(a) Consider the following atoms: \(^R_T\)X; \(^S_T\)X. (i) State the phenomenon exhibited by the two atoms. (ii) What is the difference between the atoms? ...
Question 1 Report
(a) Consider the following atoms: \(^R_T\)X; \(^S_T\)X.
(i) State the phenomenon exhibited by the two atoms.
(ii) What is the difference between the atoms?
(iii) Give two examples of elements that exhibit the phenomenon stated in (ai)
(iv) lf T is 17, write the electron configuration of the element
(b)(i) State two differences between metals and-non-metals with respect to their:
I. physical properties;
2. chemical properties.
(ii) Give one example of each for the following compounds:
I. an amphoteric oxide;
II. a hydride which evolves hydrogen when reacted with water;
Ill. a trioxocarbonate (IV) salt which is readily decomposed on heating;
IV. a chloride salt which is readily hydrolyzed in water.
(c)(i) State three characteristic properties of transition metals.
(ii) Write the electron configuration of \(_{30}Zn\)
(iii.) Explain briefly why zinc is not considered as a typical transition element.
(d) Consider the reaction represented by the following equation:- Na\(_2\)CO\(_{3(aq)}\) + MgCl\(_{2(aq)}\) ----> 2NaCl\(_{(aq)}\) + MgCO\(_{3(aq)}\). Calculate the mass of sodium trioxocarbonate (IV) needed to produce 3.36 of magnesium trioxocarbonate (IV). [C = 12.0, O = 16.0, Na = 23.0, Mg = 24:0 ]
Answer Details
(a) The atoms \(^R_TX\) and \(^S_TX\) have the same atomic number T but different mass numbers R and S.
- (i) The phenomenon exhibited is isotopy (they are isotopes).
- (ii) The difference is that they have different numbers of neutrons (hence different mass numbers), while having the same number of protons.
- (iii) Two examples of elements exhibiting isotopy: chlorine (\(^{35}Cl\) and \(^{37}Cl\)) and carbon (\(^{12}C\) and \(^{14}C\)). (Hydrogen and oxygen are also acceptable.)
- (iv) If T = 17, the electron configuration is 2, 8, 7.
(b)(i) Metals compared with non-metals:
| Metals | Non-metals | |
|---|---|---|
| Physical | Shiny/lustrous, malleable and ductile, good conductors of heat and electricity, mostly solids with high melting points. | Dull, brittle (if solid), poor conductors (except graphite), many are gases or low-melting solids. |
| Chemical | Form basic oxides; are electropositive, lose electrons to form positive ions (reducing agents). | Form acidic oxides; are electronegative, gain electrons to form negative ions (oxidizing agents). |
(ii) Examples:
- I. Amphoteric oxide: zinc oxide, \(ZnO\) (or \(Al_2O_3\), PbO).
- II. Hydride evolving hydrogen with water: sodium hydride, \(NaH\) (\(NaH + H_2O \rightarrow NaOH + H_2\)).
- III. Trioxocarbonate(IV) salt readily decomposed on heating: copper(II) trioxocarbonate(IV), \(CuCO_3\) (or \(ZnCO_3\)).
- IV. Chloride salt readily hydrolysed in water: aluminium chloride, \(AlCl_3\) (or \(FeCl_3\)).
(c)(i) Three characteristic properties of transition metals: they show variable oxidation states, form coloured ions/compounds, and act as catalysts (they also form complex ions).
(ii) Electron configuration of \(_{30}Zn\): 2, 8, 18, 2 (\(1s^2\,2s^2\,2p^6\,3s^2\,3p^6\,3d^{10}\,4s^2\)).
(iii) Zinc is not regarded as a typical transition element because its 3d subshell is completely filled (3d^{10}); it shows only one oxidation state (+2) and forms mainly white/colourless compounds, so it lacks the characteristic transition-metal properties.
(d) \(Na_2CO_3 + MgCl_2 \rightarrow 2NaCl + MgCO_3\). To produce 3.36 g of \(MgCO_3\):
Molar mass of \(MgCO_3 = 24 + 12 + (3 \times 16) = 84\,g\,mol^{-1}\)
\[\text{moles of } MgCO_3 = \frac{3.36}{84} = 0.04\,mol\]
From the equation, 1 mole \(Na_2CO_3\) gives 1 mole \(MgCO_3\), so moles of \(Na_2CO_3 = 0.04\,mol\).
Molar mass of \(Na_2CO_3 = (2 \times 23) + 12 + (3 \times 16) = 106\,g\,mol^{-1}\)
\[\text{mass of } Na_2CO_3 = 0.04 \times 106 = 4.24\,g\]
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