Chemical Calculations | MCQs

Explanation

Number of neutrons = Atomic mass - Atomic number

= 27 - 13 = 14

Atomic number (13) gives the number of protons, and subtracting it from the atomic mass gives the neutrons.

Explanation

Oxygen has 8 protons and typically 8 neutrons, giving it a mass number of 16.

Mass number = Number of protons + Number of neutrons.

Explanation

The mass of one mole of electrons is 0.55g.      

- Mass of one electron ≈ 9.109 × 10⁻³¹ kg

- 1 mole of electrons = 6.022 × 10²³ electrons

- So, mass of 1 mole of electrons ≈  

  9.109 × 10⁻³¹ kg × 6.022 × 10²³ ≈ 5.48 × 10⁻⁴ kg ≈ 0.548 g

So the correct value is about 0.55 g

Explanation

Similarly, you could input the percentages normally and then divide by $100$:

${\text{M}}_r\left(\text{Ga}\right)=\frac{(68.9256\cdot 60.108)+(70.9247\cdot 39.892)}{100}$

${\text{M}}_r\left(\text{Ga}\right)=69.7231\text{to 4 decimal places}$

Explanation

The percentage by mass of an element in a compound is calculated using the formula:

Percentage by mass = (Mass of element in 1 mole of compound / Molar mass of compound) x 100