Answer : The chemical formula of pure substances are different from those of mixtures because all the matter that exists on earth can be classified into two categories namely; pure substances and mixtures.
A pure substance always consists of a single element or compound. Example Oxygen is formed only of oxygen (O) atoms; whereas the table salt which is formed only by sodium chloride (NaCl) molecules is a compound which is made up of pure elements. A pure substance cannot be further divided into its components.
A mixture is made up of different compounds and/or elements. It can be easily separated using any physical method. Example, sand, salt and saw dust mixed together as a mixture. Also, it will not have a definite chemical formula.
Please refer the attachment for better understanding.
Answer:
Mole percent of water in azeotrope is 69%
Explanation:
Clearly, the azeotrope consists of water and perchloric acid.
So, 72% perchloric acid by mass means 100 g of azeotrope contains 72 g of perchloric acid and 28 g of water.
Molar mass of water = 18.02 g/mol and molar mass of perchloric acid = 100.46 g/mol
So, 72 g of perchloric acid = 
of perchloric acid = 0.72 mol of perchloric acid
Also, 28 g of water = 
of water = 1.6 mol of water
Hence total number of mol in azeotrope = (1.6+0.72) mol = 2.32 mol of azeotrope
So, mole percent of water in azeotrope = [(moles of water)/(total no of moles)]
%
Mole percent of water = 
% = 69%
Answer: 1mole of NaCl
Explanation:
Looking at the given equation :CaCl2 (aq) + Na2CO3 (aq) → CaCO3 (s) + 2 NaCl (aq)
The following deductions can be made,
1 mole of CaCl2 reacted with 1 mole of Na2CO3 to produce 1mole of CaCO3 and 2NaCl.
If 0.500 mole of CaCO3 was produced from this same reaction,it therefore means that we multiply the coefficients of both reactants and product by 0.500 to know the moles of NaCl that will also come out from this same reaction..
So we have the new equation to be:
0.5CaCl2 (aq) + 0.5 Na2CO3 (aq) → 0.5 CaCO3 (s) + 1 NaCl (aq)
From the new equation,1mole of NaCl will be produce alongside 0.5mole of CaCO3,when 0.5mole of CaCl2 reacts with.0.5mole Na2CO3.
