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2010 WAEC Chemistry Practical Burette readings (initial and final) must be given to two decimal places. Volume or pipete...

Chemistry
WAEC 2010

Burette readings (initial and final) must be given to two decimal places. Volume or pipete used must also be recorded but no account of experimental procedure is required. All calculations must be done in your answer book.

A is a solution containing 12.0g dm\(^{-3}\) NaHSO\(_4\) NaHSO\(_4\) P is a solution containing NaOH

(a) Put A into the burette and titrate it against 20.0cm\(^3\) or 25.0m\(^3\) portions of B using methyl orange as an indicator. Repeat the titration to obtain consistent titres. Tabulate your readings and calculate the average volume A used. The equation for the reaction involved in the titration is ;

NaHSO\(_{4(aq)}\) + NaOH\(_{(aq)}\) \(\to\)  Na\(_2\)SO\(_{4(aq)}\) + H\(_2\)O\(_{(l)}\)

[H 1.00, O = 16.0; Na = 23.0, S = 32.0]

 

(b) From your results and the information provided above calculate the:

(i) concentration of A in mol dm\(^{-3}\) 

(ii) concentration of B in mol dm\(^{-3}\)

(iii) mass of Na\(^+\) formed in solution during the titration.

 

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Explanation

(a) Volume of base used (pipette) = 25.00 cm\(^3\); indicator - methyl orange 

Burette reading cm\(^3\) Rough  1st Titration  2nd Titration 
Final burette readings (cm\(^3\)) 21.70 43.30 31.90
Initial burette readings (cm\(^3\)) 0.00 21.60 10.30
Volume of acid used (cm\(^3\)) 21.70 21.60 21.60

 

Average volume of acid = \(\frac{21.60 + 21.60}{2}\)

V\(_A\) = 21.60cm\(^3\)

 

(b)(i) Congratulation of A in mol dm\(^{-3}\) 

Molar mass of NaHSO\(_4\) = 23 + 1 + 32 + (4 x 16) = 120g mol\(^{-1}\)

(ii) concentration of Bin mol dm\(^{-3}\) 

\(\frac{C_AV_A}{C_BV_B}\) = 1

C\(_B\) = \(\frac{C_AV_A}{V_B}\)

= \(\frac{0.10 \times V_A}{20/25}\) 

= a mol dm\(^{-3}\) (3 s.fig)

 


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WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
NECO June/July 2024 - Get offline past questions & answers - Download objective & theory, all in one app 48789
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
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Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
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NECO June/July 2024 - Get offline past questions & answers - Download objective & theory, all in one app 48789
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