Class 9 Science CBSE worksheet for Atoms and Molecules

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.

Very Short Answer Questions:

1. Define term mole.
2. What is Avogadro's Number?
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 aluminum 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?

ANSWERS

Fill in the blanks:

1. Masses
2. Definite
3. Polyatomic
4. Chemical formula
5. 86.022 x 1023, 12g
6. Molar mass
7. Symbol
8. Molecular formula
9. Simple ins
10. Metal and non- metals
11. Equal
12. Mass of atoms & number of atoms
13. Mole

True / False:

1. True
2. True
3. False
4. True
5. False
6. True
7. False
8. True
9. True
10. False
11. True

Very Short Answer Questions:
1. The mole is the amount of substance that contains the same number of particles (atoms/ ions/ molecules/ formula units etc.) as there are atoms in exactly 12 g of carbon-12.

2. The Avogadro constant $6.022 \times 10^{23}$ is defined as the number of atoms in exactly 12 g of carbon-12.

3.Gram atomic weight is the mass in gram of 1mole of atoms in a monoatomic chemical element

4. $CO_2$ means 1 molecule of carbondioxide $2CO_2$ means 2 molecules of carbon dioxide

5. Phosphate Carbon and Sulfur dioxide

6. 1:2

7. Sodium atoms = $1.56 \times 10^{21}$
Avogadro number = $6.022 \times 10^{23}$
$Moles = \frac {1.56 \times 10^{21}} { 6.022 \times 10^{23}}$
$Moles = 0.26 \times 10^{-2}$

8.The molar mass of any substance is its atomic mass, molecular mass, or formula mass in grams per mole.

9. 1 Mole of Silver is 107.86 gm
0.263 mol of silver will be = 107.86 * 0.263=28.367 gm

10. 1 mol of Pb = 207.2g
or 207.2 g has $6.022 \times 10^{23}$ atoms
$1.00 \times 10^{-9}$ will have = $\frac {6.022 \times 10^{23}}{207.2 g} \times {1.00 \times 10^{-9}}=2.91 \times 10^{12}$ atoms.

11.Molecular weight of Fe = 55.85
Molecular weight of O = 16.00
Molecular weight of $Fe_2O_3 = (55.85) \times 2 + (16) \times 3 = 111.7+48 = 149.70$
For 48 gm O, Fe required is 111.7 gm
So for 25.6 gm O, Fe required is 59.57 gm

12.Mass of 1 mole of aluminium atoms = 27 g. Mass of 4 moles of aluminium atoms = (27 x 4) = 108 g.

13. $6.022 \times 10^{23}$ atom of Helium weight 4g
Therefore $6.022 \times 10^{22}$ atoms of Helium will weighs

$= \frac {4 \times 6.022 \times 10^{22}}{6.022 \times 10^{23}} =0.4g$

14. $6.022 \times 10^{23}$ is 1 mole
$3.011 \times 10^{22}$ will be .05 mole

15. molar mass of $H_2SO_4$ = 98.078 g/mol
No of moles = $\frac {45.8}{98.078}=0.467$ moles

16. Molecular mass of Fe= 55.845 g/mol
1 mole of Fe weighs= 55.845g
5 moles of Fe weigh=$55.845 \times 5 =279.225$ g

17.Molar mass of $NaCl$ = 58.4 g/mol
Number of moles in 20.0 g NaCl is = $\frac {20}{58.4}= .342 $ mol

18. Molecular mass of $CaCO_3$ = $40 + 12 + 16 \times 3=100$
No of moles in 50 gram = $\frac {50 }{ 100} =0.5$
1 $CaCO_3$ molecule has three oxygen atoms so one mole $CaCO_3$ atom has 3 mole oxygen atom or 48 gm of oxygen
So .5 moles will have = .5 *48 =24 grams of oxygen

19. molecular mass of $CO_2$ = 44
Mass = number of moles * molecular mass
= 0.1 * 44= 4.4 g

20. Mass of mole of Oxygen atom , i.e one O is present = O = 16 grams
Mass of mole of $O_2$ ,Oxygen gas = $O_2$= 16 + 16 = 32 grams
So a mole of oxygen atoms has only half the mass of a mole of oxygen molecules

21.A formula unit in chemistry is the empirical formula of any ionic or covalent network solid compound used as an independent entity for stoichiometric calculations. It is the lowest whole number ratio of ions represented in an ionic compound.

 

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