2025/2025 WAEC/NECO Answers: 2025 Neco Gce. Chemistry practical 1

(1)

Indicator used Methyl Orange 

Volume of burette = 50.00cm3 

Volume of pipette = 25.00cm

(i)

TABULATE:

Titration| 1 | 2 | 3|

First Burette readings (cms) | 21.80 | 21.50 | 24.00

Initial burette reading (cm3) |  01.30 | 01.00 | 03.50

Volume of acid used (cm) | 20.50 | 20.50 | 20. 50

(ii) average volume of A used = 1st + 2nd + 3rd/3

= 20.50 + 20.50 + 20.50/ 3

= 20.50cm3

(iii) Con in g/dm3 = 4.0g/dm3

Con + B moldm-3 = Conc in g/dm-3/molar mass

= 4/40 = 0.1moldm-3

Molar mass of NaOH ==> 23 + 1c + 1

= 40g/mole

Conc of B is 0.1moldm-3

(biii)

Concordant readings are the readings within 0.20cm3 of each other 

(iv)

Methy orange is used because te titration is between or involving strong acid and strong base 

(v)

- I ensure I took the measure below menisons 

- I avoided shaking of pipette while the reading is going on

(vi)

NaOH is soapy to touch 

(1ci)

(i) A is a mono base acid since the mole is 1

A could be HCL, HNO3

(cii)

Equation of the reaction is NaOH +2HCL ==> NaCl + H2O

(2a)

C is soluble salt

(2ai)

- Zn^2+ or Al^3+ present

- Zn^2+ or Al^3+ present

(2aii)

- Zn^2+ or Al^3+ present

- Zn^2+ is confrim

(2bi)

SO3^2- or SO4^2-present

(2bii)

SO3^2- present

(2biii)

SO3^2- confrim

(2c)

ZnSO3

(3a)

(i) Co2 can be removed by adding canstic soda i.e sodium hydroxide

(ii) purity of water can be determined through it boiling point as it is noted that pure water boils at 100oc

(iii)

AgN03 produce brown fumes as NO2 is produced on heating as 2AgNO3 (s) ==> 2Ag(s) + O2(g) 2NO2(g)

(iv) 

It changes the litmus paper red as the hydrogen ion in the wet litmus forms as acid on exposure to the litmus paper.

(3b) 

(i) it don't like drowing

(ii) it cannot be collected by displacement of air because nitrogen constitutes to large percentage of the air constitutes (78%)

(iii) HCL gas or ammonia gas

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