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Chemistry > past Paper 2021: 1,2 And 3 > Flashcards

past Paper 2021: 1,2 And 3 Flashcards

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1
Q

Magnesium chloride dissolves in water. Give an equation giving state symbols to represent the process that occurs when the Enthalpy of solution of magnesium chloride is measured

A

MgCl2 (s) —> Mg2+ (as) + 2Cl-(aq)

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2
Q

SUGGEST WHY THE ENTHALPY OF HYDRATION of Ca2+ is less exothermic than Mg2+

A

Ca2+ ion bigger , there is a lower charge to size ratio, weaker attraction to Od- in water

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3
Q

Define the mass number of an atom

A

Number of protons and neutrons in the nucleus of an atom

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4
Q

Give an equation including state symbols for the reaction of sodium with water, suggest why it is dangerous to react a similar piece of sodium with a lot more water in a boiling tube

A

2Na(s) + 2H2O(l) —> 2NaOH(aq) + H2(g)
Temperature will go up more causing reactants to shoot out or explode

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5
Q

Give an equation foe the reaction of phosphorous oxide with water and suggest a pH for this

A

P4O10 + 6H2O —> 4H3PO4
1

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6
Q

Explain in terms of crystal structure and bonding, why silicon oxide has a higher melting point than phosphorous oxide

A

SiO2 is macromolecular with strong covalent bonds between atoms or covalent bonds need a lot of energy to be overcome
P4O10 is molecular or simple covalent with weak induced dipole dipoles between molecules- require little energy to overcome

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7
Q

Am element in period 3 forms an oxide that is insoluble in water- it reacts with sulfuric acid and aqueous potassium hydroxide, give the formula of this oxide and an equation for its reaction with sulfuric acid

A

Al2O3
Al2O3 + 3H2SO4 —> Al2(SO4)3 + 3H2O

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8
Q

Give the formula of a hydroxide ion of an element in period 3 using in medicine

A

Mg(OH)2

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9
Q

identity the element in period 3, from sodium to chlorine, that has the largest atomic radius

A

Na

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10
Q

2SO2 + O2 = 2SO3
State and explain the effect of a decrease in overall pressure of the equilibrium yield of SO3

A

Decrease, equilibrium shifts to the left to oppose decrease in pressure

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11
Q

Explain why the value of Kw increases as temperature increases

A

Forward reaction is endothermic, equilibrium shifts to the right to oppose increase in temperature so concentration of H+ increases

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12
Q

Suggest why the ph probe is washed with distilled water

A

Different solutions must not contaminate each other

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13
Q

Explain why the volume of sodium hydroxide added between each pH measurement is smaller as the end point of titration is approached

A

To avoid missing the endpoint

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14
Q

How to determine if a an indicator is suitable

A

Changes pH within the vertical region

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15
Q

Explain why the standard entropy for CO2 is greater than that of carbon

A

CO2 is a gas so there is more disorder

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16
Q

Name the type of compound shown by formula RCOOK ans state its use

A

Carboxylic salt- soap

17
Q

Suggest why aqueous ethanol is a suitable solvent when heating the coconut oil with KOH, give a safety precaution used when heating the mixture

A

It dissolves both oil and KOH
Use a water bath as ethanol is flammable

18
Q

State the meaning of fraction as used in the term petrol fraction

A

Group of hydrocarbons with similar boiling point

19
Q

Give a reason why carbon dioxide absorbs infrared radiation

A

Vibrate at the same frequency as IR

20
Q

Bioethanol is used as an alternative to fossil fuels
Evaluate the statement: “the fact that bioethanol is a carbon-neutral fuel outweighs the environmental disadvantages of producing bioethanol”

A

Photosynthesis: 6CO2 + 6H2O —> C6H2O6 + 6O2
Fermentation: C6H12O6 —> 2C2H5OH + 2CO2
Combustion: 2C2H5OH + 6O2 —> 6H2O 4CO2
Environmental impacts: deforestation, loss of biodiversity, 6CO2 in and 6CO2 out isn’t carbon neutral as fuel is used in production

21
Q

The student considered using a glass beaker on a tripod and gauze instead of the clamped copper calorimeter
Suggest two disadvantages of using a glass beaker beaker on a tripodd gauze

A

Tripod and gauze so reduced heat transfer
Doesn’t conduct heat as well as copper

22
Q

Suggest two reasons why the value of Enthalpy of combustion for this experiment is less exothermic than the data value

A

Heat lost, incomplete combustion may have occured

23
Q

Suggest one addition to apparatus to improve accuracy

A

Use a lid to prevent heat loss

24
Q

Explain why benzene is more thermodynamically stable

A

Electrons delocalised

25
Q

Suggest the importance of fewer steps and higher percentage atom economy in experiments

A

Fewer steps-better yield
Less waste

26
Q

State why the ozone layer is beneficial for living organism

A

Prevents harmful UV

27
Q

State how chlorofluorocarbons form chlorine in the upper atmosphere

A

C-Cl bonds broken homolytically

28
Q

Suggest why the 1cm portions of the reaction mixture are added to an excess of NaHCO3 solution

A

The sodium Hydrogencarbonate solution neutralises the acid so stops the reaction

29
Q

Suggest why the order of this reaction in respect to propanone can be ignored

A

Concentration is almost constant
The concentration is much larger than the concentration of iodine

30
Q

Explain how the graph shows 0 order

A

Has a constant gradient so the rate of reaction does not change as the concentration of iodine changes

31
Q

Describe how the crystalline solid is separated and purified

A

Filter, dissolve in minimum volume of hot solvent cool and filter under reduced pressure, wash with cold solvent and dry

32
Q

Suggest a reason why KCN is used rather than HCN

A

KCN dissociates to provide the CN- nucleophile

33
Q

1.dilute nitric acid is added to the solution
2.aqueous silver nitrate is added to the solution
3. A pale yellow ppt forms
Excess dilute aqueous ammonia is added to the mixture
Some of the precipitate dissolves and a darker yellow ppt remains
Give a reason for the use and explain the observations using equation

A

HNO3 to remove hydroxide ions that may give other pts with AgNO3
AgNO3 produces pts with ions
Ag+ + Cl- —> AgCl
NH3 dissolves AgCl
AgCl + 2NH3 —> Ag(NH3)2+ + Cl-

Chemistry (25 decks)

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