chem prelim

Question 1

heterogeneous mixture

Answer 1

the constituents are not uniformly mixed throughout the mixture, eg water and oil

Question 1

homogenous mixture

Answer 1

constituents are uniformly mixed meaning mixed the same throughout the mixture eg solution

Question 2

aqueous form

Answer 2

when dissolved in water

Question 3

pure substance

Answer 3

only homogenous cannot be separated into two or more substances by physical means, fixed composition and same properties

Question 4

mixture

Answer 4

can be separated into two or more pure substances, may be homogenous or heterogenous, variable properties reflect parts that make it up

Question 5

separate substances of different particle sizes

Answer 5

sieving

Question 6

separating mixture of solids and liquids

Answer 6

filtration, if particles of solid are very coarse or dense use sedimnetation(solids settle at bottom of container) or decantation( carefully pouring off the liquid and leaving the solid undisturbed at the bottom of container)

Question 7

separating dissolved solids from liquid if only want solid

Answer 7

evaporation, if only want solid

Question 8

separating dissolved solid from liquid if want both liquid and solid

Answer 8

crystallisation(slower evaporation)

Question 9

separate two or more liquids from one another

Answer 9

distillation(process of evaporating then condensing gas back into liquid in separate apparatus so liquids are separated) only if boiling points differs by at least 40 or 50 celsius

Question 10

if the liquids are close in boiling point use

Answer 10

fractional distillation

Question 11

immiscible liquids

Answer 11

do not mix due to density and must be separated using a separating funnel

Question 12

steps of gravimetric analysis

Answer 12

dissolve same mole if not already in solution, adjust ph so that proper precipitate forms and to prevent formation of others, add chemical that favours precipitating material you want, filter solution, dry precipitate, weigh the precipitate

Question 13

percentage composition

Answer 13

mass of one substancex100 on mass of total sample

Question 14

pure substance has

Answer 14

characteristic colour

Question 15

isotopes are

Answer 15

atoms that can vary in their number of neutrons thus leading to different mass numbers

Question 16

calculate weighted average of isotopes

Answer 16

percentage of each isotope times it’s weight and add them together

Question 17

electron configuration of bromine

Answer 17

1s2,2s2,2p6,3s2,3p6,4s2,3d10,4p5

Question 18

ionisation energy trends

Answer 18

increases left to right and increases going down

Question 19

electronegativity trends

Answer 19

increases as you go right, decreases as you go down

Question 20

melting point trends

Answer 20

increase as you go right until group 4 then decreases

Question 22

electronegativity trends

Answer 22

increases going right and decreases going down

Question 23

melting point and boiling point trends

Answer 23

increases going right until group 4 then decreases, same group have similar melting points

Question 24

group 4 trends

Answer 24

group 4 is covalent networks with high melting points compared to low melting points of covalent molecular

Question 25

covalent molecular compound trends

Answer 25

low boiling and melting points, tend to be soft and flexible, tend to be more flammable than ionic, when dissolved in water do not conduct electricity, mostly don’t dissolve well in water, many soluble in non polar liquids but not water, more flammable than ionic

Question 26

ionic compounds trends

Answer 26

form crystals, high melting and boiling points, hard and brittle, conduct electricity when dissolved in water or melted, good insulators, soluble in water but not in non polar liquid, less flammable

Question 27

are most crystals ionic or covalent

Answer 27

ionic

Question 28

what are allotropes

Answer 28

different physical forms of same element such as diamond and graphite for carbon

Question 29

what are the intermolecular forces

Answer 29

dispersion,dipole dipole, hydrogen bonding