moles

Question 1

define molar mass

Answer 1

the mass in g, per mole of a substance (gmol-1)

Question 2

define a mole

Answer 2

the amount of a substances containing as many particles as there are exactly 12 grams of carbon in carbon-12

Question 3

define molar gas volume

Answer 3

the gas volume per mole of a substance. This is 24.0 dm3mol-1 at room and temp and pressure

Question 4

define avogodros constant

Answer 4

the number of particles per mole of a substance (6.02x10^23)

Question 5

define relative atomic mass

Answer 5

the weighted mean of mass of an atom compared with 1/12th the mass of an atom of Carbon-12

Question 6

define relative molecular mass

Answer 6

the weighted mean mass of a simple covalent molecule compared with 1/12th of the mass of an atom of carbon-12

Question 7

formula for number of particles

Answer 7

Na x moles

particles can be atoms ions or molecules

Question 8

whats the standard size for a beaker?

Answer 8

250cm3

Question 9

what does continuous monitoring give?

Answer 9

a rate

Question 10

what does a concentrated solution contain?

Answer 10

a large amount of solute per dm3

Question 11

what does the concentration give?

Answer 11

an accurate indication of the amount in moles of solute thats dissolved in a volume (1dm3)of the solution

Question 12

given conc and volume in dm3, whats the formula for mole?

Answer 12

conc x volume

Question 13

given conc and volume in cm3, whats the formula for mole?

Answer 13

c x v/1000

Question 14

how to convert from gdm-3 to moldm-3?

Answer 14

divide by the Mr

Question 15

define standard solution?

Answer 15

solutions of a known concentration

Question 16

what would you need to do in order to make up a given volume of a solution with a precise conc?

Answer 16

-work out the amount of moles of the solute required
-calculate the mass needed for the chosen volume of water

Question 17

what 2 ways can standard solutions be made by?

Answer 17

1. dissolving a solid to form a solution of known concentration
2. diluting a solution to form a solution of known concentrations

Question 18

what glasswear are standard solutions prepared in?

Answer 18

volumetric flasks

Question 19

method to prepare a standard solution

Answer 19

1. accurately weigh solid in weighing boat (using mass by difference method)
2. transfer solid to a 50cm3 beaker and dissolve solid fully with distilled water
3. transfer solution to 250cm3 volumetric flask. rinse beaker with distilled water and add rinsings
4. fill flask with distilled water until the bottom of the meniscus lines up exactly with the 250cm3 graduation mark. use a dropping pipette when near
5. invert flask several times to mix fully

Question 20

when making a standard solution, why is it important to add rinsings of weighing boat?

Answer 20

ensure all solution successfully transferred to volumetric flask
if not, would result in a lower concentration

Question 21

whats the importance of lining the bottom of the meniscus up with the graduation mark?

Answer 21

if meniscus goes above graduation mark, the volume will be greater and conc will be less

if meniscus is lower than the graduation mark, then volume is less and conc is greater

Question 22

what is an acid-base titration a type of?

Answer 22

volumetric analysis

Question 23

what signifies the end point?

Answer 23

change in colour

Question 24

what can be assumed of an end point in an acid-base titration?

Answer 24

moles of H+ ions from the acid = moles of OH- ions from the alkali

Question 25

before the titration how should you prepare glass wear?

Answer 25

washing and conditioning

Question 26

whats the formula for % uncertainty in titre

Answer 26

( uncertainty/ mean titre ) divide readings taken

(2 normally)

Question 27

suggest errors when making a standard solution which would result in solution in being less concentrated?

Answer 27

-not rinsing mass boat and adding the rinsings
-conical flask washed, rinsed but not dried fully