The index of hydrogen deficiency is a measure of the 'double bond equivalents' in a molecule.

Any ring counts as 1, as does a double bond. So a benzene ring counts as four, that is three double bonds and a ring!

Therefore the correct answer is 6.

That is five double bonds and one ring.

The equation can be used (but it is easier just to count the rings and double bonds) where the letters represent the appropriate elements and X represents any halogen (oxygen can be ignored): (Aspirin C₉H₈O₄)

\(IHD = (C+1)-{(H-N+X) \over 2}\)

IHD = (9+1) – (8–0+0)/2 = 10 – 4 = 6

¹H-NMR spectroscopy would be effective because ethanol and ethanal have different numbers of hydrogens in different environments; (3:2:1) and (3:1) respectively.

Infrared (IR) spectroscopy would be effective because the O−H bond in ethanol would give a different band in the spectrum to the C=O bond in ethanal.

Mass spectrometry would be effective because ethanol and ethanal have different molecular masses (and different fragmentation patterns).

1, 2 and 3 is therefore the correct answer.

If we are processing an uncertainty by addition or subtraction we should add the absolute/raw uncertainties.

0.3+0.2=0.5

Therefore the correct answer is 25.0±0.5

To process uncertainties the absolute uncertainties should be converted to % uncertainties and then added together:

(Percentage uncertainty = absolute uncertainty / measurement value × 100%)

0.2/20.0 × 100 is 1% and 2/10 × 100 is 20%

Thus the correct answer is 21 %.

Bond vibrations can be identified by infrared (IR) spectroscopy.

Infrared (IR) is therefore the correct answer.

When recording an uncertainty in chemistry, we tend to record the raw uncertainty to one significant figure, and to the smallest increment of the measurement.

Therefore the correct answer is 7.00±0.01

¹H-NMR spectroscopy summary (Core):

Peaks: The number of peaks tells us the number of different hydrogen environments.

Ratio: The integration trace or whole number written adjacent to each peak tells us the ratio of the number of hydrogens in each environment.

Shift: The chemical shift table (data book) can help us with the types of hydrogens (functional groups etc.) in the molecule.

(Knowledge of spin-spin splitting is also required at HL)

Therefore The total number of hydrogen environments is the correct answer. Since ¹H-NMR will not always tell us the total number of hydrogen atoms in a molecule (as sometimes we are just given the ratio).

(The bonds present in a molecule can be ascertained through IR spectroscopy, and molecular mass through mass spectrometry.)

The compound 2-methylbutane is (CH₃)₂CHCH₂CH₃ (3D image below). The hydrogens in the two CH₃ groups to the left are equivalent, so form one environment. The hydrogens in the CH, CH₂ and the CH₃ group on the right all contain hydrogens which are in different environments, that is another three environments.

Therefore there are 4 different hydrogen environments in total, and the ratio of areas under each signal will be 6 : 1 : 2 : 3.

6 : 1 : 2 : 3 is therefore the correct answer.

The compound 3-methylbutan-1-ol is shown in 3D below. The hydrogens in the two CH₃ groups to the right are equivalent, so form one environment. The hydrogens in the CH, CH₂, CH_2, and OH groups, moving left across the image, all contain hydrogens which are in different environments; that is another four environments.

Therefore there are 5 different hydrogen environments in total.

5 is the correct answer.

It is conventional in chemistry to quote raw uncertainties to the same precision (decimal places) as the reading, and to one decimal place.

Thus 12.25cm³ is the correct answer as it is the only answer given to two decimal places.