Definitions [4]
Definition: Percentage Composition
Percentage composition of a compound, is the percentage by weight of each element present in it.
Definition: Empirical Formula
The empirical formula of a compound is the simplest formula, which gives the simplest ratio in whole numbers of atoms of different elements present in one molecule of the compound.
Definition: Empirical Formula Mass
The empirical formula mass is the sum of atomic masses of various elements present in the empirical formula.
Definition: Molecular Formula
The molecular formula of a compound denotes the actual number of atoms of different elements present in one molecule of the compound.
Formulae [1]
Formula: Percentage Composition
Percentage of an element in a compound \[=\frac{\text{Total wt. of the element in one molecule}}{\text{Gram molecular weight of the compound}}\times100\]
Key Points
Key Points: Determination of Empirical Formula
- Find missing %: If any element’s percentage is missing, subtract the known percentages from 100.
- Convert to moles: Divide each element’s % by its atomic mass to get the number of moles.
- Water of crystallisation: Divide % of water (if present) by 18 to get moles of water.
- Simplify ratio: Divide all mole values by the smallest one to get the simplest whole-number ratio.
- Write formula: Use element symbols with the simplified ratios as subscripts to form the empirical formula.
Important Questions [11]
- A Compound of X and Y Has the Empirical Formula Xy2. Its Vapor Density is Equal to Its Empirical Formula Weight. Determine Its Molecular Formula
- Identify the Term Or Substance Based on the Descriptions Given Below: the Property by Virtue of Which the Compound Has the Same Molecular Formula but Different Structural Formulae.
- A gaseous hydrocarbon contains 82.76% of carbon. Given that its vapor density is 29, find its molecular formula. [C = 12, H = 11]
- If the Empirical Formula of a Compound is Ch and It Has a Vapor Density of 13, Find the Molecular Formula of the Compound.
- Consider the Following Reaction and Based on the Reaction Answer the Questions that Follow: the Quantity in Moles of (Nh4)2cr2o7 If 63gm Of(Nh4)2cr2o7 is Heated. and the Quantity in Moles of Nitrogen Formed. and the Volume in Liters Or Dm3 of N2 Evolved at S.T.P. and He Mass in Grams of Cr2o3 Formed at the Same Time
- A Compound Made up of Two Elements X and Y Has an Empirical Formula X2y. If the Atomic Weight of X is 10 and that of Y is 5 and the Compound Ha a Vapor Density 25, Find Its Molecular Formula
- Ethane Burns in Oxygen to Form Co2 and H2o According to the Equation:He Volume of `Co_2` Formed and the Volume of Unused `O_2`
- Give the Appropriate Term Defined by the Statements Given Below : the Formula that Represents the Simplest Ratio of the Various Elements Present in One Molecule of the Compound.
- Find the Empirical Formula and the Molecular Formula of an Organic Compound from the Data Given Below : C = 75.92%, H = 6.32% and N = 17.76% the Vapour Density of the Compound is 39.5.
- The Empirical formula of an organic compound is CHCl2. If its relative molecular mass is 168, what is its molecular formula? [At. Wt. C = 12, H = 1, Cl = 35.5]
- Calculate: Write the empirical formula of C8H18.
