topic 1: Calculations involving masses

Question 1

How do you calculate relative formula mass?

Answer 1

Add together the relative atomic masses in a compound

Question 2

What is empirical formula?

Answer 2

The simplist whole number ratio of atoms in a molecule

Question 3

What is the empirical formula of C3H6?

Answer 3

CH2

Question 4

What is the empirical formula of Mg2O2?

Answer 4

MgO

Question 5

What is meant by conservation of mass?

Answer 5

During a chemical reaction, the mass of the reactants is the same as the mass of the products

Question 6

What is a closed system?

Answer 6

A system where reactants and products cannot move in or out. E.g. a sealed flask

Question 7

What is a non-enclosed system?

Answer 7

A system where products and reactants can move in our out, e.g. burning a substance in air

Question 8

What is concentration?

Answer 8

The amount of solute in a solution

Question 9

Which units can be used to measure concentration?

Answer 9

grams per decimetre cubed (g/gm3) or moles per decimetre cubed (mol/dm3)

Question 10

How can you convert cm3 to dm3?

Answer 10

divide by 1000

Question 11

How is concentration in g/dm3 calculated?

Answer 11

mass solute (g) / volume of solution (dm3)

Question 12

What is a mole?

Answer 12

The mass of 6.02x10^23 particles of that substance. The relative particle mass

Question 13

How is number of moles calculated?

Answer 13

moles = mass (g) / atomic or formula mass

Question 14

Why do scientists use moles instead of mass when investigating chemical reactions?

Answer 14

masses do not take into account the fact that different particles are different sizes.