chem mod 2⚛️

Question 1

what is a salt

Answer 1

H+ ion in an acid is replaced by a metal ion

Question 2

why does first ionisation energy decrease down group

Answer 2

• bigger atomic radius
• more shielding
• nuclear attraction decreases

Question 3

what is first ionisation energy

Answer 3

-energy required to remove one electron from each atom in one mole of gaseous atoms

Question 4

why is second ionisation energy greater than first

Answer 4

• ion is smaller
• less electron repulsion
• same number of protons attracting less electrons

Question 5

explain trend of ionisation energy across period

Answer 5

• generally increases
• number of protons increases
• atomic radius decreases
• so greater nuclear attraction
• from group 2 to 3 there is a decrease
• as group 3 elements have outer electron in p shell which has a higher energy level
• from group 5 to 6 there is a decrease
• in group 5 the outer electrons are on their own in the orbital (eg nitrogen 2p3)
• in group 6 one pair of the outer electrons have to share an orbital so there is greater repulsion (eg oxygen 2p4)

Question 6

shape and angle for 4 bonding pairs around central atom

Answer 6

tetrahedral

109.5

Question 7

what is a mole

Answer 7

• amount of substance that has the same number of particles as there are atoms in 12 g of carbon 12
• avogadros number
• 6.02x 10^23

Question 8

when reacting calcium with hcl, why does more calcium react than expected

Answer 8

ca + h2o -> ca(oh)2 + h2

-calcium reacts with water

Question 9

shape and angle for two bonding pairs around central atom

Answer 9

• linear

- 180

Question 10

shape and angle for 3 bonding pairs around central atom

Answer 10

• trigonal planar

- 120

Question 11

angle and shape for 3 bonding pairs 1 lone pair around central atom and why

Answer 11

• pyramidal
• 107
• lone pairs repel more than bonded pairs

Question 12

shape and angle 2 bonding pairs 2 lone pairs (water)

Answer 12

• bent

- 104.5

Question 13

5 bonding pairs shape

Answer 13

trigonal bipyramid

Question 14

6 bonding pairs shape

Answer 14

octahedral

Question 15

sulfide compounds contain what

formula for ammonium sulfide

Answer 15

contain S

(NH4)2S

Question 16

are silver compounds solid or aq

Answer 16

most are solid except like nitrates etc

Question 17

what is uncertainty

Answer 17

half of smallest division

Question 18

how to calculate percentage error

Answer 18

uncertainty/reading x100

if 2 readings eg titrations then double

Question 19

how to reduce percentage error

Answer 19

• more precise equipment (more dp)

- use larger amounts eg volume or mass

Question 20

how to ensure all water of crystillation is removed

Answer 20

heat to constant mass

Question 21

ionic equation for displacement of bromine by chlorine

Answer 21

Cl2 + 2Br- —> 2Cl- +Br2

Question 22

problem with combustion of chlorohydrocarbon

Answer 22

formation of HCl

Question 23

IE trend down group

Answer 23

• decreases
• larger atomic radius
• more shielding
• weaker nuclear attraction
• easier to remove electron

Question 24

why does IE decrease from mg to al

Answer 24

Mg electron removed from 3(s)
Al electron removed from 3(p)
Al electron has higher energy level

Question 25

what is a weak acid

Answer 25

partially dissociates

Question 26

test for sulfates

Answer 26

BaCl2

forms white precipitate

Question 27

0 degrees celsius in kelvin

Answer 27

273K

Question 28

what shape would a molecule with 3 bonding pairs have and why

Answer 28

trigonal planar

because electron pairs repel

Question 29

why are carbon and oxygen p block elements

Answer 29

highest energy electron is in p orbital

Question 30

explain in terms of electrons whether magnesium is oxidised or reduced

Answer 30

oxidised because loses 2 electrons

Question 31

how to get solid from solution after reaction

Answer 31

filter to obtain solid

dry solid

Question 32

relative isotopic mass

Answer 32

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

Question 33

relative atomic mass

Answer 33

weighted mean mass of an atom of an element relative to 1/12th of the mass of carbon 12

Question 34

dm3 to m3

Answer 34

divide by 1000

Question 35

why is yield not 100%

Answer 35

• purification may result in some loss

- reaction ma not have gone to completion

Question 36

what is a strong acid

Answer 36

completely dissociates in water

Question 37

what is an alkali

Answer 37

releases OH- ions into solution

Question 38

what id an isotope

Answer 38

atom of an element with different neutrone number

Question 39

ehat is electronegativity

Answer 39

ability of an atom to attract electrons in a covalent bond