[Borek]

http://chemistryolympiad.weebly.com/preparatory-problems.html - collection of links to preparatory problems.

http://superhimiki.at.tut.by/default_en.html - in English

In other languages:
http://www.olchem.edu.pl/ - unfortunately, you have to navigate to the questions manually, select ZADANIA, Olimpiady krajowe (National Olympiads) or Olimpiady międzynarodowe (International Olympiads)

http://superhimiki.at.tut.by/links/default.html

http://www.chem.msu.ru/rus/olimp/welcome.html

[Rutherford]

USA chemistry competition: http://www.acs.org/content/acs/en/education/students/highschool/olympiad/pastexams.html
Ukrainia chemistry competition: http://www-chemo.univer.kharkov.ua/olympiad.htm
UK chemistry competition: http://www.rsc.org/Education/events-and-competitions/Olympiad/olympiad-questions-answers.asp
New Zealand chemistry competition: http://www.chem.canterbury.ac.nz/Olympiad/selection_exams/previous_selection_exams.shtml
Australia chemistry competition: https://www.asi.edu.au/site/past_exams.php
Cambridge chemistry challenge: http://www.c3l6.org/downloads
Past IChO tests (1-40): http://www.iuventa.sk/en/Subpages/ICHO/PAST-COMPETITION-TASKS.alej
Some German competition: http://www.chds.de/aufg.php

[Borek]

China: http://www.ccho.org.cn/en/?c=index&p=3&n=6 (as posted elsewhere by Raderford)

[Rutherford]

Here are some Indian tests: http://olympiads.hbcse.tifr.res.in/subjects/chemistry/papers.

[SinkingTako]

A (more complete) collection of prep problems (with solutions!!!). Site is in Italian, but almost all the stuff are in English and should be easy to navigate.

http://www.pianetachimica.it/olimpiadi/test_olimpiadi.htm

[Rutherford]

Nice, but I already saw a mistake. The solution for problem 11 part 4. is surely incorrect. The phosphate group will dissociate to a significant amount. But at last I found an acceptable solution for the last problem.

[SinkingTako]

Haha, I think the team leaders for each country should have already received the official answer key. (Though I don't have it. I think is released for public sometime in May.) Yeah some of the solutions they proposed are wrong for this year. But for most of the other years the official answers are up there. Saves the trouble of looking.

[Rutherford]

Austria: http://www.oecho.at/bewerb/aufgaben/2012/

[oldbabie]

Please tell me where i could download some other national chemistry olympiads.
Example: Belarusian 2011, 2012, 2013, 2014?
Japanese Chemistry Olympiads...
Taiwan chemistry Olympiad (I have 16, 18, 19 and 20th, but i have not the others).

Thank so much,

[PoetryInMotion]

Sweden
http://kemiolympiaden.nu/tidigare-prov/

Denmark
http://www.emu.dk/modul/dansk-kemiolympiade-opgaver

Norway
http://foreninger.uio.no/kjemiolympiaden/oppgaver/

[hsgsno1]

Please give me some links to mendeleev international chemistry olympiad in english
Thank you

[zhangtianzong]

Please give me some links to Mendeleev international chemistry Olympiad in English
Thank you

Sadly, only 2014&2015 Mendeleev international chemistry Olympiad have problems in English version, while test before 2013 haven't (at least I can't find it on GOOGLE). You may also buy a book called "21th century chemistry :Mendeleev international chemistry Olympiad", which offers English problems of IMO from 2001 to 2007.

[luvynva]

Please give me link to Germany National Chemistry Olympiad 2011 in english. I just find problems of it from 2003. Thank you!!!

[AWK]

These are quite easy to find Google: German National Chemistry Olympiad 2011

The first link is:

http://wettbewerbe.ipn.uni-kiel.de/icho/aufgaben/archiv/German_Problems_2011.pdf

[luvynva]

These are quite easy to find Google: German National Chemistry Olympiad 2011

The first link is:

http://wettbewerbe.ipn.uni-kiel.de/icho/aufgaben/archiv/German_Problems_2011.pdf

Oh, sorry! I made a mistake. Actually, I want to find German National Chemistry Olympiad 2001:P