CHEMISTRY EXAM Flashcards
2 differences between physical properties of elements in group 1 and those of transition metals
Transition are stronger, harder and denser
How metals conduct electricity
Their delocalised electrons carry electrical charge through the metal
Plan a method to investigate the effect of changing the mass of sodium carbonate powder on the highest temperature reached
Measure equal volumes of hydrochloric acid in polystryene cup
Add different masses of sodium carbonate to separate trials
how can a reaction profile show the reaction is exothermic
Overall change is negative
How the student should obtain crystals of zinc chloride from a solution of zinc chloride.
Warm mixture and stir
Continue to add zinc oxide to beaker until all of dilute hydrochloric acid has reacted
Remove excess zinc oxide
Obtain crystals of zinc chloride from solution
Zn + CuCl2 → ZnCl2 + Cu
+2 +2
Zn + Cu → Zn + Cu
why rubidium is more reactive than potassium.
larger atomic size
lower ionization energy
Greater tendency to lose electrons and form positive ions in chemical reactions
Equation for the reaction of rubidium with water
2Rb + 2H2O ——–> 2RbOH + H2
Calculate relative atomic mass of neon
20.179
Correct half equation for production of sodium
+ -
2Na + 2e —–> 2Na
Why products of electrolysis must be kept apart
To prevent them from reacting with each other and interfering with the desired chemical processes
Which type of particle passes through the mesh in the electrolysis of molten sodium chloride
Ions pass through the mesh
Which two ions are present in aqueous sodium chloride solution in addition to sodium ions and chloride ions
Sodium Na+
Chloride ions Cl-
Aqueous sodium chloride solution is electrolysed in a different industrial process.
Two gases and an alkaline solution are produced
Name the alkaline solution produced
Sodium hydroxide
Explain how the alkaline solution has produced sodium hydroxide
Reduction at the cathode
Oxidation at the Anode
The released electrons flow through the external circuit back to the cathode, where they participate in the reduction of water molecules
Why aluminum is more expensive than carbon
Aluminium is more reactive than carbon so it must be extracted from its compounds using electrolysis
Why the products are difficult to separate if magnesium is used to reduce silicon dioxide
They are both solids
Why pH of acid depends on concentration of acid
Higher concentrations produce a greater number of hydrogen ions, resulting in a lower pH value
Why does the pH of an acid depend on the strength of the acid
Strong acids dissociate completely and produce a high concentration of H+ ions, resulting in a lower pH
25.00 cm’ of the hydrochloric acid reacted with 23.50 cm’ of the 0.100 mol/dm3 barium hydroxide solution.
The equation for the reaction is:
2HClaq) + Ba(OH)2(aq) → BaCl(aq) + 2H2O(I)
Calculate the concentration of the hydrochloric acid in mol/dm?.
3
0.188 mol/dm
Explain why the electrical conductivity of the mixture was zero when the sulfuric acid had just been neutralised
All hydrogen and hydroxide ions are consumed in neutralization reaction to form water
No free ions left in the solution to conduct electricity
Ekectrical conductivity becomes 0 as there are no ions available to carry the electric current
The student then added a further 10 cm’ of barium hydroxide solution
The electrical conductivity of the mixture increased
Why?
Due to the increase in the concentration of hydroxide ions in the solution, which can conduct electricity
Element Q is a dull solid with a melting point of 44 °C.
Element Q does not conduct electricity.
Which section of the periodic table in Figure 1 is most likely to contain element Q?
D
Element R forms ions of formula R2* and R3+
Which section of the periodic table in Figure 1 is most likely to contain element R?
B
Transition metals
Suggest why poly(butene) insulation must be removed from scrap copper wire before the copper is recycled.
If insulation not removed, can burn or produce harmful gases when exposed to high temperatures,
This affects quality of recycled copper and damaging the recycling equipment.
How scrap copper wire can be recycled to make new copper water pipes.
Melting down the scrap copper wire
Refining the molten copper
Forming it into pipes.
Suggest two reasons why recycling scrap copper is more sustainable than extracting copper from copper ores.
No need for landfills
Cheaper than mining and extracting new copper
Which solution can be added to copper sulfate solution to show the presence of copper(Il) ions
Sodium hydroxide solution can be added
Formation of a pale blue precipitate of copper(II) hydroxide
Describe one test to show the presence of sulfate ions in copper sulfate solution.
Give the result of the test
Test
Result
Add a small amount of barium chloride solution to the copper sulfate solution
A white precipitate of barium sulfate forms if sulfate ions are present in the copper sulfate solution
Determine the mass of the empty test tube
25.6g - 2.0g = 23.6g
Explain why the mass of the test tube and contents decreased
Hydrated cobalt chloride
The mass of the sample decreases because the water molecules are lost as gas
Suggest why the test tube and contents were heated until the mass did not change.
To ensure all water was removed from hydrated cobalt chloride
When 238 g of hydrated cobalt chloride is heated until the mass does not change, 88.1 kJ of energy is taken in.
The student heated 2.00 g of hydrated cobalt chloride until the mass did not change.
Calculate the energy taken in during this reaction.
(88.1 x 2.00) ➗ 238
176.2 ➗ 238
0.739kJ
What type of reaction takes place when hydrated cobalt chloride is heated?
Dehydration reaction
Evaluate the use of glass for milk bottles compared with the use of a polymer for milk bottles
Raw material extraction - glass requires high energy, polymers require moderate energy
Manufacturing process - glass - high energy consumption, polymer - moderate energy consumption
Transportation - glass heavier than polymer leads to high tranportation costs
Glass high durability, polymer moderate durability
Glass fully recyclable, Recyclable, but with limitations due to potential degradation of material quality
Glass - does not release harmful chemicals during incineration, polymer may release harmful chemicals during incineration
Milk is also sold in cardboard cartons.
A carton is made using 40 cm’ of cardboard.
The density of the cardboard is 0.40 g/cm?.
Calculate the mass of the carton
Mass = density x volume
0.40 x 40 = 16g
The two useful materials produced from feedstock for the petrochemical industry are
Detergents
Solvents
Balanced symbol equation for complete combustion of C9H20
C9H20 + 14O2 —————> 9CO2 + 10H2O
Why sulfur impurities are removed before the petrol is burned in car engines
Sulfur impurities are removed from petrol before it’s burned in car engines because sulfur can lead to air pollution, health problems, and engine damage
Viscosity
A measure of the resistance of a substance to flow
A student predicted that heavy fuel oil is more viscous than kerosene
The student’s prediction was correct
Justify the student’s prediction
In table 4 the heavy fuel oil fraction has a wider range of carbon atoms in each molecule compared to kerosene
This shows heavy fuel oil molecules are larger and more complex than kerosene molecules
They are likely to have strong intermolecular forces hplding them together as a result heavy fuel oil will have higher viscosity compared to kerosene
Conditions for cracking
High temperature 450-750 C
High pressure around 1-70atm
Prescence of catalyst for catalytic cracking
Which pair of hydrocarbon molecules turn bromine water colourless
C7H16
C8H18
Describe how sewage is treated to remove organic matter
Screening to remove large objects (sticks, leaves plastic’
Sewage enters a primary settling tank
The partially treated sewage is then transferred to a biological treatment tank
Tertiary treatment may be used
Sludge collected undergoes further treatment to reduce its volume
Treated sewage may undergo disinfection to kill harmful pathogens
The pair of concentrations that could represent X in Table 5 after the desalination process for sea water is
Na + : 0.5mol/dm3
Cl- : 0.003mol/dm3
Explain why the concentrations of sodium ions and of chloride ions in the ground water in Table 5 are unchanged by Process 1
Because ground water is not desalinated during process 1
Explain why the ground water in Table 5 requires Process 2 before the water is safe to drink
To ensure ground water is safe for human to drink by removing or reducing contaminants, pathogens and impurities
Suggest what the company means by ‘pure’.
The water meets certain quality standards or criteria for purity suitable for its intended use
Describe the test for chlorine gas
Collect a sample of chlorine gas
Bubble gas through solution of potassium iodide in water
Observe the color change in the solution
Result of chlorine gas
If chlorine gas present, it reacts with potassium iodide solution to produce iodine
Explain the change in the percentage of gas in the region labelled A on Figure 3
Reflects transition from an atmosphere dominated by carbon dioxide to one with increasing levels of oxygen
Explain the change in the percentage of gas in the region labelled B on Figure 3
Reflects long-term removal of carbon dioxide from atmosphere
Explain the change in the percentage of gas in the region labelled C on Figure 3
Reflects long-term increase in oxygen levels in Earth’s atmosphere
What process caused the changes in the percentages of gases in the region labelled C on Figure 3
Photosynthesis
Natural gas is a fossil fuel
Describe how deposits of natural gas were formed
Millions years ago organic matter accumulated on the ocean floor
Layers of sediment accumulated over organic matter
Subjected to high temperature and high pressure
Give the sources of the nitrogen and of the hydrogen used in the Haber process
Nitrogen - air
Hydrogen - natural gas
How does the equation for the reaction show that the atom economy of the forward reaction is 100%?
There is only 1 product
Explain how the ammonia produced is separated from the unreacted nitrogen and hydrogen in X
Mixture is cooled so only ammonia liquefies
Determine the percentage yield of ammonia at 450 °C and 500 atmospheres
500
Explain why these conditions are chosen for economical production of ammonia in the Haber process
Higher temperature gives higher rate and shifts position of equilibrium to the left
Use of catalyst gives higher rate because activation energy lowered
High pressure shifts position of equilibrium to the right
Use of catalyst has no effect on position of equilibrium
Sulfur produced in reaction
Why does mixture become cloudy
Sulfur is insoluble
Exothermic reaction
When energy is transferred to the surroundings, this is called an exothermic
The percentage of light reaching the light sensor decreases by 1% when 7.1 × 10-5 moles of sulfur is produced
Determine the rate of reaction in mol/s for the production of sulfur at 30 seconds.
-3
2.13 x 10 moles/s
Why rate of reaction changes between 0 and 60 seconds
Rate decreases because concentration of reactants decreases
Greatest rate at start
Greatest concentration of reactants at start
The line of best fit on Figure 8 is horizontal between 80 and 120 seconds because the reaction stopped.
Why did the reaction stop?
Hydrochloric acid all used up
How could the student improve the method so that the same percentages of light reached the light sensor
Stop light from other sources reaching light sensor
Name given to similar results obtained on different days under the same conditions by same student
Repeatable
Which expression represents the relationship between the volume (V) of sodium thiosulfate solution used and the mass (m) of sulfur produced?
V O( m
Weird shape
Determine the simplest whole number ratio of the volumes of
sodium thiosulfate solution : hydrochloric acid
Volume of NaS2O3 solution
______________________________
Volume of hydrochloric acid
= 0.25
1:4
