Form 4 - Chapter 3

Why carbon-12 was chosen as a reference standard for relative atomic mass, RAM?

• Carbon has three isotopes

• Carbon is a nonmetal element

• Carbon is a solid and easier to be handled

• Carbon is located in Group 14 in the Periodic Table of Elements

The chemical formula for potassium hexacyanoferrate(III) is K₃Fe(CN)₆. What is its relative formula mass?

[Relative atomic mass: C=12, N=14, K=39, Fe=56]

• 121

• 199

• 251

• 329

What is the meaning of Avogadro constant, N_A?

• Mass of one mole of a substance

• Pressure of one mole of a substance

• Volume occupied by one mole of gas

• Number of particles in one mole of a substance

The diagram shows two balloons filled with oxygen gas and hydrogen gas respectively.

Which of the following statements is true about the two gases?

Recap: Both oxygen and hydrogen molecules contain two atoms inside a molecule, bonded by covalent bond.

• The number of mole of oxygen gas is greater than hydrogen gas

• The number of moles of oxygen gas and hydrogen gas are equal

• The number of oxygen gas molecules is greater than hydrogen gas molecules

• The number of oxygen gas molecules is fewer than hydrogen gas molecules

Which of the following gases contains 0.4 mol of atoms at room condition?

[1 mol of gas occupies the volume of 24dm³ at room condition]

Tips: Consider number of atoms of each gas.

• 4.8 dm³ He

• 4.8 dm³ H₂

• 4.8 dm³ SO₃

• 4.8 dm³ CO₂

How many molecules are there in 150 cm³ of carbon dioxide, CO₂ at room condition?

[Avogadro constant, N_A = 6.02x10²³

mol^-1; Molar volume of gas is 24 dm³ mol-1 at room conditions]

• 3.76x10²¹

• 3.76x10²⁴

• 9.63x10²²

• 9.63x10²¹

Diagram above shows the composition of coral reef.

What is the empirical formula of the compound in the coral reef?

[Relative atomic mass: X=40, Y=12, Z=16]

• XYZ

• XYZ₃

• XYZ₄

• X₃YZ

Which compound has the empirical formula of CH₂O?

• HCOOH

• CH₃COOH

• CH₃COOCH₃

• HCOOC₂H₅

The ionic formula of calcium nitrate and potassium phosphate are Ca(NO₃)₂ and K₃PO₄ respectively.

What is the ionic formula of calcium phosphate?

• CaPO₄

• Ca₂PO₄

• Ca₂(PO₄)₃

• Ca₃(PO₄)₂

Which chemical compound is correctly named ?

• MgO - magnesium oxide

• SO₃ - sulphur oxide

• CO - carbon oxide

• Fe₂O₃ - Iron(II) oxide