Quantitative chemistry

Question 1

What is concentration measured in?

Answer 1

Measured in Molarity (M), Molality (m), or Percentage (%)

Question 2

what is relative formula mass, Mr?

Answer 2

if you have a compound, the relative formula mass is the total of all the relative atomic masses of all the atoms

Question 3

how to calculate the percentage mass of an element in a compound?

Answer 3

(Ar X number of atoms of that element) / Mr of the compound X 100

Question 4

What is the Avogadro constant?

Answer 4

6.02 X 10^23

Question 5

What is “the mole”?

Answer 5

The mole is the name given to an amount of a substance

Question 6

why do we use Avogadro constant?

Answer 6

the mass of that number of atoms or molecules of any substance is exactly the same number of grams as the relative atomic mass (Ar) or relative formula mass (Mr) of the element or compound

Question 7

How do you calculate the number of moles?

Answer 7

mass in g / Mr

Question 8

What is the conservation of mass?

Answer 8

During a chemical reaction, no atoms are destroyed and no atoms are created. This means there are the same number and types of atoms on each side of a reaction equation

Question 9

why might the mass in a reaction increase?

Answer 9

One of the reactants is a gas that is found in air and all the products are solids, liquids or aqueous

Question 10

why might the mass in a reaction decrease?

Answer 10

One of the products is a gas and all the reactants are solids, liquids or aqueous

Question 11

How to balance equations using reacting masses?

Answer 11

1) divide the mass of each substance by its relative formula mass to find the number of moles
2) divide the number of moles of each substance by the smallest number of moles in the reaction
3) if any of the numbers are not all whole numbers, multiply all numbers by the same amount so they are all whole numbers
4) write the balanced symbol equation for the reaction by putting these numbers in front of the chemical formulas

Question 12

What is a limiting reactant?

Answer 12

The reactant that runs out first, causing a reaction to stop. All other reactants will be in excess.

Question 13

How to find the mass of a product formed in a reaction, using the mass of the limiting reactant and the balanced reaction equation?

Answer 13

1) write out the balanced equation
2) work out the relative formula masses (Mr) of the reactant and product you want
3) use the balanced equation to work out how many moles there’ll be of the other substance
5) use the number of moles to calculate the mass

Question 14

How to calculate the volume of gas?

Answer 14

mass of gas / Mr of gas X 24

Question 15

What is concentration?

Answer 15

the amount of a substance in a certain volume of a solution is called its concentration

Question 16

how to calculate concentration in g/dm^3?

Answer 16

concentration = mass of solute / volume of solvent

Question 17

how to calculate concentration in mol/dm^3?

Answer 17

concentration = number of moles of solute / volume of solvent

Question 18

what does the atom economy tell you?

Answer 18

how much of the mass of the reactants was wasted when manufacturing a chemical and how much ends up as useful products

Question 19

how to calculate atom economy?

Answer 19

relative formula mass of desired products / relative formula mass of all reactants X 100

Question 20

What does the percentage yield tell you?

Answer 20

The overall success of an experiment. It compares what you think you should get (theoretical) to what you get (actual)

Question 21

how to calculate percentage yield?

Answer 21

mass of product actually made / maximum theoretical mass of product X 100

Question 22

What will a yield always be?

Answer 22

It will always be less than 100%

Question 23

why might you not get 100% yield?

Answer 23

1) not all reactants reacted to make the product
2) there might be side reactions
3) you lose some product when separating it from the reaction mixture