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Olympiad (Class 9) Atoms and Molecules — practice questions

Explore 30 free Atoms and Molecules questions in Olympiad (Class 9) Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Atoms and Molecules questions and exercises with answers

Showing questions 1–30 of 30.

A sealed flask is weighed before and after a reaction inside it. The total mass:Read the answer and worked solution →Water from a river, a well and a tap all give hydrogen and oxygen in the mass ratio:Read the answer and worked solution →Decomposing 9 g of water always gives 1 g of hydrogen and how much oxygen?Read the answer and worked solution →Nitrogen and hydrogen in ammonia are always present in a mass ratio of:Read the answer and worked solution →The law of definite proportions was first stated by the chemist:Read the answer and worked solution →The atomic theory explaining both laws of chemical combination was given by:Read the answer and worked solution →According to Dalton, the tiny particles that take part in chemical reactions are:Read the answer and worked solution →Dalton's postulate that atoms cannot be created or destroyed explains the law of:Read the answer and worked solution →Dalton held that atoms of one element are identical in mass and in their:Read the answer and worked solution →Dalton said atoms combine to make compounds in ratios that are:Read the answer and worked solution →Later work showed Dalton was wrong about one point, because atoms are made of:Read the answer and worked solution →Since 1961 the standard reference chosen for measuring atomic masses has been:Read the answer and worked solution →One atomic mass unit is defined as a mass equal to what share of a carbon 12 atom?Read the answer and worked solution →The combining capacity of an element, which tells how its atoms link up, is its:Read the answer and worked solution →A group of atoms carrying a charge, such as sulphate, is called a:Read the answer and worked solution →Adding up the atomic masses of every atom in a molecule gives its:Read the answer and worked solution →Hydrogen has atomic mass 1 u and oxygen 16 u. The molecular mass of water is:Read the answer and worked solution →Using H as 1, N as 14 and O as 16, the molecular mass of nitric acid works out to:Read the answer and worked solution →For sodium chloride, whose particles are ions, chemists calculate the:Read the answer and worked solution →With Na as 23 and Cl as 35.5, the formula unit mass of common salt is:Read the answer and worked solution →The SI unit used for the amount of a substance is the:Read the answer and worked solution →One mole of any substance contains how many particles, to four figures?Read the answer and worked solution →Catch Dalton's postulatesRead the answer and worked solution →Pop the mass wordsRead the answer and worked solution →Run the chemistry gatesRead the answer and worked solution →Slice the chemistry termsRead the answer and worked solution →Law or theoryRead the answer and worked solution →Sort the chemistry ideasRead the answer and worked solution →Type the numberRead the answer and worked solution →Atoms bingoRead the answer and worked solution →

Worked practice questions

A sealed flask is weighed before and after a reaction inside it. The total mass:

  1. Stays same
  2. Goes down
  3. Goes up
  4. Goes zero
Show answer and solution

Correct answer: A. Stays same

1. Mass can neither be created nor destroyed in a reaction. 2. A sealed flask lets nothing escape. 3. So the total mass stays the same. _Source: syllabus Science Class IX, Chapter 3, Atoms and Molecules._

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Water from a river, a well and a tap all give hydrogen and oxygen in the mass ratio:

  1. 1 to 6
  2. 1 to 8
  3. 1 to 4
  4. 1 to 2
Show answer and solution

Correct answer: B. 1 to 8

1. A compound always holds its elements in fixed proportion. 2. In water the hydrogen to oxygen mass ratio is fixed. 3. That ratio is 1 to 8. _Source: syllabus Science Class IX, Chapter 3, Atoms and Molecules._

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Decomposing 9 g of water always gives 1 g of hydrogen and how much oxygen?

  1. 8 g
  2. 2 g
  3. 4 g
  4. 6 g
Show answer and solution

Correct answer: A. 8 g

1. The mass ratio in water is one part hydrogen to eight parts oxygen. 2. One gram of hydrogen therefore pairs with eight of oxygen. 3. So 8 g of oxygen is obtained. _Source: syllabus Science Class IX, Chapter 3, Atoms and Molecules._

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