chemistry - atoms and molecules

Class 9 - Chemistry

Atoms and Molecules

MCQ
Q&A
Notes
Question:
(a) Give two symbols which have been derived from the"English names"of the elements.
(b) Give two symbols which have been derived from the "Latin names"of the elements.
Answer:



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Questions and Answers


Atoms and Molecules - Questions
1. Give examples of triatomic molecules.
Answer
2. What is valency of an element?
Answer
3. What is gram-atomic mass of an element?
Answer
4. What is the mass of
(a) 1 mole of nitrogen atoms?
(b) 4 moles of aluminium atoms (Atomic mass of aluminium = 27)?
(c) 10 moles of sodium sulphite (Na2SO3)?
Answer
5. Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
Answer
6. Fill in the blanks:
Mass of 2 Hydrogen atoms is __________.
Answer
7. Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Answer
8. Fill in the blanks:
_________ are building block of all matter.
Answer
9. Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Answer
10. Who proposed the chemical notation based on first two letters of the name of the element?
Answer
11. Name the international organization who approves names of elements.
Answer
12. Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Answer
13. What is the atomic mass unit?
Answer
14. What is relative atomic mass of an element? How it is related to atomic mass unit?
Answer
15. Fill in the blanks:
An element has only one type of __________.
Answer
16. Fill in the blanks:
____________ is formed by the loss of one or more electrons by an atom.
Answer
17. What are polyatomic ions? Give examples?
Answer
18. Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Answer
19. What is Formula Unit Mass? How it is different from molecular mass?
Answer
20. Calculate the formula unit masses of ZnO, Na2O, K2CO3, given atomic masses of Zn = 65 u, Na = 23 u, K = 39 u, C = 12 u, and O = 16 u.
Answer
21. What is gram-molecular mass of a substance?
Answer
22. What is molar mass?
Answer
23. When 'mole' was chosen internationally standard way to express larger number of chemical units?
Answer
24. Give an example to show Law of conservation of mass applies to physical change also.
Answer
25.

A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.


Answer
26. Fill in the blanks:
The number of atoms present in 12 grams of carbon 12 which is equal to __________atoms . This is also known as ____________.
Answer
27. Fill in the blanks:
Atomic radius is measured in __________.
Answer
28. Fill in the blanks:
A negatively charged ion is called a/an _____________.
Answer
29. What is the significance of a chemical symbol?
Answer
30.

Define molecule. What are its important properties?


Answer
31. Fill in the blanks:
According to Dalton's atomic theory, atoms of different elements differ in ______, size and chemical properties.
Answer
32. Fill in the blanks:
The chemical symbol of flourine is ________.
Answer
33.

Based on type of substance, how molecules are classified?


Answer
34. Fill in the blanks:
Hydrogen and oxygen combines to form H2O and H2O2. These two compounds obey the law of ____________________.
Answer
35. What is meant by the term chemical formula?
Answer
36. Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide
Answer
37. Write the chemical formulae of the following. Also identify the ions present.
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate.
Answer
38. How many atoms are present in a
(i) H2S molecule and
(ii) PO43- ion?
Answer
39. (a) Write a chemical formula of a compound using zinc ion and phosphate ion.
(b) Calculate the ratio by mass of atoms present in a molecule of carbon dioxide.
(Given C =12, O =16)
Answer
40. Who introduced the term 'mole' in chemistry?
Answer
41. Convert into moles: (a) 12 g of oxygen gas (b) 20 g of water (c) 22 g of carbon dioxide
Answer
42. Calculate the number of molecules of phosphorus (P4) present in 31 gram of phosphorus.
Answer
43. What is the law of conservation of mass?
Answer
44. Explain with example that law of conservation of mass is valid for chemical reactions.
Answer
45. What are the postulates of Dalton's atomic theory?
Answer
46. Fill in the blanks:
The mass of 5 moles of ammonia (NH3) is __________.
Answer
47. Which of the following statements is NOT true about an atom?
(a) Atoms are the building blocks from which molecules and ions are formed.
(b) Atoms cannot exist independently.
(c) Atoms are neutral in nature
(d) Atoms combine together to form matter that we can see, feel or touch.
Answer
48. What is the chemical symbol for iron?
Answer
49. Can atoms of an element exist independently? Give examples of elements which exist in atomic form. Give examples of elements that do not exist in atomic form.
Answer
50. Magnesium is two times heavier than C-12 atom, what shall be the mass of Mg atom in terms of atomic mass units? (Given mass of C-12 atom = 12u)

Answer
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