Topics: Atom, Ion, Molecule Pages: 5 (1242 words) Published: October 14, 2013
Extrascore Sample Questions - Answers
Q.1: What are the µlaws of chemical combination¶?
 Ans: There are two important laws of chemical combination established by Lavoisier,are as follows:  
(i) Law of Conservation of Mass
The law of conservation of mass states that mass can neither be created nor destroyedin a chemical reaction.(ii) Law of Constant Proportions  
The Law of Constant Proportions which is also known as the Law of DefiniteProportions, was established by Proust. According to this law, in a chemical substancethe elements are always present in definite proportion by mass. All pure samples of acompound contain the same elements combined together in the same proportion bymass. For example, a sample of water would always contain hydrogen and oxygen inthe ratio of 1:8 by mass irrespective of the source of water  

Q.4: What are the postulates of Dalton¶s Atomic Theory of matter ?  
 Ans: According to Dalton¶s atomic theory, all matter, whether an element, a compoundor a mixture is composed of small particles called atoms. The different postulates of Dalton¶s atomic theory are stated as follows:  

(1) All matter is made of very tiny particles called atoms.
(2) Atoms are indivisible particles, which can not be created or destroyed in a chemicalreaction.  
(3) Atoms of a given element are identical in mass and chemical properties.  
(4) Atoms of different elements have different masses and chemical properties.  
(5) Atoms combine in the ratio of small whole numbers to form compounds.  
(6) The relative number and kinds of atoms are constant in a given compound.Q.5: What is the full form of IUPAC? What is the present accepted norm of IUPAC for naming symbols of elements? Ans: The full name of IUPAC is International Union of Pure and Applied Chemistry.Many of the symbols are the first one or two letters of the element¶s name in English.The first letter of a symbol is always written as a capital letter (upper case) and thesecond letter is always a small letter (lower case). For example, Hydrogen is written asH and Aluminium is written as Al. Some symbols are formed from the first letter of thename and a letter, appearing later in the name. For example, Chlorine as Cl and Zinc as

Zn. Some other symbols are taken from the names of elements in Latin, German or Greek. For example, the symbol of Iron is Fe from Latin name ferrum.Q.6: Write the names of symbols of five elements where the symbols are taken fromtheir name in English. Ans: The symbols of the following elements have been taken from their name inEnglish: Calcium (Ca), Oxygen (O), Zinc (Zn), Magnesium (Mg) etc.Q.7: Write the names of symbols of five elements where the symbols are taken fromtheir name in a language other than English. Ans: The names of symbols of the following elements have been taken from their namein a language other than English: Silver (Ag), Gold (Au), Lead (Pb), Sodium (Na), Iron(Fe) etc.Q.8: Define and explain atomic mass of an element. Ans: The atomic mass of an element is the relative mass of its atom as compared withthe mass of a particular atom of Carbon-12 ( 12

C) isotope taken as 12 units. Thus theatomic mass of an element indicates the number of times one atom of an element isheavier than 1/12 th of a Carbon-12 ( 12
C) isotope atom. For example, the atomic massof oxygen is 16 which indicates that an atom of oxygen is 16 times heavier than 1/12 thof a Carbon-12 ( 12
C) isotope atom.Q.9: Distinguish between a µmolecule¶ and a µcompound¶.  
 Ans:Molecule - a molecule is usually formed when at least two atoms of the same or different kinds combine. If two or three atoms of the same kind of element combine,then it is referred to as a molecule of an element or simply Molecule. For example,molecule of oxygen(O 2

) is formed by the combination of two oxygen atoms. However,there are exceptions such as argon (Ar), helium (He) which are made up of only oneatom of that element.Compound - Molecule formed by...
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