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Answers to Readers' Questions on Chemistry:
Water
The following 3 comments and questions have been sent in. They are listed according to date.
List of first 10 items
- Volume of gases in electrolysis of water
- Can you separate salt from water by freezing the water?
- How does electrolysis work?
Volume of gases in electrolysis of water
Question
October 30, 2007
What is the volume of oxygen and hydrogen produced at atmospheric pressure by breaking down 1 litre of water by electrolysis.
Richard - South Africa
14675
Answer
There would be two units of Hydrogen and one unit of Oxygen gas. The volume of the gases would depend on the pressure, as well as how much of the gases where separated.
Can you separate salt from water by freezing the water?
Question
October 22, 2007
Can you seperate salt from water by freezing the water?
Eduardo - USA
14619
Answer
If you have enough salt in the water, it will precipitate out as you cool the water. It will collect on the bottom. But if there is not enough salt in the water, the salt water will freeze before the salt precipitates out.
How does electrolysis work?
Question
July 3, 2007
Hi Im Jose,, Im interesting in know more about electrolysis
My question is: what is the exactly current or/and voltage applied to the water for the molecule to brake into hydrogen and oxygen?
What is the exact process that occurs in an electrolysis?
Is the speed of breaking the molecule varies depending on the current or/and voltage applied to the water?
Jose - USA
14018
Answer
Electrolysis is a method of separating bonded elements and compounds by passing an electric current through them. It is often used to separate water.
Since pure water does not readily conduct electricity, the experiment is often done by adding salt or mild acid to the water to increase its conductivity. In such a case, a 6VDC battery should be sufficient to create electrolysis.
As electrons pass through the water solution, some water molecules are broken into hydrogen(+) and oxygen(-) ions. The hydrogen ions are attracted to the negative (-) electrical terminal, were they combine to form H2 gas bubbles. The oxygen ions collect at the (+) terminal and combine to form O2 gas bubbles. The chemical equation is 2H2O --> 2H2 + O2.
A higher current means it will be passing more electrons and results in a faster rate of collection at the cathode and anode terminals. A higher voltage means there is more energy to create H2 and O2. When the water is not pure, the required voltage is reduced.
A good description of electrolysis of water can be seen at:
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/electrol.html
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