Tag Archives: electrolyte

Electrolytes — Strong, Weak, and Non Electrolytes

Electrolytes are chemicals that break into ions (ionize) when they are dissolved in water. The positively-charged ions are called cations, while the negatively charged ions are called anions. Substances can be categorized as strong electrolytes, weak electrolytes, or nonelectrolytes.

Strong Electrolytes

Sodium Hydroxide

Sodium hydroxide is a strong base and strong electrolyte. (Ben Mills)

Strong electrolytes completely ionize in water. This means 100% of the dissolved chemical breaks into cations and anions. However, it does not mean the chemical completely dissolves in water! For example, some species are only slightly soluble in water, yet are strong electrolytes. This means that not very much dissolves, but all that does dissolve breaks into ions. An example is the strong base strontium hydroxide, Sr(OH)2. It has a low solubility in water, but dissociates completely into Sr2+ and OH ions. While a flask of sodium hydroxide (NaOH) in water would contain Na+ and OH ions in water, but no actual NaOH, a flask of aqueous strontium hydroxide would contain Sr2+ and OH ions, Sr(OH)2, and water.

Examples: Strong acids, strong bases, and salts are strong electrolytes.

Weak Electrolytes

Ammonia

Ammonia is a weak base and a weak electrolyte. (Ben Mills)

Weak electrolytes partially ionize in water. Pretty much any dissociation into ions between 0% and 100% makes a chemical a weak electrolyte, but in practice, around 1% to 10% of a weak electrolyte breaks into ions.

Examples: Weak acids and weak bases are weak electrolytes. Most nitrogen-containing molecules are weak electrolytes. Water is considered a weak electrolyte by some sources because it partly dissociates into H+ and OH ions, but a nonelectrolyte by other sources because only a very small amount of water dissociates into ions.

Nonelectrolytes

If a substance doesn’t ionize in water at all, it’s a nonelectrolyte.

Examples: Most carbon compounds are nonelectrolytes. Fats, sugars, and alcohols are largely nonelectrolytes.

Why Should You Care?

The most important reason to know whether a chemical is an electrolyte or not and how strongly it dissociates in water is because you need this information to determine the chemical reactions that can take place in water. Also, if you have a container of a chemical in water, it’s a good plan to know whether that substance dissolves in water (its solubility) and whether it dissociates into ions.

A classic example of why this matters is a sodium cyanide (NaCN) solution. You probably know cyanide is reactive and extremely toxic, so would you open a bottle of sodium cyanide in water? If you recognize sodium cyanide is a salt, you’ll know you’re safe (providing you don’t drink the solution) because there is no sodium cyanide in the water, just Na+ and CN ions in water. The cyanide ions aren’t volatile and won’t make you sick. Contrast this with a bottle of hydrogen cyanide (HCN) in water. Would you open that bottle? If you recognize hydrogen cyanide is a weak acid, you’ll know the bottle contains hydrogen cyanide gas, hydrogen ions, cyanide ions, and water. Opening that bottle could cost you your life!

How Do You Know What Chemicals Are Electrolytes?

Now that you’re motivated to know what an electrolyte is, you’re probably wondering how to tell what type of electrolyte a chemical is based on its name or structure. You do this by the process of elimination. Here are some steps to follow to identify strong, weak, and non electrolytes.

  1. Is it a strong acid? There are only 7 of them and you’ll encounter them a lot in chemistry, so it’s a good plan to memorize them. Strong acids are strong electrolyte.
  2. Is it a strong base? This is a slightly larger group than the strong acids, but you can identify the strong bases because they are metal hydroxides. Any element from the first two columns of the periodic table combined with a hydroxide is a strong base. Strong bases are strong electrolytes.
  3. Is it a salt? Salts are strong electrolytes.
  4. Does the chemical formula contain nitrogen or “N”? It may be a weak base, which would make it a weak electrolyte.
  5. Does the chemical formula start with hydrogen or “H”? It may be a weak acid, which would make it a weak electrolyte.
  6. Is it a carbon compound? Most organic compounds are nonelectrolytes.
  7. Is it none of the above? There’s a good chance it’s a nonelectrolyte, though it may be a weak electrolyte.

Table of Strong Electrolytes, Weak Electrolytes, and Nonelectrolytes

CH3OH (methyl alcohol)

Strong Electrolytes
strong acidsHCl (hydrochloric acid)
HBr (hydrobromic acid)
HI (hydroiodic acid)
HNO3 (nitric acid)
HClO3
HClO4
H2SO4 (sulfuric acid)
strong basesNaOH (sodium hydroxide)
KOH (potassium hydroxide)
LiOH
Ba(OH)2
Ca(OH)2
saltsNaCl
KBr
MgCl2
Weak Electrolytes
weak acidsHF (hydrofluoric acid)
HC2H3O2 (acetic acid)
H2CO3 (carbonic acid)
H3PO4 (phosphoric acid)
weak basesNH3 (ammonia)
(“N” compounds)C5H5N (pyridine)
Non Electrolytes
sugars and carbohydrateC6H12O6 (glucose)
fats and lipidscholesterol
alcoholsC2H5OH (ethyl alcohol)
other carbon compoundsC5H12 (pentane)







Lithium Free Flexible Batteries

Rice Flex Battery

Thin-film battery attached to a polymer backing can retain its properties after being flexed 1,000 times. Credit: Jeff Fitlow/Rice University

Chemists at Rice University have developed a material that can function as an ultra-thin and flexible rechargeable battery and contains no lithium. Lithium is a common element used in many rechargeable batteries today. Lithium ion batteries can hold a lot of charge in a small package and can be reused and recharged over and over with little loss in capacity. Lithium also reacts exothermically with water, so ruptured batteries are a serious concern. The Rice University material keeps the benefits of lithium ion batteries without the lithium.

Their material consists of layers of nanoporous nickel-fluoride electrodes sandwiching a solid electrolyte. It is constructed by depositing nickel onto a polymer backing and chemically etching nanometer holes to increase surface area. The backing is removed and the electrodes are layered around an potassium hydroxide and polyvinyl alcohol electrolyte.

Capacity can be scaled up by simply adding more layers. Each nickel-fluoride layer is only a micron thick and the finished product is only a tenth of a millimeter thick. These thin batteries would be ideal for wearable powered products since they can withstand flexing and still retain their capacitance. They also show promise to possibly replace lithium ion batteries in some devices.

Manufacture techniques and testing of this material was published online on the Journal of the American Chemical Society‘s website on April 15, 2014.

 

New Electrolyte Combination Creates Longer Life For Batteries

Lithium Coin Battery

Panasonic Li-CFx button battery. Batteries like this one could get extended life thanks to new electrolyte.

Traditional batteries contain three parts: a cathode, anode and an electrolyte. Each part serves a function. The cathode generates a positive charge, the anode carries a negative charge, and the electrolyte carries ions between the two electrodes.

Scientists at Oak Ridge National Laboratory have found a way to alter the arrangement. They created a combination of electrolytes that serves as both an ion conductor and a supplement cathode. The researchers took a lithium carbon fluoride (Li-CFx) battery and added solid lithium thiophosphate to the electrolyte. As the battery discharges, the lithium fluoride salt catalyzes the electrolyte reactions at the battery electrodes.

This translates into extra life for the battery, which offers immediate benefits. There are many cases where changing a battery in a device is inconvenient. For example, pacemaker batteries are usually Li-CFx batteries. Surgery is required to swap out the batteries. Imagine a pacemaker battery lasting 30 years instead of only 10?

This research appears in the Journal of the American Chemical Society.