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chemistry > Exam Questions Got Wrong > Flashcards

Exam Questions Got Wrong Flashcards

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1
Q

Why did mendeleev reverse the order of elements

A

Arrange in. Groups with similar properties

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2
Q

In the modern periodic table, the elements are arranged in order of

A

Atomic number

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3
Q

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

A
  • mendeleev left spaces for later discovered elements- predicted properties of
  • elements were discovered- properties matched missing gap
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4
Q

Sodium and chlorine- what would you see

A
  • flame
  • (white) solid form
  • colour of gas disappear
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5
Q

Limitation of using a dot and cross diagram to represent ammonia molecule

A
  • does not show the shape of the molecule

- is 2 dimensional

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6
Q

Control variables w/ chemical cell experiments o

A
  • same ions used in electrolyte
  • same volume of electrolyte is used
  • same temp of solution
  • same conc of solutions
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7
Q

Why are hydrogen fuel cells considered ‘new steam trains’

A
  • in fuel cell, hydrogen reacts w/ oxygen produce water

- water produced vapour/steam

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8
Q

Why must excess hydrogen be burnt off

A
  • must not be released into atmosphere

- as is explosive

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9
Q

What must a molecule have to have intermolecular forces between particles

A
  • made of molecules
  • covalentlu bonded
  • not giant covalent, ionic, metallic structures
  • eg. Poly(ethene), water
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10
Q

How to compare reactions of metals with an acid

A

-rate of bubbles forming
Or
-exothermic temp change

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11
Q

Metal and acid type of energy change

A

Exothermic

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12
Q

Why want reactions with high atom economy

A
  • economic reasons

- less waste is made

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13
Q

Changes bohr made to nuclear model

A
  • electrons orbiting

- fixed/specific distance from nucleus

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14
Q

Diff nuclar model of atom and plum pudding model

A
  • no empty space in plum pudding model
  • no electron shells
  • positive charge all in nucleus
  • mass conc iin nucleus
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15
Q

Activation energy

A

-(minimum) energy needed for particles to react/energy needed for a reaction to occur

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16
Q

Advantages of hydrogen fuel cells over rechargable cells to poer cards

A
  • no toxic chemicals dispose of at end of cell’s life
  • less time to refuel (than to recharge)
  • travel further before refuelling (than before recharging rechargable cells)
  • no loss of efficiency (over time)
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17
Q

Trend of boiling points in halogens (4 marks)

A
  • bp increase as go down groups
  • relative formula mass increase
  • intermolecular forecs increase
  • more energy needed to overcome these intermolecular forces
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18
Q

Why is it not correct to say that the boiling point of a single bromine molecule is 59C?

A

Boiling point is a bulk property

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19
Q

Why should reactiions with halogen gasses be done in a fume cupboard

A

-halogen gases are toxic if inhaled

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20
Q

Why is there a difference between metal and polystyreme cup experiment

A
  • energy from surroundings conducted through metal container

- metal better conductor than polystyrene

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21
Q

Why is there an anomalous point above line (reaction citric acid and sodium hydrocarbonate solution)

A

-dont stir the solution enough-endothermic reaction

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22
Q

Why is a burette used for acid

A
  • add in small increments- good for measuring variable volumes
  • more accurate than measuring cylinder
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23
Q

Titration experiment (3 marks)u

A
  • swirl
  • white tile
  • repeat and calulate mean
  • add citriic acid drop by drop
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24
Q

What colour is the final solution

A

The colour of the molecule that is seperated to the rest of the solution

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25
Q

What are the products of electrolysing potassium iodine solution

A

Cathode- hydrogen

Anode-iodine

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26
Q

Why is the ball and stick model not a true representation of the structure of an ionic compound

A

there are no gaps/sticks between the potassium ions and sulfide ions

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27
Q

Suggest the safety precaution the students should take- heat the contents of the evaporating dish with a bunsen burner until salt crystals start to form

A

wear safety spectacles

• wear an apron

28
Q

How to make soluble salt

A
  • add excess copper carbonate (to dilute hydrochloric acid)
  • filter (to remove excess copper carbonate)
  • heat filtrate to evaporate some water or heat to -point of crystallisation
  • leave to cool (so crystals form)
29
Q

Why is an atom economy of one reaction lower

A

-an aditional product is made

30
Q

Which of the metals used was the least reactive

A

copper is the least reactive
because it gave the most negative voltage when it was metal 2
or
it gave the biggest voltage with chromium
or
it gave the most positive voltage when it was metal

31
Q

Reactions that take place at electrodes in hydrogen fuel cell

A

H2 → 2H+ + 2e−

O2+4H++4e− →2H2O

32
Q

Why would less carbon dioxide be produced (when sodium carbonate react with hydrochloric acid)

A

bung not put in
firmly/properly
• gas lost before bung put in
• leak from tube

33
Q

How to give a more accurate result-apparatus

A

use a pipette/burette to measure the acid
because it is more accurate volume than a measuring cylinder or
greater precision than a measuring cylinder
or
use a gas syringe to collect the gas
so it will not dissolve in water
or
use a flask with a divider
so no gas escapes when bung removed

34
Q

Why does the results not made difference as the first few bubbles of gas collected were air

A

they should be collected because carbon dioxide is left in flask at end
and it has the same volume as the air collected/displaced

35
Q

What is meant by a strong acid

A

sulfuric acid is) completely/fully ionised

In aqueous solution or when dissolved in water

36
Q

Explain how a covalent bond holds two atoms together

A

electrostatic force of attraction between shared pair of negatively charged electrons
and both positively charged nuclei

37
Q

Explain how the overall energy change for the reaction of ethene with chlorine will differ than with bromine

A

Size and strength
• chlorine atoms have fewer electron energy levels/shells • chlorine atoms form stronger bonds
• Cl−Cl bond stronger then Br−Br
• C−Cl bond stronger that C−Br
Energies required
• more energy required to break bonds with chlorine
• more energy given out when making bonds with chlorine
• overall energy change depends on sizes of energy changes
Conclusions
• if C−Cl bond changes less, then less exothermic
• if C−Cl bond changes more then more exothermic
• can’t tell how overall energy change will differ as do not
know which changes more.

38
Q

What shape is a buckminsterfullerene

A

Sphericaal

39
Q

buckminsterfullerene formula

A

C60

40
Q

Structure of graphite

A
  • giant covalent structure
  • hexagonal rings
  • weak intermolecular forces between layers
41
Q

Why the discovery of gallium helped mendeleev’s periodicttable to become accepted

A

gallium) fitted in a gap (Mendeleev had left)

gallium’s) properties were predicted correctly (by Mendeleev

42
Q

Observations make when a small piece of potassium is added to water

A
  • (potassium) floats
  • (potassium) melts
  • (potassium) moves around • potassium becomes smaller • (lilac) flame
  • effervescence
43
Q

Explain why the reactivity of elements changes going down group 1

A

reactivity increases (going down the group)

(because) the outer electron / shell is further from the nucleus
(so) there is less attraction between the nucleus and the outer electron / shell
(so) the atom loses an electron more easily

44
Q

Expplain why sodium oxide has a high melting point

A

giant structure

(with) strong (electrostatic) forces of attraction between (oppositely charged) ions
(so) large amounts of energy are needed to break the bonds / forces

45
Q

Why is a product added in excess

A

To ensure all of the other reactant reacts

46
Q

How should the filtrate be evaporated gently

A

using a (boiling) water bath
or
using an electric heater

47
Q

Explain why alloys are harder than pure metals

A

in an alloy) the atoms are of different sizes
(so) the layers (of atoms in an alloy) are distorted
(so in an alloy) the layers slide over each other less easily (than in a pure metal)

48
Q

Describe a method that student 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
same concentration / volume of solution
or
same mass / moles of metal
the greater the temperature change the more reactive

49
Q

Explain the difference between the processes in electrolysis and in a chemical cell

A

electrolysis uses electricity to produce a chemical reaction

(but) cells use a chemical reaction to produce electricity

50
Q

Some of the copper produced did not stick to the negative electrode but fell to the bottom of the beaker. Suggest how the students could find the total mass of copper produced

A

filter the mixture
wash and dry the copper / residue
weigh the copper collected
add to the increase in mass of the electrode

51
Q

Suggest why the blue colour of the copper nitrate solution fades during the electrolysis

A

copper ions are discharged (from the solution

52
Q

Improvements to the titration method that woul increase the accuracy of the result

A 
swirl (the solution)
• white tile (under the flask)
• add (ethanedioic) acid
dropwise (near the endpoint)
• repeat and calculate mean
53
Q

Substance that can react with an acid to form a soluble salt

A 
metal
• (metal) hydroxide 
• (metal) carbonate  
• alkali
-metal oxides
54
Q

What to do with acid when making soluble salt

A
  • measure
  • add to beaker
  • warm
55
Q

Diff between irona and sodium

A 
iron has a high(er) melting /
boiling point
• iron is dense(r)
• iron is hard(er)
• iron is strong(er)
• iron is less reactive
• iron has ions with different charges
• iron forms coloured compounds
• iron can be a catalyst
56
Q

Why can alkaline batteries not be recharged

A

the reaction is not reversible

57
Q

Define the mass number of an atom

A

sum of protons and neutrons

58
Q

Describe a method to find the position of an unknown metal in this reactivity series

A

add the unknown metal to copper sulfate solution (1) measure temperature change (1)
place the metals in order of temperature change (1)
any one from (1):
• same volume of solution
• same concentration of solution • same mass / moles of metal
• same state of division of metal

59
Q

Why would electrolysis not take place when the electrolyte is solid

A

solid (zinc chloride) does not conduct (electricity)
or
zinc chloride needs to be in solution or molten
(because) ions cannot move in the solid
or
(as) ions can (only) move in liquid / solution

60
Q

Why should change test tubes to collect the gas from electrolyte

A

use measuring cylinders (instead of test tubes)
(because) test tubes cannot measure volume
or
(because) test tubes have no graduations / scale

61
Q

How to describe trends shown in the results

A
  • directly proportional?
  • calc rate
  • pick out points on graph when changed and rate
62
Q

Suggest a reason for the difference in volume of each gas (even though same mol amount)

A

One gas reacts with water/dissolves in the solution

63
Q

Explain why chlorine is more reacive than iodine

A

chlorine’s) outer electrons / shell closer to the nucleus
(so) the chlorine nucleus has greater attraction for
outer electrons / shell
(so) chlorine gains an electron more easily

64
Q

Give a reason why it would be hazardous if water came into contact with sodium

A

very exothermic reaction

produces a corrosive solution

Produces hydrogen, whcih is explosive/flammable

65
Q

Why would you not expect titanium chloride to be a liquid at room temp

A

metal chlorides are usually ionic
(so)(metal chlorides) are solid at room temperature
or
(so)(metal chlorides) have high melting points
(because) they have strong (electrostatic) forces between the ions
or
(but) must be a small molecule or covalent

chemistry (14 decks)

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