Thermal Decomposition Of Metal Carbonates

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Thermal Decomposition Of Metal Carbonates

Aim: To investigate a range of metal carbonates and see if they thermally decompose.

Written By Tauqir Sharif

Research:

When a metal is thermally decomposed the bond between the metal and its carbonate (carbon and oxygen) is removed and the carbonate is released as carbon dioxide.

Metal Carbonate = Metal Oxide + Carbon Dioxide

Malachite is an ore of copper. It is made mostly of copper carbonate. It can be crushed into a green powder. If this powder is heated it changes colour. A new substance has been made. The new substance is a black powder. This is called copper oxide. The copper carbonate has been decomposed.

Copper oxide is made by thermal decomposition of copper carbonate. Carbon dioxide is also made. The formula for this is:

Copper Carbonate = Copper Oxide + Carbon Dioxide

(CuCO3 = CuO + CO2)

The reactivity series determines how fast this reaction occurs. The reactivity series is the order of metals in the periodic table. The most reactive metals are placed at the top of the reactivity series. The least reactive materials are placed at the bottom of the reactivity series. From preliminary work that I have already done I know that Potassium and sodium are the most reactive metals, and that gold and platinum are the least reactive metals. To determine the order of how reactive a metal is and where to place it in the reactivity series you have to see how the metal reacts to:

> Oxygen (air)

> Water

> Acid

When metals are heated they react with oxygen in the air. As the metal is heated it reacts with the oxygen to form an oxide. The most reactive metals such as potassium and sodium burn brightly when they are heated. The less reactive metals do not burn brightly, and take longer to form their oxide. With some metals there is no reaction at all. These are the metals at the bottom of the reactivity series, such as gold. Also the most reactive metals form their oxides much quicker than the less reactive metals. This type of reaction is called an oxidation reaction, because the metal gains oxygen.

The formula for the reaction with air is:

Metal + Oxygen = Metal Oxide

Metals can also be placed in water to see how they react. Again the extremely reactive metals potassium and sodium react more vigorously compared to the less reactive metals. In preliminary work that I have already done when potassium is placed in cold water it immediately begins to react vigorously with the water. The metal also sets on fire as it darts around the water. Hydrogen is also given off by the potassium as it reacts with the cold water. Calcium which is also a very reactive metal does not react in the same way as potassium. Calcium reacts slower as it is placed in cold water. The calcium falls to the bottom of the beaker, whereas potassium floats on the top. Bubbles rise from the metal, a signal that hydrogen is being given off. Magnesium also reacts in this way. The fairly reactive metals such as iron and zinc don't react with cold water. They do however react with steam to give off hydrogen. Lead, copper and the least reactive metals don't react with cold water or steam.

The formula for how a metal reacts with water (or steam) is:

Metal + Water = Metal Hydroxide (or oxide) + Hydrogen

The most violent reaction a metal can have occurs when the metal is placed in dilute acid. This type of reaction is called a displacement reaction. The metal takes the place of the hydrogen in the acid, which means that hydrogen is given off. It is too dangerous to do this reaction with Potassium, sodium and calcium, because these metals violently explode when they are placed in dilute acid. The less reactive metals such as Aluminium and Zinc can be placed in dilute acid to see how they react because they don't react in a dangerous way. The metal upon being placed in the acid does not explode or burn. The metal gives off bubbles, which we already know is hydrogen.
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Hydrogen and metals below this do not react with acid. Therefore gold won't react with acid because it is below hydrogen in the reactivity series, and therefore can't displace hydrogen.

The formula for how a metal reacts with dilute acid is:

Metal + Acid = Metal Salt + Hydrogen

The hydrogen that is given off in the above reactions can be identified by capturing the hydrogen in a test tube. Having done this you can then place a glowing splint inside the test tube. A pop sound can be heard if hydrogen is present ...

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