In this explainer, we will learn how to describe and explain the properties of the element sodium and its compounds.
Sodium is an incredibly important and interesting element for chemists to study. It is vital for many industrial processes, and compounds of sodium are frequently found in everyday household items. Sodium is not just important for modern society; it is also essential for regulating basic bodily functions. Our bodies need sodium and potassium ions to perform essential homeostatic processes, such as the maintenance of fluid volume and blood pressure.
Sodium is a group 1 element and, like other alkali metals, it is a powerful reducing agent. Sodium is generally considered to be a very reactive element because it can readily lose its single valence electron. It is therefore unsurprising that sodium is not found in an isolated state and is always found bonded to other elements. Sodium is most commonly found in sodium chloride () mineral salts.
In order for us to isolate sodium metal from sodium chloride, electrolysis of the molten salt is used, often using a flux to reduce the melting point of the halide salt.
During the electrolysis process, electrons are gained at the cathode as shown in the equation and lost at the anode as shown in the equation
Example 1: Identifying Oxidation and Reduction during the Electrolysis of Molten Sodium Chloride
Sodium metal could be prepared from its ore by the electrolysis of molten sodium chloride. Which of the following best describes this process?
- Chloride ions are oxidized at the cathode and sodium ions are reduced at the anode.
- Chloride ions are reduced at the anode and sodium ions are oxidized at the cathode.
- Chloride ions are oxidized at the anode and sodium ions are reduced at the cathode.
- Chloride ions are reduced at the cathode and sodium ions are oxidized at the anode.
The electrolysis of sodium chloride can be simplified through the use of half-equations that describe reactions that happen at the two separate electrodes.
During the electrolysis of sodium chloride, positive sodium ions are attracted to the negative cathode where they gain an electron to become an atom of sodium metal. The negative chloride ions are attracted to the positive anode where they give up electrons and form covalently bonded chlorine molecules. Oxidation and reduction can be considered in terms of the gain and loss of electrons, where the gain of electrons is reduction and the loss of electrons is oxidation.
Combining these pieces of information, we know that chloride ions are oxidized at the anode and that the sodium ions are reduced at the cathode, leading us to the correct answer, C.
We will be covering a large number of reactions in this explainer and we will start by looking at the reactions that are related to the element itself rather than the compounds of sodium.
Perhaps the most well-known reaction involving sodium metal is sodium metal’s reaction with water, which is a highly exothermic reaction producing a strongly alkaline solution and hydrogen gas that can ignite during the reaction:
In a similarly vigorous reaction, sodium will react with dilute mineral acids to produce salt solutions and hydrogen gas, such as in this reaction with hydrochloric acid:
Sodium can also react in a direct combination reaction with hydrogen to form sodium hydride:
The hydride can then be reacted with water to form the hydroxide and hydrogen gas in a similar fashion to the reaction between sodium metal and water:
Other direct combination reactions involving sodium metal are the reactions with halogens to form the well-known ionic halide compounds:
In other direct combination reactions, sodium metal reacts with elemental sulfur and phosphorus to form sodium sulfide and sodium phosphide respectively:
The final reactions we will examine involving sodium metal are the reactions with oxygen, which form different oxides. The simplest of these reactions produces a common group 1 oxide:
It is also possible to make different peroxides and superoxides when sodium reacts with oxygen. Sodium can react with oxygen and form the compound sodium peroxide ():
Sodium can even react with oxygen and make the sodium superoxide molecule:
Peroxides and superoxides are themselves also very reactive compounds, and they can react with water to form hydrogen peroxide in alkaline solutions:
Peroxides and superoxides also react with dilute mineral acids:
In a fascinating piece of chemical history, a form of sodium dioxide () was once used in the development of escape apparatus for early submarines at the start of the 20th century.
The compound known as “oxylithe” was secured inside the helmet of the submariner and the carbon dioxide in the seamen’s breath caused a reaction that produced oxygen, theoretically preventing the seamen from suffocating. A similar reaction is
However, this design was not without issues, and as we have seen, these superoxides are incredibly reactive, meaning that the sodium dioxide had a tendency to ignite when coming into contact with water, an occurrence that was highly plausible during the early days of submarines!
Example 2: Identifying Products and Reactants in the Reaction between Sodium Peroxide and Water
Sodium metal is reacted with oxygen to form a peroxide, . In , the oxidation number of oxygen is . is then reacted with water to form a caustic chemical and a second aqueous species, .
- What is the chemical formula of ?
- What is the correct identification of ?
In order to correctly identify the chemical formula of , we are given a piece of information about the oxidation number of oxygen. We may already know the formula of , but if we do not, we know that the oxidation number of sodium is always and that sodium can form different oxides such as , , and . Using simple math, we can identify the formula of the peroxide as .
When sodium peroxide reacts with water, sodium hydroxide is formed, which is the caustic chemical mentioned in the question. The other product formed in this reaction is hydrogen peroxide.
As we move now into the second half of this explainer, we begin to examine some of the properties and reactions of common sodium compounds.
Perhaps one of the most common sodium compounds is sodium hydroxide, the white hygroscopic compound shown below. It is soapy to the touch and corrosive to the skin.
Hygroscopic substances have a tendency to attract and hold water molecules from the air by absorption or adsorption.
Example 3: Identifying the Correct Safety Symbol for Corrosive Substances
Which of the following safety symbols might you see on a container of sodium hydroxide?
It is important for all chemists and students of chemistry to have a very secure understanding of the meanings of different safety symbols. The symbol in answer A indicates that the chemical is flammable, that in answer B indicates that the chemical may be harmful to the environment, and that in answer C indicates that the chemical may be corrosive, which is our correct answer. Answer D indicates that the chemical is an explosion hazard, and answer E indicates that the chemical is oxidizing. As such, the correct answer is C.
Sodium hydroxide is frequently dissolved in water to form an alkaline solution, and it can be reacted with hydrochloric acid to make sodium chloride:
Sodium hydroxide can also be reacted with sulfuric acid to make sodium sulfate:
Sodium hydroxide has many uses. Among the most important of these uses is its use in the production of soap, synthetic silks, and papers; it is also used by the petroleum industry for the treatment of acidic impurities.
Sodium hydroxide can also be used to detect the presence of basic radicals, such as copper(II) ions. Initially, the hydroxide ions react with the copper ions to form the insoluble pale blue precipitate of copper(II) hydroxide:
The identity of the copper(II) hydroxide can be confirmed through heating, as copper(II) hydroxide will decompose to copper(II) oxide, which has a characteristic black color:
Another example of sodium hydroxide’s uses is the qualitative analysis and detection of aluminum ions through the production of a white precipitate. First, there is the initial production of the insoluble aluminum hydroxide:
After that, the additional aqueous sodium hydroxide solution dissolves the solid hydroxide, forming sodium meta-aluminate:
Other white precipitates, such as magnesium hydroxide, do not dissolve in excess alkali in the same way as aluminum hydroxide.
Another sodium compound is sodium nitrate and although potassium nitrate will explode when heated, sodium nitrate will, in fact, undergo thermal decomposition to give a nitrite and oxygen gas:
A very important sodium compound with industrial importance is sodium carbonate (), which can be prepared in the laboratory by passing carbon dioxide gas through a hot solution of sodium hydroxide:
The sodium carbonate formed in the previous reaction is the hydrated form of the carbonate and is sometimes referred to as “washing soda“ with the chemical formula . The term “washing soda“ relates to the ability of this compound to remove calcium and magnesium ions from hard water sources through the precipitation of insoluble carbonates:
When large quantities of sodium carbonate are needed on an industrial scale, the Solvay process is used. This involves two steps. First, sodium hydrogen carbonate is produced from a saturated sodium chloride solution, which has ammonia and carbon dioxide gas bubbles through it:
Then, the resulting hydrogen carbonate is thermally decomposed to produce the required sodium carbonate:
Large quantities of sodium carbonate are produced, as it has a wide number of uses due to the fact that it can be dissolved in water to produce a weakly basic solution and is resistant to decomposition, unlike lithium carbonate that decomposes into lithium oxide and carbon dioxide gas. Sodium carbonate can also be used to neutralize acids:
It is these reactions and others that make sodium carbonate vital to the glass, paper, and textile industries as well as to the softening of water in towns and cities.
Example 4: Identifying the Common Uses of Sodium Carbonate
Which of the following is not a common use of sodium carbonate?
- Sodium carbonate is added to silica and other compounds in the production of glass.
- Plant material is boiled in sodium carbonate solution in the production of paper.
- Sodium carbonate is used to soften water by removing magnesium and calcium ions.
- Sodium carbonate is the main ingredient in oven cleaners and drain-unclogging solutions.
- Sodium carbonate is used for curing fibers as well as for dyeing and printing in the textile industry.
We know that sodium carbonate is vital to the glass, paper, and textile industries and that it is also used to soften water. With this information in mind, let us look more closely at the proposed uses in this question.
Answer A involves the use of silica and sodium carbonate in the production of glass, which is a common use of sodium carbonate and so not the correct answer. Similarly, answer B gives us some additional information, but once again, we know that sodium carbonate is used in the paper industry. So, it seems likely that answer B is not the answer we are looking for. In answer C, sodium carbonate is used to soften water, and we know that magnesium and calcium carbonates are both insoluble carbonates and that this is the principle behind which sodium carbonate can be used to soften hard water. So, answer C is incorrect. As such, the correct answer is D.
Answer D involves sodium carbonate being used to clean ovens and unclog drains. However, such cleaning tasks require a caustic substance and it is, in fact, sodium hydroxide that is often used for both of these jobs, meaning answer D is likely the answer we are looking for. In order to eliminate answer E, we can see that sodium carbonate here is used during steps of the dyeing and printing processes in the textile industry, which we know is a common use. So, answer D is the correct answer.
As we have discovered in this explainer, sodium has a myriad of different reactions, compounds, and uses and is as vital to reactions taking part inside the cells of our body as it is to reactions producing millions of tons of products on an industrial scale all over the world.
- Sodium is a group 1 metal that is very reactive and must be isolated using electrolysis.
- Sodium reacts with nonmetals such as oxygen, hydrogen, sulfur, and phosphorus.
- Sodium is capable of forming different types of oxides, such as , , and .
- Sodium hydroxide is a common compound of sodium that is caustic in nature, has many uses, and undergoes many different chemical reactions.
- Sodium carbonate is another industrially relevant compound that is produced en masse using the Solvay process.