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Sulfur, S, and polonium, Po, are both elements in Group VI of the Periodic Table.
Sulfur has three isotopes.
(a) Explain the meaning of the term isotope.
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(b) A sample of sulfur has the following isotopic composition by mass.
| isotope mass | 32 | 33 | 34 |
|---|---|---|---|
| % by mass | 95.00 | 0.77 | 4.23 |
Calculate the relative atomic mass, $A_r$, of sulfur to two decimal places.
$A_r = \text{................}$ [2]
(c) Isotopes of polonium, proton number 84, are produced by the radioactive decay of several elements including thorium, Th, proton number 90.
The isotope $^{213}_{84}\text{Po}$ is produced from the thorium isotope $^{232}_{90}\text{Th}$.
Complete the table below to show the atomic structures of the isotopes $^{213}_{84}\text{Po}$ and $^{232}_{90}\text{Th}$.
| isotope | number of protons | number of neutrons | number of electrons |
|---|---|---|---|
| $^{213}_{84}\text{Po}$ | |||
| $^{232}_{90}\text{Th}$ |
Radiochemical reactions, such as nuclear fission and radioactive decay of isotopes, can be represented by equations in which the nucleon (mass) numbers must balance and the proton numbers must also balance.
For example, the nuclear fission of uranium-235, $^{235}_{92}\text{U}$, by collision with a neutron, $^{1}_{0}\text{n}$, produces strontium-90, xenon-143 and three neutrons.
$$^{235}_{92}\text{U} + ^{1}_{0}\text{n} \rightarrow ^{90}_{38}\text{Sr} + ^{143}_{54}\text{Xe} + 3 ^{1}_{0}\text{n}$$
In this equation, the nucleon (mass) numbers balance because: $235 + 1 = 90 + 143 + (3 \times 1)$.
The proton numbers also balance because: $92 + 0 = 38 + 54 + (3 \times 0)$.
(d) In the first stage of the radioactive decay of $^{232}_{90}\text{Th}$, the products are an isotope of element $E$ and an alpha-particle, $^{4}_{2}\text{He}$.
(i) By considering nucleon and proton numbers only, construct a balanced equation for the formation of the isotope of $E$ in this reaction.
$^{232}_{90}\text{Th} \rightarrow \text{................} + ^{4}_{2}\text{He}$
Show clearly the nucleon number and proton number of the isotope of $E$.
nucleon number of the isotope of $E$ ..........
proton number of the isotope of $E$ ..........
(ii) Hence state the symbol of the element $E$.
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563
511
569
When 0.42 g of a gaseous hydrocarbon \(A\) is slowly passed over a large quantity of heated copper(II) oxide, \(CuO\), \(A\) is completely oxidised.
The products are collected and it is found that 1.32 g of \(CO_2\) and 0.54 g of \(H_2O\) are formed. Copper is the only other product of the reaction.
(a) (i) Calculate the mass of carbon present in 1.32 g of \(CO_2\).
Use this value to calculate the amount, in moles, of carbon atoms present in 0.42 g of \(A\).
(ii) Calculate the mass of hydrogen present in 0.54 g of \(H_2O\).
Use this value to calculate the amount, in moles, of hydrogen atoms present in 0.42 g of \(A\).
(iii) It is thought that \(A\) is an alkene rather than an alkane.
Use your answers to (i) and (ii) to deduce whether this is correct.
Explain your answer.
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(b) Analysis of another organic compound, \(B\), gave the following composition by mass: \(C,\ 64.86\%\); \(H,\ 13.50\%\); \(O,\ 21.64\%\).
(i) Use these values to calculate the empirical formula of \(B\).
(ii) The empirical and molecular formulae of \(B\) are the same.
\(B\) is found to be chiral.
Draw displayed formulae of the two optical isomers of this compound, indicating with an asterisk (*) the chiral carbon atom.
(iii) There are three other structural isomers of \(B\) which are not chiral but which contain the same functional group as \(B\).
In the boxes below, draw the structural formulae of these isomers.
538
507
534
(a) Give the equation, including state symbols, for the first ionisation energy of carbon.
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(b) (i) Explain why sodium has a lower first ionisation energy than magnesium.
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(ii) Explain why magnesium has a higher first ionisation energy than aluminium.
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(iii) Explain why helium, He, and neon, Ne, occupy the two highest positions on the diagram.
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(iv) Explain why the first ionisation energy of argon, Ar, is lower than that of neon, which is lower than that of helium.
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(c) (i) The first ionisation energies of the elements Na to Ar show a variation. Some physical properties show similar variations.
The atomic radius of the elements decreases from Na to Cl.
Give a brief explanation of this variation.
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(ii) The cations formed by the elements Na to Al are smaller than the corresponding atoms.
Give a brief explanation of this change.
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(d) The oxides of the elements of the third Period behave differently with NaOH(aq) and HCl(aq). In some cases, no reaction occurs.
Complete the table below by writing a balanced equation for any reaction that occurs, with heating if necessary. If you think no reaction takes place write 'no reaction'.
You do not need to include state symbols in your answers.
[Table_1]
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574
503
566
(a)
(i) What is the empirical formula of compound T?
...................
(ii) Draw the skeletal formula of compound S.
(b)
(i) Compounds S and U are isomers.
What type of isomerism do they show?
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(ii) Two of the six formulae P – U can each be drawn in two forms which are known as stereoisomers.
Which two compounds have formulae that can be drawn in two forms?
What type of stereoisomerism does each show?
Identify each compound by its letter.
[Table_1]
compound type of stereoisomerism
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(c) Compound S can be converted into compound R.
(i) What type of reaction is this?
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(ii) What reagent would you use for this reaction?
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(iii) Write the structural formula of the compound formed when T undergoes the same reaction using an excess of the reagent you have used in (c)(ii).
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(d) Compound P may be converted into compound Q in a two-step reaction.
$$
\begin{align*}
\text{CH}_3\text{CH} = \text{CHCH}_2\text{CH}_3 & \xrightarrow{\text{step 1}} \text{intermediate} \xrightarrow{\text{step 2}} \text{CH}_3\text{CH}_2\text{COCH}_2\text{CH}_3 \\
\text{P} & \hspace{3em} \text{Q}
\end{align*}
$$
(i) What is the structural formula of the intermediate compound formed in this sequence?
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(ii) Outline how step 1 may be carried out to give this intermediate compound.
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(iii) What reagent would be used for step 2?
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596
542
551
Each of the three organic compounds, $V$, $W$, and $X$, has the empirical formula $CH_2O$. The number of carbon atoms in each of their molecules is shown in the table.
[Table_1]
V gives a brick red precipitate when warmed with Fehling's reagent; $W$ and $X$ do not.
$W$ is a fruity smelling liquid.
In $X$, the carbon atoms are bonded directly to one another.
$X$ gives an effervescence when shaken with $Na_2CO_3(aq)$; $V$ and $W$ do not.
(a) Give the structural formula of $V$.
[1]
(b) (i) What functional group is present in $W$?
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(ii) Give the structural formula of $W$.
[2]
(c) When $X$ is heated under reflux with acidified $K_2Cr_2O_7$, the product, $Y$, gives no reaction with 2,4-dinitrophenylhydrazine reagent.
(i) Give the structural formula of $X$.
(ii) Give the structural formula of $Y$, the compound formed from $X$.
[2]
(d) When $X$ is warmed with a little concentrated sulfuric acid, a small amount of a cyclic compound, $Z$, is formed.
$Z$ has the molecular formula $C_6H_8O_4$.
(i) Suggest a displayed formula for $Z$.
(ii) What type of reaction occurs when $Z$ is formed from $X$?
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[2]
590
578
554
