IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => IGCSE/ GCSE => Sciences => Topic started by: Mia on June 06, 2010, 06:56:25 am

Title: CHEM PAPER 3 PLEASEEE HELPPP
Post by: Mia on June 06, 2010, 06:56:25 am
Does anybody have notes or can explain reversible reactions and redox - oxidation and reduction [extended section] ? PLEASE... i rlly need ur help.. ?
Title: Re: CHEM PAPER 3 PLEASEEE HELPPP
Post by: elemis on June 06, 2010, 07:19:55 am
To understand what oxidation is memorise this :

OILRIG = Oxidation Is Loss Reduction Is Gain            In this case I am talking about the Gain and Loss of ELECTRONS.

Oxidation can also mean an INCREASE in the oxidation NUMBER :

Mg + Fe2+ -------> Mg2+ + Fe

In the above case Magnesium DISPLACED the less reactive IRON from its SALT. IRON gained ELECTRONS to form IRON ATOMS. It was REDUCED.

However, Look at Iron's oxidation numbers. It went from 2+ to 0. IT REDUCED, thus this confirms REDUCTION OCCURED.

Apply this to Mangesium and you should determine that it was OXIDISED.

Title: Re: CHEM PAPER 3 PLEASEEE HELPPP
Post by: Mia on June 06, 2010, 08:09:57 am
Thank you soo much :)
Title: Re: CHEM PAPER 3 PLEASEEE HELPPP
Post by: ~$VJ DJ$~ on June 06, 2010, 12:25:58 pm
What is, and what are the diffrences between sacrifical protection and cathodic protection????

help me please
Title: Re: CHEM PAPER 3 PLEASEEE HELPPP
Post by: bored2death on June 06, 2010, 12:53:46 pm
Quote from: ~$VJ DJ$~ on June 06, 2010, 12:25:58 pm
What is, and what are the diffrences between sacrifical protection and cathodic protection????

help me please
sacrifical protection is like coating a ship made of steel with zinc. Zinc will "sacrifice" its electrons to the steel which will gain these electrons and become coated. Zinc is more reactive metal and has a greater tendency to lose electrons. get it? or u need more?
cathodic protection is like the electrolysis or electroplating of metals .. like for example a spoon made of silver (crap silver for example|) and you want to protect it from corroding hence u will place it in an electrolysis cell on the cathode electrode and as you know at the cathode reduction occurs which means it also will gain electrons more silver electrons for example and become coated.
I'm sorry if i suck at explaining
Title: Re: CHEM PAPER 3 PLEASEEE HELPPP
Post by: J.Darren on June 06, 2010, 01:17:47 pm
Quote from: ~$VJ DJ$~ on June 06, 2010, 12:25:58 pm
What is, and what are the diffrences between sacrifical protection and cathodic protection????

help me please
Sacrifical protection is when you coat steel with zinc. Zinc, the more reactive metal, gets corroded and forms Zinc ions (i.e. Zinc gets oxidised). The iron accepts electrons onto its surface, since it does not lose electrons, it is not corroded. Sacrifical protection does not require electricity, and the steel does not need to be fully coated with Zinc.

Cathodic protection involves an inert electrode (usually Titanium), it needs electricity (i.e a power supply). Oxidation occurs at the inert electrode , electrons flow through the external circuit to the steel cathode.
Title: Re: CHEM PAPER 3 PLEASEEE HELPPP
Post by: ~$VJ DJ$~ on June 06, 2010, 01:29:56 pm
thx really helpful
Title: Re: CHEM PAPER 3 PLEASEEE HELPPP
Post by: ColdStorm on June 06, 2010, 09:29:55 pm
Excuse Me Guys  How Many Marks Can i Afford To Still Be able To Get An A Or An A*
need quick REplies please :P or around how much  ::)
Title: Re: CHEM PAPER 3 PLEASEEE HELPPP
Post by: TheRock on June 06, 2010, 10:25:28 pm
Lose 30 for an A, around 15 for an A* just in case.
Title: Re: CHEM PAPER 3 PLEASEEE HELPPP
Post by: ColdStorm on June 06, 2010, 11:42:57 pm
Lose 30 Over All Or 30 In Paper 3 Only Thx By the way :)
Title: Re: CHEM PAPER 3 PLEASEEE HELPPP
Post by: TheRock on June 10, 2010, 07:10:43 pm
P3 only.
Title: Re: CHEM PAPER 3 PLEASEEE HELPPP
Post by: AshWINNER on August 14, 2010, 06:48:08 am
Thank god gettin an A star in chem and phy are easy. 17 percent people get em.

Additional maths. sh*t. You cant afford to lose even 7 marks overall out of 160