions due to their low reactivity.

• Higher metals react with water to release hydrogen gas.
• Magnesium reacts with steam rather than cold water.
• Low reactivity metals do not react with dilute acids.

The reactivity series guides the extraction of metals from their ores. Highly reactive metals like potassium and sodium are extracted by electrolysis because they cannot be reduced by carbon.

Less reactive metals such as iron and zinc can be extracted by reduction with carbon, as carbon is more reactive than these metals.

The series also explains why some metals corrode easily and others, like gold and silver, are used for jewellery due to their resistance to corrosion.

• Extraction method depends on metal reactivity.
• Carbon can reduce metals below it in the series.
• Low reactivity metals are corrosion resistant.

The reactivity series allows prediction of displacement reactions. A more reactive metal will displace a less reactive metal from its compound. For example, zinc can displace copper from copper sulfate solution because zinc is higher in the series.

It also predicts whether a metal will react with water or acids. Metals above hydrogen will react with acids to produce hydrogen gas, while those below will not.

This knowledge is useful in practical chemistry and industrial processes to anticipate reaction outcomes and select appropriate metals for specific purposes.

• More reactive metals displace less reactive metals.
• Metals above hydrogen react with acids to release hydrogen gas.
• Predictions aid in practical and industrial chemistry.

The reactivity series is a list of metals arranged in order of decreasing reactivity. Metals at the top react more vigorously with substances like water and acids, while those at the bottom are much less reactive or unreactive. This series helps predict how metals will behave in chemical reactions, such as displacement reactions, corrosion, and extraction methods.

Potassium, sodium, and calcium are near the top of the series, indicating high reactivity. Magnesium, zinc, and iron are moderately reactive, while copper, silver, and gold are low in reactivity, often called noble metals.

Understanding the reactivity series allows chemists to anticipate which metals will react with water or acids and which will not, aiding in practical applications and safety considerations.

• Reactivity series ranks metals from most to least reactive.
• Position in series predicts reaction with water and acids.
• Highly reactive metals react vigorously; low reactivity metals often do not react.

Potassium, sodium, and calcium react readily with cold water due to their high reactivity. When these metals come into contact with water, they lose electrons easily to form positive ions and produce hydrogen gas and metal hydroxides.

For example, sodium reacts with cold water as follows:

2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g) ↑ (hydrogen gas)

• Potassium reacts vigorously, often with flames and sparks.
• Sodium reacts quickly, producing hydrogen gas and a strong alkaline solution.
• Calcium reacts less vigorously but still produces hydrogen gas and calcium hydroxide solution.
• Hydrogen gas released can be tested by a 'pop' sound when ignited.

Magnesium does not react significantly with cold water because it forms a protective oxide layer that prevents further reaction. However, when heated in steam, magnesium reacts to form magnesium oxide and hydrogen gas.

The reaction is: Mg (s) + H₂O (g) → MgO (s) + H₂ (g) ↑

This reaction requires steam (water in gaseous form) and heat to proceed, showing magnesium's moderate reactivity compared to metals that react with cold water.

• Magnesium reacts with steam, not cold water.
• Produces magnesium oxide (a white solid) and hydrogen gas.
• Reaction requires heating to produce steam.

Magnesium, zinc, and iron react with dilute hydrochloric acid to produce hydrogen gas and their respective metal chlorides dissolved in solution.

General reaction: Metal + 2HCl (aq) → Metal chloride (aq) + H₂ (g) ↑

Examples: Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g) ↑ Zn (s) + 2HCl (aq) → ZnCl₂ (aq) + H₂ (g) ↑ Fe (s) + 2HCl (aq) → FeCl₂ (aq) + H₂ (g) ↑ These reactions occur because these metals are more reactive than hydrogen and can displace it from the acid. The rate of reaction decreases down the series: magnesium reacts fastest, iron slowest among these three.

• Magnesium reacts vigorously with dilute HCl.
• Zinc reacts moderately with dilute HCl.
• Iron reacts slowly with dilute HCl.
• Hydrogen gas is produced in all cases and can be tested by ignition.

Copper, silver, and gold do not react with dilute hydrochloric acid because they are less reactive than hydrogen and cannot displace it from the acid. These metals are found near the bottom of the reactivity series and are often called noble metals due to their resistance to corrosion and chemical attack.

This lack of reaction is important in practical applications, such as using copper pipes for plumbing and gold for jewellery, as they do not corrode easily in acidic environments.

• Copper, silver, and gold do not react with dilute HCl.
• They are less reactive than hydrogen and cannot displace it.
• Their chemical inertness makes them useful for corrosion-resistant applications.

Reactivity refers to how readily a metal undergoes chemical reactions, especially with water, acids, or other metal compounds. More reactive metals react faster and more vigorously, often producing observable effects such as bubbles of gas, heat, or colour changes.

Experimental indicators of reactivity include the rate of hydrogen gas evolution when a metal reacts with dilute acid, the temperature rise during the reaction, or the ability of one metal to displace another from its compound in solution.

For example, magnesium reacts with dilute hydrochloric acid producing hydrogen gas rapidly, while copper shows no reaction under the same conditions, indicating magnesium is more reactive than copper.

• Reactivity is linked to how easily a metal loses electrons to form positive ions.
• Faster reactions and greater gas volumes indicate higher reactivity.
• Displacement reactions provide comparative evidence of reactivity.

One common method to compare metal reactivity is to measure the rate at which hydrogen gas is produced when metals react with dilute acids. The faster the gas is produced, the more reactive the metal.

For example, if 1.0 g samples of magnesium and zinc are separately added to 50 cm³ of dilute hydrochloric acid, the volume of hydrogen gas collected over time can be measured using a gas syringe.

If magnesium produces 40 cm³ of hydrogen in 30 seconds, and zinc produces 15 cm³ in the same time, magnesium is inferred to be more reactive than zinc because it reacts faster and produces more gas in the same period.

• Rate of gas production is a quantitative measure of reactivity.
• Consistent sample masses and acid concentrations are essential for valid comparisons.
• Plotting volume of gas against time can help visualise differences in reactivity.

Displacement reactions occur when a more reactive metal displaces a less reactive metal from its salt solution. This provides clear evidence of relative reactivity.

For example, placing a strip of zinc metal into a copper sulfate solution results in zinc displacing copper ions, forming zinc sulfate and depositing copper metal. This shows zinc is more reactive than copper.

If no reaction occurs, it suggests the metal is less reactive than the metal ion in solution. For instance, copper metal placed in zinc sulfate solution shows no reaction, confirming copper is less reactive than zinc.

• Displacement reactions demonstrate reactivity differences directly.
• Observation includes colour changes, solid metal deposition, or solution changes.
• No reaction indicates the metal is less reactive than the metal ion in solution.

To accurately infer reactivity order, experiments must control variables such as metal mass, acid concentration, temperature, and surface area.

Repeating experiments and averaging results reduce random errors and improve reliability.

Safety precautions include wearing goggles and gloves when handling acids and metals, and conducting reactions in well-ventilated areas to avoid hydrogen accumulation, which is flammable and explosive in air concentrations above 4%.

• Control variables to ensure fair comparison.
• Repeat trials to confirm consistency.
• Use appropriate safety equipment and procedures.

Data from experiments can be tabulated showing metal, volume of hydrogen produced, time taken, and calculated reaction rate (e.g., cm³ H₂ per second).

Calculating reaction rate: rate = volume of hydrogen produced / time taken. For example, if 30 cm³ of hydrogen is produced in 60 seconds, rate = 30 ÷ 60 = 0.5 cm³/s.

Plotting graphs of volume of hydrogen against time for different metals helps visualise and compare reactivities clearly, aiding inference of the order of reactivity.

• Calculate reaction rates for quantitative comparison.
• Use tables and graphs to organise and interpret data.
• Clear presentation supports valid conclusions about reactivity order.