# Q&A - Ask Doubts and Get Answers

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Q 2.     Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56 u)?

The number of moles of 100 g Na atoms : The number of moles in 100 g of Fe atoms : As we know, the one-mole atoms contain  atoms.  So,  more the number of moles, more the number of atoms. and hence 100 g of Na atom has a greater number of atoms than 100 g Fe.

Q 1.     If one mole of carbon atoms weighs 12 grams, what is the mass (in grams) of 1 atom of carbon?

As we know, Now,  the mass of 1 mole or   = 12  g The mass of 1 atom :   Hence the mass of 1 atom of Carbon is   .

Q 2.     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

Given,  the atomic mass of Zn = 65 u, the atomic mass of Na = 23 u, the atomic mass of K = 39 u, the atomic mass of C = 12 u, and the atomic mass of O = 16 u Now, Formula unit mass of ZnO = Atomic mass of Zinc + Atomic mass of O                                           =   65 u + 16 u                                           =   81 u. Formula unit mass of Na2O = 2 * Atomic mass of Na+ Atomic...

Q 1.     Calculate the molecular masses of

The molecular mass of  : = 2 * Atomic mass of Hydrogen  = 2 * 1u =2u. The molecular mass of  : = 2 * Atomic mass of Oxygen = 2 * 16u = 32u. The molecular mass of  : = 2 * Atomic mass of Chlorine = 2 * 35.5uu = 71u. The molecular mass of  : = Atomic mass of Carbon +2 * Atomic mass of Oxygen = 12u + 2 * 16u = 44u. The molecular mass of  : = Atomic mass of Carbon +4 * Atomic mass of Hydrogen = 12u...

Q 4.     How many atoms are present in a

(ii)          ion?

ion has one atom of Phasphorus and 4 atoms of Oxygen. And Hence, Total 5 atoms are present in    ion.

Q 4.      How many atoms are present in a

(i)      molecule

molecule has 2 atoms of Hydrogen and 1 atom of Sulphur. and hence, Total of 3 atoms are present in  molecule .

Q 3.     What is meant by the term chemical formula?

The chemical formula of a compound is a symbolic representation of its composition. For example, The chemical formula for common salt is NaCl as it is made up of Sodium (Na) and Chlorine (Cl).

Q 2.     Write down the names of  compounds represented by the following formulae:

(i)

(ii)

(iii)

(iv)

(v)

The Names of the following compounds are :  (i)            =Aluminium Sulphate   (ii)                 =Calcium Chloride  (iii)                =Potessium Sulphate   (iv)                = Potessium Nitrate   (v)                   =Calcium Carbonate.

Q 1.     Write down the formulae of

(i) sodium oxide

(ii) aluminium chloride

(iii) sodium suphide

(iv) magnesium hydroxide

The Formula of given compounds are :  (i) sodium oxide :   (ii) aluminium chloride: (iii) sodium sulphide:  (iv) magnesium hydroxide:

Q 2.     Why is it not possible to see an atom with naked eyes?

We can't see the atom with the naked eye because they are miniscule in nature. they are measured in the nanometres. Also, except for noble gases, all-atom do not exist independently.they exist in the form of any compound.

Q 1.     Define the atomic mass unit.

An atomic mass unit is a unit of mass used to express the weight subatomic particles, where one unit is equal to exactly one-twelfth the mass of a carbon-12 atom.

Q 4.     Which postulate of Dalton’s atomic theory can explain the law of definite proportions?

The postulate of Dalton’s atomic theory can explain the law of definite proportions is "The relative number and kinds of atoms are equal in given compounds."

Q 3.     Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?

The postulate of Dalton’s atomic theory is the result of the law of conservation of mass is "Atoms can neither be created nor can be destroyed".

Q 2.     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?

Given: Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. Now, For every 1 g of Hydrogen, 8 g of oxygen is needed for the reaction to take place.  Therefore, for 3 g of Hydrogen, the mass of oxygen needed = 8 * 3 = 24 g. Hence, 24 g of Oxygen is needed to complete reaction with 3 g of Hydrogen.

Q 1.     In a reaction, 5.3 g of sodium carbonate reacted with 6 g of acetic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium acetate. Show that these observations are in agreement with the law of conservation of mass.

sodium carbonate + acetic acid → sodium acetate + carbon dioxide + water

Given, the reaction   sodium carbonate + acetic acid → sodium acetate + carbon dioxide + water         5.3g                       6g                     8.2g                     2.2g               0.9g Now, Total Mass on the Left Hand Side = 5.3g + 6g = 11.3g Total Mass on the Right Hand Side = 8.2g + 2.2g + 0.9g = 11.3g As Mass on the LHS is equal to RHS, the observation is in agreement with...
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