module 2

Question 1

isotope definition

Answer 1

atoms of same element with different numbers of neutrons and different masses

Question 2

why do isotopes all react in same ways

Answer 2

• diff isotopes of same element have same number of electrons but diff number of neutrons
• the number of neutrons in an element has no effect on reactions of an element

Question 3

relative isotopic mass definition

Answer 3

mass of an isotope relative to 1/12th of the mass of an atom of carbon 12

Question 4

relative atomic mass definition

Answer 4

• also known as Ar
• weighted mean mass of an atom of an elememt relative to 1/12th of the mass of an atom of carbon 12

Question 5

how does a mass spectrometer work

Answer 5

• sample is placed in mass spectrometer
• sample is vapourised then ionised to form positive ions
• the ions are accelerated. heavier ions move more slowly and are more difficult to deflect than lighter ions so the ions of each isotope are separated.
• the ions are detected on a mass spectrum as a mas to charge ratio (m/z).
• each ion reaching the detector adds a signal so the greater the abundance, the larger the signal

Question 6

binary compound

Answer 6

contains two elements only

Question 7

ammonium ion charge

Answer 7

NH4 1+

Question 8

hydroxide ion

Answer 8

OH-

Question 9

nitrate ion

Answer 9

NO3 1-

Question 10

carbonate ion

Answer 10

CO3 2-

Question 11

sulfate ion

Answer 11

SO4 2-

Question 12

manganate ion

Answer 12

MnO4 1-

Question 13

dichromate ion

Answer 13

Cr2O7 2-

Question 14

what is avogadros constant

Answer 14

6.02 x 10 ^23
its the number of particles in each mole of carbon 12

Question 15

equation linking mass, mole and Mr

Answer 15

moles = mass / molar mass (Mr)

Question 16

molecular formula

Answer 16

number of atoms of each element in a molecule

Question 17

empirical formula

Answer 17

simplest whole number ratio of atoms of each element in a compound

Question 18

relative molecular mass

Answer 18

compares mass of molecule with mass of an atom of carbon 12

Question 19

relative formula mass

Answer 19

compares mass of a formula unit with mass of an atom of carbon 12

Question 20

what are some assumptions/reasons why real experiments might not give u the same water of crystalisation number/ratio

Answer 20

1. we assume all the water has been lost. good solution is to heat till constant mass when the crystals are reheated till the mass of the residue no longer changes suggesting all water has been removed
2. many salts can decompose further when heated such as wen u heat copper sulfate, it can decompose to form black copper oxide, this can be difficult to judge if theres no colour change

Question 21

equation linking concentration moles and volume

Answer 21

conc = mols / volume

Question 22

what is the molar gas volume

Answer 22

volume per mole of gas molecules at a stated temperature and pressure

Question 23

what is the molar gas volume at room temperature and pressure

Answer 23

24dm3/mol
v in dm3 -> V/24
v in cm3 -> V/24000

Question 24

ideal gas equation

Answer 24

pV = nRT
p is pressure in Pa
V is volume in metres cubed
n is amount of gas molecules
R is ideal gas constant = 8.31
T is temperature in kelvin (degrees c + 273)

Question 25

what are the assumptions made for the molecules making up an ideal gas constant

Answer 25

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

Question 26

reasons why theoretical yield from percentage yield is not made

Answer 26

• reaction may not have gone to completion
• other side reactions may have taken place alongside main reaction
• purification of the product may have resulted in loss of some product

Question 27

what is a strong acid

Answer 27

an acid that releases all its hydrogen atoms into solution as H+ ions and completely dissociates in aqueous solution

Question 28

what is a weak acid

Answer 28

it only releases a proportion of its available hydrogen atoms into solution as H+ ions. it partially dissociates in aqueous solution

Question 29

what is an alkalai

Answer 29

a base that dissolves in water releasing hydroxide ions into the solution.

Question 30

acid + alkalai

Answer 30

salt + water
- same as metal oxides.
- H+ + OH- -> H20

Question 31

acid + carbonate

Answer 31

salt + water + carbon dioxide

Question 32

three things that titrations can be used for

Answer 32

• finding concentration of a solution
• identifying unknown chemicals
• finding purity of a substance

Question 33

what is a standard solution

Answer 33

• a solution of known concentration

Question 34

how to prepare a standard solution

Answer 34

1. weigh solid accurately
2. dissolve solid in a beaker using less distilled water than will be needed to fill volumetric flask
3. transfer this solution to volumetric flask and rinse the last traces of the solution with distilled water
4. carefully fill flask to graduation line by adding distilled water drop by drop till bottom of meniscus lines up exactly with mark
5. place lid and slowly invert the volumetric flask several times to mix solution thoroughly

Question 35

what would happen if too much water is added to the volumetric flask

Answer 35

the solution will be too dilute and must be prepared again

Question 36

what would happen if u do not invert the volumetric flask before performing your titration

Answer 36

the titration results are unlikely to be consistent as solution is not mixed thoroughly enough

Question 37

oxidation number of oxygen

Answer 37

• normally -2
• in peroxides it is -1
• when bonded to F it is +2

Question 38

oxidation number of hydrogen

Answer 38

• normally +1
• in metal hydrides it is -1

Question 39

oxidation number of fluorine

Answer 39

always -1