[3 Mark Question Answer]

Question 13 Marks

Compare the effect of soaps and detergents on hard water.

Answer

Water that contains Ca2+ and $Mg^{2+}$ ions is called hard water. When soap is added to hard water, insoluble compounds form which appears as sticky scum. This scum leaves a deposit on clothes, skin, and hair. You could have a ring around the collar. Detergents have replaced soap for many cleaning jobs around the home.
The development of synthetic detergents by chemists was a great advantage for people with relatively hard tap water in their homes.

Column A	Column B
(a) Blue salt changes to white and then black	(i) Ammonium dichromate
(b) Orange coloured compound changes to green.	(ii) Iodine
(c) Red compound changes to brown and then yellow.	(iii) Zinc Nitrate
(d) White to yellow when hot and white when cold.	(iv) Copper sulphate
(e) Violet solid changes to violet vapours.	(v) Red Lead

Sodium sulphide	Sodium sulphite
Sodium sulphite is the sodium salt of sulphurous acid having molecular formula $Na_2SO_3$, can be made by dissolving NaOH in $H_2SO_3$. In Sodium sulphite, the oxidation state of Sulphur is +4.	Sodium sulphite ($Na_2SO_3$) will effervesce when dilute acid is added giving off a colourless gas with a choking smell (sulphur dioxide), which, if bubbled through acidified dichromate solution will turn it green.
>With Sulphuric acid, sodium sulphide liberates $H_2S$. >$\ce{Na2S + H2SO4 -> Na2SO4 + H2S}$	>With sulphuric acid, sodium sulphite liberates $SO_2$ along with water. >$\ce{Na2SO3 + H2SO4 -> Na2SO4 + H2O + SO2}$

Copper	Magnesium
Copper does not react with dilute sulphuric acid as its reduction potential is higher than that of hydrogen.	Magnesium metal dissolves readily in dilute sulphuric acid to form solutions containing the aquated Mg(II) ion together with hydrogen gas, $H_2.$
Copper does not displace hydrogen from non-oxidising acids like HCl or dilute $H_2SO_4.$	Corresponding reactions with other acids such as hydrochloric acid also give the aquated Mg(II) ion.

Sodium Sulphite	Sodium carbonate
Sodium sulphite is the sodium salt of sulphurous acid having molecular formula $Na_2SO_3$, can be made by dissolving $NaOH$ in $H_2SO_3$. In Sodium sulphite, the oxidation state of Sulphur is $+4.$	Sodium carbonate ($Na_2CO_3$) will effervesce when dilute acid is added and a colourless, odourless gas (carbon dioxide) will be given off which, if bubbled through lime-water, will turn it cloudy.
The gas evolved is carbon dioxide.	Gas evolved is $SO_2$

	Ammonium Chloride	Iodine
Residue left	No residue	No residue
Colour of residue	The colour of the residue is white sublimate.	The colour of the residue is Violet sublimate.
Gas produced	Hydrogen chloride and ammonia gas are produced.($HCl + NH_3$)	Iodine vapours are produced.

	Copper sulphate	Copper carbonate
Residue left	Anhydrous($CuSO_4$)	Copper oxide(CuO)
Colour of residue	The colour of the residue is Dirty white.	The colour is black solid.
Gas produced	Water vapour ($H_2O$) is produced.	Carbon dioxide($Co_2$) is produced.

	Zinc nitrate	Copper nitrate
Residue left	Zinc oxide(ZnO)	Copper oxide(CuO)
Colour of residue	Yellow when hot and White when cold	Black Solid
Gas produced	The gas produced is Nitrogen dioxide and oxygen$(NO_2 + O_2)$	The gas produced is Nitrogen dioxide and oxygen($NO_2 + O_2)$

	Zinc carbonate	Copper carbonate	Lead carbonate
Residue left	Zinc oxide(ZnO)	Copper oxide(CuO)	Lead Oxide (PbO)
Colour of residue	Yellow when hot and white when cold	Colour is Black solid.	Colour is yellow.
Gas produced	Carbon dioxide gas is produced.	Carbon dioxide gas is produced.	Carbon dioxide gas is produced.

	Hydrogen	Oxygen	Carbon dioxide	Chlorine
Litmus test
Apply a burning splint to the gas
Colour of gas	colourless	colourless	colourless	greenish-yellow
Odour of gas

CHEMISTRY [3 Mark Question Answer]

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