Tap water is also known as running water or municipal water. It is supplied to the households by the government agencies and the supply standards differ from one country to another. It is used for cooking, cleaning, etc.
Tap water is different from the freshwater collected from natural water sources or hand pumps, etc. It is obtained by treating water collected from different sources with various purification techniques.
It is majorly provided in the urban and sub-urban areas and involves a complex system of collection, storage, purification, and supply.
So, Is tap water a mixture? Yes, tap water is a mixture. Tap water consists of minerals (CaCO3, Mg, etc.), microbes (bacteria or other pathogens), purifying agents (like chlorine), and other impurities in variable amounts. However, these are only mixed physically, and hence, it is a mixture. These substances are dissolved in water and form a solution in which the composition of different substances remains constant throughout. Hence, tap water is a homogeneous mixture.
Let us study it in more detail.
Why is Tap Water a Mixture?
A mixture is formed when two or more substances are mixed with each other only physically.
There is no chemical association between the mixed substances i.e. the chemical properties of all the substances participating in the formation of the mixture remain the same without losing the original identity of the substance.
The physical properties of the combining substances also remain the same. However, the physical properties of the mixture may differ from any or all of its constituents.
The constituents of a mixture can be easily separated from each other making use of their physical properties by boiling, distillation, electrolysis, chromatography, etc.
A few examples of the mixture are air, ink, crude oil, salt in water, sand & sugar, etc.
Tap water is a mixture because the various substances mixed with water are not associated chemically. As no chemical bonds are formed the chemical properties of water, as well as the other substances, remain unaltered.
The physical properties of water such as boiling point, melting point, etc. may be slightly affected based on the impurities and their percentage in the mixture.
It is actually a solution in which various impurities, which act as a solute, are dissolved in water, which is here a solvent.
The solvent, as well as solute particles, are evenly distributed across the mixture.
Types of Mixture
Mixtures, based on their properties, are divided into two types:
1. Homogeneous Mixture: In such mixtures, all the components of the mixture, viz. elements or compounds, are uniformly distributed throughout.
This means that if a particular quantity of the mixture is taken from the different points of that very mixture, the number of different components remains the same indicating that the properties and combination of different components are identical for the entire mixture.
They have only one visible phase. For example tap water, alloys, salt solution, etc.
2. Heterogeneous Mixture: The mixtures in which the composition and properties of the mixture differ from one point to another are known as heterogeneous mixtures.
The constituent substances of such mixtures are distributed unevenly and can be easily distinguished from each other just on the basis of appearance.
A few examples include air, crude oil, sand & salt mixture, etc.
Why is Tap Water a Homogeneous Mixture?
In tap water, a number of substances like minerals, salts or impurities, etc. are dissolved in water. They form a solution with water working as the solvent and the impurities as solute.
The different molecules are uniformly distributed throughout the solution and cannot be distinguished based on their appearance i.e. have one visible phase.
However, the chemical, as well as physical properties of the constituent particles, remain the same.
The properties of tap water, on the other hand, differ from pure water.
Is Tap Water a Pure Substance?
Pure substances are the form of matter composed of only one type of atom or molecule.
Therefore, elements are considered pure substances as they are composed of only one type of atoms while in compounds the two or more types of atoms are chemically combined together to form a molecule which is their basic unit, and hence, compounds are also pure substances.
Pure substances have uniform composition. For example, Aluminium Oxide is a compound consisting of numerous Al2O3 molecules in which the proportion of aluminum and oxygen atom remains constant throughout i.e. 2:3 ratio.
Moreover, pure compounds have definite chemical and physical properties irrespective of the source from which they were collected. They require chemical processes of separation to part away from the basic constituent particles.
Tap water is not a pure substance as it is composed of more than one type of atom and molecule.
Further, the properties of tap water may change from one sample to another depending upon the percentage of added minerals or impurities present in that particular sample.
This also affects the physical and chemical properties of tap water which vary depending upon its composition and the constituent units may be separated from each other using mechanical or thermal (physical) measures.
Tap Water Vs. Distilled Water
Tap water is usually collected from either natural sources of water like rivers or man-made sources like canals or rain-fed lakes etc. It is disinfected and purified using various chemicals.
After undergoing a few processes the tap water is made usable for household purposes.
However, some unwanted substances are still present in the water due to which the tap water may be unfit for drinking or human consumption.
You would have heard cases of water poisoning, or other water-borne diseases like typhoid, cholera, etc.
Therefore, tap water is further processed or purified to make it suitable for consumption. Usually, three methods are used in various water purification systems:
• Reverse Osmosis: In this water is made to pass through a semi-permeable membrane against osmotic pressure. It removes the impurities and salts but allows the minerals to pass through, thus obtaining clean water.
• Deionization: It removes the minerals, salts, impurities, etc. from water.
• Distillation: In this process water is boiled and the steam obtained is collected in a vessel which is then cooled and again turned to water.
This removes all the minerals, salts, impurities, etc. from the water, and distilled water is obtained.
The distilled water, therefore, is obtained after the purification of tap water using the distillation technique. It is considered good for human consumption as any disease-causing microbe or any other impurity is clearly removed.
However, this process also removes the essential minerals and salts from water which are required for the active functioning of the human body.
Therefore, consumption of distilled water for a prolonged period of time may result in deficiency diseases.
Below is an interesting video of the process of reverse osmosis.
Why does tap water conduct electricity while distilled water does not?
The tap water consists of various minerals and salts. When these salts and minerals are dissolved in water they dissociate into their constituent ions.
These ions are freely moving entities that carry their own charge both positive as well as negative.
To conduct electricity through tap water a positive (cathode) and a negative (anode) electrode is inserted into it after being connected to a source of charge.
As the charge is applied through tap water the ions present start responding to the electric field according to their charge.
The positive ions are attracted to the anode while negative ions are attracted to the cathode. Therefore, the current starts flowing through tap water with the movement of charges.
The distilled water on the other hand is devoid of any minerals or salts and hence, no ions are present in it. As the ions or charged particles are responsible for the flow of current distilled water does not conduct electricity.
You must also read out the article I wrote on does distilled water conduct electricity.
Water is a colorless, odorless, tasteless liquid. However, the properties of tap water cannot be completely ascertained as they depend upon the various dissolved components.
Nevertheless, the important properties of water are given in the table below.
Any deviation from these properties is an indicator of impurities some of which might be dangerous and such water will be considered unsuitable for human use.
|Molar mass||18.0151 grams per mole|
|Melting point||0 °C|
|Boiling point||100 °C|
|Density||0.99701 grams per cm3 (25 °C)|
|Maximum density||1 gram per cm3 (at 3.98 °C)|
|Vapour pressure||23.75 torr (25 °C)|
|Heat of vaporization||40.65 KJ per mole (100 °C)|
|Heat of formation||−285.85 KJ per mole (25 °C)|
|Heat of fusion||6.010 KJ per mole (0 °C)|
|Entropy of vaporization||118.8 joules per °C mole (25 °C)|
|Surface tension||71.97 dynes per cm (25 °C)|
Tap water is used for cooking, cleaning, drinking, washing, toilet flushes, and other domestic purposes. It is also used for watering household plants etc.
• Tap water is a mixture as it contains various minerals, salts, and impurities that are not chemically bonded.
• It is a homogeneous mixture as the various components are dissolved in water making it a solution. Therefore, the composition of tap water is uniform throughout.
• Tap water is not a pure substance as it contains more than one type of atoms and molecules that are not bonded chemically.
• Distilled water is different from tap water as it does not contain any minerals or salts. Therefore, distilled water does not conduct electricity but tap water is a good conductor of electricity due to the presence of free ions.
• Tap water is used for domestic or household purposes.