CHEMISTRY..SOME SIMPLE Q&A..

Q1. Define the term precision and accuracy?

Ans. The term precision refers for the closeness of set of values obtained from identical
measurement of a quantity, whereas accuracy is a related term, refers to the closeness of a single
measurement to its true value.

Q2-What do you mean by significant figure?

Ans. Total number of digits in a number including the last digit whose value is uncertain is called the
number of significant figure.

Q4. Define the law of conservation of mass ?

Ans. Matter can neither be created nor destroyed in the course of a Physical or chemical process
although it may change from one form to another.

Q5- How many significant figure are present in the following ?

(I)  0.0025 (II) 208 (III) 5005   (IV) 126000

Ans.- (I) 2    (II) 3      (III) 4    (IV) 3

Q6  Define Molarity ?

Ans.  It is the number of moles of the solute dissolved per litre of the solution.
Q.7  Define Molality ?

Ans.    It is the number of moles of the solute dissolved per 1000 g of the solvent.

Q8  Define mole?

Ans.  The amount of substance that contains the same number of entities(atoms, molecules, ions
or other particles) as the number of atoms present in 12g of carbon-12 isotope.

Q9   How are 0.50 m Na2CO3 and 0.50 M Na2CO3 different?

Ans.   0.50 m Na2CO3 solution means that 0.5 mol (or 53g) of Na2CO3 are present in 1000 g of
solvent.
0.50 M Na2CO3 solution means that 0.5 mol (or 53g) of Na2CO3 are present in 1L of solution

Q10.   a) Why Molarity varies with temperature?
b) Which concentration term is suitable when solute is present in very minute quantities or
traces?
c) What is the sum of mole fraction of all the components of a solution?

Ans.  a) Because it is number of moles of solute per litre of solution, and volume varies with
temperature.
b) ppm(Parts per million)
c) 1

Q11.   Calculate the mass of an atom of silver (atomic mass= 108)

Ans.  Mass of 6.022x10
23
atoms of Ag = 108 g
Mass of one atom of Silver
108
6.022X10
23
= 1.79x10
-22
g

Q12.   Calculate the number of moles of iodine in a sample containing 1.0x10
22
molecules?

Ans.  6.022x10
23
molecules of iodine = 1 mol of iodine
1.0x10
22
molecules of iodine =
1
6.022X10
23X1.0 X10
22
= 0.0166 mol of iodine

Q13. Calculate the volume occupied by 10 mole of CO2 at STP. ?

Ans.  1 mol of CO2 atSTP = 22.7 L
10 mole of CO2 at STP = 22.7 x 10 =227 L

Q14 A solution is prepared by dissolving 2g of the substance A in 18 g of water. Calculate the mass
percentage of solute ?

Ans.  Mass of solute A = 2g
Mass of water = 18g
Mass of solution = 2+18 = 20g

Mass percentage =
Mass of A/
Mass of solution
*100g
=
2/
20
* 100

Q15   In three moles of ethane (C2H6) calculate the following:
(a)  Number of moles of carbon
(b)  Number of moles of hydrogen atom
(c)  Number of moles of ethane

Ans.  (a)   1 mole of C2H6 contain = 2 moles of carbon
3 moles of C2H6 contain = 6 moles of carbon
b)    1 mole of C2H6 contain = 6 moles of hydrogen atom
3 moles of C2H6 contain = 18 moles of hydrogen atom
c)  1 moles of C2H6 contain = 6.022 x 10
23
molecules
3 moles of C2H6 contain = 6.022 x 10
23
x 3 = 1.0807 x 10
24
molecules.

Q17  A solution is 25% H2O, 25% C2 H5 OH and 50% acetic acid by mass. Calculate mole fraction of each component.

Q18  Calculate the molarity of pure water (density of water = 1 g mL
-1
) . (L 3)

Ans.  Density of water = 1 g mL
-1
Mass of 1000 mL of water = Volume x Density
1000 x 1 = 1000 g
Moles of water =
1000/18
= 55.55

Q18  Calculate the weight of carbon monoxide having same number of oxygen atoms as are
present in 88 g of carbon dioxide.