PSPM · Malaysia · Predicted papers

PSPM ChemistrySK015/SK025

2 papers200 marks4 h

What we predict comes up

From the syllabus weighting and how the papers are usually set. The papers below follow it.

Matter and atomic structure14.5%Mole calculations, redox balancing and the hydrogen spectrum open almost every SK015 paper, usually as the first two questions.
Periodic table and chemical bonding14.5%Period 3 ionisation energy trends and VSEPR shapes with formal charges are core SK015 outcomes and are tested every semester.
Chemical and ionic equilibria14.5%Kc, Kp, pH, buffers and salt hydrolysis are calculation heavy and carry the closing SK015 questions.
Thermochemistry and electrochemistry14.5%Calorimetry, Hess's law, Born-Haber cycles, cell potentials, the Nernst equation and Faraday's law are reliably examined.

SK015

Semester 1: Chemistry 1

2 h · 100 marks · Calculator allowed

120:00

This question paper consists of 7 structured questions.
Answer all questions.
Write your answers in the answer booklet provided. Show all working for calculations.
Non-programmable scientific calculators may be used.
Data: Avogadro constant $L = 6.02 \times 1 0^{23} mol^{- 1}$ , gas constant $R = 8.314 J K^{- 1} mol^{- 1} = 0.08206 L atm K^{- 1} mol^{- 1}$ , Faraday constant $F = 96500 C mol^{- 1}$ , Planck constant $h = 6.63 \times 1 0^{- 34} J s$ , speed of light $c = 3.00 \times 1 0^{8} m s^{- 1}$ .

Answer or mark a question and your score adds up here.

Answer all questions100 marks

115 marks

(a)A sample of element X was analysed in a mass spectrometer. The isotopes found and their relative abundances are given in the table. Calculate the relative atomic mass of X to two decimal places.[3]

Isotope mass	Relative abundance (%)
24.0	78.99
25.0	10.00
26.0	11.01

(b)In acidic solution, the dichromate(VI) ion,

C r_{2} O_{7}^{2 -}

, oxidises the sulfite ion,

S O_{3}^{2 -}

, to the sulfate ion,

S O_{4}^{2 -}

, and is itself reduced to

C r^{3 +}

. Using the ion-electron method, write the two half-equations and the balanced overall ionic equation.[4]

c m^{3}

of a sodium sulfite solution required 18.60

c m^{3}

of 0.0200

mol d m^{- 3}

acidified potassium dichromate(VI) for complete reaction. Using your equation in (b), calculate the concentration of the sodium sulfite solution in

mol d m^{- 3}

.[4]

(d)An organic compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Its molar mass is 180 g mol⁻¹. Determine its empirical formula, and hence the number of empirical formula units in one molecule, and write its molecular formula. (Relative atomic masses: C = 12.0, H = 1.0, O = 16.0)[4]

214 marks

The Rydberg equation for the hydrogen atom is

\frac{1}{λ} = R_{H} (\frac{1}{n _{1}^{2}} - \frac{1}{n _{2}^{2}})

, where

R_{H} = 1.097 \times 1 0^{7} m^{- 1}

(a)Calculate the wavelength, in nm, of the radiation emitted when the electron in a hydrogen atom falls from the fourth energy level to the second energy level.[3]

(b)Calculate the energy of one photon of this radiation. Give your answer in units of

1 0^{- 19}

J.[2]

(c)Name the spectral series to which this line belongs and state the region of the electromagnetic spectrum in which it is found. Explain why the lines of this series get closer together towards higher frequency.[2]

(d)Write the electronic configurations of chromium, Cr (Z = 24), and the copper(II) ion, Cu²⁺ (Z = 29). Explain why the configuration of chromium does not follow the Aufbau principle strictly.[3]

(e)Give one possible set of the four quantum numbers (n, l, m, s) for the outermost electron of a potassium atom, K (Z = 19).[2]

(f)Describe in words the shape and orientation of a

2 p_{z}

orbital and of a

3 d_{xy}

orbital.[2]

313 marks

The first ionisation energies of the elements of Period 3 are given in the table.

Element	Na	Mg	Al	Si	P	S	Cl	Ar
First ionisation energy (kJ mol⁻¹)	496	738	578	787	1012	1000	1251	1521

(a)Explain the general trend in first ionisation energy across Period 3.[2]

(b)Explain why the first ionisation energy of aluminium is lower than that of magnesium, and why that of sulfur is lower than that of phosphorus.[3]

(c)The first five successive ionisation energies of an element Y in Period 3, in kJ mol⁻¹, are 578, 1817, 2745, 11 577 and 14 842. Deduce the group of Y in the Periodic Table, identify Y, and explain your reasoning.[3]

(d)State and explain the trend in atomic radius across Period 3. Explain why the radius of

N a^{+}

is smaller than that of the Na atom.[2]

(e)Write balanced equations to show the reaction of sodium oxide with water, and of aluminium oxide with hydrochloric acid and with aqueous sodium hydroxide. State the acid-base nature of each oxide.[3]

4 more questions

Every paper, every question, the answers and the mark scheme. Free with a Knomi account.

100% free · No card

Not included: The laboratory practical assessment, which is marked as coursework and not in the PSPM written paper, is not included.