$$$6 \quad \mathbf{P}, \mathbf{Q}$$$ and $$$\mathbf{R}$$$ are three different hydrocarbon molecules. The mass spectrum of hydrocarbon $$$\mathbf{R}$$$ is recorded. Information about the two peaks with $$$m / e$$$ greater than 135 is shown in Fig. 6.1. (i) Use Fig. 6.1 to deduce the number of carbon atoms in a molecule of $$$\mathbf{R}$$$. Show your working. number of carbon atoms = .......................... (ii) Use Fig. 6.1 and your answer to (c)(i) to deduce the molecular formula of $$$\mathbf{R}$$$. (iii) Suggest the molecular formula of the fragment of $$$\mathbf{R}$$$ with $$$m / e=57$$$.

Chemistry

IGCSE&ALevel

CAIE

Exam No：9701_s25_qp_24 Year：2025 Question No：(c)

Answer:

22.2.1 analyse mass spectra in terms of m/e values and isotopic abundances (knowledge of the working of the mass spectrometer is not required)

22.2.2 calculate the relative atomic mass of an element given the relative abundances of its isotopes, or its mass spectrum

22.2.3 deduce the molecular mass of an organic molecule from the molecular ion peak in a mass spectrum

22.2.4 suggest the identity of molecules formed by simple fragmentation in a given mass spectrum

22.2.5 deduce the number of carbon atoms, n, in a compound using the M +1 peak and the formula

22.2.6 deduce the presence of bromine and chlorine atoms in a compound using the M +2 peak