Electrolytes and Non-Electrolytes
Senior 2 · Chemistry
Electrolytes and Non-Electrolytes
Lesson 3 of 3
20 min
Diarrhoea is still a leading cause of death among young children worldwide, and the reason is not the germ alone. The body loses water and the dissolved salts that keep its cells working. A packet of oral rehydration salts, which costs very little at a health centre, replaces both. It is one of the most important applications of electrolyte chemistry, and there are many others in your home, your phone and the workshops of your town.
Your blood and the fluids in and around your cells contain dissolved ions: sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), chloride (Cl−), hydrogencarbonate (HCO3−) and hydrogenphosphate (HPO42−). In medicine these ions are simply called "electrolytes". They:
Sweating during hard work or sport, vomiting and diarrhoea all remove water and electrolytes. Losing too much causes dehydration, cramps, weakness and, in severe cases, heart problems.
An ORS sachet contains sodium chloride, potassium chloride, sodium citrate and glucose, measured to be dissolved in a stated volume of clean water, usually 1 litre. The three salts are electrolytes and replace the lost ions. Glucose is a non-electrolyte, but it is essential: the gut absorbs sodium together with glucose, so the glucose helps the body take up the salt and, with it, the water.
The volume of water matters. A sachet dissolved in too little water makes a solution that is too concentrated, which can pull even more water into the gut and make dehydration worse. Always follow the instructions on the packet, and ask a health worker for advice.
Many foods are also rich in electrolytes: bananas, avocados, potatoes and beans supply potassium, and milk supplies calcium. Sports drinks contain sodium and potassium salts for athletes who sweat for hours.
Every battery has an electrolyte between its two electrodes. Inside the battery, ions carry the charge from one electrode to the other and so complete the circuit.
A conductivity meter gives a quick measure of how many ions are dissolved in a sample. It is used to check the purity of drinking water and of water for laboratories and hospitals, and to monitor salt levels in irrigation water and soil.
Because natural water always contains dissolved ions, it conducts. Never touch switches, plugs or appliances with wet hands; keep electrical equipment away from water; and never use electrical devices while standing in water. Sweat on your skin also contains salts, which is another reason electricity and wet skin are a dangerous mix.
An ORS sachet lists glucose, sodium chloride, potassium chloride and sodium citrate. Which are electrolytes, and what would happen if the sachet were dissolved in half the stated volume of water?
Tip
Three places electrolytes work for you: body, battery, bath
Body: ions for nerves and muscles, replaced by ORS. Battery: an electrolyte carries charge between the electrodes. Bath: the plating bath, a salt solution in which metal is deposited by electrolysis. In an application question, name the electrolyte and say what the ions do.
Name three electrolytes (ions) in the human body and give one job they do.
Solution: For example Na+, K+ and Cl− (also Ca2+, Mg2+, HCO3−). They carry nerve signals, make muscles contract and control water balance.
Why does ORS contain glucose even though glucose is not an electrolyte?
Solution: The gut absorbs sodium together with glucose, so glucose helps the body take up the salts, and with them water, more quickly.
What is the electrolyte in a car battery?
Solution: Dilute sulfuric acid.
In copper-plating a steel key, which electrode is the key, and which electrolyte is used?
Solution: The key is the negative electrode (cathode), and the electrolyte is a copper salt solution such as copper(II) sulfate solution.
Pure water is a very poor conductor. Why is it still dangerous to touch a switch with wet hands?
Solution: The water on your hands is not pure: it contains dissolved salts from the tap and from your sweat. These ions let the water conduct, so a current could pass through your body.
Summary
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
