JK-TK/Newdata huggingface dataset:
It has molecular formula N2. It has atomic number 7 and atomic weight 14.08 and its electronic configuration of 2,5. Besides combining with hydrogen and forming NH3 , nitrogen combines with oxygen in different ratios and forms five different oxides. The oxides of nitrogen and the details of the oxygen states of nitrogen and the N:O ratio can be presented in a tabular form as: Name Formula Oxidation state of N Ratio of N:O 1) Nitrogen Oxide or nitrous oxide NO +2 1:1 2) Nitrogen dioxide NO2 +4 1:2 3) Nitrous oxide (also called laughing gas) N2O +1 2:1 All of these oxides of nitrogen are gases, excepting NO and N2O the other oxides are brownish gases. Except the oxides of NO and N2O all the other oxides are acidic. NO and N2O are neutral. The other oxides are prepared in the laboratory using different methods characteristic to each oxide. Example of Oxides of Nitrogen (nitric Oxide - NO) Structure:
Laboratory Preparation: The oxide is prepared in the laboratory by treating the metallic copper with a moderately concentarted nitric acid (1:1) at room temperature. The reaction is given as : 2Cu + 8 HNO3 ------> Cu(NO3)2 + 2NO + 4H2O The gas is collected by downward displacement of water.The apparatus used is Wolfe's apparatus. The purification is done by absorbing the NO gas in frashly prepared ferrous sulphate solution. Ferrous sulphate absorbs all the NO gas and forms Fe(H2O)5 NO and the solution becomes brown. On heating this solution pure Nitric Oxide is obatined. Physical Properties: NO is not a combustible gas. At high temperature around 1000°C it decomposes into N2 and O2 . 2NO = N2 + O2 at high temperature From the equation above we can see that once the decomposition starts 50% O2 gets evolved and this O2 supports combustion thus making the reaction more violent.
Physical Properties: NO is not a combustible gas. At high temperature around 1000°C it decomposes into N2 and O2 . 2NO = N2 + O2 at high temperature From the equation above we can see that once the decomposition starts 50% O2 gets evolved and this O2 supports combustion thus making the reaction more violent. Chemical properties: 1) NO acts as an oxidising agent, oxidising SO2 in presence of water to give H2SO4: SO2 + 2NO + H2O → H2SO4 + N2O 2) NO acts as a reducing agent, i) reducing an acidified solution of potassium permanganate (pink) to colorless manganous salt. 3KMnO4 + 6H2SO4 + 5NO2 → 3KHSO4 + 3MnSO4 + 2H2O + 5NO3
ii) It can also reduce aqueous solution of I2 to HI 3I2 + 2NO + 4H2O → 2HNO3 + 6HI 3) With halogens NO can form addition compounds as 2NO + Cl2 → 2NOCl (NOCl is nitrosyl chloride) It reacts in the same way with flourine and bromine. 4) With ferrous sulphate NO forms an addition compound as FeSO4 + 5H2O + NO = [Fe(H2O)5NO]SO4 penta aqua nitrosyl iron (II) sulphate This is the famous brown ring test used to identify the nitrate radical or the NO radical. Uses: NO is used to prepare nitric acid. Nitrogen Dioxide - NO2 Structure: Laboratory Preparation: In the laboratory NO2 is prepared by thermal decomposition of Pb(NO3)2. Thus 2Pb(NO3)2 → 2PbO + 4NO2 + O2 Care is taken to ensure the use of dried Pb(NO3)2 as hydrated nitrate salts on heating react violently and explode. Physical Properties: NO2 is a poisonous gas, main source being the exhaust of automobiles. 1) At room temperature it is a deep brown gas. 2) It does not support combustion. 3) It is not combustible. Chemical Properties: 1) With cold water NO2 reacts to give a mixture of HNO2 and HNO3 acid.
2) It does not support combustion. 3) It is not combustible. Chemical Properties: 1) With cold water NO2 reacts to give a mixture of HNO2 and HNO3 acid. 2NO2 + H2O → HNO2 + HNO3 2) With hot water the reaction is 3NO2 + H2O → 2HNO3 + NO 3) Being acidic it reacts with bases as 2NO2 + KOH → KNO3 + H2O + KNO2 4) It is also a strong oxidising agent. H2S + NO2 → NO + H2S + S 5) With excess oxygen and water NO2 gives HNO3. 4NO2 + O2 + 2H2O → 4HNO3 6) It reacts with concentrated H2SO4 to give nitrosyl hydrogen sulphate 2NO2 + H2SO4 → SO2(OH)ONO + HNO3 Uses: NO2 is used as a fuel in rockets besides being used to prepare HNO3 . Nitrous Oxide - N2O (laughing Gas) Structure:
Laboratory Preparation: N2O can be prepared in the laboratory by heating NH4NO3 below 200°C to avoid explosion. Sometimes as a safety measure instead of directly using NH4NO3, a mixture of (NH4)2SO4 and NaNO3 are heated to give NH4NO3 which decomposes further to give N2O. NH4NO3 → N2O + H2O (endothermic reaction) Physical Properties: 1) N2O has a faint sweet smell and produces a tickling sensation on the neck when inhaled and makes people laugh hysterically. Excess of inhalation leads to unconsiousness. 2) Unlike other oxides of nitrogen, N2O supports combustion though it does not burn itself. Chemical Properties: 1) At very high temperature N2O decomposes to N2 and O2 2N2O → 2N2 + O2 If a glowing piece of Mg, Cu, or P is introduced in such an environment, these pieces burn brightly due to the O2 produced from decomposition of N2O. 2) With Sodium and potassium N2O reacts to give the corresponding peroxides liberating N2 in the process.
2) Unlike other oxides of nitrogen, N2O supports combustion though it does not burn itself. Chemical Properties: 1) At very high temperature N2O decomposes to N2 and O2 2N2O → 2N2 + O2 If a glowing piece of Mg, Cu, or P is introduced in such an environment, these pieces burn brightly due to the O2 produced from decomposition of N2O. 2) With Sodium and potassium N2O reacts to give the corresponding peroxides liberating N2 in the process. 2N2O + 2Na → Na2O + 2N2. Na2O is sodium peroxide Uses: 1) It is used as propellent gas. 2)Used in combination with oxygen in the ratio N2O : O2 = 1:10 as a mild anaesthetic. 1 16.0.0 SULPHUR AND ITS COMPOUNDS (25 LESSONS) A.SULPHUR (S) Sulphur is an element in Group VI Group 16)of the Periodic table . It has atomic number 16 and electronic configuration 16 and valency 2 /divalent and thus forms the ion S2- A. Occurrence. Sulphur mainly occurs : (i) as free element in Texas and Louisiana in USA and Sicily in Italy. (ii)Hydrogen sulphide gas in active volcanic areas e.g. Olkaria near Naivasha in Kenya (iii)as copper pyrites(CuFeS2) ,Galena (PbS,Zinc blende(ZnS))and iron pyrites(FeS2) in other parts of the world. B. Extraction of Sulphur from Fraschs process Suphur occurs about 200 metres underground. The soil structure in these areas is usually weak and can easily cave in. Digging of tunnels is thus discouraged in trying to extract the mineral. Sulphur is extracted by drilling three concentric /round pipes of diameter of ratios 2:8: 18 centimeters. Superheated water at 170oC and 10atmosphere pressure is forced through the outermost pipe. The high pressures ensure the water remains as liquid at high temperatures instead of vapour of vapour /gas. The superheated water melts the sulphur because the melting point of sulphur is lower at about at about 115oC.
Superheated water at 170oC and 10atmosphere pressure is forced through the outermost pipe. The high pressures ensure the water remains as liquid at high temperatures instead of vapour of vapour /gas. The superheated water melts the sulphur because the melting point of sulphur is lower at about at about 115oC. A compressed air at 15 atmospheres is forced /pumped through the innermost pipe. The hot air forces the molten sulphur up the middle pipe where it is collected and solidifies in a large tank. It is about 99% pure. 2 Diagram showing extraction of Sulphur from Fraschs Process C. Allotropes of Sulphur. 1. Sulphur exist as two crystalline allotropic forms: (i)Rhombic sulphur (ii)Monoclinic sulphur Rhombic sulphur Monoclinic sulphur Bright yellow crystalline solid Has a melting point of 113oC Has a density of 2.06gcm-3 Stable below 96oC Has octahedral structure Pale yellow crystalline solid Has a melting point of 119oC Has a density of 1.96gcm-3 Stable above 96oC Has a needle-like structure Rhombic sulphur and Monoclinic sulphur have a transition temperature of 96oC.This is the temperature at which one allotrope changes to the other. ‘Sketch of Octahedral structure ofRhombic sulphurSulphuratomsvalent bondNan-der-waalsforcesu Covalentbonds Sketch of the needle-like structure of monoclinic sulphur
4 2. Sulphur exists in non-crystalline forms as: (i)Plastic sulphur- Plastic sulphur is prepared from heating powdered sulphur to boil then pouring a thin continuous stream in a beaker with cold water. A long thin elastic yellow thread of plastic sulphur is formed .If left for long it turn to bright yellow crystalline rhombic sulphur. (ii)Colloidal sulphur- Colloidal sulphur is formed when sodium thiosulphate (Na2S2O3) is added hydrochloric acid to form a yellow precipitate. D. Heating Sulphur. A molecule of sulphur exists as puckered ring of eight atoms joined by covalent bonds as S8.
D. Heating Sulphur. A molecule of sulphur exists as puckered ring of eight atoms joined by covalent bonds as S8. On heating the yellow sulphur powder melts at 113oC to clear amber liquid with low viscosity and thus flows easily. On further heating to 160oC the molten liquid darkens to a brown very viscous liquid that does not flow easily. This is because the S8 rings break into S8 chain that join together to form very long chains made of over 100000 atoms of Sulphur. The long chains entangle each other reducing their mobility /flow and hence increases their viscosity. On continued further heating to above 160oC, the viscous liquid darkens but becomes more mobile/flows easily and thus less viscous. This is because the long chains break to smaller/shorter chains. At 444oC, the liquid boils and forms brown vapour of a mixture of S8 ,S6 ,S2 molecules that solidifies to S8 ring of “flowers of sulphur” on the cooler parts. Summary of changes on heating sulphur
5 Observation on heating Explanation/structure of Sulphur Solid sulphur Heat to 113oC Amber yellow liquid Heat to 160oC Liquid darkens Heat to 444oC Liquid boils to brown vapour Cool to room temperature Yellow sublimate (Flowers of Sulphur) Puckered S8 ring Puckered S8 ring in liquid form (low viscosity/flow easily) Puckered S8 ring break/opens then join to form long chains that entangle (very high viscosity/very low rate of flow) Mixture of S8 ,S6 ,S2 vapour Puckered S8 ring E. Physical and Chemical properties of Sulphur.(Questions) 1. State three physical properties unique to Sulphur Sulphur is a yellow solid, insoluble in water, soluble in carbon disulphide/tetrachloromethane/benzene, poor conductor of heat and electricity. It has a melting point of 115oC and a boiling point of 444oC. 2. Moist/damp/wet blue and red litmus papers were put in a gas jar containing air/oxygen. Burning sulphur was then lowered into the gas jar. State and explain the observation made.
Moist/damp/wet blue and red litmus papers were put in a gas jar containing air/oxygen. Burning sulphur was then lowered into the gas jar. State and explain the observation made. Observations -Sulphur melts then burns with a blue flame Colourless gas produced that has a pungent smell Red litmus paper remains red. Blue litmus paper turns red. Explanation Sulphur burns in air and faster in Oxygen to form Sulphur(IV)Oxide gas and traces/small amount of Sulphur(VI)Oxide gas. Both oxides react with water to form the corresponding acidic solution i.e (i) Sulphur(IV)Oxide gas reacts with water to form sulphuric(IV)acid (ii) Sulphur(VI)Oxide gas reacts with water to form sulphuric(VI)acid Chemical equation
6 S(s) + O2(g) -> SO2(g) (Sulphur(IV)Oxide gas) 2S(s) + 3O2(g) -> 2SO3(g) (Sulphur(VI)Oxide gas traces) SO2(g) + H2O(l) -> H2 SO3 (aq) ( sulphuric(IV)acid) SO3(g) + H2O(l) -> H2 SO4 (aq) ( sulphuric(VI)acid). 3. Iron filings were put in a test tube containing powdered sulphur then heated on a Bunsen flame. Stop heating when reaction starts. State and explain the observations made. Test the effects of a magnet on the mixture before and after heating. Explain. Observations Before heating, the magnet attracts iron filings leaving sulphur After heating, the magnet does not attract the mixture. After heating, a red glow is observed that continues even when heating is stopped.. Black solid is formed. Explanation Iron is attracted to a magnet because it is ferromagnetic. When a mixture of iron and sulphur is heated, the reaction is exothermic giving out heat energy that makes the mixture to continue glowing even after stopping heating. Black Iron(II)sulphide is formed which is a compound and thus not ferromagnetic. Chemical equation Fe(s) + S(s) -> FeS(s) (Exothermic reaction/ -∆H) Heated powdered heavy metals combine with sulphur to form black sulphides.
When a mixture of iron and sulphur is heated, the reaction is exothermic giving out heat energy that makes the mixture to continue glowing even after stopping heating. Black Iron(II)sulphide is formed which is a compound and thus not ferromagnetic. Chemical equation Fe(s) + S(s) -> FeS(s) (Exothermic reaction/ -∆H) Heated powdered heavy metals combine with sulphur to form black sulphides. Cu(s) + S(s) -> CuS(s) Zn(s) + S(s) -> ZnS(s) Pb(s) + S(s) -> PbS(s) 4.The set up below show the reaction of sulphur on heated concentrated sulphuric(VI)acid. 7 (i)State and explain the observation made. Observation Yellow colour of sulphur fades Orange colour of potassium dichromate(VI)paper turns to green. Explanation Hot concentrated sulphuric(VI)acid oxidizes sulphur to sulphur (IV)oxide gas. The oxide is also reduced to water. Traces of sulphur (VI)oxide is formed. Chemical equation S(s) + 3H2 SO4 (l) -> 3SO2(g) + 3H2O(l) +SO3(g) Sulphur (IV)oxide gas turns Orange potassium dichromate(VI)paper to green. (ii)State and explain the observation made if concentrated sulphuric (VI) acid is replaced with concentrated Nitric (V) acid in the above set up. Observation Yellow colour of sulphur fades Colurless solution formed Brown fumes/gas produced. Explanation Hot concentrated Nitric(V)acid oxidizes sulphur to sulphuric (VI)acid. The Nitric (V) acid is reduced to brown nitrogen(IV)oxide gas. Chemical equation S(s) + 6HNO3 (l) -> 6NO2(g) + 2H2O(l) +H2SO4 (l) NB: Hydrochloric acid is a weaker oxidizing agent and thus cannot oxidize sulphur like the other mineral acids. 5.State three main uses of sulphur . Sulphur is mainly used in: (i)Contact process for the manufacture/industrial/large scale production of concentrated sulphuric(VI)acid. (ii)Vulcanization of rubber to make it harder, tougher, stronger, and more durable.
5.State three main uses of sulphur . Sulphur is mainly used in: (i)Contact process for the manufacture/industrial/large scale production of concentrated sulphuric(VI)acid. (ii)Vulcanization of rubber to make it harder, tougher, stronger, and more durable. (iii)Making gun powder and match stick heads (iv) As ointments to treat fungal infections
8 6. Revision Practice The diagram below represents the extraction of sulphur by Fraschs process. Use it to answer the questions that follow. (a)Name the substances that passes through: M Superheated water at 170oC and 10 atmosphere pressure L Hot compressed air N Molten sulphur (b)What is the purpose of the substance that passes through L and M? M- Superheated water at 170oC and 10 atmosphere pressure is used to melt the sulphur L- Hot compressed air is used to force up the molten sulphur. (c) The properties of the two main allotropes of sulphur represented by letters A and B are given in the table below. Use it to answer the questions that follow. A B Appearance Bright yellow Pale yellow Density(gcm-3) 1.93 2.08 Melting point(oC) 119 113 Stability Above 96oC Below 96oC I.What are allotropes? Different forms of the same element existing at the same temperature and pressure without change of state. II. Identify allotrope: A. Monoclinic sulphur B . Rhombic sulphur III. State two main uses of sulphur.
Monoclinic sulphur B . Rhombic sulphur III. State two main uses of sulphur. -Manufacture of sulphuric(VI)acid -as fungicide -in vulcanization of rubber to make it harder/tougher/ stronger -manufacture of dyes /fibres L M N
9 (d)Calculate the volume of sulphur (IV)oxide produced when 0.4 g of sulphur is completely burnt in excess air.(S = 32.0 ,I mole of a gas occupies 24 dm3 at room temperature) Chemical equation S(s) + O2(g) -> SO2(g) Mole ratio S: SO2 = 1:1 Method 1 32.0 g of sulphur -> 24 dm3 of SO2(g) 0.4 g of sulphur -> 0.4 g x 24 dm3 = 0.3 dm3 32.0 g Method 2 Moles of sulphur used = Mass of sulphur => 0.4 = 0.0125 moles Molar mass of sulphur 32 Moles of sulphur used = Moles of sulphur(IV)oxide used=>0.0125 moles Volume of sulphur(IV)oxide used = Moles of sulphur(IV)oxide x volume of one mole of gas =>0.0125 moles x 24 dm3 = 0.3 dm3
10 B.COMPOUNDS OF SULPHUR The following are the main compounds of sulphur: (i) Sulphur(IV)oxide (ii) Sulphur(VI)oxide . (iii) Sulphuric(VI)acid (iv) Hydrogen Sulphide (v) Sulphate(IV)/SO32- and Sulphate(VI)/ SO42- salts (i) Sulphur(IV)oxide(SO2) (a) Occurrence Sulphur (IV)oxide is found in volcanic areas as a gas or dissolved in water from geysersand hot springs in active volcanic areas of the world e.g. Olkaria and Hells gate near Naivasha in Kenya. (b) School laboratory preparation In a Chemistry school laboratory Sulphur (IV)oxide is prepared from the reaction of Method 1:Using Copper and Sulphuric(VI)acid.
(iii) Sulphuric(VI)acid (iv) Hydrogen Sulphide (v) Sulphate(IV)/SO32- and Sulphate(VI)/ SO42- salts (i) Sulphur(IV)oxide(SO2) (a) Occurrence Sulphur (IV)oxide is found in volcanic areas as a gas or dissolved in water from geysersand hot springs in active volcanic areas of the world e.g. Olkaria and Hells gate near Naivasha in Kenya. (b) School laboratory preparation In a Chemistry school laboratory Sulphur (IV)oxide is prepared from the reaction of Method 1:Using Copper and Sulphuric(VI)acid. Method 2:Using Sodium Sulphate(IV) and hydrochloric acid. 11 (c)Properties of Sulphur(IV)oxide(Questions) 1. Write the equations for the reaction for the formation of sulphur (IV)oxide using: (i)Method 1 Cu(s) + 2H2SO4(l) -> CuSO4(aq) + SO2(g) + 2H2O(l) Zn(s) + 2H2SO4(l) -> ZnSO4(aq) + SO2(g) + 2H2O(l) Mg(s) + 2H2SO4(l) -> MgSO4(aq) + SO2(g) + 2H2O(l) Fe(s) + 2H2SO4(l) -> FeSO4(aq) + SO2(g) + 2H2O(l) Calcium ,Lead and Barium will form insoluble sulphate(VI)salts that will cover unreacted metals stopping further reaction thus producing very small amount/quantity of sulphur (IV)oxide gas.
Method 2:Using Sodium Sulphate(IV) and hydrochloric acid. 11 (c)Properties of Sulphur(IV)oxide(Questions) 1. Write the equations for the reaction for the formation of sulphur (IV)oxide using: (i)Method 1 Cu(s) + 2H2SO4(l) -> CuSO4(aq) + SO2(g) + 2H2O(l) Zn(s) + 2H2SO4(l) -> ZnSO4(aq) + SO2(g) + 2H2O(l) Mg(s) + 2H2SO4(l) -> MgSO4(aq) + SO2(g) + 2H2O(l) Fe(s) + 2H2SO4(l) -> FeSO4(aq) + SO2(g) + 2H2O(l) Calcium ,Lead and Barium will form insoluble sulphate(VI)salts that will cover unreacted metals stopping further reaction thus producing very small amount/quantity of sulphur (IV)oxide gas. (ii)Method 2 Na2SO3(aq) + HCl(aq) -> NaCl(aq ) + SO2(g) + 2H2O(l) K2SO3(aq) + HCl(aq) -> KCl(aq ) + SO2(g) + 2H2O(l) BaSO3(s) + 2HCl(aq) -> BaCl2(aq ) + SO2(g) + H2O(l) CaSO3(s) + 2HCl(aq) -> CaCl2(aq ) + SO2(g) + H2O(l) PbSO3(s) + 2HCl(aq) -> PbCl2(s ) + SO2(g) + H2O(l)
12 Lead(II)chloride is soluble on heating thus reactants should be heated to prevent it coating/covering unreacted PbSO3(s) 2.State the physical properties unique to sulphur (IV)oxide gas. Sulphur (IV)oxide gas is a colourless gas with a pungent irritating and choking smell which liquidifies easily. It is about two times denser than air. 3. The diagram below show the solubility of sulphur (IV)oxide gas. Explain.
3. The diagram below show the solubility of sulphur (IV)oxide gas. Explain. Sulphur(IV) oxide is very soluble in water. One drop of water dissolves all the Sulphur (IV) oxide in the flask leaving a vacuum. If the clip is removed, atmospheric pressure forces the water up through the narrow tube to form a fountain to occupy the vacuum. An acidic solution of sulphuric (IV)acid is formed which turns litmus solution red. Chemical equation SO2(g) + H2O(l) -> H2 SO3 (aq) ( sulphuric(IV)acid turn litmus red)
13 4.Dry litmus papers and wet/damp/moist litmus papers were put in a gas jar containing sulphur(IV) oxide gas. State and explain the observations made. Observations (i)Dry Blue litmus paper remains blue. Dry red litmus paper remains red. (ii) Wet/damp/moist blue litmus paper turns red. Moist/damp/wet red litmus paper remains red. Both litmus papers are then bleached /decolorized. Explanation Dry sulphur(IV) oxide gas is a molecular compound that does not dissociate/ionize to release H+(aq)ions and thus has no effect on dry blue/red litmus papers. Wet/damp/moist litmus papers contain water that dissolves /react with dry sulphur(IV) oxide gas to form a solution of weak sulphuric(IV)acid (H2 SO3 (aq)). Weak sulphuric(IV)acid(H2 SO3 (aq)) dissociates /ionizes into free H+(aq)ions: H2 SO3 (aq) -> 2H+(aq) + SO32- (aq) The free H+(aq)ions are responsible for turning blue litmus paper turns red showing the gas is acidic. The SO32- (aq) ions in wet/damp/moist sulphur(IV) oxide gas is responsible for many reactions of the gas. It is easily/readily oxidized to sulphate(VI) SO42- (aq) ions making sulphur(IV) oxide gas act as a reducing agent as in the following examples: (a)Bleaching agent Wet/damp/moist coloured flowers/litmus papers are bleached/decolorized when put in sulphur(IV) oxide gas.
Weak sulphuric(IV)acid(H2 SO3 (aq)) dissociates /ionizes into free H+(aq)ions: H2 SO3 (aq) -> 2H+(aq) + SO32- (aq) The free H+(aq)ions are responsible for turning blue litmus paper turns red showing the gas is acidic. The SO32- (aq) ions in wet/damp/moist sulphur(IV) oxide gas is responsible for many reactions of the gas. It is easily/readily oxidized to sulphate(VI) SO42- (aq) ions making sulphur(IV) oxide gas act as a reducing agent as in the following examples: (a)Bleaching agent Wet/damp/moist coloured flowers/litmus papers are bleached/decolorized when put in sulphur(IV) oxide gas. This is because sulphur(IV) oxide removes atomic oxygen from the coloured dye/ material to form sulphuric(VI)acid. Chemical equations (i)Formation of sulphuric(IV)acid SO2(g) + H2O(l) -> H2 SO3 (aq) (ii)Decolorization/bleaching of the dye/removal of atomic oxygen. Method I. H2 SO3 (aq) + (dye + O) -> H2 SO4 (aq) + dye (coloured) (colourless) Method II. H2 SO3 (aq) + (dye) -> H2 SO4 (aq) + (dye - O) (coloured) (colourless)
14 Sulphur(IV) oxide gas therefore bleaches by reduction /removing oxygen from a dye unlike chlorine that bleaches by oxidation /adding oxygen. The bleaching by removing oxygen from Sulphur(IV) oxide gas is temporary. This is because the bleached dye regains the atomic oxygen from the atmosphere/air in presence of sunlight as catalyst thus regaining/restoring its original colour. e.g. Old newspapers turn brown on exposure to air on regaining the atomic oxygen. The bleaching through adding oxygen by chlorine gas is permanent. (b)Turns Orange acidified potassium dichromate(VI) to green Experiment: (i)Pass a stream of Sulphur(IV) oxide gas in a test tube containing acidified potassium dichromate(VI) solution.