Exam Questions Got Wrong Flashcards
Why did mendeleev reverse the order of elements
Arrange in. Groups with similar properties
In the modern periodic table, the elements are arranged in order of
Atomic number
Why did mendeleev’s periodic table become more widely accepted than previous versions?
- mendeleev left spaces for later discovered elements- predicted properties of
- elements were discovered- properties matched missing gap
Sodium and chlorine- what would you see
- flame
- (white) solid form
- colour of gas disappear
Limitation of using a dot and cross diagram to represent ammonia molecule
- does not show the shape of the molecule
- is 2 dimensional
Control variables w/ chemical cell experiments o
- same ions used in electrolyte
- same volume of electrolyte is used
- same temp of solution
- same conc of solutions
Why are hydrogen fuel cells considered ‘new steam trains’
- in fuel cell, hydrogen reacts w/ oxygen produce water
- water produced vapour/steam
Why must excess hydrogen be burnt off
- must not be released into atmosphere
- as is explosive
What must a molecule have to have intermolecular forces between particles
- made of molecules
- covalentlu bonded
- not giant covalent, ionic, metallic structures
- eg. Poly(ethene), water
How to compare reactions of metals with an acid
-rate of bubbles forming
Or
-exothermic temp change
Metal and acid type of energy change
Exothermic
Why want reactions with high atom economy
- economic reasons
- less waste is made
Changes bohr made to nuclear model
- electrons orbiting
- fixed/specific distance from nucleus
Diff nuclar model of atom and plum pudding model
- no empty space in plum pudding model
- no electron shells
- positive charge all in nucleus
- mass conc iin nucleus
Activation energy
-(minimum) energy needed for particles to react/energy needed for a reaction to occur
Advantages of hydrogen fuel cells over rechargable cells to poer cards
- 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)
Trend of boiling points in halogens (4 marks)
- bp increase as go down groups
- relative formula mass increase
- intermolecular forecs increase
- more energy needed to overcome these intermolecular forces
Why is it not correct to say that the boiling point of a single bromine molecule is 59C?
Boiling point is a bulk property
Why should reactiions with halogen gasses be done in a fume cupboard
-halogen gases are toxic if inhaled
Why is there a difference between metal and polystyreme cup experiment
- energy from surroundings conducted through metal container
- metal better conductor than polystyrene
Why is there an anomalous point above line (reaction citric acid and sodium hydrocarbonate solution)
-dont stir the solution enough-endothermic reaction
Why is a burette used for acid
- add in small increments- good for measuring variable volumes
- more accurate than measuring cylinder
Titration experiment (3 marks)u
- swirl
- white tile
- repeat and calulate mean
- add citriic acid drop by drop
What colour is the final solution
The colour of the molecule that is seperated to the rest of the solution
What are the products of electrolysing potassium iodine solution
Cathode- hydrogen
Anode-iodine
Why is the ball and stick model not a true representation of the structure of an ionic compound
there are no gaps/sticks between the potassium ions and sulfide ions
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
wear safety spectacles
• wear an apron
How to make soluble salt
- 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)
Why is an atom economy of one reaction lower
-an aditional product is made
Which of the metals used was the least reactive
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
Reactions that take place at electrodes in hydrogen fuel cell
H2 → 2H+ + 2e−
O2+4H++4e− →2H2O
Why would less carbon dioxide be produced (when sodium carbonate react with hydrochloric acid)
bung not put in
firmly/properly
• gas lost before bung put in
• leak from tube
How to give a more accurate result-apparatus
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
Why does the results not made difference as the first few bubbles of gas collected were air
they should be collected because carbon dioxide is left in flask at end
and it has the same volume as the air collected/displaced
What is meant by a strong acid
sulfuric acid is) completely/fully ionised
In aqueous solution or when dissolved in water
Explain how a covalent bond holds two atoms together
electrostatic force of attraction between shared pair of negatively charged electrons
and both positively charged nuclei
Explain how the overall energy change for the reaction of ethene with chlorine will differ than with bromine
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.
What shape is a buckminsterfullerene
Sphericaal
buckminsterfullerene formula
C60
Structure of graphite
- giant covalent structure
- hexagonal rings
- weak intermolecular forces between layers
Why the discovery of gallium helped mendeleev’s periodicttable to become accepted
gallium) fitted in a gap (Mendeleev had left)
gallium’s) properties were predicted correctly (by Mendeleev
Observations make when a small piece of potassium is added to water
- (potassium) floats
- (potassium) melts
- (potassium) moves around • potassium becomes smaller • (lilac) flame
- effervescence
Explain why the reactivity of elements changes going down group 1
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
Expplain why sodium oxide has a high melting point
giant structure
(with) strong (electrostatic) forces of attraction between (oppositely charged) ions
(so) large amounts of energy are needed to break the bonds / forces
Why is a product added in excess
To ensure all of the other reactant reacts
How should the filtrate be evaporated gently
using a (boiling) water bath
or
using an electric heater
Explain why alloys are harder than pure metals
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)
Describe a method that student could use to compare the reactivity of metal Q with that of zinc
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
Explain the difference between the processes in electrolysis and in a chemical cell
electrolysis uses electricity to produce a chemical reaction
(but) cells use a chemical reaction to produce electricity
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
filter the mixture
wash and dry the copper / residue
weigh the copper collected
add to the increase in mass of the electrode
Suggest why the blue colour of the copper nitrate solution fades during the electrolysis
copper ions are discharged (from the solution
Improvements to the titration method that woul increase the accuracy of the result
swirl (the solution) • white tile (under the flask) • add (ethanedioic) acid dropwise (near the endpoint) • repeat and calculate mean
Substance that can react with an acid to form a soluble salt
metal • (metal) hydroxide • (metal) carbonate • alkali -metal oxides
What to do with acid when making soluble salt
- measure
- add to beaker
- warm
Diff between irona and sodium
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
Why can alkaline batteries not be recharged
the reaction is not reversible
Define the mass number of an atom
sum of protons and neutrons
Describe a method to find the position of an unknown metal in this reactivity series
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
Why would electrolysis not take place when the electrolyte is solid
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
Why should change test tubes to collect the gas from electrolyte
use measuring cylinders (instead of test tubes)
(because) test tubes cannot measure volume
or
(because) test tubes have no graduations / scale
How to describe trends shown in the results
- directly proportional?
- calc rate
- pick out points on graph when changed and rate
Suggest a reason for the difference in volume of each gas (even though same mol amount)
One gas reacts with water/dissolves in the solution
Explain why chlorine is more reacive than iodine
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
Give a reason why it would be hazardous if water came into contact with sodium
very exothermic reaction
produces a corrosive solution
Produces hydrogen, whcih is explosive/flammable
Why would you not expect titanium chloride to be a liquid at room temp
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
