Mass spectrometry

Which molecule does not produce a mass spectrum containing a peak at m / z = 29?

This question is about spectra.

The mass spectrum for Br₂ has peaks at m/z values of 79, 81, 158, 160 and 162. The peaks at m / z 79 and 81 have virtually the same relative abundance.

Complete the table to show the number of protons, neutrons and electrons in the particles that cause the peaks at m/z 79 and 81.

Explain why there are peaks with m / z values of 158, 160 and 162 and predict their relative abundances.

Explanation........

Relative abundances........

This question looks at proton NMR spectra of dibromoalkanes.

These questions are from different areas of chemistry.

Ammonia, NH₃, and ammonium nitrate, NH₄NO₃, are compounds of nitrogen.

The boiling point of NH₃ is –33 °C.

The boiling point of NH₄NO₃ is 210 °C.

Explain why there is a large difference in boiling points.

Two students discuss the oxidation numbers in ammonium nitrate, NH₄NO₃.

One student claims that the two nitrogen atoms have the same oxidation number. The other student disagrees and claims that the nitrogen atoms have different oxidation numbers.

Explain with reasons which student is correct.

What are the percentage compositions of copper and zinc in the brass sample?

Calculate the relative atomic mass of zinc in the sample of brass.

Give your answer to 2 decimal places.

Fill in the table to predict the splitting patterns in the proton NMR spectrum of the

The table shows the chemical shifts for the peaks in the proton NMR spectrum at proton environments 2 and 3.

Proton environment	2	3
Chemical shift,	2.5 ppm	3.6 ppm

Suggest why the peaks for proton environments 2 and 3 have the chemical shifts which are shown in the table.

Glycine, H₂NCH₂COOH, is an -amino acid.

Glycine reacts with NaOH to form the salt H₂NCH₂COONa.

Glycine reacts with HCl to form the salt HOOCCH₂NH₃Cl.

The salts have different H–N–H bond angles.

State the different H–N–H bond angles and explain why they are different.

H₂NCH₂COONa H–N–H bond angle =........ °

HOOCCH₂NH₃Cl H–N–H bond angle =........ °

Glycine reacts with aqueous copper(II) ethanoate to form copper(II) glycinate, Cu(H₂NCH₂COO)₂, and ethanoic acid. Copper(II) glycinate is a complex which exists as two square planar isomers.

Write an equation for this reaction and draw the structures of the two square planar isomers of the complex Cu(H₂NCH₂COO)₂.

equation

Which peak would be in the mass spectrum of propanal, CH₃CH₂CHO, but not in the mass spectrum of propanone, CH₃COCH₃?

A m / z = 15

B m / z = 29

C m / z = 43

D m / z = 58

Sir Humphry Davy discovered several elements including sodium, potassium, magnesium, calcium and strontium.

Explain which block in the Periodic Table sodium and magnesium belong to.

A sample of magnesium, A_r= 24.305, is found to consist of three isotopes. The accurate relative isotopic masses and % abundances of two of the isotopes are shown in the table.

Determine the relative isotopic mass of the third isotope of magnesium in the sample.

Give your answer to 5 significant figures.

A student adds an excess of calcium oxide to water in a test tube. In a separate test tube, the student adds an excess of strontium oxide to water.

Write the equation for the reaction of calcium oxide with water.

State symbols are not required.

Suggest the approximate pH of the two solutions formed in the test tubes.

pH with calcium oxide........

pH with strontium oxide........

The table below shows enthalpy changes involving potassium, oxygen and potassium oxide,

The incomplete Born–Haber cycle below can be used to determine the lattice enthalpy of potassium oxide.

In the boxes, complete the species present in the cycle. Include state symbols for the species.

Calculate the lattice enthalpy of potassium oxide.

lattice enthalpy =........ kJ mol⁻¹

A similar Born–Haber cycle to potassium oxide in (d) can be constructed for sodium oxide.

The first ionisation energy of sodium is more endothermic than that of potassium.

Explain why.

The lattice enthalpy of sodium oxide is more exothermic than that of potassium oxide.

Explain why.

This question is about esters.

The structure of ester A is shown below.

What is the systematic name of ester A ?

Name the type of reactions of ester A shown in (ii).

A polyester is formed from 200 molecules of 4-hydroxybenzoic acid.

What is the relative molecular mass, M_r, of the polyester?

M_r =........ g mol⁻¹

* A student intends to synthesise ester C.

Plan a two-stage synthesis to prepare 12.75 g of ester C starting from 2-methylpropanal, (CH₃)₂CHCHO. Assume the overall percentage yield of ester C from 2-methylpropanal is 40%.

In your answer include the mass of 2-methylpropanal required, reagents, conditions and equations where appropriate.

Purification details are not required.

A sample of boron contains the isotopes¹⁰B and¹¹B. The relative atomic mass of the boron sample is 10.8.

What is the percentage of¹¹B atoms in the sample of boron?

A 8.0%

B 20%

C 80%

D 92%

Your answer

The mass spectrum of (CH₃)₂CHCH₂OH is shown below.

Which ion is responsible for the peak with the greatest relative intensity?

A CHCH₂OH⁺

B CH₃CH₂CH⁺

C (CH₃)₂CH⁺

D CH₃CO⁺