Exam Questions Got Wrong
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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