Chemistry 9701 · AS & A Level · The Periodic Table: chemical periodicity

The Periodic Table: chemical periodicity — practice question

Magnesium, Mg, proton number 12, is a metal that is used in many strong and lightweight alloys. It occurs naturally as several isotopes.
(a)[2]

State what the term isotope means.

(b)[2]

Fill in the table for two magnesium isotopes, $^{24}\text{Mg}$ and $^{26}\text{Mg}$, by stating the number of protons, neutrons and electrons in each.

(c)[2]

A magnesium sample contained these isotopes: $^{24}\text{Mg}$, $78.60\%$; $^{25}\text{Mg}$, $10.11\%$; $^{26}\text{Mg}$, $11.29\%$. Calculate the relative atomic mass, $A_r$, of magnesium in this sample. Give your answer to an appropriate number of significant figures.

(d)[1]

Construct a balanced equation for the reaction of magnesium with chlorine.

(e(i))

When a $2.45\,\text{g}$ sample of antimony was heated in chlorine under suitable conditions, $4.57\,\text{g}$ of a chloride A were formed. Calculate the amount, in moles, of antimony atoms that reacted.

(e(ii))

Calculate the amount, in moles, of chlorine atoms that reacted.

(e(iii))

Use your answers to (i) and (ii) to find the empirical formula of A.

(e(iv))[5]

The empirical and molecular formula of A are the same. Construct a balanced equation for the reaction between antimony and chlorine.

(f(i))

Chloride A melts at $73.4\,^{\circ}\text{C}$, whereas magnesium chloride melts at $714\,^{\circ}\text{C}$. What type of bonding is present in magnesium chloride?

(f(ii))[2]

Suggest what type of bonding is present in A.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: Atoms of one element that have the same proton (atomic) number / the same number of protons

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