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chem spec > exam questions i got wrong > Flashcards

exam questions i got wrong Flashcards

1
Q

alcohols are flammable. explain how the mixture of alcohols should be safely heated so that ethanol can be collected.

A

heat the mixture using a water bath/electric heater

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2
Q

a student is given a mixture of salt and sand. describe a method the student could use to separate the mixture. the student should obtain salt crystals and dry sand. name all of the apparatus you will use.

A
  • place mixture in a beaker
  • add water to the mixture
  • stir using a stirring rod
  • filter the mixture using a filter funnel and filter paper
  • residue is sand; dry this in a warm oven
  • pour the salt water into an evaporating basin
  • evaporate some of the water from the filtrate using a water bath
  • allow solution to cool
  • crystals form
  • remove and dry crystals
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3
Q

describe what you would see when sodium is added to water

A
  • effervescence
  • dissolves
  • melts
  • floats
  • moves on the surface
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4
Q

mendeleev changed the position of iodine in his version of the periodic table so it was in the same group as chlorine. give two reasons why he put iodine in the same group as chlorine.

A
  • similar properties to other elements in group 7
  • similar reactivity to other elements in group 7
  • iodine reacts with metals
  • iodine is diatomic
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5
Q

describe how the number of protons and electrons in atoms are used to place elements in the modern periodic table

A
  • elements placed in order of atomic number
  • elements in same group have same number of outer electrons
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6
Q

compare the position of the subatomic particles in the plum pudding model with the nuclear model

A
  • PPM has single ball of positive charge and NM has positive charges in nucleus
  • PPM has electrons in random positions and NM has electrons in fixed positions
  • PPM has no nucleus and NM has nucleus
  • PPM has no neutrons and NM has neutrons in nucleus
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7
Q

explain why titanium conducts electricity

A
  • electrons in the outer shell of the metal atoms are delocalised
  • and so electrons are free to move
  • through the whole structure
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8
Q

give two limitations of the particle model for the three states of matter

A
  • no forces shown between spheres
  • atoms are not solid spheres
  • atoms are not all the same size
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9
Q

in 1931 a scientist discovered that there are hydrogen atoms with mass number 2 as well as hydrogen atoms with mass number 1. a year later, another scientist discovered neutrons. explain why the discovery of neutrons could explain the presence of hydrogen atoms with different mass numbers.

A
  • all hydrogen atoms have just one proton
  • some hydrogen atoms also have one neutron
  • protons and neutrons have the same relative mass so mass number of these atoms is 2
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10
Q

why are group 1 metals called alkali metals

A
  • they form hydroxides
  • that give alkaline solutions in water
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11
Q

state two differences between hydrogen and the elements in group 1

A
  • hydrogen is a non-metal
  • hydrogen is a gas at RTP
  • hydrogen doesnt react with water
  • hydrogen forms covalent bonds
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12
Q

compare the structure and bonding of the three compounds
- carbon dioxide
- magnesium oxide
- silicon dioxide

A
  • both carbon dioxide and silicon dioxide are made up of atoms
  • but magnesium oxide is made up of ions
  • both silicon dioxide and magnesium oxide are giant structures
  • but carbon dioxide is a small molecule
  • with weak intermolecular forces
  • all three compounds have strong bonds
  • both carbon dioxide and silicon dioxide are formed from two non-metals
  • so bonds formed are covalent
  • so electrons are shared between atoms
  • but magnesium oxide is formed from a metal and a non-metal
  • so bonds in magnesium oxide are ionic
  • so electrons are transferred
  • from magnesium to oxygen
  • two electrons are transferred
  • bonds in silicon dioxide are single bonds
  • where each silicon forms four bonds
  • and each oxygen forms two bonds
  • but in carbon dioxide the bonds are double bonds
  • where carbon forms two double bonds
  • and oxygen forms one double bond
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13
Q

explain why nitrogen is a gas at room temperature

A
  • weak forces
  • between molecules
    or
  • intermolecular
  • which need little energy to overcome
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14
Q

suggest why buckminsterfullerenes are good lubricants

A
  • molecules are spherical
  • so molecules will roll
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15
Q

suggest why it is cheaper to use nanoparticles of silver rather than coarse particles of silver

A
  • nanoparticles have a larger SA:V ratio
  • so less can be used for the same effect
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16
Q

give one reason why the ball and stick model is not a true representation of the structure of potassium sulfide

A

there are no gaps between the potassium ions and sulfide ions

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17
Q

explain why sodium oxide has a high melting point

A
  • giant ionic lattice
  • with strong electrostatic forces of attraction between oppositely charged ions
  • so large amounts of energy needed to break the bonds
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18
Q

a student wants to compare reactivity of unknown metal Q with that of zinc.
both metals are more reactive than silver.

the student is provided with:
silver nitrate solution, metal Q powder, zinc powder, a thermometer, normal lab equiment

describe a method they could use to compare the reactivity of metal Q with that of zinc

A
  • measure temperature change
  • when each metal is added to silver nitrate solution
  • use same concentration/volume of solution
    OR
  • use same mass/moles of metal
  • the greater the temperature change the more reactive
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19
Q

explain the trend in boiling points of the halogens

A
  • boiling point increases down the group
  • because relative formula mass increases
    OR
  • because size of molecule increases
  • so intermolecular forces increase in strength
  • so more energy needed to overcome the intermolecular forces
20
Q

why is it not correct to say that the boiling point of a single bromine molecule is 59C when thats the boiling point of bromine

A
  • boiling point is a bulk property
    OR
  • boiling point is related to intermolecular forces so more than one molecule is involved
21
Q

explain why the reactivity of the halogens decreases going down the group

A
  • outer electrons become further from the nucleus
  • so the nucleus has less attraction for the outer electrons
  • so an electron is gained less easily
22
Q

give one use of brass

A
  • ornaments
  • musical instruments
  • hinges / knobs / screws
23
Q

give two reasons why alloys of gold are used instead of pure gold to make jewellery

A
  • alloy of gold is harder
  • alloy of gold is cheaper
  • aesthetic reasons
24
Q

explain why reaction between ammonia and oxygen is exothermic if it has an overall energy change of -1272 kJ

A
  • energy released in making bonds is greater than energy used in breaking bonds
    OR
  • products have 1272 kJ less energy than reactions
  • so energy is released to surroundings
25
Q

explain why zinc ions move towards negative electrode

A
  • zinc ions are positive
  • and opposite charges attract
26
Q

alloys can be bent. some alloys return to their original shape when heated. what name is used for these alloys?

A

shape memory alloys

27
Q

explain why an acid can be described as both strong and dilute

A
  • strong because completely ionises (in aqueous solution)
  • dilute because small amount of acid per unit volume
28
Q

explain why the student should use a pipette to measure the dilute sulfuric acid and a burette to measure the sodium hydroxide solution

A
  • pipette measures a fixed volume (accurately)
  • burette measures a variable volume
29
Q

what type of substance is an alloy

A

a mixture
ALLOYS ARENT CHEMICALLY COMBINED

30
Q

add one spatula of metal powder to the hydrochloric acid and stir
- suggest one way to make this step more repeatable

A

use the same mass of metal powder

31
Q

a student is given three metals, X, Y and Z to identify. the metals are magnesium, iron and copper. plan an investigation to identify the three metals by comparing their reactions with dilute hydrochloric acid.
your plan should give valid results.

A
  • add the metals to dilute hydrochloric acid
  • measure temperature change

for copper:
- no reaction
- shown by no temperature change

for magnesium and iron:
- magnesium increases in temperature more than iron

control variables:
- same concentration / volume of HCl
- same mass / moles of metal
- same particle size of metal
- same temperature of acid

32
Q

iron is a transition metal.
sodium is a group 1 metal.
give two differences between the properties of iron and sodium

A
  • iron has a higher melting / boiling point
  • iron is denser
  • iron is harder
  • iron is stronger
  • iron is less reactive
  • iron has ions with different charges
  • iron forms coloured compounds
  • iron can be a catalyst
33
Q

why is this reaction carried out in an atmosphere of argon and not in air
TiCl4 + 4Na -> Ti + 4NaCl

A
  • argon is unreactive / inert
  • oxygen from air would react with sodium / titanium
    OR
  • water vapour from air would react with sodium / titanium
34
Q

copper nitrate solution is blue. suggest why the blue colour of the copper nitrate solution fades during the electrolysis.

A

copper ions are discharged from the solution

35
Q

what observation would be made at each electrode if a metal was produced at the negative electrode and a gas was produced at the positive electrode

A

metal produced at negative electrode:
- solid produced

gas produced at positive electrode:
- bubbles / fizzing / effervescence

36
Q

what factors affect the voltage produced by a hydrogen fuel cell

A
  • type of electrode
  • type of electrolyte
  • temperature of electrolyte
  • concentration of electrolyte
37
Q

advantages of hydrogen fuel cells

A
  • no toxic chemicals to dispose of at end of cell’s life
  • takes less time to refuel than rechargeable batteries
  • no loss of efficiency over time
  • can travel further before refuelling than rechargeable batteries
  • hydrogen can be renewable if made using electrolysis
  • produces a constant voltage
38
Q

the hydrogen gas needed to power a car would occupy a large volume. suggest one way this volume can be reduced

A
  • under higher pressure
  • cool
  • adsorb in a solid
39
Q

describe how to make a 12v battery using 1.5v cells

A
  • connect cells in series
  • you need 8 cells
40
Q

disadvantages of hydrogen fuel cells

A
  • hydrogen is made from fossil fuels
  • hydrogen is difficult to store
  • hydrogen is flammable / explosive
  • costs more to refuel than rechargeable batteries
  • costs more to manufacture than rechargeable batteries
41
Q

a newspaper article referred to trains running on hydrogen fuel cells as the new ‘steam trains’. explain why

A
  • hydrogen is oxidised to produce water
  • water is released as vapour / steam
42
Q

why is the cell described as an alkaline fuel cell

A

contains OH- ions

43
Q

chadwick’s experimental work on the atom led to a better understanding of isotopes. explain how.

A
  • he provided the evidence to show the existence of neutrons
  • this was necessary because isotopes have the same number of protons
  • but a different number of neutrons
44
Q

explain why you would not expect titanium chloride to be a liquid at room temperature

A
  • metal chlorides are usually ionic
  • which are solid at room temperature
  • because they have strong electrostatic forces between the ions
45
Q

why did mendeleev’s periodic table become more widely accepted than previous versions

A
  • mendeleev had predicted properties of missing elements
  • elements were discovered that filled the spaces
  • properties of these elements matched mendeleev’s predictions
46
Q

describe what you would see when sodium reacts with chlorine

A
  • flame
  • white solid forms
  • colour of gas / chlorine disappears / fades
47
Q

sodium metal and chlorine gas are produced by the electrolysis of molten sodium chloride. explain why sodium chloride solution cannot be used as the electrolyte to produce sodium metal

A
  • hydrogen gas would be produced instead of sodium
  • because sodium is more reactive than hydrogen

chem spec (12 decks)

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