19.2 CHAPTER 19. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE
a. KOH
b. FeCl 3
c. Mg(OH) 2
2. How many moles are present in:
a. 10 g of Na 2 SO 4
b. 34 g of Ca(OH) 2
c. 2 , 45 × 1023 molecules of CH 4?
3. For a sample of 0 , 2 moles of magnesium bromide (MgBr 2 ), calculate:
a. the number of moles of Mg2+ions
b. the number of moles of Br−ions
4. You have a sample containing 3 mol of calcium chloride.
a. What is the chemical formula of calcium chloride?
b. How many calcium atoms are in the sample?
5. Calculate the mass of:
a. 3 moles of NH 4 OH
b. 4 , 2 moles of Ca(NO 3 ) 2More practice video solutions or help at http://www.everythingscience.co.za(1.) 007q (2.) 007r (3.) 007s (4.) 007t (5.) 007uComposition ESAGB
Knowing either the empirical or molecular formula of a compound, can help to determine
its composition in more detail. The opposite is also true. Knowing thecompositionof a
substance can help you to determine its formula. There are four different types of compo-
sition problems that you might come across:1. Problems where you will begiven the formulaof the substance and asked tocalcu-
latethepercentage by massof each element in the substance.
2. Problems where you will begiven the percentage compositionand asked tocalcu-
late the formula.
3. Problems where you will begiven the productsof a chemical reaction and asked to
calculate the formulaof one of the reactants. These are often referred to as combus-
tion analysis problems.342 Chemistry: Chemical change