Quantative Chemistry

Question 1

How do you find percentage by mass

Answer 1

Total relative mass of atom
———/———-
Relative formula mass X100

Question 2

What arE isotopes

Answer 2

Atoms of the same Element but with a different number of neutrons

Question 3

What is a mole

Answer 3

The amount of substance which contains the Avogadro constant of a specified particle or formula unit

Question 4

What is avogadros constant

Answer 4

Number of atoms in 12g of carbon 12

. One mole of anything contains 6x1023 atoms

Question 5

What is the molar mass

Answer 5

Same as the relative formula mass

Question 6

What is the equation linking RFM mass and mol

Answer 6

Mol = mass
——
RFM

Question 7

What is the emperical formula

Answer 7

Simplest whole number ratio of atoms in a compound

Question 8

How do you calculate emperical formula

Answer 8

Write mass or percentage of each element down
Divide each mass or percentage by RAM of element to convert to moles
Simplify the mole ratio by dividing each number by the smallest
If this doesn’t give a hole number multiply each by an appropriate figure

Question 9

What is molecular formula

Answer 9

The actual number of each atom in one molecule of a molecular substance this is useful for simple molecular substance

Question 10

What must the molecular formula be

Answer 10

A whole number multiple of the empirical formula
E.g a compound has the empirical formula CH2O and a relative molecular mass of 120 what’s the molecular formula ?
Relative mass CH2O = 30
120/30= 4 so there must be 4 lots of CH20 to give mass of 120 so molecular formula is C4H8O4

Question 11

How do you do reacting mass calculations

Answer 11

Calculate the number of miles given by the mass of an element in the question
Write a balanced equation for the reaction
Use ratio given by balancing the equation to find the number of moles in other elements
Convert the moles back to mass

Question 12

Why are yields in experiments less than predicted

Answer 12

Reaction may not be completed
May be side reactions which use up reactants but make different products
May not be possible to separate all of the products from the mixture

Question 13

Equation for percentage yield

Answer 13

Actual yield from experiment
—–//////————
Theoretical maximum yield X100

Question 14

What is the equation of moles and gases volume at room temperature and pressure

Answer 14

Moles of gas = volume of gas dm3
———-/////—–
24

Question 15

How do you convert from cm and m to dm

Answer 15

Dm to cm = x1000

Dm To m = /1000

Question 16

Equation for concentration

Answer 16

Volume
= concentración (mol/dm3)

Concentration (g/dm3) = mass
———-
Volume