Question

Which of the following has the least number
of atoms?
1) 0.5 g atom of Zn 2) 0.645g of Zn
3) 0.25 mole of Zn 4) 6.45x1020 amu of Zn​

Answer 1

Answer:

0.5 g atom of Zn has least number of atoms

Answer 2

0.5 g of atom contains least number of atoms

Explanation:

• To determine least number of atoms in following amount of Zinc we need to calculate the Number of atoms in each condition

• As we know Atomic mass of Zn is 65.32 and 1 mole of element contains 6.022 × 10²³ atoms we will use these values to determine number of atoms in Zn in given quantities.

1) Number of atoms in 0.5 g atom of Zn  

⇒ No. of moles in Zn = given weight/ atomic mass

= 0.5g / 65.32 g = 0.007654

Number of atoms in 1 mole Zn = 6.022 × 10²³ atoms  

Number of atoms in 0.007654 mole = 6.022 × 10²³ × 0.007654

= 0.04609 × 10²³ atoms = 4.609 × 10²³ atoms

2) Number of atoms in 0.645g of Zn

No. of moles in Zn = given weight/ atomic mass  

= 0.645g / 65.32g = 0.009874 moles

No of atoms in 1 mole Zn = 6.022 × 10²³ atoms

⇒ No of atoms in 0.009874 moles Zn = 6.022 × 10²³ × 0.009874 atoms

= 0.059461 × 10²³ atoms = 5.9561×10²¹

3) Number of atoms in 0.25 mole of Zn

No of atoms in 1 mole Zn = 6.022 × 10²³ atoms

⇒ No of atoms in 0.25 moles of Zn = 6.022 × 10²³ × 0.25

= 1.5055 × 10²³ atoms

4) Number of atoms in 6.45x10²⁰ amu of Zn​

Number of atoms in 65.32 amu of Zn = 6.022 × 10²³ atoms

⇒ Number of atoms in 6.45x10²⁰ amu = (6.022 × 10²³/ 65.32)× 6.45x10²⁰

= 5.9464 × 10²³.10²⁰ = 5.9464×10⁵² atoms

Here,  

5.9464×10⁵² atoms > 1.5055 × 10²³ atoms > 5.9561×10²¹ > 4.609 × 10²³ atoms

From above calculations 0.5 g atom of Zn contains least number of atoms

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