Reactions with Metals PDF

Reactions with metals  Properties of metals Properties of metals Properties of non-metals Good conductor of electricity Poor conductor of electricity (except graphite) Good conductor of heat Poor conducto...

Reactions with metals  Properties of metals Properties of metals Properties of non-metals Good conductor of electricity Poor conductor of electricity (except graphite) Good conductor of heat Poor conductor of heat (except graphite) Shiny (lustrous) Dull High density (heavy for its size) Low density (light for its size) Malleable (can be hammered into Brittle( will break when hammered) different shapes) Ductile (can be pulled into wires) Brittle( will break when a pulling force is applied) Sonorous (make a ringing sound when Not sonorous (make a dull sound when hit) hit)  Writing balanced symbol equations with state symbols ► Example 1: 2Mg(s) + O2(g) →2MgO(s) ► In the balanced equation above, (s) and (g) are state symbols ► (s) means “solid” ► (g) means “gas” ► Other state symbols include: ► (l) means “liquid” ► (aq) means “aqueous solution” ► Example 2: NaOH(aq)+HCl(aq)→NaCl(aq)+H2O(l)  Different metal reactions ► Metals react with oxygen to form metal oxides ► Metal oxides are basic (they form bases) ► For example: Magnesium + oxygen→ magnesium oxide ► Group I metals react very rapidly with water forming soluble hydroxides (alkalis) and hydrogen gas. ► Other metals are less reactive. Transition metals do not react with water or react only with steam. Tests for gases 2H2(g) + O2(g) → 2H2O(l) Ca(OH)2(aq) + CO2(g) → +CaCO3(s) + 2H2O(l)  Rusting ► Causes of rust ► Chemicals in the air may attack metals causing the surface to be eaten away. ► This is known as corrosion. ► The corrosion of iron and steel is called rusting. ► For rusting to occur, both oxygen and water are needed. ► Rusting is speeded up by electrolytes such as salt. ► A layer of rust is very weak and it soon flakes away from the surface. ► The newly-exposed surface then begins to rust. ► Stopping the rust ► Rusting destroys about 20% of the world’s iron and steel every year, so it is important to stop rusting. ► Rusting can be prevented by the following methods: ► 1) Painting – for bridges and cars ► 2) Coating with plastic – for garden furniture and wire netting for fencing. ► 3) Greasing and oiling – for tools and moving parts of machinery. ► 4) Metal plating - this involves the electroplating of iron and steel with another metal such as chromium or tin. ► 5) Galvanising – this involves coating iron with zinc by dipping the iron or steel in molten zinc. The zinc forms a coating that stops oxygen and water from reaching the iron or steel. ► However, zinc protects the iron or steel beneath it in another way. When exposed to water, zinc with react and corrode because zinc is more reactive than iron. The metal beneath the zinc remains protected. ► This method is also known as sacrificial protection because zinc is sacrificed to protect iron or steel.  The reactivity series ► The reactivity series refers to a list of metals based on how they react to water, oxygen and hydrochloric acid. ► Elements below hydrogen do not react with cold water, steam or hydrochloric acid Things to remember about the reactivity series ► 1. The reactivity series is a way to classify metals based on how quickly they react. ► 2. A metal will react with a compound of a less reactive metal by pushing out the less reactive metal and taking its place. ► 3. The more reactive the metal, the more stable its compounds ► 4. the more the reactive the metal, the more difficult it is to extract from its ore, since they are stable compounds. ► 5.The less reactive the metal, the less it likes to form compounds. This is why silver, gold and copper are found as elements in the Earth’s crust. Most metals exist as compounds.  Metal reactions with water or steam Most Metal Reaction with water or reactive steam Potassium Very violent with cold water, catches fire Sodium Violent with cold water Calcium Reacts rapidly with cold water Magnesium Reacts very slowly with cold water and rapidly with steam Zinc Reacts slowly when powdered and heated with steam Iron Reacts very slowly with steam Least Copper No reaction reactive Silver /gold No reaction  Comparing metal reactions with acids and with oxygen Metal Reaction with dilute Reaction with oxygen Most acid reactive Magnesium Reacts very vigorously Burns vigorously Zinc Reacts steadily Burns less vigorously Iron Reacts steadily Burns Lead Reacts slowly in Does not burn, forms concentrated acid an oxide layer when heated Copper No reaction, even in Does not burn, forms concentrated acid an oxide layer when heated Silver /gold No reaction, even in No reaction Least concentrated acid reactive  Displacement reactions ► If metal X is more reactive (will more easily form a compound) than metal Y, then X will displace Y from a solution of a compound of Y ► For example: ► Iron + copper sulphate iron sulphate + copper ► Iron is more reactive than copper, so it will displace copper from its compound, copper sulphate  Oxides in displacement reactions ► Some oxides can also be displaced by more reactive metals. ► Displacing a metal from its oxide is a way by which metal can be extracted from ore. ► For example: Aluminium is more reactive than iron. It displaces iron from its ore. ► Aluminium + iron oxide aluminium oxide + iron ► This reaction is known as the thermite reaction. ► In this reaction, powdered aluminium and powdered iron oxide are mixed together and heated strongly. The reaction is highly exothermic, and the mixture becomes so hot that the iron melts. ► Other metal-metal oxide reactions include: ► Iron + copper oxide iron oxide + copper ► Iron can displace copper, but copper cannot displace iron because copper is less reactive than iron.  Extracting metals ► Most metals found in the Earth’s crust exist as metal compounds. ► A rock containing a metal compound from which a metal can be extracted is known as an ore. ► The way a metal is extracted depends on its position in the reactivity series. ► The higher up the metal is in the reactivity series, the more difficult it is to extract from its ore. ► Metals at the bottom of the reactivity series (below hydrogen): ► Gold, silver and platinum are unreactive metals found at the bottom of the reactivity series. ► These metals exist as elements in the Earth’s crust, NOT as compounds. ► They are also known as native metals. ► For this reason, metals such as gold can easily be separated from the substances it is mixed with. ► Metals in the middle of the reactivity series (between hydrogen and carbon): ► Metals such as iron, zinc and lead exist as oxides ► Carbon is used to extract these metals. ► When these metals are heated with carbon, the carbon reacts with the oxygen in the oxides and forms carbon dioxide. ► This is because carbon is more reactive than the metals below it and so displaces the metal from its compound. ► Metals at the top of the reactivity series (above carbon): ► Metals such as aluminium and sodium are near the top of the reactivity series ► These metals are highly reactive and so are very difficult to extract. ► These metals are extracted from their compounds by electrolysis. ► Electrolysis involves the use of an electrical current to “break up” a metal compound