A Level OCR Chemistry A – Paper 3 (June 2025) Mark Scheme | Complete Answers & Examiner Feedback Guide

A Level OCR
Chemistry A – Paper 3
(June 2025) Mark
Scheme | Complete
Answers & Examiner
Feedback Guide

,Isotopes - CORRECT ANSWER-Different atomic forms of the same element.
Atoms with the same number of protons but a different number of neutrons



Relative atomic mass - CORRECT ANSWER-The mean mass of an atom of
an element, compared to 1/12th of the mass of an atom of carbon-12



Concentration= - CORRECT ANSWER-Number of moles ÷ Volume



One mole - CORRECT ANSWER-6.02×10^23



Number of moles= - CORRECT ANSWER-mass ÷ molar mass



r.t.p - CORRECT ANSWER-25 ºC

100 kPa (1 atm)



Molar gas volume - CORRECT ANSWER-24 dm³ / mol

One mole of any gas always has the same volume at r.t.p



Number of moles= - CORRECT ANSWER-Volume (dm^3) ÷ Molar gas
volume (24 dm^3 / mol)



R- Gas constant - CORRECT ANSWER-8.314 J / K / mol



Gas equation - CORRECT ANSWER-pV =

nRT (Pa)(m³)(K)

Assumes forces between molecules are negligible and the molecules have
a negligible size

, Empirical formula - CORRECT ANSWER-The smallest whole number ratio
of atoms of each element in a compound



Molecular formula - CORRECT ANSWER-The actual number of atoms of
each element in a compound



Ions:

Nitrate

Carbonate

Sulfate

Hydroxide

Ammonium

Zinc ion

Silver ion - CORRECT ANSWER-Formula:

NO3-

CO3²-

SO4²-

OH-

NH4+

Zn²+

Ag+



Acids - CORRECT ANSWER-Proton donors - produce H+ ions in water



Alkalis - CORRECT ANSWER-Proton acceptors - produce OH- ions in water