Chemical Reactions and Equations PDF

Thursday, 23 May 2024 Chemical reactions and equations Activity-1.1 Step-1-Clean a magnesium ribbon about 2 cm long by rubbing it with sandpaper. step-2-Hold it with a pair of tongs. Burn it using a spirit lamp or burner and collect the ash so formed in a watch-glass as shown in Fig. 1.1. Burn t...

Thursday, 23 May 2024 Chemical reactions and equations Activity-1.1 Step-1-Clean a magnesium ribbon about 2 cm long by rubbing it with sandpaper. step-2-Hold it with a pair of tongs. Burn it using a spirit lamp or burner and collect the ash so formed in a watch-glass as shown in Fig. 1.1. Burn the magnesium ribbon keeping it as far as possible from your eyes. The magnesium ribbon burn with a bright a dazzling white flame and changes into a white powder(Magnesium Oxide MgO) Activity-1.2 Take lead nitrate solution in a test tube. Add potassium iodide solution to this. Observation:- A yellow precipitate is formed (PbI~2~) Pb(NO~3~)~2~+2Kl---------\>PbI~2~+2KNO~3~ Actvity-1.3 Take a few zinc granules in a conical flask or a test tube. Add dilute hydrochloric acid or sulphuric acid to this (Fig. 1.2). CAUTION: Handle the acid with care. Do you observe anything happening around the zinc granules? Touch the conical flask or test tube. Is there any change in its temperature? Observation:- Zinc reacts with sulphuric acid to form zinc sulphate giving out hydrogen Zn+H~2~SO~4~ →ZnSO4 +H~2~ ~TYPES\ OF\ CHEMICAL\ REACTIONS~ ~DECOMPOSTION\ REACTION~ ~COMBINATION\ REACTION~ ~DISPLACEMENT~ ~DOUBLE\ DISPLACEMENT~ ~OXIDATION\ AND\ REDUCTION~ ~Exothermic\ reaction:-\ An\ exothermic\ reaction\ is\ a\ chemical\ reaction\ that\ releases\ energy\ by\ light\ or\ heat~ ~Endothermic\ reaction:-\ An\ endothermic\ reaction\ is\ a\ chemical\ reaction\ that\ absorbs\ heat~ ~Activity-1.4~ ~Calcium\ oxide\ reacts\ vigorously\ with\ water\ to\ produce\ slaked\ lime\ (calcium\ hydroxide)\ releasing\ a\ large\ amount\ of\ heat.~ ~CaO(s)\ +\ H2O(l)\ →Ca(OH)2(aq)\ (1.13)\ (Quick\ lime)\ (Slaked\ lime)~ ~Combination\ reaction:-~ ~A\ reaction\ in\ which\ a\ single\ product\ is\ formed\ from\ two\ or\ more\ reactants\ is\ known\ and\ combination\ reaction~ ~Decomposition\ reaction:-~ ~2FeSO\ (s)\ Heat\ Fe\ O\ (s)\ +\ SO\ (g)\ +\ SO\ (g)\ (1.19)\ 4⎯⎯⎯⎯→23\ 2\ 3~ ~(Ferrous\ sulphate)\ (Ferric\ oxide)~ ~2Pb(NO\ )\ (s)\ Heat\ 2PbO(s)\ +\ 4NO\ (g)\ +\ O\ (g)\ (1.21)\ 32⎯⎯⎯⎯→\ 22~ ~(Lead\ nitrate)\ (Lead\ oxide)\ (Nitrogen\ (Oxygen)~ ~Activity-1.7~ ~Take\ a\ plastic\ mug.\ Drill\ two\ holes\ at\ its\ base\ and\ fit\ rubber\ stoppers\ in\ these\ holes.\ Insert\ carbon\ electrodes\ in\ these\ rubber\ stoppers\ as\ shown\ in\ Fig.\ 1.6.~ ~Connect\ these\ electrodes\ to\ a\ 6\ volt\ battery.~ ~Fill\ the\ mug\ with\ water\ such\ that\ the\ electrodes\ are\ immersed.\ Add\ a\ few\ drops\ of\ dilute\ sulphuric\ acid\ to\ the\ water.~ ~Take\ two\ test\ tubes\ filled\ with\ water\ and\ invert\ them\ over\ the\ two\ carbon\ electrodes.~ ~Switch\ on\ the\ current\ and\ leave\ the~ ~apparatus\ undisturbed\ for\ some\ time.~ ~You\ will\ observe\ the\ formation\ of\ bubbles~ ~at\ both\ the\ electrodes.\ These\ bubbles\ displace\ water\ in\ the~ ~test\ tubes.~ ~Is\ the\ volume\ of\ the\ gas\ collected\ the\ same\ in\ both\ the\ test\ tubes?~ ~Once\ the\ test\ tubes\ are\ filled\ with\ the\ respective\ gases,\ remove~ ~them\ carefully.~ ~Test\ these\ gases\ one\ by\ one\ by\ bringing\ a\ burning\ candle\ close~ ~to\ the\ mouth\ of\ the\ test\ tubes.~ ~CAUTION:\ This\ step\ must\ be\ performed\ carefully\ by\ the\ teacher.~ ~What\ happens\ in\ each\ case?~ ~Which\ gas\ is\ present\ in\ each\ test\ tube?~ ~Activity\ 1.8~ ~Take\ about\ 2\ g\ silver\ chloride\ in\ a\ china\ dish.\ What\ is\ its\ colour?~ ~Place\ this\ china\ dish\ in\ sunlight\ for\ some\ time(Fig.\ 1.7).~ ~Observe\ the\ colour\ of\ the\ silver\ chloride\ after\ sometime.~ ~Conclusion:-You\ will\ see\ that\ white\ silver\ chloride\ turns\ grey\ in\ sunlight.\ This\ is\ due\ to\ the\ decomposition\ of\ silver\ chloride\ into\ silver\ and\ chlorine\ by\ light.~ ~2AgCl(s)\ ------------\>2Ag(s)\ +\ Cl~2 ~(g)(In\ sunlight)~ ~Silver\ bromide\ reacts\ in\ the\ same\ way~ 2AgBr\[s\]------------\>in sunlight 2Ag+Br2 Displacement reaction- a chemical reaction in which a highly reactive element displaces a lesser reactive element from its solution. Activity 1.9 Observation- iron nail becomes brownish in colour, and the blue colour of copper sulphate solution fades Zn(s) + CuSO4(aq) → (Copper sulphate) ZnSO4(aq) + Cu(s) (Zinc sulphate) Pb(s)+CuCl2(aq) → (Copper chloride) PbCl2(aq) + Cu(s) (Lead chloride) Double displacement reaction:- Double displacement reactions are those in which two chemical substances react by exchanging ions to produce two new molecules. Positive ions exchange negative ions in the double displacement process. Ionic chemicals dissolved in water undergo a lot of double displacement processes. Activity 1.10 Take about 3 mL of sodium sulphate solution in a test tube. In another test tube, take about 3 mL of barium chloride solution. Mix the two solutions (Fig. 1.9). What do you observe? Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq) Conclusion:-You will observe that a white substance, which is insoluble in water, is formed. This insoluble substance formed is known as a precipitate. Any reaction that produces a precipitate can be called a precipitation reaction In a double displacement reaction The white precipitate of BaSO4 is formed by the reaction of SO-2 4 (the four is the subscript and -2 is the charge of sulphate) and Ba2+.The other product formed is sodium chloride which remains in the solution. Such reactions in which there is an exchange of ions between the reactants are called double displacement reactions. The white precipitate(BaSO4)which is insoluble(doesnt mix with water) forms a precipitate(because it doesnt mix it settles at the bottom), the precipitate Double displacement is a chemical reaction In which there is an exchange of ions between the reactants Oxidation and Reduction:- Oxidation-It is defined as the addition of oxygen to the substance or the removal of hydrogen from the substance.For example; C ( s ) + O 2 ( g ) → CO 2 ( g ) Carbon Oxygen Carbon dioxide Reduction-A chemical reaction which involves addition of hydrogen or removal of oxygen or gain of electron(s) CuO + H2 → Cu + H2O(removal of oxygen) H2 → 2NaH (addition of hydrogen) Redox-The reaction in which both oxidation and reduction occur together. Oxidation: It is defined as the reaction in which the addition of oxygen to the substance or removal of hydrogen from a substance takes place. Activity 1.11 Heat a china dish containing about 1 g copper powder (Fig. 1.10). What do you observe? The surface of copper powder becomes coated with black copper(II) oxide. Why has this black substance formed? This is because oxygen is added to copper and copper oxide is formed. 2Cu+O2----\>2CuO(on heating) If hydrogen gas is passed over this heated material (CuO), the black coating on the surface turns brown as the reverse reaction takes place and copper is obtained. CuO+H~2~ ⎯⎯⎯⎯\>Cu+H~2~O(on heating) If a substance gains oxygen during a reaction, it is said to be oxidised. If a substance loses oxygen during a reaction, it is said to be reduced. During this reaction (1.29), the copper(II) oxide is losing oxygen and is being reduced. The hydrogen is gaining oxygen and is being oxidised. In other words, one reactant gets oxidised while the other gets reduced during a reaction. Such reactions are called oxidation-reduction reactions or redox reactions. CuO+H~2------\>~ Cu+H~2~O In this chemical reaction copper is reduced and hydrogen is oxidised In a redox reaction has occurred Some examples- ZnO + C → Zn +CO MnO~2~ +4HCl→MnCl~2~ +2H~2~O + Cl~2~ ~Corrosion\ and\ Rancidity~ ~Corrosion\ is\ the\ process\ by\ which\ a\ metal\ surface\ is\ attacked\ by\ a\ certain\ substance\ such\ as\ air\ or\ water.\ The\ most\ common\ occurrence\ of\ corrosion\ is\ the\ rusting\ of\ iron\ by\ air\ and\ moisture\ to\ form\ a\ reddish-brown\ layer\ of\ triferric\ tetraoxide(Fe3O4)~ ~When\ fats\ and\ oils\ stay\ in\ open\ for\ long,\ they\ get\ oxidized\ and\ become\ rancid\ (old\ and\ stale),\ and\ their\ smell\ and\ taste\ change.\ This\ process\ is\ known\ as\ rancidity.~