2 Amount of substance

Question 1

define relative atomic mass (Ar)

Answer 1

average mass of an atom of an element on a scale where an atom of carbon-12 is 12

Question 2

define relative molecular mass (Mr)

Answer 2

verage mass of a molecule on a scale where an atom of carbon -12 is 12.M

Question 3

define and state the value of the avogadro consatnt

Answer 3

number of atoms in 12g of carbon-12

Question 4

define the mole

Answer 4

the amount of substance that contains 6.022 x 10^23 aprticles

Question 5

what is the formula to calculate the number of particles/atoms

Answer 5

number of particles =number of moles x avagadros constant

Question 6

what is the formula to calculate the number of moles using the Mr

Answer 6

moles=mass/Mr

Question 7

define the concentration of a solution

Answer 7

how many moles are dissolved per dm^3 of solution the units are mol dm^-3

Question 8

what is the formula to calculate the number of moles using the concentraion

Answer 8

moles =concentration x volume(dm^3)

Question 9

what is the formula of the ideal gas equation with SI units

Answer 9

pv=nrt p=pressure (pa)
v=volume(m^3)
n=number of mole
r=8.31 jk^-1 mol^-1
t=temperature(k)

Question 10

how do you go from degrees to kelvin

Answer 10

add 273

Question 11

how do you go from cm^3 to dm^3 to m^3

Answer 11

cm^3 —-> dm^3=x10^-3
dm^3 —-> m^3 = x10^-3
cm^3 —-> m^3 = x10^-6

Question 12

how do you go from kPa to Pa

Answer 12

x 1000

Question 13

define empirical formula

Answer 13

Empirical formula is the simplest whole number ratio of

atoms of each element in a compound.

Question 14

define molecular formula

Answer 14

Molecular formula is the actual number of atoms of each element in a compound.

Question 15

what are the rules for ionic equtions

Answer 15

involves ions that happens in solution only the reacting particles and the products they form are included the overall charges are balanced

Question 16

what is a spectator ions

Answer 16

ion thats present in the reaction mixture but doesnt get involved in the reaction

Question 17

write an ionic equation from this balanced equation HNO3 + NaOH —> NaNO3 + H2O

Answer 17

1.HNO3 + NaOH —> NaNO3 + H2O

2. ionic substances break up into ions
   H+ + NO3- + Na+ + OH- —>Na+ + NO3- + H20

3.cancel out ions on both sides
H+ + OH- —> H20

Question 18

What is the theoretical yield

Answer 18

mass of product that should be formed in a chemical reaction
it assumes no chemicals are lost in the process

Question 19

what is actual yield

Answer 19

mass of product that actually is obtained in a recation

Question 20

why is the percentage yield never 100%

Answer 20

not all reactants had reacted fully
content is lost during transfers between containers
some solution gets left on filter paper

Question 21

what is the formula to work out percentage yield

Answer 21

percentage yield= Actual yield/theorteical yield X 100

Question 22

what does the percentage yield tell us

Answer 22

tells us how wasteful a process is as it is based on how much of the product is lost during the process

Question 23

what is atom economy

Answer 23

tells us in theory how many atoms must be wasted in a reaction

Question 24

what is the formula to work out atom economy

Answer 24

%atom economy= molecular mass of desired product/sum of molecular masses of all reactants x 100

Question 25

what are Economic, ethical and environmental advantages for society and for industry of developing chemical processes with a high atom economy.

Answer 25

economic: less expensive as the company will spend less on seperating the desired product from the waste product and also less on treating waste
ethical: chemical companies can find easier, cheaper ways to mass produce medicines and other useful chemicals, this means that the chemicals can be sold for lower prices and therefore be made available to more people
environmental: produce less waste

Question 26

explain and describe the mothod of tittartion

Answer 26

fill burette with acid
measure amounts of alkali using pippete
add the alkali to a clonical flask with a few drops of suitbale indicator
add the acid from the burette drop by drop until the colour changes
repeat process until you get at least two concordant results

Question 27

what are the colour changed in the tiration using phenolphthalein and methyl orange

Answer 27

phenolphthalein-colourless in acid and pink in alkali

methyl orange - red in acid to yellow in alkali