Cambridge IGCSE Chemistry (0620) Flashcards

24 sample cards from the Chemistry (0620) deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Define an acid, a base and an alkali (proton/ion definitions).

   An acid is a proton ($\ce{H+}$) donor that produces $\ce{H+}$ ions in aqueous solution. A base is a proton acceptor (often a metal oxide/hydroxide). An alkali is a soluble base that produces $\ce{OH-}$ ions in aqueous solution.

2. Give the colours of litmus, thymolphthalein, and methyl orange in acid and alkali.

   Litmus: red in acid, blue in alkali. Thymolphthalein: colourless in acid, blue in alkali. Methyl orange: red in acid, yellow in alkali.

3. State the general products of: acid + metal, acid + base, and acid + carbonate.

   Acid + metal $\to$ salt + hydrogen. Acid + base (neutralisation) $\to$ salt + water. Acid + carbonate $\to$ salt + water + carbon dioxide.

4. Write the reactivity series for these metals from most to least reactive: K, Na, Ca, Mg, Al, Zn, Fe, Cu, Ag, Au.

   Potassium > Sodium > Calcium > Magnesium > Aluminium > (Carbon) > Zinc > Iron > (Hydrogen) > Copper > Silver > Gold.

5. Name the raw materials and main reactions in the blast furnace extraction of iron.

   Raw materials: iron ore (haematite, $\ce{Fe2O3}$), coke, limestone and hot air. Key reactions: $\ce{C + O2 -> CO2}$; $\ce{CO2 + C -> 2CO}$; $\ce{Fe2O3 + 3CO -> 2Fe + 3CO2}$. Limestone forms slag: $\ce{CaCO3 -> CaO + CO2}$ then $\ce{CaO + SiO2 -> CaSiO3}$.

6. What two conditions are needed for iron to rust, and name two methods of rust prevention?

   Rusting needs both oxygen (air) and water. Prevention: barrier methods (painting, greasing, plating) and sacrificial protection (e.g. galvanising with zinc, or attaching a more reactive metal such as zinc/magnesium).

7. Give the chemical tests for these gases: hydrogen, oxygen, carbon dioxide, ammonia, chlorine.

   Hydrogen: lighted splint gives a 'squeaky pop'. Oxygen: relights a glowing splint. Carbon dioxide: turns limewater milky/cloudy. Ammonia: turns damp red litmus blue. Chlorine: bleaches damp litmus paper white.

8. Describe the flame test colours for lithium, sodium, potassium, calcium and copper(II) ions.

   Lithium $\ce{Li+}$: red. Sodium $\ce{Na+}$: yellow. Potassium $\ce{K+}$: lilac. Calcium $\ce{Ca^2+}$: orange-red. Copper(II) $\ce{Cu^2+}$: blue-green.

9. How are sulfate, chloride and carbonate ions identified in solution?

   Sulfate: add dilute nitric acid then barium nitrate/chloride — white precipitate. Chloride: add dilute nitric acid then silver nitrate — white precipitate. Carbonate: add dilute acid — effervescence of $\ce{CO2}$ that turns limewater milky.

10. List the main gases of clean, dry air and their approximate percentages.

    Nitrogen about $78\%$, oxygen about $21\%$, argon (noble gases) about $1\%$, and carbon dioxide about $0.04\%$ (plus variable water vapour).

11. Name two atmospheric pollutants from car engines and state how each forms and its harmful effect.

    Carbon monoxide ($\ce{CO}$) from incomplete combustion — a toxic gas reducing oxygen transport in blood. Oxides of nitrogen ($\ce{NO_x}$) from nitrogen and oxygen reacting at high engine temperatures — cause acid rain and respiratory problems.

12. Explain how a catalytic converter reduces pollution, giving an equation.

    A catalytic converter (platinum/rhodium catalyst) converts harmful gases into less harmful ones, e.g. $\ce{2CO + 2NO -> 2CO2 + N2}$, removing carbon monoxide and nitrogen oxides.

13. How does carbon dioxide contribute to climate change (the greenhouse effect)?

    $\ce{CO2}$ (a greenhouse gas, like methane) absorbs and re-emits infrared (heat) radiated from the Earth's surface, trapping heat in the atmosphere and raising the average global temperature (enhanced greenhouse effect).

14. Define a homologous series and state three of its characteristics.

    A homologous series is a family of organic compounds with the same general formula and similar chemical properties. Members differ by $\ce{CH2}$, show a gradual trend in physical properties down the series, and share the same functional group.

15. What is structural isomerism? Give the molecular formula common to the butane isomers.

    Structural isomers are compounds with the same molecular formula but different structural (atom arrangement) formulae. For example, butane and methylpropane both have the formula $\ce{C4H10}$.

16. State the general formulae of alkanes and alkenes.

    Alkanes: $\ce{C_nH_{2n+2}}$ (saturated). Alkenes: $\ce{C_nH_{2n}}$ (unsaturated, containing a $\ce{C=C}$ double bond).

17. How do you test for the presence of a carbon-carbon double bond (an alkene)?

    Add bromine water (orange/brown). An alkene decolourises bromine water (turns it colourless) via an addition reaction; a saturated alkane does not.

18. What is cracking, why is it carried out, and give an example equation?

    Cracking is breaking large, less useful long-chain alkanes into smaller, more useful alkanes and alkenes using heat and a catalyst. Example: $\ce{C10H22 -> C8H18 + C2H4}$. It produces more petrol-range fuels and alkenes for plastics.

19. Compare a substitution reaction of alkanes with an addition reaction of alkenes.

    Alkanes (saturated) undergo substitution, e.g. with chlorine in UV light: $\ce{CH4 + Cl2 -> CH3Cl + HCl}$. Alkenes (unsaturated) undergo addition across the double bond, e.g. $\ce{C2H4 + Br2 -> C2H4Br2}$.

20. Name the functional group of alcohols and give two ways to manufacture ethanol.

    Alcohols contain the hydroxyl group $\ce{-OH}$. Ethanol is made by (1) fermentation of glucose: $\ce{C6H12O6 -> 2C2H5OH + 2CO2}$ (yeast, $\sim 30\,^{\circ}\text{C}$), and (2) catalytic addition of steam to ethene: $\ce{C2H4 + H2O -> C2H5OH}$.

21. What is produced when a carboxylic acid reacts with an alcohol, and name the catalyst?

    An ester (plus water) is produced in esterification, catalysed by concentrated sulfuric acid. Example: ethanoic acid + ethanol $\to$ ethyl ethanoate + water.

22. Distinguish between addition polymerisation and condensation polymerisation.

    Addition: many small unsaturated monomers (alkenes) join to form one long polymer with no other product, e.g. ethene $\to$ poly(ethene). Condensation: monomers with two functional groups join, losing a small molecule (e.g. water) each time, forming polymers like polyesters and nylon.

23. Describe the repeat unit relationship for poly(ethene) made from ethene.

    Ethene monomer $\ce{CH2=CH2}$ undergoes addition polymerisation; the double bond opens and units link to give poly(ethene) with repeat unit $\ce{-(CH2-CH2)-}_n$.

24. Why are many synthetic addition polymers a disposal problem, and give a drawback of two disposal methods?

    They are non-biodegradable (microorganisms cannot break them down). Landfill wastes space and they do not decompose; incineration (burning) can release toxic gases such as $\ce{HCl}$ and carbon dioxide (a greenhouse gas).

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