Quantitative Chemistry

Question 1

What is a mole? (not the animal u imbecile)

Answer 1

A mole is the unit used to measure the chemical amounts of atoms, molecules and ions.
The mass of one mole of a substance is equal to the relative atomic or formula mass (Ar or Mr) in grams.

Question 2

What is the equation for no. of moles?

Answer 2

Mass / Mr = moles

Question 3

How do you calculate the Mr?

Answer 3

Work out how many atoms of each element there are in the chemical formula.
Add up the relative atomic mass of each element.

Question 4

Describe the law of conservation of mass.

Answer 4

No atoms are lost or made in a chemical reaction. Instead, the atoms join together to form products. The total mass of products is equal to the total mass of reactants, as are the relative formula masses.

Question 5

What is a closed system?

Answer 5

A system in which no substances can enter or leave during a chemical reaction, such as a stoppered flask.

Question 6

What is the formula for calculating the percentage mass of an element in a compound?

Answer 6

(Ar x number of atoms / Mr) x 100

Question 7

What is Avogadro’s constant?

Answer 7

6.022 x 10^23

The number of particles in one mole of a substance.

Question 8

Calculate the number of water molecules in 0.5 mol of water. Show your working.

Answer 8

6.022 x 10^23 x 0.5

= 3.011 x 10^23

Question 9

Calculate the mass of 0.25 mol of carbon dioxide molecules (Mr of CO^2 = 44)

Answer 9

Mass = relative formula mass x amount.
= 44 x 0.25
= 11g