Ncert- science – class 7- Chapter 5 – Physical and Chemical Changes 2

Welcome to your Ncert- science - class 7- Chapter 5 – Physical and Chemical Changes 2

A substance appears coloured because:

Which of the following is the most common solvent used for crystallization?

Which of the following is a physical change

Which conditions are necessary for rusting?

What effect does salt have on the corrosion of iron?

Which of the following represents correct statement(s)?

When a magnesium ribbon burns in air, the ash formed is dissolved in water:

Vacuum desiccator is used _____

Which of the following is/are true when milk changes into curd?

(i) Its state is changed from liquid to semi-solid.
(ii) It changes colour.
(iii) It changes taste.
(iv) The change cannot be reversed.

Chemical changes are:

Anaerobic bacteria digest animal waste and produce biogas(Process-A). The biogas is then burnt as fuel(Process-B). The following statements pertain to these changes. Choose the correct one.

Your lab partner mixed two colorless solutions in the test tube. He sees no observable changes in the resulting mixture and is unable to detect any temperature change. Based on these observations, what type of change has taken place?

Which of the following is an example of a physical change?

Take some clean iron nails and place them in the three test tubes prepared as under:

 
Test tube A: Contains boiled water and a thin layer of oil.
 
Test tube B: Contains dry air.
 
Test tune C: Testube half-filled with water. 
 
All the test tubes are tightly closed after placing the nails. After some time what will you observe?

What type of protection is galvanising?

While forming crystals, it is important to :

When magnesium ribbon burns in the air, it forms white ash. The chemical name of white ash is:

$$H_{2}O_{(l)}\rightleftharpoons H_{2}O_{(g)}$$
What type of change is represented by the equation above?

Which of the following is a physical change?

a) Hammering of a red hot iron rod to make a flat sheet.
b) Formation of ice by cooling of water.
c) Rising of water vapors from sea to make clouds.
d) Heating of charcoal in the air to high temperature till it begins to flow.

Which of the following BEST describes the differences between particles of solid and particles of liquid?

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