Chapter 1 2019/2020

i. By comparing the number of sub-atomic particles of these isotopes, explain what is meant by the term isotopes . 

[3 Marks]

ii. Determine the number of electrons of Br- ions. 

[1 Marks]

b) In a complete combustion, 1.00 g sample W (CXHYOZ) was burnt to produce 2.52 g of carbon dioxide, CO2 and 0.443 g of water vapour, H2O. Determine the empirical formula of the compound. 

[6 Marks]  

c) Calcium acetate, Ca(C2H3O2)2 solution is the substance used for reducing phosphate level in late-stage kidney failure. In an experiment, 250 mL of 0.25M Ca(C2H3O2)2 solution was prepared. Determine the molality of the solution with a density of 1.509 gmL-1.  

[7 Marks]  

d) Magnesium hydroxide, Mg(OH)2 is an antacid that is used to relieve indigestion, sour stomach and heartburn. It can be prepared by reacting magnesium chloride, MgCl2 and sodium hydroxide, NaOH with the by-product of sodium chloride, NaCl. In an experiment, a student allowed 15.1g of MgCl2 to react with 9.35g of NaOH. Calculate the mass (in grams) of Mg(OH)2 that could be obtained at the end of the experiment.   

[9 Marks]