Question

16. a) While diluting a solution of salt in water a student accidentally added acetone boiling
point 58°C) to it. What technique can be applied to get back acetone and what is principle
involved in the technique?
b) Write three differences between physical and chemical change.
Or
Calculate:
a) The mass of 1.0505x102 molecules of carbon dioxide (CO2)
b) The number of molecules of 0.25 moles of NH;
c) The molecular mass of Na2SO3
(Atomic mass: Na=23 u, S=32 u, O=16 , H=1u, NA=6.022x10 moll) (-12
ciclo dicoradabad
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Answer 1

a) Acetone is soluble in water, a homogeneous mixture is obtained and hence separation by separating funnel cannot be used. Acetone can be get back by simple distillation because the difference in the boiling points of acetone and water is more than 25°C.

Boiling point of acetone - 56°C

Boiling point of water -100°C

In distillation flask, acetone will boil at 56°C and change into vapours and can be collected in flask after condensation.

b)•A change in which the molecules are rearranged, but their internal composition remains same is called Physical Change. A process in which the substance transforms into a new substance, having a different chemical composition, it is known as Chemical Change.

•Some common examples of physical change vaporisation, condensation, freezing/melting/boiling of water. On the contrary, the examples of chemical change are combustion, metabolism, cooking of egg, etc.

•Physical change is a temporary; they are easily reversible. As against this, the chemical change is permanent in nature, i.e. they cannot be reversed, even by reversing conditions.

Answer 2

16. a) Distillation

b) PHYSICAL CHANGES:

1. NO NEW SUBSTANCE IS FORMED .

2.IT IS A TEMPORARY CHANGE

3 . IT IS REVERSIBLE.

CHEMICAL CHANGES:

1.NEW SUBSTANCE IS FORMED.

2. IT IS PERMANENT CHANGE.

3. IT IS IRREVERSIBLE.

..................OR................

a) .& b) & c) is in pic