Question

Ramesh describes how roti is made in his house in 5 steps. Here are the 5 steps:

i). Wheat grains are ground to make flour.

ii). Flour is mixed with water to make soft dough.

iii). Small balls of dough are flattened out with a rolling pin.

iv). The flat round dough is cooked on a pan.

v). The crisp roti is coated with a layer of butter.

In which of the above steps does a physical change take place and in which one does a chemical change take place?

Accepted Answer

Physical changes:

Physical changes are changes in a substance's physical properties, such as its shape, size, or phase, that do not result in the formation of a new substance.

i) Grinding wheat grains to make flour is a physical change because the physical properties of wheat grains change when they are ground into flour, but no new substance is formed.

ii) Mixing flour with water to make soft dough is also a physical change because the physical properties of the mixture change, but no new substance is formed.

iii) Flattening the small balls of dough with a rolling pin is a physical change because the shape and size of the dough change, but no new substance is formed.

v) Coating the cooked roti with a layer of butter is a physical change because the physical properties of the roti change when it is coated with butter, but no new substance is formed.

Chemical Changes:

These are the changes that result in the formation of one or more new substances with different properties.

iv) Cooking the flat round dough on a pan is a chemical change because the heat causes the starches and proteins in the dough to change, forming a new substance with different properties, such as a cooked roti.

Important Questions on Physical and Chemical Changes

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