chem mock mc

1) CuO is reduced to Cu. The burner is turned off but the hydrogen is kept flowing until the tube is cool.

what's the main reason why the hydrogen is kept flowing ?
a ) to lessen the risk of explosion
c) to prevent the water from reacting with the air.

個ans 係 c ...點解a唔岩 ?



2) 係 electroplating ..個size of current 應該大d好定細定好 ? .. if the tme is the same


3) 3g of Mg is added to 100cm3 of Mg(NO3)2 solution Calculate the molarity of Mg(NO3)2 after 50cm3 of 1.5m HNO3 is added into the solution.

a) 0.25M
B)0.75M
C)1.58M
D)2.38 M

ANS 係 C .. 點計 ?



4) pH of HCL is 2.. what will be the pH of the acid after adding 10g of NaCl ?

個ans 都係 pH 2 .. why ?



sorry 有好多唔識..