The question was attempted by many candidates and the performance was good.
In (a), candidates were able to correctly carry out the titration experiment, tabulate the burette readings and calculate the average volume of acid used. However, some of them lost marks because they lacked the knowledge of concordancy in precision measurement and cancelled out their tables to retabulate in order to conform with the supervisor’s titre values.
In (b)(i), most candidates calculated correctly the concentration of E in moldm-3 as follows:
(i) CDVD = 1
CE VE 1
CE = CDVD
= 0.095 xVD
= P moldm-3 say
1000 cm3 of D contain 0.095 moles of HCI
\ VD of D will contain 0.095 x VD moles of HCI
From the equation,
1mole of HCI reacts with 1 mole of NaHCO3
∴ 0.095 x VD mole HCI will react with 0.095 x VD moles of NaHCO3
20/25 cm3 of E contain 0.095 x VD moles of NaHCO3
∴ 1000 cm3 of E will contain 0. 095 x VD X 1000
= 0. 095 x VD = P moldm-3 say
In (b)(ii), only few candidates correctly calculated the solubility of NaHCO3 thus:
The dilution factor of solution E is 10:1000 = 1:100
Solubility of NaHCO3 = 100 x P moldm-3 = Q moldm-3
CfVf = C1V1
C1 = CfVf
= P x 1000
= 100 x P = Q Say
In (c)(i), candidates correctly stated that damp blue litmus paper would turn red/claret/pink or there is no effect on damp red litmus paper.
In (c)(ii) candidates stated that the gas when passed into lime water turns it milky.
In (d), candidates were able to correctly name one chemical industry that uses the gas and listed two other processes that release the gas into the atmosphere to include:
(i) manufacture of Na2CO3/solvay process/food/drinks industry (aerated drinks, soda water/beer/dry ice)
(ii) - respiration
- burning of fossil fuel
- decay of organic matter
- volcanic eruption
- fermentation of sugars etc.