Chem unit 1 pastpap3
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| MgCl may be prepared from magnesium by | reaction with chlorine or with HCL
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| Compare these two preparations in terms of the atom economies of the reactions. No calculation is required. | MG reacts with Cl to form only MgCl/ Mg reacts with Cl to form only one product / mG reacts with Hcl to form Hydro + mGcL) / mg
reacts with HCl to form more than one product / Mgcl reacts with HCL to form a waste product.
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| Define the term relative atomic mass | Average/mean mass of atom/isotopes (1/12 mass of an atom of) carbon–12
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| Explain why there are two peaks in the spectrum. | (Rubidium/it has) two isotopes
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| Suggest how you would mix the acid and the coral to ensure that no carbon dioxide escaped from the apparatus. | Any method which is likely to bring the reactants into contact after the apparatus is seale
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| Write the ionic equation to show how acids react with carbonates. State symbols are not required. | 2H+ + CO32― --> H2O + CO2
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| Write a chemical equation to show how the presence of carbon dioxide in water results in the formation of carbonic acid. State symbols are not required. | H2O + CO2 --> H2CO3
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| The overall reaction between ethane and chlorine is best described as --> | substitution.
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| Most compounds of lead are insoluble, an exception being lead(II) nitrate. Therefore a good method of preparing lead(II) sulfate is | adding dilute sulfuric acid to lead(II) nitrate solution.
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| Metals usually have high melting temperatures and boiling temperatures because there Are | strong attractions between the ions and the delocalised electrons.
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| Both equations | Mg + Cl2 --> MgCl2 and Mg + 2HCl --> MgCl2 + H2.
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| The reaction with chlorine has an atom economy which is higher / | 100%
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| Write the equation for the cracking of decane (C10H22) to form 1 molecule of propene as the only alkene. | C10H22 C7H16 + C3H6 carbon–carbon double bond in alkenes consists of a pie and a sigma bond
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| Explain, using diagrams, the difference between the pie and the sigma bond in the carbon–carbon double bond of an alkene. | bond weaker than σ (bond) / less energy needed to break π bond,π – electrons / π bonds (more) accessible (to electrophilic attack) high/higher/more electron density in π bond
(so alkenes more susceptible to electrophilic attack).
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| When propene reacts with hydrogen bromide, there are two possible products. Draw a displayed formula of each of these products and label the major product --> | 2 bromopropane(major) , bromopropane.
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| Explain, by referring to the mechanism, why the major product is formed. | Secondary carbocation (named or described or Drawn) more stable (than primary)
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| UV radiation causes poly(propene) to degrade. Suggest one advantage and one disadvantage of this. --> | polypropene will decompose (naturally) “rot” or “break down” OR polypropene will not require landfill (as it can decompose in sunlight)OR no need to incinerate /burn
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| (Disadvantage): | poly(propene) cannot be used when exposed to (bright) sunlight / UV / outdoors OR cannot be recycled / cannot be reused
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| The data book value for the enthalpy change of combustion of ethanol is –1370 kJ mol–1. (i) Calculate the percentage error in the value calculated in (a)(iii) in comparison with the data book value | 100 x (1370 ― Answer to (iii)) ÷ 1370 = value e.g. 100 x (1370 ― 682) ÷ 1370 = 50.2 %.
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| List three ways in which the design of the experiment causes the results to be so different from the data book value. (You should be specific but detailed explanations are not required.) | Heat loss (from the beaker)/
beaker not insulated/heat loss as no lid on beaker (containing the water) /no stirring (1)
Incomplete combustion (of the alcohol)/
formation of soot (on beaker) (1)
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| List three ways in which the design of the experiment causes the results to be so different from the data book value. (You should be specific but detailed explanations are not required.) | Not all of the energy from the flame is used to heat beaker and/or the water OR Too large a distance / no draught excluder (1) Heat capacity of the beaker is neglected/beaker absorbs heat/
Evaporation of the (hot) alcohol/ Evaporation of the (hot) water.
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| A molecule is --> | a group of atoms bonded by covalent bonds.
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| The relative atomic mass is defined as --> | the average mass of an atom of an element relative to 1/12 the mass of a
carbon-12 atom.
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| Suggest two reasons why the value obtained by carrying out these two experiments decomposition reaction of calcium carbonate. | Heat /energy loss OR Heat /energy loss to surroundings OR Heat /energy loss to apparatus
(1) Measured under non-standard conditions
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| Suggest two reasons why the value obtained by carrying out these two experiments decomposition reaction of calcium carbonate. | Specific heat capacity of solutions is approximate (1) Density of solution assumed to be 1 g cm−3/same as (pure) water
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