Chemical Formulae, Equations, the Mole and Gases
Competition questions
22 marksThe first six ionisation energies of an element, M, in kJ mol−1 are 660, 1267, 2218, 3313, 7863 and 9500. M forms its only chloride by heating M with chlorine. What is the equation for the formation of the chloride of M?
Source: SJChO Mock 3 P1 Q3
The relative abundances of all the isotopes present in a sample of nickel are shown.
What is the relative atomic mass of nickel calculated from these data?
SJChO Mock 3 P1 Q2
The relative atomic mass of antimony, which consists of the isotopes 121Sb and 123Sb, is 121.8. What is the percentage of 123Sb in the isotopic mixture?
2019 RVHS J1 Common Test P1 Q2
If there are n molecules in 10 g of methane, CH4, how many molecules are in 55 g of carbon dioxide?
2023 SJChO P1 Q39
Which of the following statements about 20.3 g of Co2(SO4)3 is false? [Molar mass = 406 g mol−1]
2019 RVHS J1 Common Test P1 Q1
Which of the following quantities is equal to the Avogadro constant?
2021 EJC J2 Prelim P1 Q8
Which substances contain the same number of atoms?
1 1.20 mol of NH3
2 1.445 × 1024 molecules of O2
3 36.0 g of C6H12O6
4 57.6 dm3 of Cl2 at room temperature and pressure
2024 VS O Prelim P1 Q10
Complete combustion of a sample of a hydrocarbon, Y, gave 0.66 g of carbon dioxide and 0.36 g of water. What is the empirical formula of Y?
2020 YIJC J2 Prelim P1 Q20
A 2.0 g sample containing 0.0130 mol of an organoboron compound, with the formula CxHyBOz, was burnt in an excess of oxygen. 4.58 g of CO2 and 1.76 g of H2O were produced. What is the molecular formula of the organoboron compound?
2021 SAJC J2 Prelim P1 Q3
The empirical formula of an oxide of element X is X2O5. 106.5 g of X2O5 contains 60 g of oxygen. What is the identity of X?
2025 CHIJ O Prelim P1 Q12
Sodium hydrogencarbonate, NaHCO3, can be prepared from sodium sulfide, Na2S, by the following reactions.
Na2S(s) + CaCO3(s) → CaS(s) + Na2CO3(s)
Na2CO3(s) + H2O(l) + CO2(g) → 2NaHCO3(s)
Assuming that the percentage yield in each step is identical, 20.5 kg of sodium hydrogencarbonate (Mr = 84.0) was formed from 50 kg of sodium sulfide (Mr = 78.1). What is the percentage yield of each step?
2022 VJC J1 Promo P1 Q7
What is the volume of distilled water that must be added to 50 cm3 of 0.280 mol dm−3 KMnO4 to dilute it to 0.160 mol dm−3?
2022 AMSR Topical Revision Q10
Amedeo Avogadro discovered that equal volumes of gases at the same temperature and pressure contain the same number of molecules. Two closed containers, A and B, hold gases at the same temperature and pressure. The mass of gas A is equal to the mass of gas B, but gas A has a higher density than gas B. Which of the following statements is true?
2023 SJChO P1 Q42
Which graph is a correct representation of Boyle’s law?
SJChO Mock 3 P1 Q27
0.0353 g of a sample of volatile organic compound was completely vaporised at 50 kPa and 300 K. The vapour occupied a volume of 40 cm3. On complete combustion in excess oxygen, 80 cm3 of carbon dioxide and 80 cm3 of water vapour were formed. All gaseous volumes were measured under identical conditions. What would be the molecular formula of the compound? (R = 8.31 J K−1 mol−1)
2022 NJC J2 Prelim P1 Q4
In an experiment, 0.100 g of a volatile liquid Q formed 0.0250 dm3 of vapour at 100 °C and 1 bar. What is the relative molecular mass of Q?
2022 YIJC J2 Prelim P1 Q6
Deuterium, 2H, is an isotope of hydrogen. In an experiment, 18.0 g of gas A at 40 °C is found to occupy the same volume as 0.6 g of deuterium gas, 2H2, at 20 °C. The pressure of gas A is twice that of the deuterium gas. What is the relative molecular mass of gas A?
2024 VJC J2 Prelim P1 Q5
A 20 dm3 vessel contains 0.25 mol of ammonia gas and a 30 dm3 vessel contains 0.42 mol of hydrogen chloride gas. When the two vessels were connected at 500 K, the following reaction occurs: NH3(g) + HCl(g) → NH4Cl(s). What is the resultant pressure, in Pa, in the combined vessel? (R = 8.31 J K−1 mol−1)
2023 TJC J2 Prelim P1 Q8
An equimolar mixture of H2 and O2 was placed in a sealed, rigid container at room temperature. The total pressure inside the container is P Pa. The mixture was sparked, and H2 and O2 reacted until H2 was completely consumed. What is the partial pressure, in Pa, of O2 in the container after the reaction at room temperature?
2020 RI J1 Promo P1-P3 Q6
A gaseous sample containing x dm3 of gaseous methanol, CH3OH, was burnt in 4x dm3 of oxygen to produce carbon dioxide and water vapour. The total pressure in the system after combustion was P. Which statements are correct?
1 Methanol reacts with oxygen in a 2 : 3 mole ratio.
2 The partial pressure of carbon dioxide in the system is 0.18P.
3 Assuming these gases behave ideally, they occupy an insignificant volume.
2021 DHS J2 Prelim P1 Q5
F2(g) and Xe(g) are added to a container of fixed volume. The initial partial pressure of F2(g) is 7.0 atm and that of Xe(g) is 1.6 atm. When all of the Xe(g) has reacted with F2(g) to form a solid compound, C, the pressure of unreacted F2(g) is 3.8 atm. The temperature remained constant throughout. What is the formula of the solid compound C?
2022 Gaseous State Topical Revision Q12
Analysis of a mixture of sulfur-containing gases shows that hydrogen sulfide, H2S, and carbon disulfide, CS2, are present in a 2 : 1 mole ratio. The mixture is burned in excess oxygen, forming SO2, CO2 and H2O. Which row describes the SO2 : CO2 mole ratio after complete combustion, and the relative deviation from ideal behaviour of the gases CO2 and CS2?
| SO2 : CO2 mole ratio | relative deviation | |
|---|---|---|
| A | 3 : 1 | CS2 deviates more than CO2 |
| B | 4 : 1 | CS2 deviates more than CO2 |
| C | 3 : 1 | CO2 deviates more than CS2 |
| D | 4 : 1 | CO2 deviates more than CS2 |
2024 DHS J2 Prelim P1 Q3
