C9 QUANTITATIVE CHEMISTRY

Question 1

molecular formula

Answer 1

gives the number of atoms element present in a molecule

Question 2

empirical fromula

Answer 2

give the number of atoms of each element present in a compound as the simplest whole number ratio

Question 3

converting molecular to empirical formulae

Answer 3

divide the number of each atom by the highest common factor of all of the atoms

Question 4

molecular to empirical formulae examples

Answer 4

C2H4- ch2 (divided by 2)

C6H1206-CH20 (divided by 6)

Question 5

relative atomic mass , A

Answer 5

the mass of an atom relative to 1/12th the mass of carbon-12. No units

Question 6

relative formula mass , Mr

Answer 6

the mass of one unit of a formula, found by adding the relative atomic masses of all of the atoms in it

Question 7

to calculate the empirical formulae from experimental data

Answer 7

write each elements symbol with a ratio : symbol between
write out the amount of each element from the questions
divide each amount by the Ar of the element
divide each answerably the smallest answer to get a ratio
write the empirical formulae

Question 8

to find a molecular formula from an empirical formulae

Answer 8

calculate Mr for the empirical formulae
divide the Mr of the molecular formulae by this number
multiply the empirical formula by your answer

Question 9

conservation of mass

Answer 9

the total mass of products must equal the total mass of reactants

Question 10

precipitation reaction

Answer 10

a reaction that produces a solid precipitate by mixing two solutions

Question 11

closed system

Answer 11

a system in which no chemicals can enter or leave , such as a sealed tube

Question 12

open system

Answer 12

a system in which chemicals can enter or leave - such as an open test tube

Question 13

conservation of mass in a closed system

Answer 13

no atoms are able to enter or leave , so the total mass stays the same - for example a precipitation reaction in a closed flask

Question 14

conservation of mass in an open system

Answer 14

for example , a carbonate reacting with acid producing CO2 bubbles : the mass appears to decrease because you can’t weigh the gas that goes into the air, however it is still there

Question 15

excess reactant

Answer 15

any reactant which is not used up completely in a reaction because there is more of it than needed

Question 16

limiting reactant

Answer 16

any reactant of which is completely used up in a reaction the limiting reactant determines how much product is made

Question 17

calculating reacting masses

Answer 17

write out the balanced equation
write the mass of he chemical you are given, and m for the mass you are finding under their symbols
draw a line underneath the masses to make it a division
calculate the Mr of each multiply by the big numbers and write under the line
puts an equals sign between the two or form an equation
solve for m

Question 18

moles

Answer 18

the unit of measurement of chemicals - one mole of any chemicals is the same amount

Question 19

one mole

Answer 19

an amount of a chemical such that one mole has a mass in grams that is the same as its relative formula mass

Question 20

Avogadros constant

Answer 20

6.02 x 10- 23 the number of atoms / molecules present in one mole of a substance

Question 21

calculating moles from mass

Answer 21

quantity in moles = mass / relative formula mass

Question 22

calculating moles from a number of particles

Answer 22

quantity in moles = number of particles / 6.02 x 10-23

Question 23

calculating number of particles from a mass of substance

Answer 23

number of particles = (mass/relative formula mass) x 6.02 x 10-23

Question 24

stoichometry

Answer 24

the ratio of the number of moles of each substance involved in a reaction

Question 25

stoichometric coefficient

Answer 25

the big numbers written in a balanced equation

Question 26

deducing stoichometry

Answer 26

calculate the number of moles present of each of the reactant ( or products )
find the simplest whole-number ratio
balance in the normal way to find the numbers of products (or reactants)