Ch 2Introduction to Analytical Chemistry — Class 11 Chemistry, concept-first.

Analytical chemistry is the branch of chemistry devoted to investigating the chemical composition of substances.

Analysis is always carried out on a small, carefully chosen sample of the material being tested, never on the entire bulk of it, because testing the whole bulk would usually destroy or consume the mat…

Qualitative analysis of a sample is generally carried out in one of two stages or methods. In the dry method, the sample under test is examined without first dissolving it — this is normally used as a…

Quantitative analysis puts a number on how much of a substance is present, rather than merely detecting its presence.

Because the accuracy of every measurement matters so much in analytical chemistry, and because every real measurement carries some intrinsic error, the numerical data collected in an experiment has to…

Chemists routinely have to work with numbers that are extremely large (for example, there are roughly 602,200,000,000,000,000,000,000 molecules in 2 g of hydrogen gas) or extremely small (for example,…

The goal of any measurement is to determine the true (accepted) value of a quantity as closely as possible.

Every measured value carries some uncertainty, and that uncertainty in turn carries through into any result calculated from it.

Deciding how many digits in a written number are 'significant' — that is, meaningfully measured rather than just placeholders — follows five rules.

When several measured quantities are combined in a calculation, the accuracy of the final result is limited by the accuracy of the least accurate (fewest-significant-figure) measurement used in that c…

The molecular formula of a compound is the formula that states the actual number of atoms of each constituent element present in one molecule of that compound — for example, the molecular formula says…

Compounds form when different elements combine chemically in fixed proportions, and quantitatively determining how much of each constituent element is present, by suitable analytical methods, gives th…

Calculations based on a balanced chemical equation are collectively called stoichiometric calculations, and the balanced chemical equation itself is simply the symbolic representation of a chemical re…

Problems based on stoichiometry generally fall into one of three categories, depending on what is given and what is asked for: problems based on a mass–mass relationship (a mass of one substance is gi…

In a real laboratory reaction, the reactants are almost never supplied in the exact stoichiometric proportions given by the balanced equation.

The great majority of reactions studied and used in a chemistry laboratory are carried out with the reactants dissolved in a solution, so it is essential to be able to express precisely how much of a…

Mass percent (also called weight percent, written w/w %) is one of the simplest ways to express how concentrated a solution is.

Mole fraction is a way of expressing composition purely in terms of the relative number of moles of each component in a solution, ignoring their masses or volumes altogether.

Molarity, denoted M, is the single most widely used way of expressing solution concentration in a laboratory.

Molality, denoted m, is defined as the number of moles of solute dissolved per kilogram of solvent (not per kilogram or litre of the whole solution): .

Analytical chemistry frequently needs to establish whether — and how — two or more measured properties of a system are mathematically related to each other, and the most direct way to uncover such a r…