Introduction to Chemical Analysis In chemistry, it is crucial to distinguish between pure substances and mixtures, and to analyze their compositions and propert...
In chemistry, it is crucial to distinguish between pure substances and mixtures, and to analyze their compositions and properties. This topic covers various techniques used in chemical analysis, including chromatography, qualitative tests, and instrumental methods.
Pure substances have a fixed composition and consist of only one type of particle (atoms or molecules). Mixtures, on the other hand, are combinations of two or more pure substances that are not chemically bonded together. Formulations are mixtures designed for specific purposes, such as medicines, fertilizers, or cleaning products.
Chromatography is a technique used to separate and identify components of a mixture based on their different rates of movement through a stationary and mobile phase. The most common type studied at GCSE level is paper chromatography, where a solvent travels up a piece of filter paper, separating the components of a mixture.
The retardation factor (Rf) is a measure of how far a substance travels compared to the solvent front. It is calculated as:
Rf = distance moved by substance / distance moved by solvent front
Rf values are used to identify substances by comparing them to known values.
Qualitative tests are used to identify the presence of specific gases or ions in a sample. Common tests include:
Instrumental methods, such as flame emission spectroscopy, can provide more accurate and sensitive analysis of chemical samples. These techniques use specialized equipment to measure and analyze the properties of substances.