Chemistry F.Sc Part-I,Ch#1 Topic-Combustion Analysis

ELEMENTAL ANALYSIS

• Introduction
• Types
• Combustion Analysis
• Formula
• Multiple Choice Questions

Introduction

   Elemental analysis is a process where a sample of some material (e.g., soil, waste or drinking water, bodily fluids, minerals, chemical compounds) is analyzed for its elemental and sometimes isotopic composition. Elemental analysis can be qualitative (determining what elements are present), and it can be quantitative (determining how much of each are present). Elemental analysis falls within the ambit of analytical chemistry, the set of instruments involved in deciphering the chemical nature of our world.

For organic chemists, elemental analysis or "EA" almost always refers to CHNX analysis—the determination of the mass fractions of carbon, hydrogen, nitrogen, and heteroatoms (X) (halogens, sulfur) of a sample. This information was very important to help determine the structure of an unknown compound, as well as to help ascertain the structure and purity of a synthesized compound. In present day organic chemistry spectroscopic technics (like NMR, both 1H and 13C), mass spectrometry and chromatographic procedures have replaced EA as the primary technique for structural determination, although it still gives very useful complementary information. It is also the fastest and most inexpensive method to determine sample purity.

Antoine Lavoisier is regarded as the inventor of elemental analysis as a quantitate, experimental tool to assess the chemical composition of a compound. At the time elemental analysis was based on gravimetric determination of specific adsorbant materials before and after selective adsorption of the combustion gases.[1][2] Today fully automated systems based on thermal conductivity or infrared spectroscopy detection of the combustion gases, or other spectroscopic methods are used.

Combustion Analysis

   Combustion analysis is a method used in both organic chemistry and analytical chemistry to determine the elemental composition (more precisely empirical formula) of a pure organic compound by combusting the sample under conditions where the resulting combustion products can be quantitatively analyzed. Once the number of moles of each combustion product has been determined the empirical formula or a partial empirical formula of the original compound can be calculated.

Applications for combustion analysis involve only the elements of carbon (C), hydrogen (H), nitrogen (N), and sulfur (S) as combustion of materials containing them convert these elements to their oxidized form (CO2, H2O, NO or NO2, and SO2) under high temperature high oxygen conditions. Notable interests for these elements involve measuring total nitrogen in food or feed to determine protein percentage, measuring sulfur in petroleum products, or measuring total organic carbon (TOC) in water.

Types of elemental analysis

   Quantitative analysis is the determination of the mass of each element or compound present.

   Qualitative analysis is to qualitatively determine which elements exist in a sample.

Formula

Multiple Choice Questions:

1. Amount of KOH used in combustion analysis
A) 50%
B) 60%
C) 70%
D) 80%

 A

2. Amount of oxygen in combustion analysis is determined by method of
A) Product
B) Difference
C) Addition
D) Division