Copper is a very valuable chemical element with a symbol ‘Cu’. it is classified as a metal that exists in directly usable metallic form in nature. Many students have a question about whether copper reacts with acid or not. In this article, I will answer this question in detail and also cover the surrounding topics too.
So, does copper react with acid? No, Copper does not react with non-oxidizing acid like dilute sulphuric acid, hydrochloride, hydrobromide, etc because its reduction potential is higher than that of hydrogen. Therefore, copper is present below hydrogen in the reactivity series of metal. Copper in the pure state cannot displace hydrogen atoms from acid. But copper easily reacts with oxidizing acids like concentrated and hot sulphuric acid, nitric acid.
Copper has its Latin name as Cuprum and its atomic number is 29. This metal does not react with other compounds easily. The copper atom has one single electron in its vacant shell. The electronic configuration of this metal is 3d10 4s1.
All the acid contains hydrogen atoms and they get deprotonate when they react with some metal. Strong acid deprotonates easily than a weak acid. The deprotonation of acid occurs when a metal atom replaces the hydrogen atoms. This is basically a replacement redox reaction.
It should be noted that metals that are above the hydrogen in the reactivity series can replace the hydrogen atoms. Therefore in the case of copper, it does not react with acid because copper is below the hydrogen in the electrochemical reactivity series.
The reduction potential of copper is higher than that of hydrogen. The standard reduction potential is defined by taking reference to hydrogen reduction potential as 0V. And the reduction potential of copper comes out to be positive (greater than hydrogen).
The standard reduction potential is the measure of affinity for electrons/hydrogen under standard external conditions. Greater the reduction potential of a chemical element more is the affinity for an electron.
The positive reduction potential of copper means that it undergoes a reduction at a faster rate than hydrogen. In Other words, copper releases electrons slower than hydrogen.
The standard reduction potential of an element is determined under the following external conditions::
- The temperature should be 25 degrees Celcius.
- Metals should be present in their pure states.
- The partial pressure is to be 1 atm for all gases taking part in the reaction.
- The concentration of each ion should be 1M participating in the reaction.
Copper and Nitric Acid Reaction Type
Copper, being an unreactive metal do not react with acids under normal conditions. But in the case of nitric acid (HNO3), copper does react with nitric acid as it is a strong oxidizing agent and the reaction is not as simple as of metal + acid.
Copper gets dissolved in nitric acid and reduction of nitric acid to form NO gas occurs at the cathode part. And the potential of this half-reaction is greater than the oxidation potential of half-reaction of copper to give Cu2+ ions.
In this reaction, the gases liberated can be NO, NO2. This depends upon the concentration of nitric acid. Below is the reaction for the reaction of copper metal with nitric acid in dilute and concentrated form.
Dilute nitric acid
8HNO3 + 3Cu ——–> 3Cu(NO3)2 + 4H2O + 2NO (g) (Nitrogen oxide)
Concentrated nitric acid
4HNO3 (aq) + Cu(s) ——–> Cu(NO3)2 (s) + 2H2O(l) + 2NO2(g) (Nitrogen dioxide)
Does Copper React with Sulphuric Acid?
Copper does not react with dilute sulphuric acid because of its positive reduction potential. It cannot replace hydrogen atoms in dilute sulphuric acid.
But if the sulphuric acid is hot and concentrated, then it can undergo reduction. As concentrated H2SO4 is an oxidizing agent for copper. Therefore, if concentrated sulphuric acid is heated with the copper metal, acid undergoes reduction and results in a redox reaction.
The reaction in which the oxidation-reduction process occurs and the oxidation state of an atom, ion or molecule changes by the transfer of electrons is known as a redox reaction.
In the rection between concentrated sulphuric acid and copper metal, Sulphur dioxide gas is liberated leaving behind copper(ii) Sulphate and water as residue.
Here is the reaction
Cu + 2H2SO4 (conc.) —–heat—> CuSO4 + SO2(g) + 2H2O
Does Copper React with Water?
As it is cleared now, that copper does not react with acid easily and therefore, there is no chance of copper to react with water as well.
Although copper does not react with water, it slowly reacts with the oxygen present in the atmosphere and forms a brown-black layer of copper oxide on its surface.
This layer should not be misunderstood with the layer of rust like in iron. The brown-black layer of copper oxide acts as a shield to protect the copper to gets further corrode.
It should be clear that Copper neither reacts with hot water nor cold water.
Physical Properties of Copper
- Copper exists in a soft state
- It is malleable and ductile in nature.
- On exposure to air, pure copper has orange-pinkish color.
- It is a good conductor of heat and electricity.
- The melting point of copper is around 1083.4 +/- 0.2 degrees Celcius.
- The boiling point of copper is 2567 degrees Celcius.
- The density of this metal is 8.96 g/cc.
Chemical Properties of Copper
- Copper metal does not react with water.
- It does not get corrode easily. On exposure to air, it corrodes slowly as compared to other metals.
- Copper compounds give greenish flame on combustion.
- With some compounds, copper has oxidation state +1 and with some, it has oxidation state +2.
- The aqueous solution of copper with the +1 oxidation state is colorless and with oxidation state +2 is blueish color.
Uses of Copper
- Copper metal is used in preparing alloys. Bronze and Brass are a few examples of alloys made from copper.
- The copper metal is widely used in the electrical industries.
- Copper is used in the manufacturing of utensils as it can reduce inflammation within the stomach and kill the bacteria.
- Copper is used in making motor wires as it has good electrical properties.
- It is also used for roofing of buildings as it corrodes slowly.