Conductivity of Water

What is Conductivity?

Conductivity is inversely proportional to resistance. This is the property of a metal to conduct current when voltage i.e, potential difference is passed through it. Here, resistance is measured in ohms whereas, conductivity in mhos. As such, ohm becomes mho because of the applied condition.


Electric metals and solutions of ionic salts in water are good conductors. Even though the human body has high resistance, it still conducts electricity, so we get electric shock.

Simply, the Ohm’s law can define Conductivity as:


V=IR


Where,

R is resistance,

I is current and

V is voltage present in a material


From the above formula, conductivity depends on the number of charge carriers (electrons) in the material and their mobility. In metal, it is assumed that all outer electrons are free to carry charge. Further, impedance for flow of charge is mainly due to electrons bumping each other. Hence, for metal, as the temperature increases, the resistance of the material increases. Here, electrons bump into each other more as they move faster.


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Insulators are tightly bound electrons so that nearly no electrons flow occurs; as a result, they offer a high resistance to charge flow. Free electrons are required for conductance.


The below diagram shows how conductivity of conjugated polymers like polyacetylene can vary from being an insulator to a conductor:


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Conductivity Formula

The formula for conductivity is the inverse of the resistivity that is:

σ=1/ρ​

Here

σ = refers to electrical conductivity

ρ = refers to resistivity


Water Conductivity Units

The ability of the substance to conduct or transmit heat, electricity, or sound is known as conductivity. Its SI unit is Siemens per meter [S/m], U.S customary unit is milliohms per centimeter [mmho/cm], and is denoted by k or s.


Siemens per meter (S.m−1) is conductivity unt. It is also referred to as mho- that is reciprocal of Ohm, and this is incidental by spelling Ohm backwards.


Also, conductance is reciprocal of resistance, and one Siemens is equivalent to reciprocal of one Ohm.


Conductivity of Water

The measurement of the ability of water to pass electrical flow through it is known as conductivity of water. It directly depends on the concentration of conductive ions present in water. The sources of origin for conductive ions are the inorganic material, such as chloride, carbonate, alkalis and sulfide compounds and dissolved salts.


Conductivity of water is also known as the degree to which water conducts or transmits electricity or heat or sound in it, and is denoted by s or k.


Multiple units can be used to measure the conductivity of water, some of which are mentioned below.


Units

SI units

Siemens per meter [S/m]

U.S units

Millimhos per centimeter [mmho/cm]

 

Conductance and Conductivity

  1. Conductance

One must first understand the resistance of an object to understand conductance. Resistance is an elemental property that works in areas of electronics & electricity.. The resistance of a substance tells us how hard it is for an electrical current to flow through it. Also, electrical conductance is considered as a property of the component itself.

  1. Conductivity

There are various things upon which the resistance of a component depends like the conductor's length, area of conductor, and the conductor's material. The conductivity of a material is reciprocal to resistivity and is denoted by Greek letter σ. Conductivity is a specific property of the material at a given temperature.


Electrical Conductivity of Water

The ability of water to conduct an electric current is known as EC or Electrical conductivity of water. Chemicals or salts break down and dissolve in the water as positive and negative charged ions and these free ions in water conduct electricity. As a result, water electrical conductivity depends upon the concentration of ions. 


To calculate the EC of water salinity and total dissolved solids are used, it helps to indicate the water's purity. The conductivity is less for purer water. For example, distilled water acts as an insulator, whereas saltwater is a very efficient electrical conductor.


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Sodium, potassium, calcium, and magnesium are major positively charged ions that affect the conductivity. Similarly, chloride, carbonate, sulfate, and bicarbonate are major negatively charged ions. 


Whereas, nitrates and phosphates are minor contributors to conductivity, but are important biologically. Rain, geology, and evaporation are natural impacts of EC in water. Human impacts include road salt, septic/landfill leachate, impervious surface runoff, and agricultural runoff.

FAQ (Frequently Asked Questions)

1. What is the Difference Between Conductance and Conductivity?

A brief difference between conductance and conductivity is given below:

  • Conductance is the property of components, whereas conductivity is the property of material.

  • Conductance depends on dimensions of conductor, whereas conductivity does not depend on the dimensions.

  • Conductance is measured in Siemens; whereas SI unit of conductivity is Siemens per meter.

2. Is Pure Water a Good Conductor of Electricity?

Pure water isn't a good conductor of electricity since electrical current is transported by ions present in solution. With the rise in concentration of ions, conductivity increases. Hence conductivity increases as water dissolves ionic species.

3. What is Specific Conductance?

Measurement of conductivity made at a specific temperature of 25° C is known as Specific conductance. This is known as a standardized method of achieving conductivity. Since the temperature of the water affects the conductivity reading, reporting conductivity at about 25° C allows the data to be compared easily. The specific conductance is measured in US/cm at about 25° C temperature.


When measurement of conductivity is accomplished at 25° C temperature, it is known as specific conductance. If the measurement is done at different temperatures and is subjected to 25° C temperature, then it is known as temperature coefficient.

4. What are the Types of Conductivity?

The types of conductivity are referred in point wise below:

  1. Electric Conductivity - The measures to know the ability of the material to conduct electric current.

  2. Electrolytic Conductivity - The electrical conductivity of electrolyte in solution

  3. Ionic Conductivity - Electrical conductivity taking place in ions moving position in a crystal lattice at solid-state

  4. Hydraulic Conductivity - The property of porous material ability to transmit water.

  5. Thermal Conductivity - The intensive property of material that indicates its ability to conduct heat.