Qualitative Chemical Analysis

Qualitative and Quantitative Analysis Chemistry

Qualitative and quantitative analysis is analytical techniques in Chemistry that are used for giving details about the components in an unknown sample.


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Qualitative analysis in Chemistry gives details of the presence or nonappearance of different chemical components in an unknown sample, while quantitative analysis gives the measure of various chemical components present in a given sample.

Most often, both the techniques are used together, i.e., the use of qualitative analysis followed by quantitative analysis.

On this page, we will focus on qualitative chemical analysis, qualitative inorganic analysis, and understand what qualitative analysis is in chemistry in detail.


Qualitative Analysis Definition

Now, let us understand what qualitative chemistry is. Qualitative analysis is also called subjective investigation. In the field of Chemistry, it is a part of science that examines the substance piece or chemical composition of a sample. 

It demonstrates various elements, or gatherings of elements like functional groups, and so forth present in the sample. Thus, a subjective investigation of any sample can be utilized to decide if a specific component is available in a sample or not. 

Notwithstanding, this examination doesn't give any data about the amount of that chemical component. 

The characteristics in the sample that are frequently thought to be in the investigation are colour, smell, melting point, limit, reactivity, precipitation, and so forth.


Qualitative Analysis Chemistry

The seven methods to perform the qualitative analysis of a chemical compound lie hereunder:

  1. Change in colour

  2. Flame test

  3. Distillation

  4. Extraction

  5. Precipitation

  6. Chromatography

  7. Spectroscopy


What is Qualitative Analysis in Chemistry?

Qualitative analysis in Chemistry is if two types:

  • Qualitative organic analysis

  • Qualitative inorganic analysis


1. Qualitative Organic Analysis

Qualitative organic analysis determines the chemical bonds and functional groups in a sample.


2. Qualitative Inorganic Analysis

Qualitative inorganic analysis frequently determines the ions in a given sample.

What did we understand so far?

So, in a nutshell, qualitative analysis chemistry uses techniques, like distillation, extraction, and change in colour, chromatography, etc, to determine the composition of a sample. 

In other words, these techniques are helpful in determining the presence of different chemical components in a sample.

Now, let’s focus on examples of qualitative analysis in chemistry:


Examples of Qualitative Analysis in Chemistry

Here, we will consider an of example of qualitative organic analysis:


1. Iodine Test

The iodine test is utilized to show the presence or absence of starch. It is sugar, which is a natural compound. There, liquid iodine is utilized as the marker. 

A spot test can be utilized to test in the following manner:

Take a white tile and put a few drops of the samples that will be examined. At that point add iodine solution for each drop of the test. 

On the off chance that the colour of the sample is changed to brown colour, which shows the presence of starch.

Now, let us consider an example of qualitative inorganic analysis:


2. Flame Test 

In the flame test, the presence of a specific metal or its ions can be ascertained. Diverse metallic atoms give various tones to the fire. As per the flame colour when a bit of the sample is scorched in the Bunsen burner, can decide the presence of some metal ions. 

Ex: Zinc gives a green fire colour, as we can see in the image below:

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Zine gives a green flame colour.


Qualitative Analysis

There are a few points to remember on qualitative analysis; let’s understand these:

  1. Recognition of chemical species by means of colour, reaction producing a colour, reaction producing a precipitate, a reaction involving a change of a parameter.

  2. Coloured ions are Cu2+ [Blue], Cr3+ [Green], CrO4- [Yellow], Cr2O7- [Orange], MnO4- [Violet], Ni2+ [Green], Co2+ [Pink or Blue], Mn2+ [Pink], and generally ions of transition elements.

  3. Precipitates are slightly soluble compounds: Sulfur of heavy metals, like (As, Sb, Hg, Cu, Pb, Cd, Sn, Bi, Zn, Ni, Co, Mn), BaSO4, Hg2Cl2, AgCl, PbCl2, and many hydroxides of heavy metals.


Steps Involved in Qualitative Analysis of a Sample

  • On the off chance that the sample is introduced as a solid (salt), it's critical to take note of the form and colour of any crystal. 

  • Reagents are utilized to isolate cations into groups of related components. 

  • Ions in a group are isolated from one another. After every division stage, a test is performed to affirm certain ions really were eliminated. The test isn't performed on the original sample.

  • Divisions depend on various qualities of ions. These may include redox reactions to change oxidation state, differential solvency in acid, base, or water, or precipitating certain particles.


Protocol for Qualitative Analysis of a Sample

To start with, ions are eliminated in groups from the underlying aqueous solution. After each group has been isolated, at that point testing is led for the individual ions in each group. Here is a typical group of cations: 

1. Group -  I:

 Ag+, Hg22+, Pb2+ 

Precipitated in 1 M HCl 

2. Group - II:

Bi3+, Cd2+, Cu2+, Hg2+, (Pb2+), Sb3+, Sb5+, Sn2+ and Sn4+ 

Precipitated in 0.1 M H2S arrangement at pH - 0.5 

3. Group - III: 

Al3+, Co2+, (Cd2+), Cr3+, Fe2+, and Fe3+, Mn2+, Ni2++, Zn2+ 

Precipitated in 0.1 M H2S arrangement at pH  - 9 

4. Group -  IV: 

Ca2+, Ba2+, K+, Mg2+, Na+, NH4+ 

Ba2+, Ca2+, and Mg2+ are precipitated in 0.2 M (NH4)2CO3 arrangement at pH - 10; different ions are solvent.


Point To Note:

Numerous reagents are utilized in the subjective investigation, however, a couple is engaged with virtually every gathering system. The four most usually utilized reagents are 6M HCl, 6M HNO3, 6M NaOH, 6M NH3

Understanding the employment of the reagents is useful when arranging an analysis. The common qualitative reagents are:

  1. 6M HCl

  2. 6M NaOH

  3. 6M NH3

FAQs (Frequently Asked Questions)

1. What is Quantitative Analysis?

Ans: Quantitative analysis in chemistry is a branch of chemistry that deals with the quantities of different components in a sample. 


The amount can be given as a mass, concentration, volume, relative abundance, and so forth There are compound or actual techniques that are utilized in the quantitative examination.

2. Explain the two Methods Involved in Quantitative Analysis.

Ans: The two methods involved in quantitative analysis lie hereunder:

1. Chemical Methods

Chemical methods incorporate chemical reactions, viz: oxidation, reduction, precipitation, neutralization, and so forth), titration strategies, gravimetric strategies, combustion analysis methods, and so on.


2. Physical Methods 

Physical methods examine at least one property of a sample. A few examples incorporate AES (Atomic emission spectroscopy), X-ray fluorescence spectroscopy, mass spectroscopy, and so forth.

3. List the Common Reagents Involved in Qualitative Analysis.

Ans: The three common reagents involved in qualitative analysis are:

6M HCl

Increases [H +]

Increases [Cl -]

Decreases [OH -]

Breaks up insoluble carbonates, chromates, hydroxides, a few sulfates 

Destroys hydroxo and NH 3 complexes

Precipitates insoluble chlorides

6M HNO 3

Increases [H +]

Decreases [OH -]

Breaks up insoluble carbonates, chromates, and hydroxides 

Breaks up insoluble sulfides by oxidizing sulfide ion 

Destroys hydroxo and ammonia complexes

Good oxidizing agent when hot

6M NaOH

Increases [OH -]

Decreases [H +]

Forms hydroxo complexes

Precipitates insoluble hydroxides.