quantitative chemistry

Question 1

what is Ar

Answer 1

relitive atomic mass

Question 2

how can you find the relative formula mass

Answer 2

adding the relative atomic masses of all the atoms in the compound

Question 3

what is the formula for the percentage mass of an element in a compound

Answer 3

ar x number of atoms in element your looking for/ Mr of compound x 100

Question 4

what is the formula to find the number of moles in a mass

Answer 4

moles = mass in g/ Mr

Question 5

why might the mass increase during a reaction in a unsealed reaction vessel

Answer 5

• because one of the reactants is a gas so before the reaction s floating in the air but its not contained in the vessel so it doesn’t count towards the mass
• when the gas reacts to form part of the product it becomes contained so the total mass increases

Question 6

why might the mass decrease during a reaction in a unsealed reaction vessel

Answer 6

because one or more or more of products are gases
- before reaction the reactants are contained
- vessel inst enclosed so the gases can escape from the reaction vessel so the total mass decreases

Question 7

formula for finding the concentration

Answer 7

concentration = mass of solute/volume of solute