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#Post#: 365--------------------------------------------------
staright forward questions
DIR By: Kizitombano
Date: July 7, 2012, 10:53 am
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1. (a) (i) Mention one compound that makes water
I. Temporarily hard,
II. Permanently hard.
(ii) State one method that could be used to remove
I. Only temporary hardness,
II. Both temporary and permanent hardness in water.
(iii) Write an equation to show the removal of
I. Temporary hardness,
II. Permanent hardness.
(b) State the function of each of the following substances in
the purification of water for town supply:
(i) Sodium aluminate (III) [NaAlO2];
(ii) Lime (calcium hydroxide);
(iii) Calculated amount of iodine;
(iv) Sand bed
2. (a) (i) Define each of the following terms:
I. Pollution;
II. Pollutant.
(ii) Mention three types of pollution
(iii) Give two ways by which pollution can be prevented.
3. (a) State the names of the two gases which make up most of
the air.
(b) Two common pollutants in air are carbon monoxide and the
oxides of nitrogen.
(i) Name another pollutant in air.
(ii) Describe how carbon monoxide is formed.
(iii) How are the oxides of nitrogen formed?
(iv) Explain, with the aid of chemical equations how a catalytic
converter reduces the emission of these two gases.
#Post#: 366--------------------------------------------------
Re: staright forward questions
DIR By: Michel
Date: July 8, 2012, 7:26 am
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[font=verdana]Straight forward questions, and straight forward
answers as well
1a) i) for temporary hardness, calcium and magnesium
bicarbonates, Ca(HCO3)2 and Mg(HCO3)2. These compounds are
easily decomposed by heat, hence the term temporary hardness.
They decompose to their carbonates which are insoluble.
for permanent hardness, Calcium and Magnesium sulfates, CaSO4
and MgSO4. They are not decomposed by heat.
[size=14pt][font=verdana]
[font=verdana][size=12pt][size=14pt][size=12pt]ii) Boiling
removes temporary hardness. Both Ca(HCO3)2 and Mg(HCO3)2
decompose on heating to precipitate their carbonates
eg
Ca(HCO3)2→CaCO3 + H2O + CO2
the permutit or ion exchange resin is used to remove both
temporary and permanent hardness.
Permutit are double silicates of Na or K with Al.
Eg Na2O.Al2O3.4SiO2.2H2O
When added to hard water, it precipitates the Ca2+ and Mg2+ as
their permutit
iii) eqn for removal of temporary hardness-decomposition of
CaHCO3, given earlier in this post
eqn for removal of permanent hardness:
Write a balanced equation for the reaction between calcium
sulfate and Sodium carbonate.
b) NaAlO2 is used for coagulation; consider the size of the
anion in this salt. What do you think? Read up colloids to see
why NaAlO2 is useful for coagulation of dirt particles in water.
Lime is used for softening temporarily hard water in water
purification
Iodine is used as a food supplement, most likely to add
nutritional value to the water,
sand bead acts as a filter to remove dirt
particles[size=12pt][/size][/font][/size][/font][/size][/size][/size][/font]
#Post#: 374--------------------------------------------------
Re: staright forward questions
DIR By: Kizitombano
Date: July 8, 2012, 4:43 pm
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thanks a lot...even thought the fonts are very tiny....but i
will edit with MS word...
#Post#: 378--------------------------------------------------
Re: staright forward questions
DIR By: Michel
Date: July 10, 2012, 7:12 am
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3. b) the other major culprit is sulfur dioxide, which causes
acid rain when it dissolves in rain water.
SO2 + H2O <==> H2SO3
Air around some industries that produce less active metals from
their sulfide ores usually have high concentration of SO2
CO is formed by incomplete combustion of fuels. Could be
automobile fuels or charcoal, etc.
When there is insufficient oxygen for combustion, Carbon
monoxide is produced.
Nitrogen oxides are produced when fuels are burnt at
temperatures high enough for atmospheric Nitrogen and oxygen to
react.
Depending on the H of the reaction, the temperature of the flame
may be sufficient for reaction of N and O2 to produce nitric
oxide.
And lightening of course provides electrical energy that can
trigger 2N + O2 → 2NO
Which may be further oxidized to NO2
No much ideas about the catalytic converter, but in automobile
catalytic converters, surface catalysts are used to convert
gases that would otherwise be atmospheric pollutants into
harmless gases;
eg CO is converted to CO2, NO is converted to N2.
For #2, a good text will get it done
#Post#: 398--------------------------------------------------
Re: staright forward questions
DIR By: Kizitombano
Date: July 15, 2012, 5:30 pm
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) eqn for removal of temporary hardness-decomposition of CaHCO3
#Post#: 399--------------------------------------------------
Re: staright forward questions
DIR By: Kizitombano
Date: July 15, 2012, 5:34 pm
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and one more thing..the way these questions are being answered
are very confusing and difficult to comprehend..could you
please simplify ...
#Post#: 401--------------------------------------------------
Re: staright forward questions
DIR By: Kizitombano
Date: July 15, 2012, 5:43 pm
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what i mean is that could you put the solutions to the questions
in one post...
#Post#: 402--------------------------------------------------
Re: staright forward questions
DIR By: Michel
Date: July 15, 2012, 5:55 pm
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--- Quote from: Kizitombano link ---
>
> what i mean is that could you put the solutions to the
questions in one post...
>
--- End Quote ---
Sorry for posting twice. You could review my earlier posts. The
first post is on question 1.
The second post is on question 2.
--- Quote from: Kizitombano link ---
>
> ) eqn for removal of temporary hardness-decomposition of
CaHCO3
>
--- End Quote ---
yes. Temporary hardness is removed by boiling the water. When
the water is boiled, the temperature of the water increases, and
the Ca(HCO3)2 decomposes.
Ca(HCO3)2=>CaCO3 + CO2+ H2O
--- Quote from: Kizitombano link ---
>
> and one more thing..the way these questions are being answered
are very confusing and difficult to comprehend..could you
please simplify ...
>
--- End Quote ---
sorry, :( I'll try my best to simplify
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