Measurement

• Measurement is the quantitative comparison of an object's physical quality that involves a number and a unit
• unit is the magnitude of a physical quantity that may vary as non-standard or standard
• Non-standard unit is a unit not commonly used because it might result to an error. it is not used because it is not known by all
• Standard unit is a unit known and used by all. examples are the Metric System and the Systeme International (SI)
• Metric System is based upon the power of 10 to express a very small or very large number. Base units are

  1. Length - meter
  2. Mass- gram
  3. volume - liter
• Systeme International (SI) is also called the international system of units. It uses prefixes to indicate multiples of ten.
• Prefixes are words added at the beginning of a word to change its meaning. Examples are kilo, milli, centi, deci, etc.
• The Systeme International (SI) has seven base units which are length, mass, time, temperature, electric current, amount of substance, and luminous intensity.
• Scientific Notation is the simplified expression for a very large or very smal number
• The standard for of Scientific notation is: $A +$$10^b$where 1</-A</-9.99
• To express a large number, you have to move decimal point to LEFT
• to express a small number, you have to move the decimal places to the RIGHT. negative exponent
• Conversion factor is the mathematical statement of two equivalent measurements of different units that can be expressed in fraction form and is equal to 1.
• Accuracy is the closeness to the true value. in chemistry, accuracy means "correct"
• Precision is the degree of consistency and agreement among independent measurements of the same quantity for reliability of the results
• Error = Experimental Value (EV) - Accepted Value (AV)
• Expermental Value is the value measured at the lab
• accepted value is the correct value based on reliable references
• error is the difference between EV and AV
• Percent error = $(EV - AV) (100)/ AV$
• acceptable error is between -5% and 5%
• Values less than -5% and above 5% are remeasured
• Rules of Significant figures

  1. ALL non-zero are significant
  2. CAPTIVE zeros are significant
  3. LEADING zeros are not significant
  4. TRAILING zeros are significant
  5. Every digit in scientific notation is significant
  6. Final zeros of an understood decimal point may or may not be significant