1st:( I'm sorry its a bit long) 1.0g of Zn in reacted with 50 cm3 of 1.0 mole/dm3 of H2SO4 to check the effect of some chemicals or elements on the reaction. 4 exp. are carried out in each exp. the time to collect 50cm3 of hydrogen was recorded. 1st exp. was done with nothing added to reaction mixture. It took 65s to collect 50cm3 of H2 and a colourless solution was obtained. In 2nd exp. CuSO4 was added as possible catalyst. The time taken was 10s and a colourless solution obtained with brown coating on Zn. In third exp. Cu(powdered) was added as possible catalyst . The time recorded was 19s and a colourless solution formed with brown solid at the bottom. In last exp. NaCl was added as possible catalyst. The time recorded was 65s and a colourless solution formed. The question in the book is which substance acted as a catalyst? It says the answer is: Cu and CuSO4 Why CuSo4 has been included in the ansnwer? Doesnt the defination of catalyst say it should remain chamically unchanged at the end of the reation? But here CuSO4 has been reduced to Cu. 2nd Question: In a displacement reaction an Iron rod is dipped into aq. CuSO4. Why not the reaction stops once a layed a Cu is deposited on Iron rod but instead continues until all the CuSO4 solution is used up or whole of the iron rod dissolves away? I'm asking this because the reaction between Al and O2 Al2O3 formed stops any furthur oxidation of Al. And thirdly: Is the following reaction a redox reaction. If it is a redox reaction which is an oxidizing agent and which one is a reducing agent? I know in the ionic equation of this reaction Zn is the reducing agent and Cu2+ is an oxidizing agent. But this really confuses me. CuSO4(aq) + Zn(s) -------> Cu(s) + ZnSO4(aq) Fourthly, Is it true that when an oxidizing agent is added to KI Iodine is formed which dissolves in KI to form a brown solution. And lastly, Excess of KI(a reducing agent) is added to Fe3SO4(which i think should be an oxidizing agent). What will be the colour of the mixture after the reaction is complete? Will it be Green or brown? And what exactly will be the equation for the reaction? Thanks in advance for any help.