How to Know if a Compound is a Salt

In this brief article, we will be discussing how to know if a compound is a salt and will guide you through a series of preliminary and confirmatory tests.

How to Know if a Compound is a Salt?

By definition, if a compound contains an ion and a cation it is defined as a salt. A salt is a compound that is formed as a result of the combination of one base and one acid. Salts involve the cation of the base and the anion of the acid. Salts are electrically neutral substances and the bonds between these ions are ionic bonds (1). 

In analytical chemistry, standard tests are performed, in which a sequence of reactions take place, in order to identify a salt or a mixture of salts. These reactions require chemicals that are available only in a chemistry laboratory and must be handled by trained individuals. Some of these tests are simple and can be carried out at home (2).  

Outlined below are some of the basic steps to determine if a compound is a salt.

1. Check the Appearance 

Salts are generally solid crystalline compounds and appear transparent or white.

However, the ions (positively and negatively charged atoms that make up the salt) may be colored, giving the salt different colors.

2. Check Effect of Heating

Place a small quantity of the compound in a test tube and heat it. If the heating causes condensation inside the tube, it contains water and the compound is a hydrate. 

But if the heating produces a gas, note its color and odor.

3. Try Dissolving it in Water

Dissolve a small quantity of the compound in 1 mL of water, acetone and toluene. 

If the compound is soluble, all of it will dissolve after a certain amount of stirring. 

If some of the compound dissolves and some does not, then it is moderately soluble. Identify in which of the liquids the salt dissolves better.

And if the compound does not dissolve at all, it is labeled as insoluble.

4. Perform a Flame Test

For this test, a small quantity of the compound is mixed with concentrated hydrochloric acid and heated on nickel or chromium-wire flame. 

The ions present in the compound will dissolve in the acid and change the color of the flame. Different ions will produce different color changes. Bellow are the ions and the flame color they produce (3):

ion	flame colour
Li	red
Na	strong persistent yellow-orange
K	lilac (pink)
Rb	red (reddish-violet)
Cs	blue-violet (see below)
Ca	orange-red
Sr	red
Ba	pale green
Cu	blue-green (often with white flashes)
Pb	greyish-white

5. Check Reaction with HCl (Hydrochloric Acid)

HCI is added, drop by drop, to the solution until it tests acidic on a litmus paper. 

Then, observe any reaction; positively charged ions (cations) will form an insoluble chloride and precipitate. If the salt contains carbonate there will be bubbling in the mixture.

6. Test with Na₂CO₃.

Add a small amount of salt and a small amount of water to the test tube. Add the compound Na₂CO₃ (sodium bicarbonate or baking soda). If the reaction was positive then there will be precipitation.

7. Paas it through a Sieve

Passing the salt through different-sized sieves can also identify them via their granule size. 

7. Calculate Moisture Content

To begin, weigh the salt at room temperature. After that, heat the salt to 140 degrees Celcius to let it lose all its moisture.

Then, heat the salt’s weight and measure it again. The difference between the first measurement and the second measurement is the moisture content of the salt.

What is Salt?

The chemical compound produced when an acid reacts with a base is known as salt.  This reaction is called neutralization. Salts contain a positive ion (cation) from the base and a negative ion (anion) from the acid.  

The formation reactions of salts could generally be given as follows (Salts are formed by a chemical reaction between) (1):

1) Neutralization reactions: “A base and an acid”

Acid + Base Salt + Water

2) Formation from its Elements Reactions (Synthesis):

Metal + Nonmetal Salt

3) Reactions of Metals with Acids (Redox):

Metal(active) + Acid Salt + H2 (g)

4) Reactions of Metal Oxides (basic anhydride) with Acids:

Metal oxide (basic anhydride) + Acid Salt + Water

5) Reactions of Nonmetal Oxides (acid anhydride) with base:

Nonmetal oxide (acid anhydride) + Base Salt + Water

6) The reaction of one salt with another. Salts can also form if solutions of different salts are mixed, their ions recombine, and the new salt is insoluble and precipitates.

Salt solution (A) + Salt solution (B) Salt solution (C) + Salt solution (D)

7) Some decomposition reactions form salt.

8) Substitution reactions (considering the activities)

Metal + Salt solution Salt + Metal

Nonmetal + Salt solution Salt + Nonmetal

Salt is commonly referred to as table salt, contains positive ions from the metal sodium (Na1+) and negative ions from the non-metal chlorine (CI1-).

Is Salt a Mineral or a Rock?

As mentioned previously, salt is a mineral consisting mainly of the chemical compound sodium chloride (NaCl) that belongs to a bigger class of salts. 

Salt, in its natural crystalline mineral form, is called rock salt or halite and is found in large quantities in seawater.

What are the Properties of a Salt?

The following are some of the basic properties of salt (4):

• Salt consists of molecules arranged in a fixed formation that gives it a characteristic crystal structure. This is why it appears as a white crystalline powder.
• It is transparent and colorless.
• It is generally soluble in water (under certain conditions).
• Salt is hygroscopic (capable of absorbing moisture from the atmosphere at more than 75% relative humidity otherwise it dries out).
• It melts at 801 degrees Celcius.
• It begins to vaporize at a little above 1,413 degrees Celcius.
• Salt is an electrolyte, so when dissolved in water it produces free-flowing ions that enable water to conduct electricity. 

How Do You Perform a Basic Salt Analysis?

A basic salt analysis determines its cations and anions. Here is a step-by-step guide to conducting a simple salt analysis:

1. Perform preliminary tests for negative ions (anions) till you obtain positive results. 
2. Perform preliminary tests for positive ions (cations) till you obtain positive results.
3. Perform confirmatory tests for both the ions after your initial positive results.
4. Once the cations and anions are confirmed, determine the chemical formula of the salt by balancing the charges.

Conclusion

In this brief article, we answered the question of how to know if a compound is a salt. By conducting a series of simple tests and then identifying the cations and anions through further confirmatory tests, it is very easy to identify whether a compound is a salt.

If you have any questions or comments, please let us know.

References:

1. Seçken, Nilgün. Identifying student’s misconceptions about SALT. Procedia-Social and Behavioral Sciences, 2010, 2, 234-245. 
2. Yingling, L. Identification Properties and Synthesis of an Unknown Ionic Compound, 2015. University of Wisconsin.
3. Clark, J. Flame test. 2018. Chemguide.co.uk. 
4. Sodium chloride. The National Library of Medicine.