amount of substances chp 3

Question 1

what is 1 mole equivalent to

Answer 1

one mole is the amount of a substance that contains 6.02 x 10^23

Question 2

what is 6.02 x 10^23

Answer 2

• Avagadros constant, its the number of particles in 1 mole of carbon-12

Question 3

Definition of molar mass

Answer 3

• Molar mass gives the mass in grams of a mole of substance.

Question 4

whats the formula for finding out molar mass

Answer 4

mass / moles = Mr

Question 5

Definition of relative molecular mass

Answer 5

• mass of a molecule compared to 1/12th mass of atom of carbon-12

Question 6

Definition of relative formula mass

Answer 6

• the mass of a formula unit compared to mass of an atom of carbon-12

Question 7

How is relative formula mass calculated

Answer 7

• adding together the relative atomic masses of the elements in the empirical formula

Question 8

what is the water that is part of the crystalline structure of a salt called

Answer 8

water of crystallisation

Question 9

How accurate is finding the formula of a compound using experiments

Answer 9

assumption 1- all water has been lost (if there is a colour change you only see the surface of the crystals and water could be left inside). A solution is to heat to constant mass-the crystals are reheated repeatedly until the mass of the residue no longer changes, suggesting all water has been removed.
Assumption 2- no further decomposition (many salts decompose further when heated, this can be very difficult to judge if there is no colour change)

Question 10

which volume measurements are most commonly used

Answer 10

• cubic centimetre (cm^3) or millilitre (ml) : 1cm^3 = 1 ml
• cubic decimetre (dm^3) or litre(l) : 1 dm^3 = 1000 cm^3= 1000ml = 1L

Question 11

what’s the formula for calculating moles from volume and concentration

Answer 11

mol = conc x vol

Question 12

what is a standard solution

Answer 12

a standard solution is a solution of known concentration

Question 13

How are standard solutions prepared

Answer 13

prepared by dissolving an exact mass of the solute in a solvent and making up the solution to an exact volume

Question 14

what is the relationship between a volume of any gas and the number of moles

Answer 14

-at same temp and pressure
- ^ 1 mol takes up same place

Question 15

Definition of molar volume

Answer 15

The molar gas volume (Vm) is the volume per mole of gas molecules at a stated temp and pressure

Question 16

what are the values for standard conditions

Answer 16

RTP is about 20 degrees and 101 kPa (1 atm) pressure

Question 17

what volume does 1 mole of gas take up in standard RTP

Answer 17

At RTP, 1 mole of gas molecules has a volume of approximately 24.0 dm^3=24000 cm^3

Question 18

whats the formula for calculating molar gas volume

Answer 18

Question 19

when would you use the ideal gas equation

Answer 19

when the experiment calls for a different temperature or pressure than standard or if you need to be more accurate In your calculations

Question 20

what assumptions are made about molecules when using the ideal gas equation

Answer 20

• random motion
• elastic collisions
• negligible size
• no intermolecular forces

Question 21

what is the ideal gas equation formula
what does each thing stand for

Answer 21

temperature is in kelvin (k)
pressure is in pascals (Pa)
volume is in (m^3)
amount of gas molecules is in moles (mol)
ideal gas constant is 8.314 j mol^-1K^-1

Question 22

how do you convert between the basic units used in chemistry

Answer 22

cm^3 to dm^3 = /1000
kPa to Pa = x 1000
K to °C = -273

Question 23

what is the real gas equation and how does it differ from the ideal gas equation

Answer 23

it takes into account intermolecular forces and the volume of gas molecules

Question 24

what is stoichiometry and what does it show

Answer 24

• it is the ratio of moles of each substance in a reaction
• used to find quantity of reactants needed to produce a certain amount of product
• used to find quantities of products that should be formed from a certain quantity of reactants.

ONLY FOUND IN BALANCED EQUATIONS

Question 25

what is the formula for percentage yeild

Answer 25

Question 26

why is the theoretical yeild never really obtained

Answer 26

-the reaction may not have gone to completion
-other reactions (side reactions) may have taken place -alongside the main reaction
-purification of the product may result in loss of some product

Question 27

definition of limiting reagent

Answer 27

the reactant that is not in excess and hence will be completely used up first and stop the reaction

Question 28

how would you figure out the limiting reagenbt based on the chemical equation

Answer 28

find out by working out the amount in moles of each reactant and comparing, if there where equal amounts of both reactant which one would be used up first, that one would be the limiting reagent

Question 29

what is the atom economy of a reaction

Answer 29

the atom economy of a chemical reaction is a measure of how well atoms have been utilised

Question 30

what is the formula for atom economy

Answer 30

Question 31

what do we base off of the atom economy of a reaction

Answer 31

• the sustainability of a reaction
• efficency of reaction
• ^high atom economy = efficent