Chemistry practical has three questions.

Question 1 is quantitative analysis (titration). This year we expect titration between a strong acid and weak base. The base will be a salt with water of crystalization.

Question 2 is qualitative analysis. This year we expect analysis of an organic and inorganic compound.

Question 3 is always general chemistry theory question.

This is not expo. It is for practice purpose.

Feel free to leave your questions, comments and contributions.



Question 1
A is a solution containing 0.100 moldm-3 of hydrochloric acid. B is a solution containing 5.0 g per dm3 of hydrated sodium trioxocarbonate (iv), Na2CO3.xH2O.

(a)Put A into the burette and titrate it against 20.00 cm3 or 25.00 cm3 portion of B using methyl orange as indicator. Record the volume of your pipette. Tabulate your burette readings and calculate the average volume of A used.

Equation for the reaction:
Na2CO3.xH2O(aq) + 2HCl(aq) 2NaCl(aq) + CO2(g) + (x+1)H2O(l)
(b)From your results, calculate the:
(i)Concentration of B in moldm-3.
(ii)Molar mass of Na2CO3.xH2O.
(iii)Value of x in Na2CO3.xH2O.
[H = 1.0, C = 12.0, O = 16.0, Na = 23.0]

ANSWER TO QUESTION 1
1.(a) Volume of pipette used = 25.00 cm3.
Indicator used = Methyl orange
Burette Reading 1st Titre 2nd Titre 3rd Titre
Final volume of A (cm3) 8.80 17.50 26.30
Initial Volume of A (cm3) 0.00 8.80 17.50
Volume of A used (cm3) 8.80 8.70 8.80

Average volume of Acid used = (8.80 + 8.70 + 8.80) / 3
= 26.3/3 = 8.77cm3

(b) (i) Concentration of B in moldm-3:
(Ca x Va)/(Cb x Vb) = A/B
(0.10 x 8.77)/(Cb x 25.00) = 2/1
Cb = (0.10 x 8.77)/(25.00 x 2) = 0.877 / 50 = 0.0175 moldm-3.

(ii) Molar mass of Na2CO3.xH2O = mass conc. / molar conc.
= 5.0 / 0.0175 = 285.7 g/mol
(iii) Value of x in Na2CO3.xH2O:
285.7 = 106 + 18x
x = (285.7 - 106)/18 = 179.7 / 18 = 9.98 approximately 10

Question 2: Carry out the following exercises on specimen C and D. Record your observations and identify any gases evolved. State the conclusion you draw from the result of each test:

a.(i) Add about 5cm3 of distilled water to a portion of C in a test tube. Stir thoroughly and test with litmus.
(ii). Add about 2cm3 of Fehling’s solution to the resulting mixture from (a)(i) above and heat.
b.(i) Heat a portion of D strongly in a test tube.
(ii) Put the rest of D in a boiling tube and add about 10cm3 of distilled water. Shake the mixture.
(iii) Put about 2cm3 of the mixture from b(ii) in a test tube. Add aqueous NaOH in drops and then in excess.
(iv) Put about 2cm3 of the mixture from b(ii) in a test tube. Add aqueous ammonia in drops and then in excess.

ANSWERS FOR QUESTION 2
S/N TEST OBSERVATION INFERENCE
(a)(i) C + distilled water Soluble in distilled water C is a soluble compound
+ Litmus No effect on litmus C is a neutral compound
(ii) Solution of C + Fehling’s solution + Heat Brick-red precipitate C is a reducing sugar (glucose)
(b)(i) D + heat Yellow when hot and white when cold D is zinc oxide (ZnO)
(ii) D + water Does not dissolve in water D is an insoluble compound
(iii) Mixture from (b)(ii) + NaOH(aq) in drops and in excess White precipitate. Precipitate dissolves in excess Al3+, Zn2+, Pb2+ present
(iv) Mixture from (b)(ii) + NH3(aq) in drops and in excess White precipitate. Precipitate dissolves in excess Zn2+ Confirmed

Does your school need any reagents and equipment for the WASSCE or BECE practicals? Kindly, reach 08072751837.

Just came across this and decided to correct something.
Al3+ and Zn2+ form white gelatinous precipitate with drops of NaOH that dissolve in excess sodium hydroxide, while Pb2+ forms white chalky precipitate with drops of NaOH that dissolves in excess NaOH too.
A good observer shouldn't be suspecting Pb2+ when the ppt formed is gelatinous.

I left secondary school a long time ago anyway

Oduok:
Chemistry practical has three questions.

Question 1 is quantitative analysis (titration). This year we expect titration between a strong acid and weak base. The base will be a salt with water of crystalization.

Question 2 is qualitative analysis. This year we expect analysis of an organic and inorganic compound.

Question 3 is always general chemistry theory question.

This is not expo. It is for practice purpose.

Feel free to leave your questions, comments and contributions.



Question 1
A is a solution containing 0.100 moldm-3 of hydrochloric acid. B is a solution containing 5.0 g per dm3 of hydrated sodium trioxocarbonate (iv), Na2CO3.xH2O.

(a)Put A into the burette and titrate it against 20.00 cm3 or 25.00 cm3 portion of B using methyl orange as indicator. Record the volume of your pipette. Tabulate your burette readings and calculate the average volume of A used.

Equation for the reaction:
Na2CO3.xH2O(aq) + 2HCl(aq) 2NaCl(aq) + CO2(g) + (x+1)H2O(l)
(b)From your results, calculate the:
(i)Concentration of B in moldm-3.
(ii)Molar mass of Na2CO3.xH2O.
(iii)Value of x in Na2CO3.xH2O.
[H = 1.0, C = 12.0, O = 16.0, Na = 23.0]

ANSWER TO QUESTION 1
1.(a) Volume of pipette used = 25.00 cm3.
Indicator used = Methyl orange
Burette Reading 1st Titre 2nd Titre 3rd Titre
Final volume of A (cm3) 8.80 17.50 26.30
Initial Volume of A (cm3) 0.00 8.80 17.50
Volume of A used (cm3) 8.80 8.70 8.80

Average volume of Acid used = (8.80 + 8.70 + 8.80) / 3
= 26.3/3 = 8.77cm3

(b) (i) Concentration of B in moldm-3:
(Ca x Va)/(Cb x Vb) = A/B
(0.10 x 8.77)/(Cb x 25.00) = 2/1
Cb = (0.10 x 8.77)/(25.00 x 2) = 0.877 / 50 = 0.0175 moldm-3.

(ii) Molar mass of Na2CO3.xH2O = mass conc. / molar conc.
= 5.0 / 0.0175 = 285.7 g/mol
(iii) Value of x in Na2CO3.xH2O:
285.7 = 106 + 18x
x = (285.7 - 106)/18 = 179.7 / 18 = 9.98 approximately 10

Question 2: Carry out the following exercises on specimen C and D. Record your observations and identify any gases evolved. State the conclusion you draw from the result of each test:

a.(i) Add about 5cm3 of distilled water to a portion of C in a test tube. Stir thoroughly and test with litmus.
(ii). Add about 2cm3 of Fehling’s solution to the resulting mixture from (a)(i) above and heat.
b.(i) Heat a portion of D strongly in a test tube.
(ii) Put the rest of D in a boiling tube and add about 10cm3 of distilled water. Shake the mixture.
(iii) Put about 2cm3 of the mixture from b(ii) in a test tube. Add aqueous NaOH in drops and then in excess.
(iv) Put about 2cm3 of the mixture from b(ii) in a test tube. Add aqueous ammonia in drops and then in excess.

ANSWERS FOR QUESTION 2
S/N TEST OBSERVATION INFERENCE
(a)(i) C + distilled water Soluble in distilled water C is a soluble compound
+ Litmus No effect on litmus C is a neutral compound
(ii) Solution of C + Fehling’s solution + Heat Brick-red precipitate C is a reducing sugar (glucose)
(b)(i) D + heat Yellow when hot and white when cold D is zinc oxide (ZnO)
(ii) D + water Does not dissolve in water D is an insoluble compound
(iii) Mixture from (b)(ii) + NaOH(aq) in drops and in excess White precipitate. Precipitate dissolves in excess Al3+, Zn2+, Pb2+ present
(iv) Mixture from (b)(ii) + NH3(aq) in drops and in excess White precipitate. Precipitate dissolves in excess Zn2+ Confirmed

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Firstorderwizard:
Just came across this and decided to correct something.
Al3+ and Zn2+ form white gelatinous precipitate with drops of NaOH that dissolve in excess sodium hydroxide, while Pb2+ forms white chalky precipitate with drops of NaOH that dissolves in excess NaOH too.
A good observer shouldn't be suspecting Pb2+ when the ppt formed is gelatinous.

I left secondary school a long time ago anyway

Thanks for that

y²+9y+8

Someone assist with this

Anwons:
y²+9y+8

Someone assist with this

.
Find 2 numbers whose sum give +9 and whose multiplication gives +8. They are 8 and 1.

(Y+ 8 )(Y+1)=0
°•♧ Y = -8 or -1