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Conductivity is inversely proportional to the resistance. Pure water cannot conduct electricity but due to the presence of ions in the water, it can conduct electricity. The salt dissolved in the water dissociates into ions and increases the electrical conductivity of the solution. The conductivity of any solution is affected by temperature and the concentration of the solution.
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Key Takeaways: Conductivity, Water, Resistance, Electricity, Ions, Solution, Salt, Electrical conductivity, Resistivity, Voltage
Read More: Applications of Thermal Conductivity
Conductivity
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Conductivity is the property of a body to allow an electric current to pass through it when voltage is applied. Conductivity of a substance is inversely proportional to the resistance. Resistance of a material is measured in ohms and conductance is measured in mhos or siemens. Resistivity is measured in Ωm and conductivity has an SI unit of S/m.
Electrical Conductivity
The formula of conductivity is inverse to resistivity.
σ = 1/ρ
Where,
σ is conductivity
ρ is the resistivity of a material.
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| Difference between resistance and resistivity | Conductors and Insulators | Potential difference |
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Electrical Conductivity of Water
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The capability of water to pass an electric current through it is called the electrical conductivity of water. In simple words, it is also the degree to which the water conducts or transmits electricity. Electrical conductivity is denoted by S. It is directly dependent upon the concentration of conductive ions present in the water. The main sources for these conductive ions in organic materials like chloride, carbonate, alkalis, and dissolved salts.
There are multiple units that can be used to measure conductivity of water.
- SI Unit: Siemens/meter (S/m)
- U.S Units - millimhos per centimeter (mmho/cm)
When chemicals and salts are dissolved in water as negative and positive charge ions, these free ions in water conduct electricity. That’s why the electrical conductivity depends upon the concentration of ions. Pure water is not a good conductor of electricity due to less conductivity.
Typical Conductivity of water
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- Ultra-pure water: 5.5 x 10-6 s/m
- Tap water: 0.0005-0.0008 s/m
- Sea water: 5 s/m
Electrical Conductivity of Water
Factors affecting Conductivity of Water
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Factors affecting the conductivity of water are:
- Concentration of Ions: Conductivity depends on the concentration of ions present in the solution. The higher the number of ions, the higher will be the conductivity of water.
- Type of Substance: Conductivity depends upon the type of substance that is dissolved in the water.
- Mineral Purity: Conductivity depends upon the mineral purity. If minerals as impurities are added in the water, the ionic bonds present in water conduct electricity and the electrolytic conductivity of water also increases.
- Temperature: Conductivity depends upon the temperature as electrical conductivity increases with an increase in temperature. Warm water has less viscosity and has greater electron movement; thus, it allows the free flow of electric current.
Conductivity of Water
Things to Remember
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- Free electrons present in the conducting material are responsible for the conduction of electric current in the water.
- Resistivity of a substance is inversely proportional to the number of free electrons present per unit volume.
- Elements like copper, steel can be used in electrical circuits for generating electrical conductivity.
- Substances like graphene and diamonds can be used to generate heat.
- Alloys are substances that have a very weak dependency on temperature and they have a high resistivity.
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Sample Questions
Ques. Why does distilled water not conduct electricity? (2 Marks)
Ans. Distilled water is the purest form of water. It is used in chemical reactions and thus, it doesn’t have ions present in it. Since there are no ions to conduct electricity, distilled water doesn’t conduct electricity. While tap water contains ions like magnesium, calcium, etc. which conduct electricity. Due to the acidic nature of rainwater and pollutants present in the air, it sometimes conducts electricity due to the presence of ions.
Ques. What are the applications of conductivity of water? (2 Marks)
Ans. Conductivity can be used as a measure of the quality of water. It can be used to check the salinity of water during water treatment. Environmental pollution like agricultural run-offs, acid rains, etc. can also be noticed by measuring the conductivity of the samples.
Ques. How is concentration related to conductivity? (3 Marks)
Ans. Conductivity is used as a measure of electrolytic concentration. In a solution of one electrolyte and water, the conductivity is directly proportional to the concentration. Strong electrolytes dissolve in water, giving higher conductivity values than weak electrolytes. For more electrolytes, the conductivity curve reaches a maximum value, hence reversing the slope of the curve. We can measure conductivity in the increasing and decreasing parts of the curve.
Ques. What is specific conductance? (2 Marks)
Ans. Specific conductance of a material is the capability to conduct electricity. It is the reciprocal of specific resistance. Specific conductance is defined as the conducting capacity of a solution of dissolved electrolyte and the whole solution is being placed between two electrodes. It is denoted by Kappa. Unit of specific conductance is siemens cm-1.
Ques. What are types of conductivity? (5 Marks)
Ans. Types of conductivity are:
- Electric conductivity - Measures to know the capability of a material to conduct electric current.
- Electrolytic conductivity - Electrolytic conductivity is the electrical conductivity of a solution.
- Ionic conductivity - It is the electrical conductivity that takes place in ions moving in a crystal lattice at solid-state.
- Hydraulic conductivity - It is the property of porous material’s ability to transmit water.
- Thermal conductivity - It is the intensive property of a substance that indicates the ability to conduct heat.
Ques. How is the conductivity of water tested? (2 Marks)
Ans. The electrical conductivity of water is tested by taking the resistance of solution between two flat or cylindrical rods separated by a fixed distance from both sides. An alternating voltage is applied in order to avoid the process of electrolysis. Hence, the resistance is measured by the conductivity meter.
Ques. How is conductivity achieved? (3 Marks)
Ans. Conductivity is achieved by the following methods -
- When the electrolytes dissolve in water, they separate into cation or positively charged ions and anions or negatively charged materials.
- As dissolved substances tend to separate in the water, the concentration of cations and anions remains the same.
- The ions present in the water conduct electricity due to the presence of positive and negatively charged particles present in it.
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