unit 2

• The International System of Units (SI) – is based on the seven fundamental base units
• Mass – is an unchanging measure of the quantity of matter in an object.

  Weight – is the force of attraction between an object and its surrounding, principally Earth.
• A chemical analysis is always based on mass so that the results will not depend on locality. Analytical data are based on mass rather than weight.
• The mole (abbreviated mol) is the SI unit for the amount of a chemical substance
• The molar mass 𝑀 of a substance is the mass in grams of 1 mole of that substance.
• The millimole is 1/1000 of a mole, and the mass in grams of a millimole, the millimolar mass (𝑚𝑀), is likewise 1/1000 of the molar mass.
• The molar concentration 𝑐𝑥 of a solution of a solute species X is the number of moles of that species that is contained in 1 L of the solution.
• The molar analytical concentration, or just analytical concentration, of a solution gives the total number of moles of a solute in 1 L of the solution
• The molar equilibrium concentration, or just equilibrium concentration, refers to the molar concentration of a particular species in a solution at equilibrium.
• ppm (parts per million) is a convenient way to express concentration for very dilute solutions:
• Conc. 𝝁g/m3= (𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔h𝑡)( 𝑐𝑜𝑛𝑐𝑒��𝑡𝑟𝑎𝑡𝑖𝑜𝑛, 𝑝𝑝𝑏) /24.45
• M=𝑝��𝑚 /𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠/ 1000
• Scientists frequently express the concentration of a species in terms of its p-function, or p-value. The p-value is the negative logarithm (to the base 100 of the molar concentration of that species. Thus, for the species X,
• The density of a substance is its mass per unit volume, and specific gravity is the ratio of its mass to the mass of an equal volume of water at 4°C.
• Empirical Formula – gives the simplest whole number ratio of atoms in a chemical compound.
• Molecular Formula – specifies the number

  of atoms in a molecule.
• Structural Formula – provides additional

  information about the compound.
• Errors are caused by faulty calibrations or standardizations or by random variations and uncertainties in results.
• Because measurement uncertainties and errors can never be completely eliminated, measurement data can only give us an estimate of the “true” value.
• Reliability can be assessed in several ways:

  • Experiments designed to reveal the presence of errors.

  • Comparison (standards of known composition and results)

  • Chemical literature

  • Calibrating the equ quality

  • Statistical tests
• Mean of Ungrouped Data, 𝒙

  It is also called arithmetic mean or average, is obtained by dividing the sum of replicate measurements by the number of measurements in the set.
• The abscissa or x-axis – independent variable

  • The ordinate or y-axis – dependent variable
• Line of Best Fit

  It is a straight line that depicts the trend the given scattered data plots on a graph. is also known as a trend line or line regression
• Least Square Method

  It is the process of finding the curve or line of best fit