# Atoms and Molecules Worksheet

Given below are the Class 9 Science CBSE worksheet for Atoms and Molecules
(a) Short questions
(b) True and False problems
(c) Fill in the blank's
(d) Very Short questions
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## Fill In The Blanks

1. During a chemical reaction, the sum of the _________ of the reactants and products remain unchanged.
2. In a pure chemical compound, elements are always present in a ________ proportion by mass.
3. Clusters of atoms that act as an ion are called __________ ions.
4. In ionic compounds, the charge on each ion is used to determine the ________of tye compound.
5. The Avogadro constant _________ is defined as the umber of atoms in exactly ________ of crbon-12
6. Mass of 1 mole of a substance is called its __________.
7. The abbreviation used for length names of elements are termed as their _______.
8. A chemical formula is also known as a ________.
9. Those ions which are formed from single atoms are called _________.
10. Ionic compounds are formed by the combination between ________ an ______.
11. The valency of an ion is _________ to the charge on the ion.
12. Mole is a link between the __________ and __________.
13. The SI unit of amount of a substance is __________.

## True / False

1. Formula mass of $Na_2O$ is 62 amu.
2. Those particles which have more or less electrons than the normal atoms are called ions.
3. Formula for sulphur dioxide is $SO_3$.
4. Molar mass of ethyne ($C_2H_2$) is 26 g/mol.
5. 22 gm of $CO_2$ consists of 1 mole.
6. Number of molecules in 32 gram of oxygen is $6.02 \times 10^{23}$.
7. Water is an atom.
8. Formula for sulphur dioxide is $SO_2$.
9. Clusters of atoms that act as an ion is called polyatomic ion.
10. Mass of 1 mole of a substance is called its formula mass.
11. In a pure chemical compound, elements are always present in a definite proportion by mass.

1. Define term mole.

3.What is gram atomic weight?

4. What is the difference between $CO_2$ and $2CO_2$?

5. Name the following compounds $PC_3$ and $SO_2$.

6. In the smallest whole-number ratio must N and O atoms combine to make dinitrogen to tetroxide $N_2O_4$? What is the mole ratio of the elements in this compound?

7.How many moles of sodium atoms correspond to $1.56 \times 10^{21}$ atoms of sodium?

8. What is the relationship between the formula weight of a substance and its molar mass?

9. How many grams of silver are in 0.263 mol of g?

10.How many atoms are $1.00 \times 10^{-9}$ g of lead?

11.How many grams of iron are needed to combine with 25.6g of O to make $Fe_2O_3$?

12.What is the mass of 4 moles of aluminium atoms? ( Atomic mass of AI = 27u)

13.Calculate the mass of $6.022 \times 10^{22}$ atoms of He.

14.Calculate the number of moles in $3.011 \times 10^{22}$ molecules of carbon dioxide.

15.A sample of 45.8g of $H_2SO_4$ contains how many moles of $H_2SO_4$?

16.What s the mass in grams of 5 moles of Fe?

17.How many moles of NaCI are present in 20 gm of the substance?

18.How many grams of O is present in 50 gm of $CaCO_3$?

19.How many grams of $CO_2$ are present in 0.1 mole $CO_2$?

20.Describe the difference between the mass of a mole of oxygen atoms (O) and the mass of a mole of oxygen molecules ($O_2$).

21.What do you understand by the term Formula unit?

Question 1.
Write the name of the compound (NH4)2SO4 and mention the ions present in it?
Question 2.
Why do some atoms react with other atoms to form compounds where as some do not?
Question 3.
Define mole? Calculate the number of moles in 22g of carbon dioxide?
Question 4.
State three rules for writing the chemical formulae.
Question 5.
If one mole of carbon atoms weighs 12 g, what is the mass of 1 atom of carbon?
Question 6.
Derive the formula of the compound formed between Na+ and SO4-2
Question 7.
Write the chemical formulae for the compounds formed by the calcium ion with phosphate, sulphate and hydrogen carbonate ions?
Question 8.
Write the ratio by mass of Hydrogen and oxygen in one molecule of water?
Question 9.
State the number of hydrogen atoms in 1 g of hydrogen?
Question 10.
The relative atomic mass of oxygen atom is 16. Explain its meaning?
Question 11.
Calculate the number of molecules of SO2 present in 44 g of it?
Question 12.
If one molecule of oxygen atoms weighs 16 g, find the mass of one atom of oxygen?
Question 13
The atomic mass of calcium is 40 u. What will be the number of calcium atoms in 0.4 of calcium?
Question 14.
Molar mass of nitrogen is 14 u. What will be the mass of one atom of nitrogen?
Question 15.
Calculate the number of aluminium ions present in 0.051 g of aluminium oxide?
Question 16.
Calculate the number of molecules of sulphur (S-8) present in 8g of solid sulphur?
Question 17.
State any four postulates of Daltonâ€™s atomic theory of matter. Which of his postulates does not hold correct at present?

## Match the column

Match the Column I to Column II

## Summary

This Class 9 Science worksheet for Atoms and Molecules with answers is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail.