c3 quantitative chemistry

Question 1

What is the law of conservation of mass?

Answer 1

no, atoms are lost or made during a chemical reaction, so the mass of the products will equal the mass of the reactants

Question 2

what charges will the ions from different metal groups be, and what are the exceptions

Answer 2

(group)+
eg mg2+

transition metals can form ions of different charges

Question 3

what charges will the ions from different non-metal groups be, and what are the exceptions

Answer 3

(8-group)-
eg Br-

hydrogen and ammonium are positive

Question 4

how do you find the formula of ionic compounds

Answer 4

in ionic compound, the charges on the ions have to cancel out to leave an overall charge of 0

cross multiply - charge from one ion becomes mass of other ion

Question 5

how to find formula of sodium chloride

Answer 5

Na+ Cl-
(1 charges cancel out)
NaCl

Question 6

how to find formula of calcium hydroxide (Ca2+ and OH-)

Answer 6

2 hydroxide needed to cancel single calcium
Ca(OH)2

Question 7

what is relative atomic mass and what is the symbol

Answer 7

Ar
average mass of isotopes in an element, to take into account the abundance of each isotope
(top number of element)

Question 8

what is relative formula mass and what is the symbol

Answer 8

Mr
sum of the relative atomic masses of the atoms

Question 9

how to find the percentage mass of one element in a compound

Answer 9

atomic mass x number of atoms of that element
/ Mr of compound
x 100

Question 10

what actually is a mole

Answer 10

a measurement
eg like saying “a billion”

Question 11

how do you determine how much is 1 mole of atoms

Answer 11

the relative atomic mass of the element, in grams, will be equal to 1 mole of atoms of that element

eg carbon Ar = 12, so
12g of carbon = 1mol carbon atoms

= 6.02 x 10^3 atoms

Question 12

how to calculate moles

Answer 12

mass/Mr

Question 13

how to balance an equation using moles

Answer 13

• use mass/mr to find moles of each compound, and write it as a large number
• divide all large numbers by smallest number to get the smallest ratio

Question 14

how to calculate the number of moles of an atom, in a given number of moles of the molecule the atom is in

Answer 14

number of atoms are in 1 molecule = number of moles of atoms in 1 mole of molecules

Question 15

how to calculate the number of atoms in 1 mole of a molecule

Answer 15

calculate number of atoms
1 mol = 6.02 x 10^23 molecules
number of atoms x 6.02x10^23

Question 16

how to calculate number of atoms in a given mass of an element

Answer 16

calculate moles using mass/Mr
number of moles of an atom = 6.02x10^23 atoms
so number of atoms = number of moles x 6.02x10^23

Question 17

how to calculate number of atoms in a given mass of a compound

Answer 17

calculate moles using mass/Mr
number of moles of the molecule = 6.02x10^23 molecules
so number of atoms = number of atoms in 1 molecule x 6.02x10^23

Question 18

how to calculate masses of reactants and products in a chemical reaction

Answer 18

use mol = mass/mr to find mol of reactant
multiply by scale factor of reactant to product
use mass = mol x mr to find mass

Question 19

what assumptions have been made when calculating mass of reactants & products of a chemical in a chemical reactiom

Answer 19

the other chemical is unlimited

Question 20

how to calculate masses of reactants and products in a chemical reaction, taking into account a limiting reactant

Answer 20

find moles of product using limiting reactant x scale factor of moles

calculate mass as normal

Question 21

what is the volume of one mole of gas, and under what conditions

Answer 21

24dm^3
at room temp 20 degrees, and room pressure 1 atmosphere

Question 22

equation for volume of a gas

Answer 22

number of moles x 24

Question 23

how to find volume of a gas from mass and mr of element

Answer 23

find moles using mass/mr

x 24

Question 24

how to find volume of gas in a chemical reaction

Answer 24

find moles using mass/mr
multiply by mol scale factor to find moles of gas product
x 24

Question 25

how to find volume of gas in product from volume of gas in reactant

Answer 25

volume x moles of other / moles of own

Question 26

what assumptions have been made when calculating volume of a gas from a chemical reaction

Answer 26

gas is at room temp and pressure

Question 27

what is a limiting reactant

Answer 27

the reactant that is fully used up

Question 28

what is Avogadros constant?

Answer 28

6.02 x10^23

Question 29

what is concentration and what is it measured in

Answer 29

the mass of a solute/number of moles in a solute in a given volume of solution g/dm^3 or mol/dm^3

Question 30

how to find conc of a solution in a reaction

Answer 30

- write c=, v=, and m= under both reactions and fill in conc, vol, and mol - find missing values using mol = conc x vol - multiply mol by mol scale factor to find moles of other reactant - find missing values

Question 31

what is a solute

Answer 31

chemical that is dissolved in a solvent

Question 32

how does mass of solute and volume of solution affect conc

Answer 32

increase mass, constant volume = increase conc increase volume, constant mass = decrease conc

Question 33

what is 100% yield

Answer 33

when all of the starting mass reacts to form the product

Question 34

why is 100% yield not often achieved

Answer 34

- there may be unexpected side reactions - some product may be lost when it is separated from reaction mixture - reversible reactions do not go to completion

Question 35

how to calculate percentage yield

Answer 35

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

Question 36

how to calculate percentage yield for a reaction

Answer 36

calculate theoretical mass using mol x mr mass of product actually made / maximum theoretical mass of product x 100

Question 37

what is atom economy

Answer 37

a measure of the amount of reactants that end up as useful product

Question 38

why is atom economy important

Answer 38

- high atom economy saves money, as low ones use up more resources more quickly - minimising waste increases sustainability

Question 39

how do we deal with unwanted side products

Answer 39

try to find uses for them, eg in other reactions, to not waste money

Question 40

how to calculate atom economy

Answer 40

mr of desired product/sum of mr of all reactants x 100

Question 41

what is 1dm^3 in centimetres

Answer 41

1000 cm^3

Question 42

how to calculate moles of a molecule if the element is []2

Answer 42

ignore the 2, use as single element

Question 43

how to calculate Mr is element is 2[]

Answer 43

ignore the 2, add masses

Question 44

how to find moles ratio if one of the elements is []2

Answer 44

find moles without 2 times by two when making ratio

Question 45

how to write equation from a ratio

Answer 45

take into account smaller numbers, if confused check that it would fit mol, mr, and mass

Question 46

what to do when calculate volume of gas

Answer 46

make sure everything is in dm

Question 47

how to calculate volume of a unreacted gas (not all used in reaction)

Answer 47

- calculate mol ratio - find gas needed (product side) using volume x mol of other / mol of own - total reactant gas - needed gas, to find unreacted gas

Question 48

if a product is a gas, why does law of conservation of mass appear to be disproven?

Answer 48

product is a gas 1 the gas escapes during the reaction 1 so mass at the end is less than expected 1