Summary
Key terms
Stoichiometry: It is a branch of chemistry that deals with the relative amounts of reactants and products taking part in a chemical reactions.
Molar mass: Molar mass(M), is a physical property of a given substance (chemical element or chemical compound), which is defined as the mass per amount of substance.
1 mole of an element = gram atomic mass of that element.
gram molar mass of a compound = Σ ( gram atomic masses in formula).
1 mole of a compound = gram molar mass of that compound.
1 mole of an element = gram atomic mass of that element.
gram molar mass of a compound = Σ ( gram atomic masses in formula).
1 mole of a compound = gram molar mass of that compound.
Titrations: Titration is a method of analysis which allows one to determine the precise endpoint of a reaction, and therefore the precise quantity of reactant present in the titration flask.
Percent composition: It is the percent of total mass of the compound, due to that component.
Formula of Phosphoric acid is H3PO4.
Formula of Phosphoric acid is H3PO4.
Empirical formulae: A formula which gives the information about the relative number of each type of atoms, but it provides no information about molecular structure in contrast.
Eg: The empirical formula for glucose, CH2O, specifies only two hydrogen atoms and one oxygen atom for every carbon atom in a molecule of glucose.
Eg: The empirical formula for glucose, CH2O, specifies only two hydrogen atoms and one oxygen atom for every carbon atom in a molecule of glucose.
Molecular formulae: A chemical formulae that indicates the actual numbers and types of atoms in a molecule. Molecular formulae can be obtained from empirical formula if we know the molecular weight of the compound. Molecular formulae provide greater information about molecules than do empirical formulae.
Eg: C6H12O6 is the molecular formula of a glucose. This formula specifies that in each molecule of glucose there are 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms.
Eg: C6H12O6 is the molecular formula of a glucose. This formula specifies that in each molecule of glucose there are 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms.
AMU: An amu is the mass of one twelfth the mass of one carbon-12 and has a value of 1.66056 ×10–24g. The unified atomic mass unit (u) or Dalton (Da) is used for indicating mass on an atomic or molecular scale.
Key concepts
- Stoichiometry deals with the relative quantities of reactants and products in chemical reactions. The name stoichiometry is derived from the Greek words stoicheion means "element" and metron means "measure".
- Stoichiometric calculations involve converting information with one set of units into an answer with another set of units. A conversion factor is derived from a defined relationship between two sets of units. For solving stoichiometric problems dimensional analysis is the best method to follow.
- The three fundamental laws proposed by them are Law of conservation of mass which states that there is no detectable change in the total mass of materials when they react chemically to form new materials, Law of constant proportion states a compound obtained from different source has same proportion of elements and Law of multiple proportions which describes that in two compounds of same elements relative to the other element changes in increments based on specific ratios of small whole numbers.
- Molar mass (M), is a physical property of a given substance (chemical element or chemical compound) equals to the mass of one mole or Avogadro number of particles. Relative atomic mass has no units and simply indicates the mass of one element as compared to that of another. Weight of one mole of an element is equal to the gram atomic mass of that element.
- All chemical formulas represent the ratio of atoms within the formula. We can write the relationships between a formula as a whole and the individual atoms in that formula by using this ratio.
- To perform stoichiometric calculations, the various equalities and relationships must be known. These equalities and relations can be determined by using conversion factors. It is important to understand the sequence of operations required to perform any conversions successfully and efficiently.
- Limiting reactant / reagent is a reactant(which is taken in less than the stoichimetric quantity) in a chemical reaction that limits / determines the amount of product that can be formed. The reaction will stop when all of the limiting reactant is consumed.
- Theoretical yield is the maximum amount of products that can be created by a given amount of reactants. It helps in determining the overall efficiency of the reaction. A low theoretical yield means that the conditions were not optimal and could have been improved.
- Experimental yield which is generally less than the theoretical yield is the amount of product actually formed by the reaction.
- The efficiency of the reaction which is basically the ratio of actual yield to theoretical yield can be expressed as: Yield (in %) = (actual yield (grams) / theoretical yield (grams)) × 100
- By determining the masses of different elements and compare with the standard values, percentage of composition (purity) of sample is determined by the following formula
Where n is the number of moles of elements in 1 mole of the compound. The percent composition of a component in a compound is the percent of the total mass of the compound that is due to that component. - Empirical formula is the simplest ratio of atoms represents the compounds. It tells both the relative number of each type of atom and the relative number of atoms of each element that the compound contains, but it tells nothing about molecular structure. This is the simplest, or empirical, formula because it uses as subscripts the smallest set of integers that express the correct ratios of atoms present.
- Molecular formulas are the chemical formulas that indicate the actual numbers and types of atoms in a molecule. The molecular formula of a compound is always an integer multiple of the empirical formula. If the empirical formula of a compound is known, the molecular formula can be determined by the experimental determination of the molecular weight of the compound.
- Molecules such as methane have same molecular formula and empirical formula. In methane the simplest whole number ratio(empirical) of hydrogens to carbon atoms is four hydrogen atoms to every carbon atom. This is equal to the actual ratio in the molecular formula(CH4).
- Some materials such as sodium chloride do not exist as isolated molecules so it is technically impossible to give a molecular formula for such substances.