Atom, Molecules, and Ions

In one experiment, 0.558 g element X was found to react with 0.320 g element Y to form only one product, compound Z. How many grams of compound Z were formed? 

• 0.238 g

• 0.320 g

• 0.558 g

• 0.878 g

Answer explanation

0.558 g element X + 0.320 g element Y → 0.878 g compound Z

When 24.3 g magnesium reacts completely with 16.0 g oxygen, exactly 40.3 g magnesium oxide is formed. Which of the following laws is illustrated by this observation?

• Law of Definite Proportion

• Law of Multiple Proportion

• Law of Conservation of Mass

• Law of Conservation of Energy

Answer explanation

The reaction involved as:

24.3 g magnesium + 16.0 g oxygen → 40.3 g magnesium

Represented through Law of Conservation of Mass

Which of the following statements is consistent with Dalton’s Atomic Theory?

• The atoms of element A are identical with the atoms of another element D

• The atoms of element A have the same mass as the atoms of another element D

• The atoms of element A are different from the atoms of another element D.

• The atoms of element A have the same properties as the atoms of another element D.

Answer explanation

According to Dalton’s Atomic Theory, all the atoms of an element are identical in mass and size, and are DIFFERENT FROM THE ATOMS OF ANOTHER ELEMENT.

In which of the following quantities will two subatomic particles of an element have different values?

• Atomic number

• Mass number

• Number of protons

• Number of electrons

Answer explanation

Mass number = number of protons + number of neutrons

₄⁹Be (Beryllium)

9 = Mass number

4 = Atomic number

4 = protons & electrons

5 = Neutrons

Which of the following information on the number of protons (p), electrons (e) and neutrons (n) is correct for ²³⁸₉₂U?

• 92 p, 92 n, 92 e

• 92 p, 146 n, 92 e

• 238 p, 146 n, 238 e

• 146 p, 82 n, 92 e

Answer explanation

₉₂U²³⁸

Answer: 92 p, 146 n, 92 e

92 = Atomic number

= protons

= electrons

238 = Mass number

238 mass number - 92 proton

= 146 neutrons

What is the mass number of an atom which has 11 protons, 11 electrons, and 12 neutrons?

• 11

• 12

• 22

• 23

Answer explanation

Mass number = number of protons + number of neutrons

Given:

11 protons, 11 electrons, and 12 neutrons?

11 p + 12 n = 23 Mass number

The element Tin has a proton of 50 which also indicates the number of ________ and the number of _______

• atomic number, mass number

• mass number, neutron

• electrons, mass number

• atomic number, electrons

According to the Law of Conservation of Mass, the total mass of the products is equal to the total mass of the reactant.

• True

• False

Mass number is the total number of _________ and protons present in the nucleus of an atom of an element.

• atomic number

• electrons

• isotopes

• neutrons

Who is this Chemist that formulated a concept by describing one of his experiments involving mercuric oxide?

• John Dalton

• Antoine Lavoisier

• Joseph Proust

• Democritus