Calculate the percentage composition of calcium and sulphur in calcium bisulphite. [3] Find the relative molecular mass of the following compounds: [3 a. Potassium Acetate b. Sodium Thiosulphate c. Ammonium Dichromate 3. Find the percentage mass of water in Na2SO4.10H2O [ + Give the empirical formula of - a. Benzene b. Acetic Acid 5. Write chemical reaction in which: 13 a. A white precipitate is formed b. Change of state takes place C. CO2 gas is evolved 5. Give reason:- (2 a. Molybdenum is used in the manufacture of ammonia b. Silver nitrate solution is stored in coloured bottles Write the names of the following compounds [2 a. Ba(ClO3)2 b. Na4Fe(CN)6 c. NaClos d. K3B03 B. Balance the following word equation. LE a. Barium Chloride + Sodium Sulphate → Barium Sulphate + Sodium Chloride b. Lead Dioxide + Hydrochloric Acid → Lead (11) Chloride + Water + Chlorine 3. Define- a. Atomic mass unit b. Chemical reaction c. Formula 10. Write the formula of the following: a. Lead Acetate b. Potassium Nitride c. Magnesium Arsenite d. Sodium Zincate MATKA
Answers
Answer:
FORMULAS: A chemical formula shows the elemental composition of a substance: the
chemical symbols show what elements are present and the numerical subscripts show how
many atoms of each element there are in a formula unit. Examples:
NaCl: one sodium atom, one chlorine atom in a formula unit
CaCl2: one calcium atom, two chlorine atoms in a formula unit
Mg3N2: three magnesium atoms, two nitrogen atoms in a formula unit
The presence of a metal in a chemical formula indicates an ionic compound, which is composed
of positive ions (cations) and negative ions (anions). A formula with only nonmetals indicates a
molecular compound (unless it is an ammonium, NH4
+
, compound). Only ionic compounds are
considered in this Tutorial.
There are tables of common ions in your lecture text, p 56 (cations) and p 57 (anions). A
combined table of these same ions can be found on the inside back cover of the lecture text. A
similar list is on the next page; all formulas needed in this and subsequent Tutorial problems can
be written with ions from this list.
Writing formulas for ionic compounds is very straightforward: TOTAL POSITIVE CHARGES
MUST BE THE SAME AS TOTAL NEGATIVE CHARGES. The formula must be neutral. The
positive ion is written first in the formula and the name of the compound is the two ion names.
EXAMPLE: Write the formula for potassium chloride.
The name tells you there are potassium, K+
, and chloride, Cl–
, ions. Each potassium ion is +1
and each chloride ion is -1: one of each is needed, and the formula for potassium chloride is
KCl. "1" is never written as a subscript.
EXAMPLE: Write the formula for magnesium hydroxide.
This contains magnesium, Mg2+, and hydroxide, OH–
, ions. Each magnesium ion is +2 and
each hydroxide ion is -1: two -1 ions are needed for one +2 ion, and the formula for magnesium
hydroxide is Mg(OH)2. The (OH)2 indicates there are two OH–
ions. In a formula unit of
Mg(OH)2, there are one magnesium ion and two hydroxide ions; or one magnesium, two
oxygen, and two hydrogen atoms. The subscript multiplies everything in ( ).
EXAMPLE: Write the formula for aluminum sulfate.
This contains aluminum, Al3+, and sulfate, SO4
2–, ions. The lowest common multiple of 3 and 2
is 6, so we will need six positive and six negative charges: two Al3+ and three SO4
2– ions, and
the formula for aluminum sulfate is Al2(SO4)3. Then, in a formula unit of Al2(SO4)3 there are two
aluminum ions and three sulfate ions; or two aluminum, three sulfur, and twelve oxygen atoms.
COMMON POSITIVE IONS COMMON NEGATIVE IONS COMMON NEGATIVE IONS
H+ hydrogen [Fe(CN)6]3– ferricyanide C2H3O2
– acetate
NH4
+ ammonium [Fe(CN)6]4– ferrocyanide CN– cyanide
Li+ lithium PO43– phosphate CNO– cyanate
Na+ sodium HPO42– hydrogen phosphate SCN– thiocyanate
K+ potassium H2PO4
– dihydrogen phosphate ClO– hypochlorite
Mg2+ magnesium CO32– carbonate ClO3
– chlorate
Ca2+ calcium HCO3
– hydrogen carbonate ClO4
– perchlorate
Sr2+ strontium SO32– sulfite IO3
– iodate
Ba2+ barium HSO3
– hydrogen sulfite MnO4
– permanganate
Al3+ aluminum SO42– sulfate NO2
– nitrite
Sn2+ tin(II) HSO4
– hydrogen sulfate NO3
– nitrate
Sn4+ tin(IV) S2O32– thiosulfate OH– hydroxide
Pb2+ lead(II)1 CrO42– chromate IO4
– periodate
Bi3+ bismuth Cr2O72– dichromate H– hydride
Cr3+ chromium(III)2 O2– oxide F– fluoride
Mn2+ manganese(II)3 O22– peroxide Cl– chloride
Fe2+ iron(II) S2– sulfide Br– bromide
Fe3+ iron(III) HS– hydrogen sulfide I– iodide
Co2+ cobalt(II)4
Ni2+ nickel(II)5
Cu+ copper(I)
Cu2+ copper(II) 1There is also a lead(IV)
Ag+ silver 2There is also a chromium(II)
Zn2+ zinc 3There is also a manganese(III)
Cd2+ cadmium 4There is also a cobalt(III)
Hg22+ mercury(I) 5There is also a nickel(III)
Hg22+ mercury(II)
T-8
PERCENTAGE COMPOSITION: Imagine a class of 40 boys and 60 girls: 100 students total.
40/100 of the students are boys and 60/100 girls; or, 40% boys and 60% girls. The "%" sign
means percent, or parts per 100.
Suppose a class has 10 boys and 15 girls, for a total of 25 students. If you want to find out how
many boys there would be per 100 students, keeping the same ratio of boys to girls, the
following proportion can be set up:
10 boys X boys
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