Molecular Mass and Mole Concept | Atoms and Molecules | Assessment | English | Grade 9

The value of Avogadro’s constant is ___________ .

• 6.0 × 10²⁴

• 6.01 × 10²³

• 6.022 × 10²³

• 6.022 × 10⁻²³

Answer explanation

The value of Avogadro's constant is 6.022 × 10²³.

Tags

NGSS.HS-PS1-7

The number of moles in 32 g of He is ________ .

• 4

• 8

• 16

• 32

Answer explanation

Number of moles = ᵍⁱᵛᵉⁿ ᵐᵃˢˢ⁄ₘₒₗₐᵣ ₘₐₛₛ = ³²⁄₄ = 8

If 12 g of carbon has x atoms, then the number of atoms in 12 grams of magnesium will be ____________ .

• x

• 2x

• ˣ⁄₂

• 1.5x

Answer explanation

Number of atoms = ᵍⁱᵛᵉⁿ ᵐᵃˢˢ⁄ₘₒₗₐᵣ ₘₐₛₛ × Avogadro number For carbon, x = ¹²⁄₁₂ × Avogadro number= 1 × Avogadro number For Magnesium, Number of atoms = ¹²⁄₂₄× Avogadro number = ½ × Avogadro number = ˣ⁄₂

Molecular mass of NaCl is _____ .

• 58.5 u

• 59.25 u

• 52 u

• 25 u

Answer explanation

Molecular mass of sodium = 23 u Molecular mass of Chlorine = 35.5 u Total mass of 1 mole = 23 +35.5 = 58.5 u

What is the number of atoms in 2 mole of Na atoms?

• 12.044 × 10²² atoms

• 12.044 × 10²³ atoms

• 12 × 10⁻²³ atoms

• None of the above

Answer explanation

Number of particles in 1 mole = 6.022 × 10²³ Number of particles in 2 mole = 2 ×6.022 × 10²³ =12.044 × 10²³