Original open focus revision; complete specification coverage remains unfinished.
1 · Amounts, equations and limiting reagents
mole · limiting reagent
edexcel_ial_chemistry:moles:open:1 · 2 баллов
Which step comes first in a reacting-mass calculation?
- Compare masses without an equation
- Use a balanced equation and convert mass to amount
- Assume every mole ratio is 1:1
Ответ и обоснование
Use a balanced equation and convert mass to amount
- Calculate the amount available for each reactant and divide by its coefficient. The smaller ratio limits the reaction. Use that reactant to calculate the maximum product before comparing actual yield.
edexcel_ial_chemistry:moles:open:2 · 4 баллов
Calculate amount in 5.0 g of a substance with molar mass 100 g per mole.
Ответ и обоснование
0.05 mol
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Excess acid means acid does not limit the stated calculation. A coefficient of 2 before HCl does not double the hydrogen amount.
2 · Particles, bonding and bulk properties
ionic bond · delocalized electron
edexcel_ial_chemistry:bonding:open:1 · 2 баллов
Why does molten sodium chloride conduct?
- Its ions can move
- Its atoms become electrons
- Its molecules contain no charge
Ответ и обоснование
Its ions can move
- To explain a bulk property, name the structure, particles, forces and mobile charge carriers. Simple molecular substances can have strong covalent bonds inside molecules but weak attractions between molecules.
edexcel_ial_chemistry:bonding:open:2 · 4 баллов
An atom has atomic number 17 and mass number 35. Find its number of neutrons.
Ответ и обоснование
18
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Melting a simple molecular substance usually overcomes intermolecular attractions; it does not require breaking all covalent bonds within each molecule.
3 · Organic structures and reaction pathways
functional group · isomer
edexcel_ial_chemistry:organic:open:1 · 2 баллов
What happens to the carbon skeleton when bromine adds to ethene?
- It remains two carbons long
- It becomes one carbon long
- It becomes a six-carbon ring
Ответ и обоснование
It remains two carbons long
- Distinguish addition, substitution, oxidation and polymerization by tracing bonds before and after reaction. Conditions and reagents belong to the reaction arrow; they are not interchangeable labels.
edexcel_ial_chemistry:organic:open:2 · 4 баллов
How many moles of bromine react completely with 0.15 mol ethene?
Ответ и обоснование
0.15 mol
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Bromine decolourization provides evidence of unsaturation in an appropriate test. It is not proof that an unknown sample is specifically ethene.
4 · Calorimetry and chemical energy
exothermic · enthalpy change
edexcel_ial_chemistry:energy:open:1 · 2 баллов
Which process requires energy?
- Breaking a covalent bond
- Forming every chemical bond
- Cooling a hot solution
Ответ и обоснование
Breaking a covalent bond
- Use energy transferred = mass × specific heat capacity × temperature change. Convert joules to kilojoules before dividing by reaction amount. An exothermic molar enthalpy change has a negative sign.
edexcel_ial_chemistry:energy:open:2 · 4 баллов
50 g water rises 4 °C. Use c = 4.2 J per gram per degree to find q.
Ответ и обоснование
840 J
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Heat loss usually lowers the observed temperature rise. The solution gaining heat and the reaction losing heat have opposite signs.
5 · Redox and electrolysis
oxidation · reduction
edexcel_ial_chemistry:electrolysis:open:1 · 2 баллов
What happens to Cu²⁺ at the cathode?
- It gains electrons
- It loses two protons
- It gains neutrons
Ответ и обоснование
It gains electrons
- Predict products using the specified electrolyte and electrode material. In an aqueous solution, hydrogen or oxygen may form because water-related species compete. Molten salts contain only the ions of the salt.
edexcel_ial_chemistry:electrolysis:open:2 · 4 баллов
How many moles of electrons reduce 0.20 mol of Cu²⁺ to copper?
Ответ и обоснование
0.4 mol
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Electrode signs depend on the cell type. In an electrolytic cell the cathode is negative; reduction remains the defining process at a cathode in every cell.
6 · Rates, catalysts and reliable endpoints
activation energy · rate
edexcel_ial_chemistry:rates:open:1 · 2 баллов
Two reactions reach the same final gas volume. Which can still differ?
- Their rates
- The balanced equation must be different
- The product must have different molar mass
Ответ и обоснование
Their rates
- A product-time graph has a steeper gradient where rate is larger. A tangent estimates instantaneous rate; a secant gives average rate over an interval. The final plateau reflects the total collected product under the stated conditions.
edexcel_ial_chemistry:rates:open:2 · 4 баллов
A reaction makes 24 cubic centimetres of gas in 40 s. Find average rate.
Ответ и обоснование
0.6 cm³/s
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
A catalyst does not change the equilibrium constant at a fixed temperature. A mass-loss method cannot detect all reactions, and losing gas through a leak biases a collection experiment.
7 · Titration and a defensible concentration
titre · equivalence point
edexcel_ial_chemistry:titration:open:1 · 2 баллов
Why rinse the pipette with the solution it will transfer?
- To avoid dilution by residual water
- To create more moles of analyte
- To make the solution neutral
Ответ и обоснование
To avoid dilution by residual water
- Calculate the known amount first, apply the stoichiometric ratio, then divide by the unknown solution volume in cubic decimetres. Use concordant titres as required by the school method and report the accepted values.
edexcel_ial_chemistry:titration:open:2 · 4 баллов
Burette readings are 1.40 and 23.65 cubic centimetres. Calculate titre.
Ответ и обоснование
22.25 cm³
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Adding distilled water to the flask changes volume but not the transferred amount of analyte. Do not average a rough titre with carefully measured concordant values.
8 · Chemical tests and analytical confidence
chromatography · Rf
edexcel_ial_chemistry:analysis:open:1 · 2 баллов
Why use pencil for a chromatography baseline?
- Graphite is less likely to dissolve and move with the solvent
- Pencil automatically identifies ions
- Ink is always invisible
Ответ и обоснование
Graphite is less likely to dissolve and move with the solvent
- Rf is distance travelled by a component divided by distance travelled by the solvent front, both measured from the baseline. Compare under the same conditions; an Rf value alone does not establish identity across different solvents.
edexcel_ial_chemistry:analysis:open:2 · 4 баллов
A spot travels 4.2 cm while the solvent front travels 7.0 cm. Find Rf.
Ответ и обоснование
0.6
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
A single spot can conceal substances that co-elute. Ink on the baseline can dissolve and create extra spots.
9 · Uncertainty, gradients and model testing
uncertainty · systematic error
edexcel_ial_chemistry:uncertainty:open:1 · 2 баллов
Which is most likely a systematic error?
- A balance reads 0.20 g when empty
- Repeated values fluctuate either side of the mean
- Random differences in reaction time
Ответ и обоснование
A balance reads 0.20 g when empty
- For a product or quotient, adding fractional uncertainties is a common maximum-uncertainty approximation. For a difference, add absolute uncertainties. A nonzero intercept can reveal an offset or an incomplete model.
edexcel_ial_chemistry:uncertainty:open:2 · 4 баллов
A 40 cm reading has an absolute uncertainty of 1 cm. Find percentage uncertainty.
Ответ и обоснование
2.5 %
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Repeating readings reduces random uncertainty in a mean but does not automatically remove a zero error. Do not quote more decimal places than your measurement can support.
10 · Equilibrium and changing conditions
equilibrium · reversible reaction
edexcel_ial_chemistry:equilibrium:open:1 · 2 баллов
What is equal at dynamic equilibrium?
- Concentrations of all species
- Forward and reverse reaction rates
- Masses of every reactant and product
Ответ и обоснование
Forward and reverse reaction rates
- A concentration or pressure change disturbs the balance. The system responds toward a new equilibrium. Temperature changes can also change the equilibrium constant; a catalyst changes how quickly equilibrium is reached.
edexcel_ial_chemistry:equilibrium:open:2 · 4 баллов
For A ⇌ B, calculate [B]/[A] when [B]=0.8 and [A]=0.2.
Ответ и обоснование
4
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Do not use a catalyst to claim a larger equilibrium yield. For heterogeneous equilibria, pure solids are omitted from the usual equilibrium expression.