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You wish to increase the carbon content of a slab of steel by exposing it to a carburizing atmosphere at elevated temperature. The carbon concentration in the steel before carburization is 359.5 ppm and is initially uniform through the thickness of the steel. The atmosphere of the carburizing furnace maintains a carbon concentration of 6695.0 ppm at the surface of the steel. Calculate the time required to carburize steel so that the concentration of carbon at a depth of 38.0 x 10-2 cm is one half the value of the carbon concentration at the surface. The diffusion coefficient of carbon in steel is 3.091 x 10-7 cm2/s at the carburizing temperature. Express your answer in hours.

DATA: Error Function Values erf(ξ

17 December 2012
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Reacting Carbon Dioxide with Lime water

You may often come across a question "What gas turns limewater cloudy?" The answer to this question is well known. Carbon dioxide is the only gas that turns lime water cloudy. You may be wondering what is lime water used for. Limewater is an aqueous solution of slaked lime and you will find it in antacids, medicines and lotions. But one of its most noteworthy property is that it is used to absorb carbon dioxide from the air. In this article, we have answered all the questions related to the reaction of lime water and CO_2.

What happens when Lime Water reacts to Carbon Dioxide?

Carbon dioxide reacts with limewater to form calcium carbonate, which precipitates out of the solution. The carbon dioxide and limewater react to produce water in addition to the calcium carbonate. Calcium carbonate is chalk, and when it is produced, it precipitates and solid particles of chalk appear. The appearance of this solid makes the liquid appear ‘milky’. The white milky suspension/precipitate is caused by the formation of calcium carbonate. The characteristic carbon dioxide test, is checking that the limewater is milky. This is because chalk is precipitating in the limewater. Bubbling carbon dioxide through the solution for an extended period of time makes the solution become clear and colorless. This happens as the carbon dioxide forms acidic carbonic acid when it dissolves in the water, the carbonic acid (H2CO3) reacts further with the calcium carbonate. This chemistry is important in understanding how hard water is formed and then limescale is formed in kettles and hot water boilers.

Carbon dioxide and lime water experiment
What happens when you mix carbon dioxide and lime water?

Written as an Equation

In its equation form that makes:

Ca(OH)_{2(aq)} + CO_{2(aq)} \rightarrow CaCO_{3(s)} \downarrow + H_2O_{(l)}


How to test for carbon dioxide?

Now, we will answer how to test for carbon-dioxide. One of the most effective ways to test for carbon dioxide gas is the limewater test. When carbon dioxide reacts with lime water (calcium hydroxide solution), a white precipitate of calcium carbonate is produced. The solution of calcium hydroxide is limewater and if carbon dioxide bubbles through the limewater, it turns cloudy white or milky.

How does carbon dioxide turns lime water milky?

When limewater which is a solution of calcium hydroxide, Ca (OH)_2 reacts with the carbon dioxide gas, an insoluble solid known as calcium carbonate CaCO_3 is generated. The equation of this reaction is given below:  

Ca(OH)_{2(aq)} + CO_{2(aq)} \rightarrow CaCO_{3(s)} \downarrow + H_2O_{(l)}

Now, the question arises why the solution turns milky. Well, the answer is simple, The reason for the milky solution is that calcium carbonate which is produced as a result of this reaction is a white precipitate. This nature of calcium carbonate also helps us to test for the presence of carbon dioxide gas. All you have to do is to bubble the gas through a solution of calcium hydroxide. If the gas is carbon dioxide, then the solution will turn milky. If not then the gas which is subjected to the test is not carbon dioxide. If you continue to bubble the carbon dioxide gas through limewater, you will witness another acid-base reaction that will dissolve the precipitate to generate soluble calcium hydrogen carbonate. The equation of this reaction is given below:

CO_{2(g)} + H_2O_{(l)} + CaCO_{3(s)} \rightarrow Ca(HCO_3)_{2 (aq)}

This reaction shows another phenomenon that we may have seen in our daily lives. The naturally occurring acid rain chemically erodes the limestone and results in the formation of a cave. As this solution evaporates, the reverse reaction occurs which results in the formation of stalagmites and stalactites.

What is the reaction between carbon dioxide and water?

When carbon dioxide reacts with water, it dissolves, while some of it reacts with water molecules to generate an acidic solution known as carbonic acid.  Limewater and CO_2 reaction results in a carbonic acid. It is a weak acid and it is in an aqueous form, i.e., it is a water solution. The chemical equation of this reaction is given below:

CO_{2(aq)} + H_2O \righleftharpoons H_2CO_{3(aq)}


Since it is a weak acid, therefore some of it dissociates to generate H+ ions. This depicts it is a slightly acidic solution that forms hydro carbonate ion.

H_2 CO_{3(aq)} \rightarrow H+_{(aq)} + HCO_{3 - (aq)}

HCO_{3 - (aq)} \rightarrow H+_{(aq)} + CO_{3 - 2 (aq)}


All of these reactions are reversible.

Does lime water absorb carbon dioxide?

Yes, limewater absorbs carbon dioxide. When lime water and carbon dioxide reacts, calcium carbonate is generated along with the water. Calcium carbonate is an insoluble salt. The equation of this reaction is given below:

Ca (OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O


Why is lime water used in experiments?

Limewater is used in experiments because it is the easiest way to detect the presence of CO_2 gas. Limewater is a calcium hydroxide solution that produces a white precipitate of calcium carbonate when it reacts with carbon dioxide. The white precipitate can be easily detected by the person conducting the experiment. Due to this fact, you will often see that limewater is used to detect the presence of carbon dioxide.

How does copper oxide and sulphuric acid react to eachother?

In this article, we will discuss and answer all the questions related to the reaction of copper oxide and sulphuric acid in detail. But before proceeding to the questions and their relevant answer, first, let us introduce you to sulphuric  acid and copper oxide. Sulphuric acid is a strong acid that is formed by oxidizing solutions of sulphur dioxide. The sulfuric acid formula is H_2SO_4. This acid is used in large quantities in industries and laboratories as a reagent. The concentrated form of sulphuric acid is a dense, oily, and corrosive. The other compound copper oxide is a compound that is formed when two elements copper and oxygen react with each other. Its formula is CuO.

Reacting Copper Oxide with Sulphuric Acid

Mixing copper oxide and sulphuric acid is an experiment involving an insoluble metal oxide which is reacted with a dilute acid to form a soluble salt. Copper (II) oxide, is a black solid, which, when reacted with sulphuric acid creates a cyan-blue coloured chemical called copper II sulfate. Copper (II) oxide reacts with sulfuric acid to create water and copper (II) sulfate. This reaction could be classified as a double displacement reaction or a neutralization reaction.

copper sulphate
Copper sulphate takes on a bright blue colour

Writing the Equation form of  Copper oxide + Sulphuric Acid

This chemical reaction can be written as the following:

CuO + H_2SO_4 \rightarrow CuSO_4 + H_2O

Copper oxide(solid) + Sulphuric Acid (aqueous)-> Copper Sulphate (aqueous)+ Water(liquid) To find out how you can make Copper Sulphate at home check out this article.  

What happens when the copper reacts with concentrated Sulphuric acid?

The reduction potential of diluted sulphuric acid is higher than that of hydrogen. Copper is unable to displace hydrogen from non-oxidizing acids, for instance, hydrochloric acid or diluted sulphuric acid. In other words, we can say that the copper does not react with the diluted sulphuric acid. However, it does react with the concentrated sulphuric acid because sulphuric acid in concentrated form is an oxidizing agent. When copper gets heated with concentrated sulphuric acid, there is a redox reaction and the acid turns into sulfur dioxide. The equation of this chemical reaction is given below:

Cu + 2H_2SO_4 \rightarrow CuSO_4 + SO_2 + 2H_2O

What is the balanced equation for copper oxide and Sulphuric acid?

The  copper oxide and sulphuric acid balanced equation is given below:

CuO + H_2SO_4 \rightarrow CuSO_4 +  H_2O


Why do copper oxide and Sulphuric acid turn blue?

We all know that the copper oxide + sulfuric acid reaction results in a blue-colored chemical. But have you ever wondered why copper oxide sulphuric acid reaction results in a blue-colored chemical? Well, we will answer this question in detail here. Copper oxide is a black-colored solid. When it reacts with sulphuric acid, it produces a cyan-blue colored chemical which is known as copper sulphate. The blue color is due to the formation of soluble salt. The copper and sulphate ions dissociate as the copper sulphate gets dissolved in water. Although there is no change in the effect, however, the nature of the split between t2g and eg orbitals in this new complex is such that it absorbs reddish-orange light. Due to this absorption, you will see a bluish-colored solution.  

Does sulfuric acid dissolve copper?

No, sulphuric acid cannot dissolve the copper.  However, if dissolution is observed, it can be due to one of the following two reasons:

  • There is a possibility that the surface of copper metal powder is partially oxidized into Cu_2O. Sulphuric acid can dissolve the copper surface that has been oxidized
  • The formation of a vortex during the agitation. A tiny amount of air (oxygen) that was introduced to a leach solution acted like an oxidant.


What salt is produced when copper oxide reacts with hydrochloric acid?

The reaction of copper and hydrochloric acid is not possible. However, copper oxide can react with this acid. When a  metal reacts with an acid, a redox reaction occurs. Because of the higher reduction potential of copper as compared to hydrogen, it is unable to react with non-oxidizing acids like sulphuric acid and hydrochloric acid.

But copper oxide is not a metal, rather it is a metal oxide. Metal oxides are basic substances that can react with acids to form salt and water. These acid-base reactions are also known as neutralization and are non-redox in nature.

Being a weak base, copper oxide reacts with HCL easily to generate a soluble copper chloride and water. The equation of this chemical reaction is given below:

Cu_{(s)} + 2HCL_{(aq)} \rightarrow CuCl_{2(aq)} + H_2O_{(l)}