Question

1
Classify each of the following as physical or a chemical change. Give reasons.
a) churning of milk cream to get butter
b) burning of kerosene
c) change in the colour of black tea on adding lemon juice to it.
d) drying of a shirt in the sun.
e) burning of a candle​

Answer 1

Answer:

a..is chemical....new substance is formed

Answer 2

Answer:

a) Its a chemical change because when the milk is churned the Homogenized milk and cream contains butterfat in microscopic globules.

b) Burning of kerosene is a chemical change as kerosene undergoes combustion in presence of oxygen gas to form new products such as water vapours, carbon dioxide and other gases.

c) its a chemical change because lemon juice is acidic; so it will lower the pH of your tea and, in turn, add hydrogen to some of the coloured chemicals that are in your tea; this makes them change colour because it can alter the way the electrons are distributed around the coloured molecules

d) its a physical change because drying of a shirt in the shirt is nothing but evaporation and evaporation is a physical change

e) In a burning candle, there are both physical and chemical changes. The melting of the solid wax to form liquid wax and the evaporation of liquid wax to form wax vapour are physical changes. The burning of the wax vapour is a chemical change.

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