NEB Class 11 · Past paper
The official NEB Class 11 model questions for Chemistry, all 45 questions with solved model answers.
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Why is oxalic acid described as a primary standard while sodium hydroxide is not?
A primary standard is a substance pure enough and stable enough that a weighed mass of it fixes the concentration of its solution exactly. Oxalic acid crystallises as the dihydrate, which is stable in air: it does not lose its water of c...
What is meant by a concordant reading, and why do you average only the concordant values?
Readings are concordant when two or, better, three successive titre values agree with one another within about 0.1 cm3. They show that you have repeated the same measurement with the same technique and reached the same end point each time, so the result is reproducible and the mean of those values is the best estimate of the true titre. The first titration is deliberately a rough one: you do not yet know where the end point lies, so you run the acid in quickly and overshoot slightly. Including that value in the mean would drag the answer away from the true titre. For the same reason a titration that clearly overshot, such as one where methyl orange went a full red, is rejected and repeated rather than averaged in.
Why is phenolphthalein used in the oxalic acid against sodium hydroxide titration, but methyl orange in the sodium carbonate against hydrochloric acid titration?
The indicator must change colour over the pH range in which the solution actually finds itself at the equivalence point. Oxalic acid is a weak acid and sodium hydroxide a strong base, so the salt formed, sodium oxalate, hydrolyses slight...
Why must a burette and a pipette be rinsed with the solution they are to hold, while the conical flask may be left wet with distilled water?
A burette and a pipette measure the volume of a solution of known concentration, so anything left inside them changes that concentration. Distilled water clinging to the walls would dilute the first portion delivered and the titre would ...
Define normality and equivalent mass, and give the equivalent masses of crystalline oxalic acid and anhydrous sodium carbonate.
Normality is the number of gram equivalents of solute dissolved in one litre of solution. Equivalent mass is the mass of the substance that combines with or replaces one mole of hydrogen ions, and for an acid or a base it is the molar mass divided by its basicity or acidity. Crystalline oxalic acid has a molar mass of 126 g per mole and is dibasic, so its equivalent mass is 126 divided by 2, which is 63, and a 0.1 N solution contains 6.3 g per litre. Anhydrous sodium carbonate has a molar mass of 106 g per mole and accepts two hydrogen ions in complete neutralisation, so its equivalent mass is 53 and a 0.1 N solution contains 5.3 g per litre. At the end point of any titration $N_1 V_1 = N_2 V_2$.
How do you confirm that a salt contains the carbonate radical, and why does the lime water clear again if you keep passing the gas?
Treat a little of the dry salt with dilute hydrochloric acid. A carbonate gives a brisk effervescence of a colourless, odourless gas, and when that gas is passed into freshly prepared lime water the solution turns milky because insoluble...
Describe the brown ring test for a nitrate, and explain why the concentrated sulphuric acid is added down the side of the tube.
Mix the salt solution with a freshly prepared saturated solution of ferrous sulphate in a test tube, then tilt the tube and run concentrated sulphuric acid slowly down the inner wall so that it sinks and forms a separate lower layer. A d...
Why is the barium chloride test for a sulphate carried out only after the solution has been acidified with dilute hydrochloric acid?
Barium gives a white precipitate not only with sulphate but also with carbonate, sulphite and phosphate, so an unacidified solution could show a white precipitate that has nothing to do with sulphate. Barium carbonate, sulphite and phosp...
Why is solid ammonium chloride added before ammonium hydroxide when precipitating the third group?
Ammonium hydroxide is a weak base and only partly ionised. Adding ammonium chloride supplies a large concentration of ammonium ions, and by the common ion effect this suppresses the ionisation of the ammonium hydroxide still further, so the hydroxide ion concentration in the solution is kept low. Only the hydroxides with the very smallest solubility products, those of aluminium and of iron in the ferric state, are then precipitated. If the hydroxide ion concentration were allowed to rise, the hydroxides of the fourth group cations such as zinc and manganese, and of magnesium in the sixth group, would come down at the same time and the separation would be lost. The ammonium chloride also converts any ferrous iron present, once oxidised, into a form that precipitates cleanly as the reddish brown ferric hydroxide.
Why is hydrogen sulphide passed through an acidic solution for the second group but through an ammoniacal solution for the fourth?
Hydrogen sulphide is a weak acid, so the sulphide ion concentration in its solution depends strongly on the pH. In the presence of dilute hydrochloric acid the excess hydrogen ions suppress its ionisation and the sulphide ion concentrati...
Why is the melting point of an organic solid determined in a liquid bath rather than by heating the capillary directly, and what does a wide melting range tell you?
A flame heats unevenly and far too quickly. The capillary would reach a much higher temperature than the thermometer bulb registers, the reading would be too high, and the sample might char instead of melting cleanly. A bath of liquid pa...
Why is the last drop never blown out of a pipette, and why should volumetric glassware never be dried by heating?
A bulb pipette is calibrated to deliver its stated volume, and that calibration already allows for the thin film of liquid which stays behind on the glass and for the drop which remains in the jet after free delivery has stopped. Blowing...
Which of the following contains maximum number of molecules and why? i) 0.5 g of H2 or 5 litres of N2 at STP ii) 15 litres of H2 at STP or 10 g of O2
By Avogadro, more moles means more molecules. (i) $$ \begin{aligned} n{\ce{H2}} &= \dfrac{0.5}{2} \ &= 0.25\ \text{mol} \ n{\ce{N2}} &= \dfrac{5}{22.4} \ &= 0.223\ \text{mol} \end{aligned} $$ Since $0.250.223$, 0.5 g of $\ce{H2}$ cont...
State the law of conservation of mass.
Law of conservation of mass: In any chemical reaction, matter is neither created nor destroyed; the total mass of the reactants equals the total mass of the products.
For example, in
$$ \ce{2H2(g) + O2(g) -> 2H2O(l)} $$
, $4\ \text{g}$ of $\ce{H2}$ plus $32\ \text{g}$ of $\ce{O2}$ give exactly $36\ \text{g}$ of water.
Why does the boiling point of a liquid remain constant even though the heating is continued?
At the boiling point, the heat supplied is not used to raise the temperature but is absorbed as the latent heat of vaporisation. This energy is spent breaking the intermolecular forces that hold molecules in the liquid state, converting ...
Write down the dimensional characteristics and an example of the cubic crystal system.
Cubic crystal system: all three edges are equal and all interfacial angles are right angles. - Axial lengths: $a=b=c$ - Axial angles: $\alpha=\beta=\gamma=90^\circ$ Example: sodium chloride ($\ce{NaCl}$) (others: $\ce{KCl}$, diamond,
State Hund's rule of maximum multiplicity.
Hund's rule of maximum multiplicity: When electrons are filled into a set of orbitals of equal energy (degenerate orbitals, e.g. the three $p$ orbitals), every orbital is singly occupied with electrons of parallel spin first, and pairing...
Write down the values of quantum numbers n, l, m and s for the 11th electron of sodium (Na).
Sodium ($Z=11$) has the configuration $\ce{1s^2 2s^2 2p^6 3s^1}$. The 11th electron is the $3s^1$ electron. - Principal, $n=3$ - Azimuthal, $l=0$ (for an $s$ orbital) - Magnetic, $m=0$ - Spin, $s=+\dfrac{1}{2}$
What is meant by a nuclear fusion reaction? Give one important application.
Nuclear fusion: the process in which two light nuclei combine (fuse) to form a heavier nucleus, with the release of a very large amount of energy. $$\ce{^21H + ^31H - ^42He + ^10n} + \text{energy}$$ Application: it is the source of energ...
Write down the Lewis structure of i) HNO3 ii) O3
(i) $\ce{HNO3}$: the H is bonded to one O, which is bonded to N. Nitrogen is doubly bonded to a second O and singly bonded (coordinate) to a third O. Skeleton: $\ce{H-O-N(=O)-O}$ where one N-O is a coordinate bond; N carries no lone pair...
Distinguish between polar and non-polar covalent bonds, giving an example of each.
Polar covalent bond: a covalent bond between two atoms of different electronegativity, so the shared pair is unequally shared and the bond develops partial charges ($\delta+$ and $\delta-$). Example: $\ce{H-Cl}$. Non-polar covalent bond:...
What are s-block elements? Write an important feature of such elements.
s-block elements: elements in which the last (differentiating) electron enters the outermost $s$ orbital. These are the Group IA (alkali metals) and Group IIA (alkaline earth metals), with general valence configuration $ns^{1}$ or $ns^{2}$.
Important feature: they are highly reactive, soft, electropositive metals with low ionisation energy; they readily lose their valence electron(s) to form ionic compounds and are strong reducing agents.
Calculate the oxidation number of i) N in Zn(NO3)2 ii) P in H3PO2
(i) N in $\ce{Zn(NO3)2}$: $\ce{Zn}$ is $+2$, each $\ce{O}$ is $-2$. For one $\ce{NO3-}$: $$ \begin{aligned} x + 3(-2) &= -1 \ &\Rightarrow x = +5 \end{aligned} $$ N $= +5$. (ii) P in $\ce{H3PO2}$: $$ \begin{aligned} 3(+1) + x + 2(-2) &=...
Mention the most favourable conditions for the better yield of the product SO3 in the equilibrium: 2SO2(g) + O2(g) <=> 2SO3(g) + 47 K.cal
$$\ce{2SO2(g) + O2(g) <= 2SO3(g)} \quad \Delta H = -47\ \text{kcal}$$ By Le-Chatelier's principle, the yield of $\ce{SO3}$ is favoured by: - High pressure: the forward reaction reduces gas moles ($3 \to 2$), so high pressure shifts equil...
Write down the chemical reaction for the preparation of ozone from oxygen. What happens when ozone is treated with mercury?
Preparation of ozone (silent electric discharge through cold, dry oxygen in an ozoniser): $$\ce{3O2 -[silent\ electric\ discharge] 2O3}$$ With mercury: ozone oxidises mercury to mercurous oxide. The mercury loses its bright meniscus and ...
Name the isotopes of hydrogen. Which isotope is the least abundant on the earth? Write its one application.
Isotopes of hydrogen: protium $\ce{^11H}$, deuterium $\ce{^21H}$ and tritium $\ce{^31H}$. Least abundant: tritium ($\ce{^31H}$), which is radioactive and present only in traces. Application: tritium is used as fuel in nuclear fusion reac...
Define the terms i) phosphorescence ii) photochemical smog.
(i) Phosphorescence: the property by which a substance absorbs light (or radiation) and continues to re-emit light for some time even after the exciting source is removed (delayed glow), e.g. $\ce{ZnS}$. (ii) Photochemical smog: a browni...
What happens when carbon monoxide is i) passed over heated caustic soda ii) treated with chlorine in presence of sunlight.
(i) With heated caustic soda (under pressure), CO forms sodium formate: $$\ce{CO + NaOH -[200,^\circ C][pressure] HCOONa}$$ (ii) With chlorine in sunlight, CO forms the poisonous gas phosgene (carbonyl chloride): $$\ce{CO + Cl2 -[sunlig...
Name any four metals and their areas which are found in Nepal.
Four metals (as their ores/deposits) found in Nepal and their areas: Metal Area (deposit) ------ Iron Phulchoki (Lalitpur), Those (Ramechhap) Copper Wapsa (Solukhumbu), Ilam Zinc / Lead Ganesh Himal (Rasuwa) Cobalt / Nickel Kalitar (Makw...
Give reasons: why is sodium metal i) a very good reducing agent ii) kept in kerosene.
(i) Good reducing agent: sodium has a very low ionisation energy and low electrode potential, so it loses its single $3s^1$ electron very easily ($\ce{Na - Na+ + e-}$). By readily donating electrons it reduces other species, so it is a s...
Write down the IUPAC names of the following compounds: i) CH3OCH2-CH2-OCH3 ii) CH3-CH2CONH2
(i) $\ce{CH3-O-CH2-CH2-O-CH3}$ is 1,2-dimethoxyethane (an ethane chain bearing two $\ce{-OCH3}$ groups). (ii) $\ce{CH3-CH2-CONH2}$ is propanamide (a three-carbon chain with a $\ce{-CONH2}$ amide group).
Write down the functional isomer and the IUPAC name of each of the following: i) CH3-CH2-OH ii) CH3-CO-CH3
(i) $\ce{CH3-CH2-OH}$ (ethanol, an alcohol). Its functional isomer is the ether $\ce{CH3-O-CH3}$, IUPAC name methoxymethane. (ii) $\ce{CH3-CO-CH3}$ (propanone, a ketone). Its functional isomer is the aldehyde $\ce{CH3-CH2-CHO}$, IUPAC na...
What do you mean by an anti-knocking agent? Give one example of a common anti-knocking agent.
Anti-knocking agent: a substance added in small amounts to petrol (gasoline) to reduce knocking (the premature, irregular explosion of the fuel-air mixture in the engine), thereby raising the octane number and giving smoother combustion....
Write an example of i) Wurtz reaction ii) Baeyer's test.
(i) Wurtz reaction (alkyl halide + sodium in dry ether gives a higher alkane): $$\ce{2CH3Cl + 2Na -[dry\ ether] CH3-CH3 + 2NaCl}$$ (ii) Baeyer's test (test for unsaturation; cold dilute alkaline $\ce{KMnO4}$ is decolourised by an alkene,...
How is ethyne prepared in the laboratory? Suggest a chemical reaction to convert ethyne into ethene.
Laboratory preparation of ethyne (acetylene): water is dropped onto calcium carbide in a flask; ethyne gas is evolved and collected over water. $$\ce{CaC2(s) + 2H2O(l) - Ca(OH)2(aq) + C2H2(g)}$$ (The carbide is made industrially by heati...
Define oxidation and balance the following redox reaction by oxidation number or ion-electron method: I2 + HNO3 -> HIO3 + H2O + NO2
Oxidation: a process involving loss of electrons, or an increase in oxidation number of an element.
Balancing (oxidation-number method):
To balance electrons, 10 N atoms are needed per $\ce{I2}$:
$$\ce{I2 + 10HNO3 -> 2HIO3 + 10NO2 + 4H2O}$$
Check: H $10=2+8$; N $10=10$; O $30 = 6+20+4$. Balanced.
How is bromine manufactured from carnallite? Give a reaction to show bromine is an oxidising agent.
Manufacture from carnallite ($\ce{KCl.MgCl2.6H2O}$, which carries bromides): after the carnallite is worked for potassium salts, the residual mother liquor (bittern) is rich in $\ce{MgBr2}$. It is acidified and warmed, and chlorine gas i...
Give a chemical reaction for the preparation of bleaching powder. What happens when bleaching powder is treated with i) excess dilute H2SO4 ii) ammonia? Write down the bleaching action of bleaching powder.
Preparation (slaked lime + chlorine at about $40,^\circ\text{C}$): $$\ce{Ca(OH)2 + Cl2 - CaOCl2 + H2O}$$ (i) With excess dilute $\ce{H2SO4}$ (chlorine is liberated): $$\ce{CaOCl2 + H2SO4 - CaSO4 + H2O + Cl2(g)}$$ (ii) With ammonia (nitr...
Describe the laboratory method for the preparation of sulphur dioxide gas. Give a reaction to show SO2 contains sulphur.
Laboratory preparation of $\ce{SO2}$: warm copper turnings with hot concentrated sulphuric acid (or add dilute acid to a sulphite). $\ce{SO2}$ is a colourless, pungent gas collected by upward displacement of air: $$\ce{Cu + 2H2SO4(conc) ...
What are the conclusions made from Rutherford's alpha-ray scattering experiment? Point out its one major limitation.
Conclusions of Rutherford's $\alpha$-scattering experiment: 1. Most of the atom is empty space (most $\alpha$ particles passed straight through). 2. There is a small, dense, positively charged nucleus at the centre (a few particles were ...
7.4 g of Ca(OH)2 is treated with 9.7 g of NH4Cl for the reaction Ca(OH)2 + 2NH4Cl -> CaCl2 + 2NH3 + 2H2O. i) Which is the limiting reactant? ii) What mass of water is produced? iii) Calculate the mole of CaCl2 formed. iv) How many litres of NH3 are produced at NTP? v) Find the molecules of unreacted reactant left over.
$$\ce{Ca(OH)2 + 2NH4Cl - CaCl2 + 2NH3 + 2H2O}$$ Moles: $$ \begin{aligned} n{\ce{Ca(OH)2}} &= \dfrac{7.4}{74} \ &= 0.10\ \text{mol} \ n{\ce{NH4Cl}} &= \dfrac{9.7}{53.5} \ &= 0.1813\ \text{mol} \end{aligned} $$ (i) Limiting reactant:
Sketch a neat and well-labelled diagram for the manufacture of nitric acid by Ostwald's method. Explain the chemical principle and process involved. What is meant by aqua fortis? Write down the action of i) Mg on dilute HNO3 ii) Au on aqua-regia iii) KI on conc. nitric acid.
Ostwald's process (principle): ammonia is catalytically oxidised in stages to nitric acid. $$ \begin{aligned} \ce{4NH3(g) + 5O2(g) -[Pt/Rh][~800,^\circ C] 4NO(g) + 6H2O(g)} \ \ce{2NO(g) + O2(g) - 2NO2(g)} \ \ce{4NO2(g) + O2(g) + 2H2O(...
Explain the principle and procedures involved in the extraction of sodium metal by Down's process. Why can't sodium be extracted by chemical reduction? Give reactions for the conversion of sodium into washing soda. What is meant by water glass?
Down's process (principle): sodium is obtained by the electrolysis of fused (molten) sodium chloride. A little $\ce{CaCl2}$ (and $\ce{KF}$) is added to lower the melting point from ~$800,^\circ\text{C}$ to ~$600,^\circ\text{C}$.
Electrode reactions (electrolyte $\ce{NaCl(l)}$): $$ \begin{aligned} \text{Cathode (iron): }\ce{Na+ + e- -> Na(l)} \ \text{Anode (graphite): }\ce{2Cl- -> Cl2(g) + 2e-} \end{aligned} $$ Molten sodium (lighter) rises and is collected; chlorine is a by-product.
Why not by chemical reduction: sodium is highly electropositive and is itself one of the strongest reducing agents, so no ordinary reducing agent (C, $\ce{H2}$, CO) is strong enough to reduce $\ce{Na+}$. Moreover sodium reacts with water and with carbon at high temperature, so only electrolytic reduction works.
Sodium to washing soda: $$ \begin{aligned} \ce{2Na + 2H2O -> 2NaOH + H2(g)} \ \ce{2NaOH + CO2 -> Na2CO3 + H2O} \ \ce{Na2CO3 + 10H2O -> Na2CO3.10H2O}\ \text{(washing soda)} \end{aligned} $$
Water glass: a concentrated aqueous solution of sodium silicate, $\ce{Na2SiO3}$ (made by fusing sand with sodium carbonate).
State and explain Charle's law. How did Charle's law lead to the discovery of the Kelvin scale of temperature and its relation with the celsius scale? Give the practical significance of Charle's law. A saturated hydrocarbon of formula CnH2n+2 diffuses twice as fast as SO2. How many H2 molecules are present in 4 g of the hydrocarbon and name the hydrocarbon.
Charles's law: at constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute (Kelvin) temperature: $V \propto T$, or $\dfrac{V1}{T1}=\dfrac{V2}{T2}$. Experimentally the volume changes by
Write short notes on any two: i) Homologous series and its characteristics ii) Detection of nitrogen by Lassaigne's test iii) Ionisation energy and electron affinity iv) Relation between Kp and Kc.
(i) Homologous series: a family of organic compounds with the same general formula and same functional group, successive members differing by a $\ce{-CH2-}$ unit ($14\ \text{u}$). Characteristics: same general formula (e.g. alkanes $\ce{C_nH_{2n+2}}$), similar chemical properties, gradual gradation in physical properties (b.p., density) with molar mass, and all members prepared by similar general methods.
(ii) Lassaigne's test for nitrogen: the organic compound is fused with sodium; any nitrogen is converted to sodium cyanide,
$$ \ce{Na + C + N ->[fuse] NaCN} $$
. The fused mass is extracted with water and boiled with $\ce{FeSO4}$, then acidified with dilute $\ce{HCl}$. A Prussian-blue colour of ferric ferrocyanide confirms nitrogen: $$ \begin{aligned} \ce{6NaCN + FeSO4 -> Na4[Fe(CN)6] + Na2SO4} \ \ce{3Na4[Fe(CN)6] + 4FeCl3 -> Fe4[Fe(CN)6]3(s) + 12NaCl} \end{aligned} $$
(iii) Ionisation energy vs electron affinity: Ionisation energy is the energy required to remove the most loosely bound electron from an isolated gaseous atom ($\ce{M(g) -> M+(g) + e-}$); it increases across a period and decreases down a group. Electron affinity is the energy released when a gaseous atom gains an electron ($\ce{X(g) + e- -> X-(g)}$); it too generally increases across a period (halogens highest).
(iv) Relation between $K_p$ and $K_c$: for a gaseous equilibrium, $K_p = K_c (RT)^{\Delta n}$, where $\Delta n$ is (moles of gaseous products $-$ moles of gaseous reactants). If $\Delta n = 0$, $K_p = K_c$; e.g. for
$$ \ce{N2 + 3H2 <=> 2NH3} $$
, $\Delta n = -2$ so $K_p = K_c (RT)^{-2}$.
Normality is the number of gram equivalents of solute dissolved in one litre of solution. Equivalent mass is the mass of the substance that combines with or replaces one mole of hydrogen ions, and for an acid or a base it is the molar mass divided by its basicity or acidity. Crystalline oxalic acid has a molar mass of 126 g per mole and is dibasic, so its equivalent mass is 126 divided by 2, which is 63, and a 0.1 N solution contains 6.3 g per litre. Anhydrous sodium carbonate has a molar mass of 106 g per mole and accepts two hydrogen ions in complete neutralisation, so its equivalent mass is 53 and a 0.1 N solution contains 5.3 g per litre. At the end point of any titration .
By Avogadro, more moles means more molecules. (i) Since , 0.5 g of cont...
Law of conservation of mass: In any chemical reaction, matter is neither created nor destroyed; the total mass of the reactants equals the total mass of the products.
For example, in
, of plus of give exactly of water.
Cubic crystal system: all three edges are equal and all interfacial angles are right angles. - Axial lengths: - Axial angles: Example: sodium chloride () (others: , diamond,
Hund's rule of maximum multiplicity: When electrons are filled into a set of orbitals of equal energy (degenerate orbitals, e.g. the three orbitals), every orbital is singly occupied with electrons of parallel spin first, and pairing...
Sodium () has the configuration . The 11th electron is the electron. - Principal, - Azimuthal, (for an orbital) - Magnetic, - Spin,
Nuclear fusion: the process in which two light nuclei combine (fuse) to form a heavier nucleus, with the release of a very large amount of energy. Application: it is the source of energ...
(i) : the H is bonded to one O, which is bonded to N. Nitrogen is doubly bonded to a second O and singly bonded (coordinate) to a third O. Skeleton: where one N-O is a coordinate bond; N carries no lone pair...
Polar covalent bond: a covalent bond between two atoms of different electronegativity, so the shared pair is unequally shared and the bond develops partial charges ( and ). Example: . Non-polar covalent bond:...
s-block elements: elements in which the last (differentiating) electron enters the outermost orbital. These are the Group IA (alkali metals) and Group IIA (alkaline earth metals), with general valence configuration or .
Important feature: they are highly reactive, soft, electropositive metals with low ionisation energy; they readily lose their valence electron(s) to form ionic compounds and are strong reducing agents.
(i) N in : is , each is . For one : N . (ii) P in : $$ \begin{aligned} 3(+1) + x + 2(-2) &=...
By Le-Chatelier's principle, the yield of is favoured by: - High pressure: the forward reaction reduces gas moles (), so high pressure shifts equil...
Preparation of ozone (silent electric discharge through cold, dry oxygen in an ozoniser): With mercury: ozone oxidises mercury to mercurous oxide. The mercury loses its bright meniscus and ...
Isotopes of hydrogen: protium , deuterium and tritium . Least abundant: tritium (), which is radioactive and present only in traces. Application: tritium is used as fuel in nuclear fusion reac...
(i) Phosphorescence: the property by which a substance absorbs light (or radiation) and continues to re-emit light for some time even after the exciting source is removed (delayed glow), e.g. . (ii) Photochemical smog: a browni...
(i) With heated caustic soda (under pressure), CO forms sodium formate: (ii) With chlorine in sunlight, CO forms the poisonous gas phosgene (carbonyl chloride): $$\ce{CO + Cl2 -[sunlig...
(i) Good reducing agent: sodium has a very low ionisation energy and low electrode potential, so it loses its single electron very easily (). By readily donating electrons it reduces other species, so it is a s...
(i) is 1,2-dimethoxyethane (an ethane chain bearing two groups). (ii) is propanamide (a three-carbon chain with a amide group).
(i) (ethanol, an alcohol). Its functional isomer is the ether , IUPAC name methoxymethane. (ii) (propanone, a ketone). Its functional isomer is the aldehyde , IUPAC na...
(i) Wurtz reaction (alkyl halide + sodium in dry ether gives a higher alkane): (ii) Baeyer's test (test for unsaturation; cold dilute alkaline is decolourised by an alkene,...
Laboratory preparation of ethyne (acetylene): water is dropped onto calcium carbide in a flask; ethyne gas is evolved and collected over water. (The carbide is made industrially by heati...
Oxidation: a process involving loss of electrons, or an increase in oxidation number of an element.
Balancing (oxidation-number method):
To balance electrons, 10 N atoms are needed per :
Check: H ; N ; O . Balanced.
Manufacture from carnallite (, which carries bromides): after the carnallite is worked for potassium salts, the residual mother liquor (bittern) is rich in . It is acidified and warmed, and chlorine gas i...
Preparation (slaked lime + chlorine at about ): (i) With excess dilute (chlorine is liberated): (ii) With ammonia (nitr...
Laboratory preparation of : warm copper turnings with hot concentrated sulphuric acid (or add dilute acid to a sulphite). is a colourless, pungent gas collected by upward displacement of air: $$\ce{Cu + 2H2SO4(conc) ...
Conclusions of Rutherford's -scattering experiment: 1. Most of the atom is empty space (most particles passed straight through). 2. There is a small, dense, positively charged nucleus at the centre (a few particles were ...
Moles: (i) Limiting reactant:
Down's process (principle): sodium is obtained by the electrolysis of fused (molten) sodium chloride. A little (and ) is added to lower the melting point from ~ to ~.
Electrode reactions (electrolyte ):
Molten sodium (lighter) rises and is collected; chlorine is a by-product.
Why not by chemical reduction: sodium is highly electropositive and is itself one of the strongest reducing agents, so no ordinary reducing agent (C, , CO) is strong enough to reduce . Moreover sodium reacts with water and with carbon at high temperature, so only electrolytic reduction works.
Sodium to washing soda:
Water glass: a concentrated aqueous solution of sodium silicate, (made by fusing sand with sodium carbonate).
Charles's law: at constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute (Kelvin) temperature: , or . Experimentally the volume changes by
(i) Homologous series: a family of organic compounds with the same general formula and same functional group, successive members differing by a unit (). Characteristics: same general formula (e.g. alkanes ), similar chemical properties, gradual gradation in physical properties (b.p., density) with molar mass, and all members prepared by similar general methods.
(ii) Lassaigne's test for nitrogen: the organic compound is fused with sodium; any nitrogen is converted to sodium cyanide,
. The fused mass is extracted with water and boiled with , then acidified with dilute . A Prussian-blue colour of ferric ferrocyanide confirms nitrogen:
(iii) Ionisation energy vs electron affinity: Ionisation energy is the energy required to remove the most loosely bound electron from an isolated gaseous atom (); it increases across a period and decreases down a group. Electron affinity is the energy released when a gaseous atom gains an electron (); it too generally increases across a period (halogens highest).
(iv) Relation between and : for a gaseous equilibrium, , where is (moles of gaseous products moles of gaseous reactants). If , ; e.g. for
, so .