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Chapter 3 NCERT Class 9 Science SOLUTIONS

1. Define the atomic mass unit.
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Question:

Define the atomic mass unit.

Answer:

The atomic mass unit in equal to one twelfth the mass of one atom of carbon-12. It is denoted by μ.

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(All Q's of this Chapter solved)
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Give the name of the elements present in the following compounds. (a) Quick lime (b) Hydrogen bromide (c) Baking Powder (d) Potassium Sulphate

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Write the chemical formula of the following. (a)Magnesium chloride (b) Calcium chloride (c) Copper Nitrate (d) Aluminium chloride (e) Calcium carbonate

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What are polyatomic ions ? Give example

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When 3.0g of carbon is burnt in 8.00g oxygen, 11.00g of carbon dioxide is produced what mass of carbon dioxide will be formed when 3.00g of carbon is burnt in 50.00g of oxygen ? Which low of chemical combination will govern your answer ?

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An 0.24g sample of a compound of oxygen and boron was found by analysis to contain 0.096g of boron and 0.144g of oxygen. Calculate the percentage composition of the compound by weight.

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How many atoms are present in a (a) H2S molecule and (b) PO4 3– ion ?

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What is meant by the term chemical formula ?

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Write down the name of compounds represented by the following formula :— (a)Al2(SO4)3 (b) CaCl2 (c)K2SO4 (d) KNO3 (e)CaCO3

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Write down the formula of (a)Sodium oxide (b)Aluminium chloride (c)Sodium sulphide (d)Magnesium hydroxide

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Why it is not possible to see an atom with naked eyes ?

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Which postulate of Dalton’s atomic theory can explain the law of definite propartions ?

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Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass ?

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Hydrogen and oxygen combine in the ratio of 1 : 8 by mass to form water. What mass of oxygen gas would be required to react completely with 3g of hydrogen gas ?

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In a reaction 5.3g of Sodium carbonate reacted with 6g of ethanoic acid. The products were 2.2g of Carbon dioxide, 0.9g water and 8.2g of Sodium ethonoate. Show that these observations are in agreement with the law of conservation of mass.

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