Reactions of Metals

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Look at how magnesium reacts with oxygen:

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The use of a gas jar full of oxygen can be used to combust other metals. This method can be used to compare different metals and their reactivity with oxygen by observing the reaction.

Metals that react with oxygen produce oxides as their products.

Metal: Observation: Order of reactivity: Product:
Sodium Burns quickly with a bright yellow flame. 1st - most reactive. Na2O, sodium peroxide - a yellow powder.
Magnesium Burns with a brilliant white flame. 2nd. MgO, magnesium oxide - a white ash.
Iron Does not burn. Hot metal glows in oxygen and gives off yellow sparks. 3rd. Fe203, iron oxide - an orange powder.
Copper Does not burn. Metal eventually coats with a black layer. 4th - least reactive. CuO, copper oxide - a black powder.

Of course, other metals react with oxygen, some more than sodium, for example, potassium. Others, such as gold, do not react at all.

Some metals also react with water, but like their reaction with oxygen, they react in different ways. We can observe the reaction of metals and water by placing the metals in a trough of cold water.

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Alternatively, we can observe the difference in reaction of metals using steam (hot water) instead of cold water.

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The table below illustrates the observations taken when different metals are placed in water:

Metal: Reaction: Order of reactivity: Products:
Potassium Violent reaction with cold water. Floats and catches fire. 1st - most reactive. Potassium hydroxide, KOH and hydrogen gas.
Sodium Very vigorous reaction with cold water. Floats. Can be lit with a lighted splint. 2nd. Sodium hydroxide, NaOH and hydrogen gas.
Calcium Less vigorous with cold water. 3rd. Calcium hydroxide, Ca(OH)2 and hydrogen gas.
Magnesium Very slow with cold water, but vigorous with steam. 4th. Magnesium oxide, MgO and hydrogen gas.
Zinc Quite slow with steam. 5th. Zinc oxide, ZnO and hydrogen gas.
Iron Slow with steam. 6th. Iron oxide, Fe203 and hydrogen gas.
Copper No reaction with steam. 7th - least reactive.

Note: The first three in the table above produce hydroxides and the rest, if they react, produce oxides.

The production of the hydroxide (alkali) can be tested by adding universal indicator (UI) to the reaction vessel - UI changes from green to purple in the presence of these hydroxides.

To test for the release of hydrogen gas, place a lighted splint over the reacting metal - if it 'pops' then hydrogen is present.

In the case of potassium, this reaction produces enough heat to set alight the hydrogen gas itself.

Let's now look at the reaction between metals and acids to see if they can also help distinguish difference in reactivity.

Metal: Reaction with hydrochloric acid: Order of reactivity: Products:
Magnesium Vigorously reacts with a stream of gas evolving. 1st - most reactive. Magnesium chloride, MgCl2 and hydrogen gas.
Zinc Quite slow reaction with a steady stream of gas evolving. 2nd. Zinc chloride, ZnCl2 and hydrogen gas.
Iron Slow reaction with a gentle stream of gas evolving. 3rd. Iron chloride, FeCl2 and hydrogen gas.
Lead Very slow and acid must be concentrated. 4th. Lead chloride, PbCl2 and hydrogen gas.
Copper No reaction. 5th - least reactive.

If we compare the results of the reaction of metals with acid with those of the reactions with oxygen and water, we note that the same order of reactivity is repeated.

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