(a) In an experiment, 25.0 cm$^{3}$ of H\..

Question 1 Report

(a) In an experiment, 25.0 cm$^{3}$ of H$_{2}$SO$_{4}$ completely neutralized 24.0 cm$^{3}$ of a 0.1 50 mol dm$^{-3}$ aqueous KOH using a suitable indicator.

(i) Write a balanced chemical equation for the reaction.

(ii) Calculate the concentration of the acid solution.

(b)i. A burning magnesium ribbon was placed in a gas jar containing Carbon (IV) oxide.
- Write an equation for the reaction.
- Explain briefly why the magnesium ribbon burns in carbon(lV) oxide although the gas does not support combustion.
- Calculate the percentage mass of nitrogen in magnesium trioxonitrate (V). |N = 140. O = 16.0. Mg = 24.01]

(i) State two chemical reactions which could he sed te identify the compound.

(ii) What would be observed in each of the reactions stated in c(i)

(d) Describe briefly how soap is manufactured using pellets of sodium hydroxide and vegetable oil

(e) Define the term electronegativity

Answer

(a)

i. 2KOH $_{a q}$ + H $_{2}$ SO $_{4 (a q)}$ ⟹ K $_{2}$ SO $_{4 (a q)}$ + 2H $_{2}$ O $_{(l)}$

ii. Amount of KOH used = $\frac{24}{1000} \times \frac{0.150}{1}$ = 0.0036mol

Mole ratio of acid to base = 1:2

Amount of H $_{2}$ SO $_{4}$ used $\frac{0.0036}{2}$ = 0.0018mol

$∴$

Concentration of H $_{2}$ SO $_{4}$ = $\frac{0.0018}{0.025}$ = 0.072mol dm $^{- 3}$

(b)

(i)

Molar mass Mg(NO

$_{3}$ ) $_{2}$ = 24 x 1 + 2 x [14 + (16 x 3)] 24 x 1 + 2 x [14 + 48] = 24 + 28 + 96 = 148 gmol $^{- 1}$

Mass of N $_{2}$ = 14 x 2- 28

%Nitrogen = $\frac{28}{149} \times \frac{100}{1}$ = 18.9%

(c)

i) Reaction with brominei n CCl $_{4}$ /bromine water/H $^{+}$ / K MnO $_{4}$ / H $^{+}$ / K $_{2}$ Cr $_{2}$ O $_{7}$

$_{7}$
- Reaction with aqueous NaHCO $_{3}$ / Na $_{2}$ CO $_{3}$ . OR
- Reaction with alkanol + Conc. H $+ 2$ SO $_{4}$

(ii)

- Compound will decolourize bromine in CCl $_{4}$ / bromine water
- Change H $^{+}$ /K\ $_{2}$ Cr $_{2}$ O $_{7}$ from orange to green.
- Change H $^{+}$ /KMnO $_{4}$ from purple to colourless.
- There will be effervescence/evolution of gas in reaction with NaCO $_{3 (a q)}$ /

- Production of sweet-smelling/fruity odour

(d) Add sufficient water to dissolve the pellets of NaOH.

The solution is then added to the vegetable oil, stirred, and boiled. It is cooled to precipitate the soap/salt out the soap/salt. Filter off the soap takes off the soap crust.

(e)Define the Term Electronegativity:

The tendency of an atom to pull to itself the shared pair of electrons in a covalent bond. The ability of an atom to attract shared electrons between It and another atom in a chemical bond

Read lesson note on Stoichiometry And Chemical Reactions (WAEC)

Answer Details