formulae, equations and amount of substance

Question 1

avagadros number

Answer 1

6.02 x 10^23

Question 2

equation for number of particles

Answer 2

number of particles = number of moles x Avogadros constant

Question 3

equation for the number of moles (including g and mr)

Answer 3

number of moles= mass / molar mass or atomic mass

Question 4

equation for the number of moles (including concentration and volume)

Answer 4

number of moles= concentration x volume

Question 5

cm3 to dm3 conversion

Answer 5

divide by 1000

Question 6

equation for concentration (including mass and volume)

Answer 6

concentration= mass of substance / volume

Question 7

what’s empirical formula?

Answer 7

the simplest whole number ratio of elements in a compound

Question 8

steps to calculate empirical formula

Answer 8

1. Determine mass or percentage of elements
2. Divide the given masses or percentages by mass by their respective ar
3. Divide the results by the smallest value
4. Convert into the simplest whole number ratio

Question 9

spectator ions are

Answer 9

ions that do not participate in a reaction

Question 10

how to work out theoretical masses…
(e.g: how much CaO can be made when 34g of Ca is burnt completely in oxygen)

Answer 10

Steps:
1- write out a balanced equation.
2Ca+ 02 → 2 caO
2- workout the Mr /Ar of species involved
2 Ca = 40x2=80g 2 CaO = 56x2 = 112g
3. Divide Ca side by 80 to find 1g then multiply by 34 to get 34g and do the same for the CaO side.
80g / 80= 1g
1g x 34= 34g

112g / 80 = 1.4g
1.4g x 34= 47.6g
ANSWER = 47.6g

Question 11

equation for the number of moles (including volume and molar gas volume)

Answer 11

number of moles= volume / molar gas volume (24)

Question 12

ideal gas equation

Answer 12

pV = nRT

Question 13

conversions
m - dm - cm
m2 - dm2 - cm2
m3 - dm3 - cm3

Answer 13

x10
x100
x1000
if converting the other way, decide by the same number

Question 14

steps to working out the volume of a gas from an equation
(e.g- what volume of H2 is produced when 12g of K reacts with H2O at 100kPa of pressure and 289K, gas constant is 8.31 J K -1 mol -1)

Answer 14

I. write out balanced equation. 2K+2H20 → 2KOH+ H2
2. work out moles of K n= 12g/39 n= 0.31 mol of K
3. use equation tofind molar ratio of K: H2
2 moles of K react to produce 1 mole of H2
moles of H2 is 0.31/2 = 0.155 molesof H2
A use ideal gas equation to work out the volume
V= 0. 155x8.31 × 298/100000
v = 3.84 x 10-3

Question 15

titration calculation steps (e.g: 18.3 cm3 of 0.25 mol dm-3 HCl was required to neutralise 25 cm3 оf КОН. calculate the concentration of KOH)

Answer 15

Steps: 1- write out a balanced equation HCl + KOH → KCl + H20
2-calculate number of moles in HCl
mol = 0.25x18.3x10-3 = 4. 58 x 10-3mol
3- use equation to find out molar ratio to work out moles of KOH
1:1 ratio between HCl and KOH.
so molar of KOH = mol HCl. so mol KOH = 4.58 x 10-3
4. now calculate the concentation using conc= mol / vol
4.58x10-3 / 25x10-3 = 0.18 mol dm-3

Question 16

standard solution calculations
(e.g- what mass of solid NaOH is required to make 250cm3 of 0.75mol dm-3 NaOH solution?)

Answer 16

1. work out the number of moles of the solution you wanna
   make.
   moles= conc xvol
   mol = 0. 75x250x10-3 = 0.1875
2. use number of moles from previous step to calculate the mass.
   formula mass of NaOH =40
   0.1875 x40 = 7.5g

Question 17

what’s meant by the molar volume of a gas?

Answer 17

volume /space occupied by one mole of a gas at a specified temperature and pressure/ standard conditions

Question 18

importance of atom economy…

Answer 18

• High AE produce less wase & benefits the enviornment
• High AE means that raw materials are used more efficiently - more sustainable
• Higher AE = less by - products so less time + money spent separating these from the desirable product

Question 19

% atom economy equation

Answer 19

(Mass of desired product/total mass of reactants) x 100

Question 20

atom economy is…

Answer 20

how efficient a reaction is

Question 21

% yield equation

Answer 21

(actual yield/theoretical yield) x100

Question 22

% error equation

Answer 22

(uncertainty/ reading) x100

Question 23

uncertainty is…

Answer 23

half of the smallest increment of the equipment.
can measure in either direction

Question 24

reading a meniscus…

Answer 24

read at eye level and read at the bottom of the meniscus