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.........Introduction to fundamental concepts of chemistry |
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Error
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An
error is defined as:
"The difference between the measured value and the actual value." |
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| If two persons use the same instrument for measurement for finding the same measurement, it is not essential that they may get the same results. There may arises a difference between their measurements. This difference is referred to as an "ERROR". | |||
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Types
Of Error
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| Errors
can be divided into three categories: (1) Personal Error (2) Systematic Error (3) Random Error |
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Personal
Error
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| An
error comes into play because of faulty procedure adopted by by the observer
is called "PERSONAL ERROR". Personal error comes into existence due to making an error in reading a scale. It is due to faulty procedure adopted by the person making measurement. |
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Systematic
Error
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| The
type of error arises due to defect in the measuring device is known as "SYSTEMATIC
ERROR" Generally it is called "ZERO ERROR". it may be positive or negative error. Systematic error can be removed by correcting measurement device. |
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Random
Error
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| The
error produced due to sudden change in experimental conditions is called
"RANDOM ERROR". For example: During sudden change in temperature, change in humidity, fluctuation in potential difference(voltage). It is an accidental error and is beyond the control of the person making measurement. |
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Atomic
Mass
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| Atomic mass is defined as : | |||
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"The
mass of one atom of the element compared with the mass of one atom of
C12"
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| Atomic mass is a ratio therefore it has no unit. Generally atoms mass is expressed in ATOMIC MASS UNIT(a.m.u). | |||
| One atomic mass unit is equal to 1/12 of the mass of a C12 atom. | |||
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Empirical
Formula
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"Empirical
Formula is that formula which expresses the relative number
of each kind of atoms present in the molecule of a compound" OR "The formula of a compound which expresses the ratio in which atoms of different elements are combined in a molecule" |
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Empirical formula only indicates atomic ratios but it does not indicate actual number of atoms of different kinds present in the molecule of a compound. Two or more compound may have same empirical formula. Empirical formula is determined by experiment. |
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Molecular
Formula
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The
molecular formula of a compound is defined as:
"The formula of a compound which not only expresses the relative number of atoms of each kind but also expresses the actual number of atoms of each element present in one molecule". |
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Molecular
formula and empirical formula of a compound are related as:
MOLECULAR FORMULA = (EMPIRICAL FORMULA)n |
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n
= molecular mass of compound / Empirical formula mass of compound
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| Molecular
formula of propane = C3H8. Molecular formula of sugar = C12H22O11. |
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Limiting
Reactant
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The
limiting reactant is defined as:
" The substance which produces least amount of products when it is completely consumed in a chemical reaction". |
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