CHEMISTRY EXAM Flashcards by Gabriel Selaj

2 differences between physical properties of elements in group 1 and those of transition metals

Transition are stronger, harder and denser

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How metals conduct electricity

Their delocalised electrons carry electrical charge through the metal

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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

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how can a reaction profile show the reaction is exothermic

Overall change is negative

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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

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Zn + CuCl2 → ZnCl2 + Cu

+2 +2
Zn + Cu → Zn + Cu

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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

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Equation for the reaction of rubidium with water

2Rb + 2H2O ——–> 2RbOH + H2

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Calculate relative atomic mass of neon

20.179

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Correct half equation for production of sodium

+ -
2Na + 2e —–> 2Na

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Why products of electrolysis must be kept apart

To prevent them from reacting with each other and interfering with the desired chemical processes

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Which type of particle passes through the mesh in the electrolysis of molten sodium chloride

Ions pass through the mesh

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Which two ions are present in aqueous sodium chloride solution in addition to sodium ions and chloride ions

Sodium Na+

Chloride ions Cl-

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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

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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

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Why aluminum is more expensive than carbon

Aluminium is more reactive than carbon so it must be extracted from its compounds using electrolysis

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Why the products are difficult to separate if magnesium is used to reduce silicon dioxide

They are both solids

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Why pH of acid depends on concentration of acid

Higher concentrations produce a greater number of hydrogen ions, resulting in a lower pH value

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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

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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

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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

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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

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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?

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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?

Transition metals

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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