Question

Which of the following weighs the least?
A. 2g of nitrogen (at. mass = 14)
B. $3\times {{10}^{23}}$ atoms of C (at. mass = 12)
C. 1 mole of S (at. mass = 32)
D. 7 g silver (at. mass = 108)

Answer 1

Hint: When we calculate the molecular weight of any chemical compound then it tells us how many grams are in one mole of that substance. The formula weight is simply the weight in atomic mass units of all the atoms in a given formula.

Complete Step by step solution: To calculate which of the following weighs the least we have to calculate weight of each compound one by one which is as follows:
A. 2g of nitrogen: Gram atomic mass is generally considered as mass of one mole of an element as we know that:
One mole of nitrogen weighs 14 g i.e. 1g atom of nitrogen = 14 g
So 2g of nitrogen = 28 g
B. $3\times {{10}^{23}}$ atoms of C:
One mole of carbon weighs 12 g and 1 mole of atom contains $6.022\times {{10}^{23}}$ which signifies
$6.022\times {{10}^{23}}$ atoms of carbon weighs 12 g
$\therefore 3\times {{10}^{23}}$ atoms of carbon weighs 6 g
C. 1 mole of S (at. mass = 32)
We know that 1 mole of Sulfur weighs 32 g.
D. 7g silver:
One mole of silver weighs 108 g i.e. 1g atom of silver = 108 g
So 7g of silver = 756 g

Out of all compounds, B is showing the least weight. Hence option B is correct.

Note: Formula weights are useful for finding the relative weights of reagents and products in a chemical reaction. These relative weights are calculated from the chemical equation and are known by the name equation weights. If the formula used in calculating molar mass is the molecular formula then the formula weight calculated is the molecular weight.