Quantitative Chemistry

Question 1

What is the equation for the number of moles in a given mass?

Answer 1

Mass (g) ÷ Relative formula mass

Question 2

What is a mole?

Answer 2

One mole of any substance is just the amount of that substance that contains an Avogadro number of particles. The mass of that number atoms or molecules of any substance is exactly the same number of grams as the RAM or RFM of the element (e.g. one mole of carbon is 12g).

Question 3

How much volume does one mole of any gas occupy at room temperature?

Answer 3

24dm3

Question 4

What is the formula for volume of gas at room temperature and pressure?

Answer 4

(Mass of gas ÷ RFM (Mr)) x 24

Question 5

What is the formula for concentration using mass?

Answer 5

Mass (g) ÷ Volume (dm3)

Question 6

What is the formula for concentration using moles?

Answer 6

Number of moles (mol) ÷ Volume (dm3)

Question 7

What is the formula for atom economy?

Answer 7

(RFM of desired products ÷ RFM of all products) x 100

Question 8

What is atom economy?

Answer 8

The percentage of reactants forming useful products.

Question 9

What is the percentage yield?

Answer 9

(Mass of products actually made (g) ÷ Maximum theoretical mass of product (g)) x 100

Question 10

Why are yields always less than 100%?

Answer 10

In reversible reactants, the products can turn back into reactants. There might be side reactions with the air or impurities in the reaction mixture. Some product may be lost when separating the product from the reaction mixture (e.g. during filtration).