What Is Required? You need to find the ph at a certain point in the titration using hypobromous acid and potassium hydroxide solutions.

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1 104. A chemist titrated ml of a mol/l solutio of hypobromous acid, HBrO(aq), K a = Calculate the resultig ph after the additio of ml of mol/l sodium hydroxide solutio, (aq). What Is Required? You eed to fid the ph at a certai poit i the titratio usig hypobromous acid ad potassium hydroxide solutios. What Is Give? You kow the volume of the hypobromous acid: HBrO ml You kow the cocetratio of the hypobromous acid: chbro mol/l You kow the volume of the sodium hydroxide: ml You kow the cocetratio of the sodium hydroxide: c mol/l You are give the acid dissociatio costat for hypobromous acid: K a = Pla Your Strategy Write the balaced equatio for the reactio betwee HBrO (aq) ad (aq). Use the formula c to calculate the amout i moles,, of HBrO(aq) preset before ay base was added. Use the formula c to calculate the amout i moles,, of (aq). Calculate the amout i moles,, of BrO (aq) preset after the base was added. Calculate the amout i moles of ureacted HBrO(aq). Act o Your Strategy Because is a strog base, the reactio essetially goes to completio. HBrO(aq) (aq) + (aq) NaBrO(aq) + H 2 O(l) HBrO c mol ml 1 L L 1000 ml mol c mol ml 1 L L 1000 ml mol Because the reactio goes to completio ad because the ratio of BrO to is 1:1, for every mole of added, oe mole of HBrO will be coverted ito BrO. Therefore: BrO mol excess HBrO HBrO i BrO formed mol mol mol 264 MHR Chemistry 12 Solutios Maual

2 Determie the fial volume of the solutio. Use c to determie the cocetratios of HBrO(aq) ad BrO (aq) i mol/l. Write equatios for ay equilibrium reactios occurrig ad determie whether the solutio has bufferig capacity. Write the equilibrium expressio, substitute i the calculated cocetratios ad solve for the cocetratio of the hydroium io. HBrO ml ml 1 L = ml 1000 ml L chbro mol L mol/l c BrO mol L mol/l HBrO(aq) + H 2 O(l) BrO (aq) + H 3 O + (aq) BrO (aq) + H 2 O(l) HBrO (aq) + OH (aq) The solutio has bufferig capacity. The reactios of HBrO ad BrO reactig with water balace each other ad very little chage actually occurs. Therefore, you ca use the amouts of HBrO ad BrO preset after the reactio with ad the equilibrium costat to fid the cocetratio of hydroium io, H 3 O + preset. [BrO ][H3O ] Ka [HBrO] 9 x x ( )( ) 9 2 ( )( ) 2 [H 3 O + ] = x = mol/l Uit 4 Part B MHR 265

3 Calculate ph usig: ph = log [H 3 O + ]. ph = log [H 3 O + ] = log ( ) = = 8.15 Check Your Solutio The umber of sigificat digits to the right of the decimal is the same as the umber of sigificat digits i the give K a. 266 MHR Chemistry 12 Solutios Maual

4 105. A solutio of ml of a mol/l itrous acid, HNO 2 (aq), is titrated with mol/l of potassium hydroxide, KOH(aq). Determie the resultig ph of the solutio after ml of the base has bee added. For the acid, K a = What Is Required? You eed to fid the ph at a certai poit i the titratio usig itrous acid ad potassium hydroxide solutios. What Is Give? You kow the volume of the itrous acid: ml HNO2 You kow the cocetratio of the itrous acid: c mol/l HNO2 You kow the volume of the potassium hydroxide: KOH ml You kow the cocetratio of the potassium hydroxide: ckoh mol/l You kow the acid dissociatio costat: K a = Pla Your Strategy Write the balaced equatio for the reactio betwee HNO 2 (aq) ad KOH(aq). Use the formula c to calculate the amout i moles,, of HNO 2 (aq) preset before ay base was added. Use the formula c to calculate the amout i moles,, of KOH(aq). Calculate the amout i moles,, of NO 2 (aq) preset after the base was added. Calculate the amout i moles of ureacted HNO 2 (aq). Act o Your Strategy Because KOH is a strog base, the reactio essetially goes to completio. HNO 2 (aq) + KOH(aq) KNO 2 (aq) + H 2 O(l) HNO 2 c mol ml 1 L L 1000 ml mol KOH c mol ml 1 L L 1000 ml mol Because the reactio goes to completio ad because the ratio of NO 2 to KOH is 1:1, for every mole of KOH added, oe mole of HNO 2 will be coverted ito NO 2. Therefore: NO2 KOH mol excess HNO 2 HNO2 i NO 2 formed mol mol mol Uit 4 Part B MHR 267

5 Determie the fial volume of the solutio. Use c to determie the cocetratios of HNO 2 (aq) ad NO 2 (aq) i mol/l. Write equatios for ay equilibrium reactios occurrig ad determie whether the solutio has bufferig capacity. Write the equilibrium expressio, substitute i the calculated cocetratios ad solve for the cocetratio of the hydroium io. HNO2 KOH ml ml 1 L = ml 1000 ml L chno mol L mol/l c NO mol L mol/l HNO 2 (aq) + H 2 O(l) NO 2 (aq) + H 3 O + (aq) NO 2 (aq) + H 2 O(l) HNO 2 (aq) + OH (aq) The solutio has bufferig capacity. The reactios of HNO 2 ad NO 2 reactig with water balace each other ad very little chage actually occurs. Therefore, you ca use the amouts of HNO 2 ad NO 2 preset after the reactio with KOH ad the equilibrium costat to fid the cocetratio of hydroium io, H 3 O + preset. [NO 2 ][H3O ] Ka [HNO 2 ] 2 4 ( )( x) x ( )( ) 2 [H 3 O + ] = x = mol/l 268 MHR Chemistry 12 Solutios Maual

6 Calculate ph usig: ph = log [H 3 O + ]. ph = log [H 3 O + ] = log ( ) = = 2.61 Check Your Solutio The ph is cosistet with havig ureacted HNO 2 preset. The umber of sigificat digits to the right of the decimal is the same as the umber of sigificat digits i the give K a. The aswer seems reasoable. Uit 4 Part B MHR 269

7 106. If ml of a mol/l hydrofluoric acid solutio, HF(aq), is titrated with a mol/l sodium hydroxide solutio, (aq), determie the ph that results whe ml of the base is added. For the hydrofluoric acid solutio, K a = What Is Required? You eed to fid the ph at a certai poit i the titratio of hydrofluoric acid with sodium hydroxide solutio. What Is Give? You kow the volume of the hydrofluoric acid: HF ml You kow the cocetratio of the hydrofluoric acid: chf mol/l You kow the volume of the sodium hydroxide: ml You kow the cocetratio of the sodium hydroxide: c mol/l You are give the acid dissociatio costat for hydrofluoric acid: K a = Pla Your Strategy Write the balaced equatio for the reactio betwee HF (aq) ad (aq). Use the formula c to calculate the amout i moles,, of HF(aq) preset before ay base was added. Use the formula c to calculate the amout i moles,, of (aq). Calculate the amout i moles,, of F (aq) preset after the base was added. Calculate the amout i moles of ureacted HF(aq). Act o Your Strategy Because is a strog base, the reactio essetially goes to completio. HF(aq) (aq) + (aq) NaF(aq) + H 2 O(l) HF c mol ml L mol c 1000 ml 1 L mol/ L ml 1 L 1000 ml mol Because the reactio goes to completio ad because the ratio of F to is 1:1, for every mole of added, oe mole of HF will be coverted ito F. Therefore: F mol excess HF HF i F formed mol mol mol 270 MHR Chemistry 12 Solutios Maual

8 Determie the fial volume of the solutio. Use c to determie the cocetratios of HF(aq) ad F (aq) i mol/l. Write equatios for ay equilibrium reactios occurrig ad determie whether the solutio has bufferig capacity. Write the equilibrium expressio, substitute i the calculated cocetratios ad solve for the cocetratio of the hydroium io. HF ml ml 1 L = ml 1000 ml L chf mol L mol/l c F mol L mol/l HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) F (aq) + H 2 O(l) HF(aq) + OH (aq) The solutio has bufferig capacity. The reactios of HF ad F reactig with water balace each other ad very little chage actually occurs. Therefore, you ca use the amouts of HF ad F preset after the reactio with ad the equilibrium costat to fid the cocetratio of hydroium io, H 3 O + preset. [F ][H3O ] Ka [HF] 2 4 ( )( x) x ( )( ) 2 [H 3 O + ] = x = mol/l Uit 4 Part B MHR 271

9 Calculate ph usig: ph = log [H 3 O + ]. ph = log [H 3 O + ] = log ( ) = = 2.25 Check Your Solutio The ph is cosistet with havig ureacted HF preset. The umber of sigificat digits to the right of the decimal is the same as the umber of sigificat digits i the give K a. The aswer seems reasoable. 272 MHR Chemistry 12 Solutios Maual

What Is Required? You need to determine the hydronium ion concentration in an aqueous solution. K w = [H 3 O + ][OH ] =

What Is Required? You need to determine the hydronium ion concentration in an aqueous solution. K w = [H 3 O + ][OH ] = Calculatig the [H3O + ] or [OH ] i Aqueous Solutio (Studet textbook page 500) 11. The cocetratio of hydroxide ios, OH (aq), i a solutio at 5C is 0.150 /. Determie the cocetratio of hydroium ios, H 3 O