When boron trichloride, BCl3\text{BCl}_3BCl3, and ammonium chloride, NH4Cl\text{NH}_4\text{Cl}NH4Cl, are heated together, B-trichloroborazine, B3N3H3Cl3\text{B}_3\text{N}_3\text{H}_3\text{Cl}_3B3N3H3Cl3, is formed together with HCl\text{HCl}HCl gas.
B3N3H3Cl3\text{B}_3\text{N}_3\text{H}_3\text{Cl}_3B3N3H3Cl3 has a cyclic structure similar to the Kekulé structure of benzene.
Write a balanced equation for the reaction of BCl3\text{BCl}_3BCl3 and NH4Cl\text{NH}_4\text{Cl}NH4Cl to form B3N3H3Cl3\text{B}_3\text{N}_3\text{H}_3\text{Cl}_3B3N3H3Cl3.
Calculate the percentage by mass of boron, B\text{B}B, in B3N3H3Cl3\text{B}_3\text{N}_3\text{H}_3\text{Cl}_3B3N3H3Cl3. Give your answer to 2 decimal places. (Use relative atomic masses: Ar(B)=10.8A_r(\text{B}) = 10.8Ar(B)=10.8, Ar(N)=14.0A_r(\text{N}) = 14.0Ar(N)=14.0, Ar(H)=1.0A_r(\text{H}) = 1.0Ar(H)=1.0, Ar(Cl)=35.5A_r(\text{Cl}) = 35.5Ar(Cl)=35.5.)
Suggest one example of physical or chemical evidence that could show B3N3H3Cl3\text{B}_3\text{N}_3\text{H}_3\text{Cl}_3B3N3H3Cl3 has a Kekulé structure with localized double bonds rather than a fully delocalised structure.
In a molecule of B3N3H3Cl3\text{B}_3\text{N}_3\text{H}_3\text{Cl}_3B3N3H3Cl3, all the Cl\text{Cl}Cl atoms are bonded to B\text{B}B atoms, and all the H\text{H}H atoms are bonded to N\text{N}N atoms. Suggest a possible cyclic molecular structure for B3N3H3Cl3\text{B}_3\text{N}_3\text{H}_3\text{Cl}_3B3N3H3Cl3 showing all bonds.
199 exam-style questions on OCR A A Level Chemistry Atoms and reactions, covering Atomic structure and isotopes, Compounds, formulae and equations, Amount of substance, Acids, and Redox. Each one has a worked solution and a mark scheme showing where the marks go.