Give a reason for each of the following laboratory practices: I. KMnO4 solution is not acidified with HNO3 before titration
II. FeSO4 solution is usually prepared fresh when needed
III. Alkali are not stored in glass stoped reagent bottles

See explanation

Explanation:

The acid commonly used to acidify KMnO4  is H2SO4. The reason why HNO3  is not used is because HNO3  is itself a strong oxidizing agent. HCl is not used because it can react with KMnO4.

FeSO4 solution is usually prepared fresh when needed because if the solution is prepared and left to stand for sometime, FeSO4  is oxidized to Fe2(SO4)3 by air. Fe III does not give the brown ring test.

Alkali are not stored in glass stopped reagent bottles because very strong alkali can cause the stopper to corrode and fuse to the neck of the bottle making it very difficult to open the reagent bottle.

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"

they are all solids.