BOLIVIAN OLYMPIAD OF CHEMISTRY

EXERCISE GUIDE
CHAPTER II, MATERIAL BALANCE

INTRODUCTION
2.1.- Why is the performance of a process not always 100%?
2.2.-How do you define the theoretical yield of a chemical reaction?
2.3.- How are chemical reactions classified?
2.4.-a) Enuncie la ley de la conservación de la materia b) Qué diferencia existe entre el
material balance with chemical reaction and balance without chemical reaction
Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in chemical reactions.
PERCENTAGE WEIGHT WEIGHT
2.6.-Calculate the percentage by weight of the following solutions:
25 g of Sodium Bromide + 100 g of water.
1.20 g of potassium sulfate + 500 g of water
c) 40 g of magnesium nitrate + 500 g of water.
d) 0.25 mol of acetic acid + 3.0 mol of water. R.-a) 20% b) 0.24% c) 7.4% d) 21.74%
2.7.-How many grams of a 12.5% weight solution of silver nitrate does it contain?
siguiente? a) 30 g de nitrato de plata. b) 0,4 mol de nitrato de plata. R.-a) 240 g b) 512 g
2.8.- How much solute is in each of the following solutions?
a) 65 g of 5% potassium chloride solution.
250 g of 5% potassium dichromate solution.
c) 100 g of a 6% sodium bicarbonate solution. 3.25 g
A merchant bought 100 lb of dehydrated sodium carbonate at 0.625 $us/lb.
During the storage period, the water of crystallization was lost; then the shopkeeper
He sold the carbonate for $1 USD/lb. How much money did the merchant gain or lose during the
transaction? He/She lost 25.44 $us.
2.10.-What mass of 5.5% solution can be prepared with 25 g of ClK? -554.5 g
2.11.-The physiological saline solutions used in intravenous injections have a
0.9% mass concentration of sodium chloride.
a) How many grams of sodium chloride are required to prepare 500 g of this solution?
b) How much water should be evaporated from the previous solution to reach a 9% solution?
145.4 g
4.5 g
2.12.- What is the weight percentage of a solution resulting from mixing 2 liters of ethanol
with 3.5 liters of water. The density of ethanol is 0.79 g/cc. -34.5%
2.13.-Calculate the necessary volume of sulfuric acid with a density of 1.84 g/cc and 98 % in
weight, to obtain 40 g of pure sulfuric acid. R.-22.2 cm3
2.14.-A 20EA 35% nitric acid solution has a density of 1.21 g/ml.
a) How many grams of acid are in one liter of this solution?
b) Que volumen de esta disolución contendrá 500 g de ácido? R.a) 423.5 g b) 1180.6 cc
2.15.-Find the amount of heptahydrate magnesium sulfate that should be added to 500 g of
water to form a final 15% solution in anhydrous salt. R.-207.1 g
1 Kg of nitric acid at 62.7% by weight is mixed with 1 Kg of nitric acid at 22.38.
Calculate the concentration of the resulting acid. -42.54%
2.17.- 1 liter of nitric acid with a density of 1.380 g/cc and 62.7% is mixed with 1 liter of nitric acid.
of density 1.130 g/cc and 22.38 %. If the density of the mixture is 1.26 g/cc, find a)
44.45%
2.18.-What volumes of sulfuric acid with 94.32% concentration and a density of 1.832 g/cc and acid
sulfuric of 10.56 At a density of 1.070 g/cc, xx are required to prepare 2.5 l of a
sulfuric acid solution for batteries. The acid for batteries has a density of 1.300
g/cc and 39.68 % by weight. V1 = 426 cm3 and V2 = 2185 cm3
2.19.-There are 12 tons of coal that contains 2.3% sulfur and also abundance of
2 types of coal with 0.80% and 1.10% sulfur respectively. How many tons of each?
one of these coals will have to be mixed with the first 12 tons, to obtain 20 tons with a
1.7% sulfur content? Resp.-8 tons
2.20.- Calculate the amounts of decahydrated sodium carbonate and water that are needed
to prepare 12 L of solution at 13.90% anhydrous carbonate, and with a density equal to
1.145 g/ml Resp.-5153 g of carbonate and 8587 g of water
2.21.- A mixture that contains 45% benzene and 55% toluene in weight is fed to
a distillation tower. The upper stream has a concentration of 95% benzene in
weight, while 8% of the benzene fed to the tower exits with the lower current.
The feed flow is 2000 Kg/h. Determine the upper current flow and the
mass flows of benzene and toluene in the lower stream.
Resp.-Inferior: 72 kg. benceno y 1056 kg. tolueno; Superior: 872 kg
2.22.-What amount of water must be evaporated from one ton of sulfuric acid?
density 1.260 g/ml and 35.03% to obtain an acid with a density of 1.490 g/ml and 59.24%?
Resp.-408.7 kg of water.
2.23.- How many grams of Na2SO3They will be needed to prepare 5 liters of an 8% solution (in
mass) density equal to 1.075 g/ml. Resp.-430 g
At a temperature of 25 °C, the solubility of NaCl is equal to 38 g in 100 g of water.
Find the mass % of NaCl in a saturated solution. Response -26.5%
2.25.-Starting from 400 g of a 50% (by mass) solution of H2SO4they were eliminated, due to
evaporation of 100 g of water. Find the percentage by mass of H2SO4in the dissolution
remaining. Resp.-66.7%
2.26.-Determine the % by mass in a solution obtained by mixing 300 g of a solution
25% concentration by mass and 400 g of another solution at 40% of said substance. Answer: 33.6%
2.27.- To what volume should 500 ml of a 20% mass solution of NaCl be diluted?
(density 1.52 g/cm³), to obtain a 4.5% solution (density 1.129 g/ml). Resp.-
2.49
2.28.- 500 ml of HNO3At 32% by mass (density 1.2 g/ml), 1 liter of water was added. Find
the percentage by mass of HNO3in the obtained solution. Resp.-12 %
2.29.- How many grams of a 2% mass solution of AgNO3 will be necessary to
To form 14.35 g of AgCl precipitate by reacting with an excess of NaCl? Answer - 85 g
A sample of facial cream weighing 8.41 g lost 5.83 g of moisture.
heat it to 110°C. The residue was extracted with water and, once dry, had lost 1.27g of
glycerol soluble in water. The rest were other oils. Calculate the composition of this cream.
69.3 %
2.31.-It is desired to obtain 200 kg of brass whose weight composition is 80% copper and 20% zinc.
%, there is metallic copper with 98% weight purity and zinc with 95% weight. What
How much of these metals will need to be melted? Resp.-163.3 kg of copper, 42.1 kg of zinc.
2.32.-Find the quantities of two solutions of nitric acid at 24% and 14% by weight.
nitric acid (purity) respectively, that must be mixed to prepare 1 kg of an acid
20% pure nitric. 600 g of 24% acid, 400 g of 14% acid
PERCENTAGE WEIGHT VOLUME
2.33.-Calculate the weight/volume percentage of the following solutions:
22 g of methanol dissolved in ethanol to make 100 ml of solution.
 4.2 g of sodium chloride dissolved in water to make a 125 ml solution.
5 g of sodium hydroxide dissolved in a final volume of 250 ml of solution.
0.22 moles of hydrochloric acid dissolved in a total of 100 ml of solution.
22%
2.34-45 g of nitric acid are dissolved in 250 g of water. What is the weight percentage?
volume of the resulting solution? The density of the solution is 1.15 g/cc. R.-17.54%
percentage
2.35.- What volume of 70% alcohol for friction can be prepared if only
Do you have 150 ml of isopropyl alcohol? -214.3 cm3
2.36.-What is the volume percentage of the following solutions?
10 ml of methanol dissolved in water to complete a volume of 40 ml.
b) 2.0 ml of carbon tetrachloride dissolved in benzene completed to 36 ml.
c) 40 ml of antifreeze dissolved in water and brought to a final volume of 130 ml.
25%
PARTS PER MILLION
2.37.- 70 mg of Ca is dissolved in a total of 2.5 l of water. What is the concentration of this?
solution in ppm? R.-28 ppm
2.38 - 0.002 moles of sulfuric acid is dissolved in 1 liter of solution. What is the concentration?
in ppm of sulfur? R.-64 ppm
2.39.- In a bottle of mineral water, in its composition table it has the following
-2
readings: Cl- 63 ppm470 ppm. Calculate the
amount of these components that a person ingests when drinking 2 glasses of this soda.
(each glass contains 300 ml). 37.8 mg Cl, 13.2 mg Ca, 18.0 mg Mg and 42.0 mg SO4-2
MOLARITY
2.40.-Calculate the molarity of the following solutions:
0.10 moles of solute in 250 ml of solution.
b) 2.5 mol of sodium chloride in 0.650 l of solution.
c) 0.35 mol of barium chloride in 593 ml of solution.
0.025 mol of hydrochloric acid in 10 ml. R.-a) 0.4 M b) 3.85 M c) 2.5 M d) 0.59 M
2.41.-Calculate the molarity of the following solutions:
53 g of sodium chromate in 1 liter of solution.
260g of C6H12O6in 800 ml of solution.
1.5 g of aluminum sulfate in 2 liters of solution.
d) 0,0282 g de nitrato de calcio en 1 ml de sol. R.-a) 0.33 M b) 1.80 M c) 2.2x10 –3 M
2.42.-Calculate the number of moles of solute in each of the following solutions:
40 liters of lithium chloride 1.0 M. c) 25 ml of 3.0 M sulfuric acid.
b) 349 ml of Sodium Hydroxide 0.001 M. d) 5,000 ml of Cobalt (II) Chloride 3.1 M.
R.-a) 40 b) 3.49x10-4 c) 7.5x10-2 d) 15.5
2.43.- Calculate the number of grams of solute in each of the previous solutions.
1700 g
2.44.- How many ml of 0.25 M potassium chloride solution will contain the following?
0.430 mol of potassium chloride.
c) 20.0 g of the salt. 71 g of chloride ion.
1720 ml
2.45.-What is the molarity of a nitric acid solution if the solution is 35% by weight?
and a density of 1.21 g/ml? R.-6.72 M
2.46.- How can 800 ml of 0.10 M copper sulfate be prepared from copper sulfate?
pentahydrate? A.- 19.76 g of the salt is dissolved
2.47.-Commercial vinegar is a solution of 4% acetic acid by weight. Its density is
1.006 g/ml. What is the concentration in terms of molarity? R.-0.67 M
2.48.-On the label of a bottle of mineral water, the concentration of magnesium ion is
234 ppm. Express this concentration in moles/liter. -9.6 x 10^-3 M.
2.49.-The density of a solution that contains 10.0 g of potassium sulfate in 100 g of
The solution is 1.08 g/ml. What is the molarity of this solution? R.-0.575 M.
2.50.- 1 liter of nitric acid with a density of 1.380 g/cc and 62.7% by weight is mixed with 1 liter of
nitric acid with a density of 1.130 g/cc and 22.38% by weight. The density of the formed acid is
of 1.276 g/cc.
What is the concentration of the resulting acid in % by weight?
b) What is the volume of the solution that is formed?
c) What is its molarity? 44.54 %
2.51.-What will be the molarity of the solutions that result from mixing the following
(assuming that the volumes are additive).
200 ml of 12 M HCl + 200 ml of H2O.
60 ml of ZnSO40.60 M + 150 ml of water.
c) 150 ml of 0.1 M HCl with 250 ml of 0.05 M HCl.
2.52.-Calculate the volume of concentrated reactant needed to prepare the
diluted solutions indicated below:
a) Hydrochloric acid 12 M, to prepare 400 ml of acid 6 M.
Ammonia 15 M, to prepare 50 ml of ammonia 6 M.
c) Sulfuric acid 18 M, to prepare 250 ml of 10 M acid.
2.53.- To what volume should a solution of 80 g of 96% w/w sulfuric acid be diluted, to
obtain a 0.1 M solution?
3.54.-What will be the molarity of each of the following solutions, prepared by mixing
250 ml of 0.75 M sulfuric acid with: a) 150 ml of water. b) 250 ml of sulfuric acid
0.7 M. c) 400 ml of 2.5 M sulfuric acid.
2.55.- A concentrated sulfuric acid with a density is diluted to a volume five times greater.
1.805 g/cc from 88.43 in weight. Calculate the volume of the diluted acid that is required to
prepare 5 liters of 1 normal sulfuric acid.
EQUIVALENT WEIGHT
2.56.- Determine the equivalent weight of pyrophosphoric acid when used to form: a)
Pirofosfato diácido de sodio,b)Pirofosfato ácido de sodio,c)Piro fosfato de sodio.
89 g
2.57.-Calculate the equivalent mass of the acid and the base for each of the reactions.
Next: a) HCl + NaOH = NaCl + H2O
b) 2HCl + Ba(OH)2Barium chloride2+ 2H2O
c) H2SO4+ Ca(OH)2Calcium Sulfate4+ 2H2O
d) H2SO4+ KOH = KHSO4+ H2O
e) H3PO4+ 2LiOH = Li2HPO4 + 2H2O
2.58.-Calculate the equivalent mass of the oxidizing agent and the reducing agent for each of the reactions.
following: (They are the underlined compounds)
2KMnO4+ 10 Iron(II) sulfate4+ 8H2SO4= 2MnSO4+ 5Fe2(SO4)3+ 8H2O + K2SO4
2KMnO4 + 5SnCl2 + 16HCl = 2MnCl2 + 5SnCl4 + 8H2O + 2KCl
NORMALITY
2.59.- How many equivalents are present in each mole of the following compounds?
a) Hydrochloric acid. b) Sulfuric Acid.
c) Phosphoric acid. Calcium chloride.
e) Aluminum hydroxide. Sodium sulfate.
2.60.-Express the concentration of the following solutions in normality:
25 g of hydrochloric acid dissolved in 250 ml of solution.
15 g of sulfuric acid dissolved in 250 ml of solution.
20 g of magnesium in 2 l of solution.
50 g of magnesium hydroxide in 1.5 l of solution.
R.-a) 2.74 N b) 1.22 N c) 0.83 N d) 1.15 N
2.61.-How many grams of phosphoric acid are present in 250 ml of 1 N solution?
-8.17 g
2.62.-How many equivalents are present in: 120 ml of 1 N acid solution
hydrochloric. b) 50 ml of 3 N phosphoric acid solution. c) 200 ml of 0.5 N solution of
magnesium sulfate R.-a) 0.12 b) 0.15 c) 0.1
2.63.-Calculate the volume of sulfuric acid with a density of 1.827 g/cc and 92.77% by weight.
What is needed to prepare 10 liters of 3 N sulfuric acid. -87.19 ml
2.64.- A sulfuric acid with a density of 1.805 g/cc is diluted to a volume five times greater and
of 88.43% by weight. Calculate the volume of the diluted acid needed to prepare 5 liters.
of 1 normal sulfuric acid. R.-153 ml
2.65.- 2 liters of 2 normal solution in HCl and NaCl must be prepared from an acid.
hydrochloric acid with a density of 1.165 g/cc at 33.16% by weight, and a solution of caustic soda
and 35.01% by weight of NaOH. Calculate the volumes that are
with a density of 1.380 g/cc
they need these two solutions. R.-755.86 ml of HCl and 351.55 ml of NaOH
2.66.- There is a 1% solution of potassium dichromate, whose relative density is equal
to the unit. Calculate the volume of this solution needed to prepare 250 cc of
0.1 N solution of dichromate acting as an oxidizing agent. R.-119.58 ml
2.67.-Calculate the volume of 2 normal copper sulfate solution needed to
prepare 10 g of copper oxide after precipitating copper as carbonate and calcination
posteriors of this to oxide. R.-126.58 ml
2.68.- From 100 cc of a certain sulfuric acid, by precipitation with barium chloride, it
11.75 g of barium sulfate is obtained. Find the normality of sulfuric acid. R.-1.00 N
MOLAR FRACTION
2.69.-What is the molar fraction of sulfuric acid in 100 g of a 20% w/w solution?
3.70.- 25 g of methanol are dissolved in 50 g of water. Calculate the molar fraction of methanol.
in water.
2.71.- A sulfuric acid solution has a concentration of 16.3 M. And its density is
1.84 g/cc. Calculate its molality, the molar fraction of the acid, and the molar fraction of the water.
CENTESIMAL COMPOSITION
2.72.- It has been found that atom Z is 12 times heavier than a carbon atom. It
You want to prepare a compound that contains two carbon atoms for every atom of Z. If you
If 1.00 g of carbon is used, how many grams of Z are required? Resp.-6.00
2.73.-Calculate: a) The percentage of copper present in the compounds: CuS and
CuSO4.5H2O, b) The percentage of crystallization water present in Al(SO4)2.12H20
Resp.-a) 66,46%Cu ; 25,45%Cu; b) 45,57%H20
2.74.-Calculate the percentage composition of the following compounds:
a) CaO, cal viva. b) Al203, El principal componente del rubí y el zafiro. c) NaHCO3 , polvo
for baking cakes. d) CuSO4.5H2O, copper vitriol, a fungicide.
79.47% Ca, 28.53% O
C, 57.14%O
2.75.- A sample of 10.0 g of raw mineral contains 2.80 g of HgS. What is the percentage?
of mercury in the mineral? -24.1% of Hg
2.76.- A homemade adhesive provided the following analytical data: A sample of 28.5 g at
dissolving it with acetone produced a residue of 4.6 g of aluminum powder. The filtrate, once
evaporated acetone and solvent, was composed of 3.2 g of plasticized nitrocellulose that
It contained 0.8 g of solvent-soluble plasticizer in benzene. Determine the composition of this.
adhesivo.Resp.-16.2 % de Al; 72.6 % disolvente; 2.8 % plastificante; 8.4 % nitrocel.
2.77.-White vinegar is a solution of acetic acid in water. The acid contains atoms
of carbon, hydrogen, and oxygen in the ratio of 1:2:1. If the analysis of a vinegar sample
It contains 2% of carbon, what is the actual percentage of acetic acid in vinegar? Answer: 5%.
2.78.- Calculate the percentage of water of crystallization present in the compounds: a)
Calcium chloride hexahydrate, b) Decahydrate sodium sulfate.
2.79.-Find the percentage composition of sulfur trioxide (SO3)
2.80.- A low melting point alloy is prepared by melting together 10.6 g of bismuth,
6.4 lb of lead and 3.0 lb of tin. What is the percentage composition of the alloy?
How much metal of each class is needed to prepare 70.0 g of alloy? c) What weight of
Can an alloy be prepared with 4.2 lb of tin?
53% Bi, 32% Pb, 15% Sn
EMPIRICAL FORMULA AND MOLECULAR FORMULA
A compound contains 90.6% lead and 9.4% oxygen. Find the formula.
empirical. Resp.-Pb2 03
2.82.- One gram of a carbon and hydrogen compound produces 3.30 g of CO2 upon combustion.
0.899 g of water. What is the empirical formula of the compound? Resp.-C3H4
An oxide contains 69.94% iron and 30.06% oxygen. What will be its formula?
compuesto. Datos: Peso Atómico Fe 55,85; Peso Atómico O 16. Resp.-Fe2 03
2.84.-A sample of 2,500 g of Uranium heated in air produced an oxide weighing 2,949 g.
Find the empirical formula of the oxide. Data: Atomic weights: U(238.1): O(16) Answer - U3O8
What is the empirical formula of an oxide that contains 72% by weight of Mn?
When heating 0.625g of hydrated magnesium sulfate, all of its water is released.
hydration, and weighs 0.320 g. What is the formula of the hydrated sulfate? Answer: MgSO4*XH2O
2.87.- A solid mercury chloride contains 85% mercury. Find the empirical formula.
from this compound. Data: {M.W.: Hg = 200.6 : M.W. Cl = 35.5} Response-HgCl
The empirical formula of a compound is Na2S04.xH20. If 15g of this is heated
It obtains 7.95 g of the anhydrous compound, what is the value of x in the formula? Resp.-7
2.89.-In the hemoglobin of the blood, there is approximately 33% Fe. If the molecule of
Hemoglobin has two iron atoms. What is the molecular weight of hemoglobin?
Resp.-239.39
2.90.-If compound Y contains 2.98 g of carbon per gram of hydrogen, what is its
empirical formula? Resp.-CH4
A sample of a compound has 0.667 moles of N atoms.22.688 g of
hydrogen, 2.01x1023chromium atoms, and the number of oxygen atoms corresponds to the
half the number of hydrogen atoms. What is the simplest formula of the compound?
Resp.-N2H8CrO4
2.92.- It was determined that a sample of a red pigment used in paint
antirust, with a mass of 1.597 g, contains 1.116 g of iron and the rest is oxygen. What is
What is the empirical formula of this oxide? Resp.-Fe203.
2.93.-Through a chemical analysis, it was determined that a compound contains 24.7% of C,
2.24% of H and 71.1% of O. Determine its empirical formula. Resp.-CHO2
2.94.-Deduce the empirical formulas of the minerals that have the following composition:
a) ZnS04= 56.14%; H243.86%
14.19%20 = 9.48%
Resp.-a) ZnS04.7 H2O; b) 2Mg0.3SiO2.2 H20; c) Na2Al2If3010.2 H2O
2.95.-Sodium Sulfite Na 2S03it combines with sulfur to form sodium thiosulfate,
No2SX03find the formula of sodium thiosulfate knowing that it oxidizes to sulfate and
precipitates to the state of barium sulfate BaSO₄40.318g of sodium thiosulfate gives rise to 0.939g of
barium sulfate. Resp.-Na2S2O3
A compound contains 40% by weight of carbon, 6.7% of hydrogen, and 53.3% of
oxygen. A sample of 0.10 moles of this compound weighs 6.0 g. What is the formula?
molecular of the compound? Resp.-C2H402
2.97.- A hydrocarbon, when completely burned in excess oxygen, produces 344
mg of carbon dioxide and 56.2 mg of water. What is the empirical formula of
hydrocarbon? Resp.-C5H4
2.98.- An unidentified organic compound, X, contains C, H, and O. When burned
228.4 mg of pure compound X yields 627.4 mg of CO.2171.2 mg of H2O. a)
Determine the masses of C, H, and O in the sample. b) Determine the empirical formula of
composed. Resp.-a) 171.2 mg C, 19.16 mg H, 38 mg O. b) C6H80.
2.99.- A sample of 3.245 g of titanium chloride was reduced with sodium to titanium.
metallic. Subsequently, the resulting sodium chloride was removed, the metallic titanium
The residue was dried and weighed, yielding 0.819 g. What is the empirical formula of the chloride of
titanium? Resp.-Ti Cl4
2.100.-E1 elemental analysis showed that an organic compound contained C, H, N, and O as
its only constitutive elements. A sample of 1.279 g was completely burned and
As a result, 1.60 g of CO were obtained.20.77 g of H2A separate sample of 1.625 g
of the same compound, contained 0.215 g of nitrogen. What is the empirical formula of
composed? Response-C3H7O3N
2.101.-An organic substance is composed of carbon, hydrogen, and oxygen. To
Heating it with cupric oxide, carbon is oxidized to carbon dioxide and hydrogen to water.
From 1.0000 g of substance, 0.9776 g of CO is formed.20.2001 g of H2O. The weight
The molecular weight of the compound is approximately 90. Find the molecular formula of the
substance. Resp.-C2H2O
2.102.- There are 3.1 g of a volatile substance at C.N. that contains only atoms of C, H, and O.
When the substance that burns with oxygen produces 4.5 g of H.2And 6.6 g of CO2, if M
= 124 determine the weight of oxygen in the sample. Resp.-g
EQUALITY OF EQUATIONS
2.103.-What are the steps to perform a chemical equation balancing using the
Redox method?
2.104.- Why is it important to balance a chemical equation?
2.105.-Balance the following chemical reaction:
K2Cr207HI + HCl04KClO4+ Cr(Cl04)3I2+ H2O
2.106.-Balance the equation and identify the coefficient of iodine and CO.2respectively

KAsO2+ I2+ KHCO3------- K3AsO4+ AI + CO2+ H2O.

2.107.-Balance the following equation and indicate the sum of the coefficients of the products:
KI + KMnO4+ H2SO4------ K2SO4+ MnSO4, + I2+ H2O. Resp.-21
2.108.-In the following equation, when balancing it, indicate the coefficient of water.
K2Cr2O7 + H2SO4 + H2S = KHSO4 + Cr2(SO4)3 + ~ + H2O. Resp.-7
2.109.- Balance the following equation and give as a response the sum of the coefficients.
Ferric chloride + sulfuric acid = ferrous chloride + hydrochloric acid + sulfur. Resp.-8
2.110.-What is the coefficient of orthophosphorous acid in:
P4 + I2 + H2O = H3PO3 + HI Resp.-4
2.111.-AI balance the equation. Which has the coefficient 2 in the following reaction?:
 As203 + HNO3 + H2O → H3AsO4 + NO2 Resp.- H~AsO4
2.112.- Equalize by the ion-electron method the oxidation of a nitrite to nitrate, through the
potassium permanganate in acidic medium. Write the corresponding molecular equation.
assuming that potassium nitrite is oxidized in an excess of sulfuric acid.
5 KNO2 + 2 KMnO4 + 36 H2SO4 → 5 KNO3 + 2 MnSO4 + K2SO4 + 3 H2O
2.113.-Write a balanced chemical equation that corresponds to each of the
descriptions following: a) When gaseous sulfur trioxide reacts with water, it
form a solution of sulfuric acid. b) Boron sulfide, B2S3(s) reacts
violently with water to form boric acid which remains dissolved, and sulfide of
gaseous hydrogen. c) Phosgene combusts with gaseous oxygen to form
water in gaseous state and solid tetraphosphorus decoxide. d) When mercury nitrate
(II) solid is heated, decomposes to form solid mercury (II) oxide, dioxide of
gaseous nitrogen and oxygen. e) When hydrogen sulfide gas is passed over
hot solid iron (III) hydroxide, the resulting reaction produces iron (III) sulfide
solid and gaseous water. f) When permanganate reacts with potassium chloride in acid
sulfuric gives as reaction products manganese sulfate, potassium sulfate, water, and chlorine
gaseous. g) Zinc reacts with sodium nitrate and sodium hydroxide resulting in
sodium zincate, ammonia, and water.
Resp-a) SO3 + H2O = H2SO4; B2S3 + 6 H2O = 2H3BO3 + 3H2S
4PH3 + 8O2 = 6 H2O + P4O10 2 Hg(NO3)2 = 2 HgO + 4 NO2 + O2
3H2S + 2Fe(OH)3 = Fe2S3 + 6 H2O
2KMnO4 + 10 KCl + 8 H2SO4 = 2MnSO4 + 5Cl2 + 6 K2SO4 + 8H2O
4Zn + NaNO3 + 7NaOH = 4 Na2ZnO2 + NH3 + 2H2O
2.114.-Nitric acid reacts with hydrogen sulfide resulting in
nitrogen monoxide, sulfur, and water. Write the equation and equate it using the
algebraic method.
CALCULATIONS FROM CHEMICAL EQUATIONS
2.115.-What is the concept of limiting reagent?
2.116.-In problem 3.105, if 10 kg of dichromate and 100 grams of acid are available.
Perchloric. What is the limiting reagent? Why? Perchloric acid
2.117.- What mass of oxygen will be needed to oxidize 900 kg of pyrite (FeS2); according to:
FeS2 + O2 = Fe2O3 + SO2 Resp.-660 kg
100 grams of potassium iodide react with one mole of copper sulfate.
Determine: the limiting reactant, the excess reactant, and the amount of cuprous iodide and
gaseous iodine produced.
Response - limiting reagent, excess CuSO4 57.38 g CuI, 38.2 g of I2
A mixture of sodium oxide and barium oxide weighing 6.50 g is dissolved in water, and
then the solution is treated with diluted sulfuric acid. Barium sulfate precipitates, while
that sodium sulfate remains in the solution. Barium sulfate is collected by
filtration and once dry, it is found to weigh 7.61 g. What percentage of the sample
Is it barium oxide? Resp.-76.9%
2.120.- Iron is obtained in the blast furnace, by reduction of ferric oxide, and assuming
let the reaction that takes place there be represented by the equation:
Fe2O3 + CO = Fe + CO + CO2
a) Equal the equation. Determine b) the amount of iron obtained, with 4% carbon,
what will be obtained per ton of mineral. e) Amount of C needed to produce CO
employee, per ton of mineral.
Resp.-b) 728,.5 kg de lingote. c) 676.2 kg de C para 1000 toneladas de mineral.
2.121.-Aspirin, C9H8O4, is produced from salicylic acid, C7H6O3, and anhydride.
acetic, C4H6O3, according to the following unbalanced reaction:
C7H6O3 + C4H6O3 = C9H8O4 + HC2H302
a) How much salicylic acid is required to produce 1.5x102Kg of aspirin, assuming that
Does all salicylic acid turn into aspirin?; b) How much salicylic acid will be required if
only 80% of salicylic acid is converted into aspirin?; c) What is the theoretical mass of aspirin that is produced
What is obtained if 185 Kg of salicylic acid reacts with 125 Kg of acetic anhydride?; d) If in
In part c) 182 Kg of aspirin is produced, what is the percentage of yield?
Resp.-a) 1.2x102kg, b) 9.5x102kg, c) 2.2x105g., d) 82.4 %.
2.122.- When reacting hydrochloric acid with hydrogen sulfide and potassium nitrate
nitrogen dioxide, sulfur, and potassium chloride are produced. a) Write and balance the
chemical equation by the ion-electron method, b) Write the half-reactions of
oxidation and reduction, c) indicate the reduced and oxidized substances, d) If 30 are available
pounds of potassium nitrate with 75% purity and the reaction yield is 85%.
Calculate the amount of sulfur produced. e) The amount of potassium nitrate needed to
obtain 100 grams of potassium chloride. Resp.-d) 1374.3 g of S 212.66 g of Nitrate
2.123.-80 grams of oxalic acid are treated with 10% excess of potassium permanganate,
the chemical equation is:
Oxalic Acid + Potassium Permanganate + H2SO4 = Potassium Sulfate + Manganous Sulfate + CO2+H20
What volume of potassium permanganate solution with a specific weight of 1.1 that contains the
20% by weight of permanganate must be taken, b) What volume of CO?2saturated at 40% of
Humidity will be collected at 21°C and 700mmHg? (The vapor pressure at 21°C is 17.5 mmHg)
What is the oxidized substance and why?
What is the equivalent weight of the oxidizing agent in this reaction? (The equation must be)
equalize by the ion electron method. Resp.-a) V= 280,8 cc, b) V= 46,8 l de
C02, c) C2O4H2loses electrons, d) KMnO4electron gains, e) Peq = 31.6g
2.124.- The industrial preparation of ethylene glycol, which is used as an antifreeze for
Automobiles and the preparation of polyester fiber is represented by:
C2H4O + H2O == C2H6O2
Ethylene oxide Ethylene glycol water
If 165 g of ethylene oxide reacts with 75.0 g of water, calculate: a) What amount
in grams of ethylene glycol is obtained?, b) The amount of moles of excess reactant that
remains at the end of the reaction, c) The yield, if 215 g of ethylene is actually obtained
glycol. 232 g
2.125.-In the following chemical reaction:
potassium chlorate + chromium oxide + potassium hydroxide = potassium chloride + potassium chromate + water.
Equalize by the ion-electron method
100 g of potassium chlorate with 100 g of chromium oxide and with excess of hydroxide of
potassium, determine the limiting reagent, d) Calculate with the previous data the pounds
obtained from potassium chromate, if the yield is 80%, e) Calculate the number of
potassium hydroxide molecules, if introduced with a 20% excess.
Resp.-b) Clorato de potasio; c) óxido crómico; d) 0.45 Ib; e) 1.9 x 1024.
2.126.-A1 Reacting zinc with nitric acid produces zinc nitrate, ammonium nitrate, and
water. a) Equalize by the ion-electron method, b) Indicate which substance is reduced and explain.
why, c) What amount of 65% nitric acid by weight is required to obtain 2
tons of ammonium nitrate, if the process yield is 90%.
Resp.-b) nitric acid (gains electrons); c) 26,896 tons.
FUNDAMENTAL LAWS
2.127.- A flash light for photography, which contains a metal and oxygen, is weighed and then
difference between the weights, before and after the flash? If not, why not? Explain your answer.
answer.
7.3 g of HCl was mixed with 4 g of NH.3How many grams of NH?4How did they form?
Find the mass of the gas that remains after the reaction.
-10.7 g of NH4Cl; 0.6 g of NH3
2.129.- A sample of 2,000 g of an element X reacted with oxygen, and formed
2.5292 g of compound X02. If it is considered that the atomic weight of oxygen is 16.00
What is element X? Tin
2.130.-Calculate the mass of the crystalline hydrate Cu(N0 3)2x3H2O, obtained by dissolution of
10g of Cu in HNO3and the subsequent evaporation of the mixture. Resp.-38g
2.131.-Starting from 3.426 g of a weighed sample of cast iron shavings, after the
corresponding treatment, 0.0998 g of SiO was obtained.2Calculate the mass percentage
of silicon in the analyzed cast iron. Resp.-1.36 g
CONSTANT PROPORTIONS
2.132.- State the law of constant proportions and give an example of its application.
2.133 - 50 g of S reacts with 50 g of Zn. Calculate the weight of zinc sulfide formed.
and the weight of the element that remains in excess.
2.134.- 5 moles of hydrochloric acid react with 5 moles of iron resulting in
ferric chloride and hydrogen products, determine the limiting reagent and the excess reagent.
A match is burned in a limited amount of oxygen to obtain a compound.
whose mass percentage composition is 56.4% P and 43.5% O. Suppose that 10 are burned
with 5 g of oxygen and one of the elements is consumed. a) Which element is it?
completely consumed?. b) What mass of the other element remains unreacted?. c)
What mass of the compound is obtained? Answer: a) O. b) 3.5 g. c) 11.5 g.
MULTIPLE PROPORTIONS
2.136.- State the law of multiple proportions and give an example of application.
2.138.- Hydrogen and oxygen form two compounds A and B, whose compositions are:
A: 11.11% by weight of hydrogen and 88.89% of oxygen and B: 5.88% by weight of hydrogen and
94.12% by weight of oxygen. a) Demonstrate Dalton's law. b) Write the formulas of the two.
compounds based on this law.
2.139.- Two iron oxides have been found in nature, where compound A: is
composed of 77.78% in Fe and compound B: by 72.41% in Fe. a) Verify the law of
the multiple proportions. b) Write the formulas of compounds A and B.
2.140.- Two sulfur oxides contain 33.33% (compound A) and 60% (compound B) of
Check Dalton's law
molecular between A and B.
2.141.- Three manganese oxides contain 46.60%, 36.68%, and 30.38% of oxygen. These
Oxides are an example of the law of multiple proportions. a) Demonstrate it b)
Write the three chemical formulas based on this law.
2.142.- Mercury and chlorine form two chlorides. Through analysis it was determined that in
In 0.787 g of one of them, there is 0.118 g of chlorine, and in 1.335 g of the other, there is 1 gram of
mercurio. a) Demostrar que se cumple la ley de Dalton . b) encuentre los moles que hay en 1
pound of the first compound.
2.143.- The analysis of two lead oxides shows that 2.351 g of the first contains
2.1824 g of lead and that 3.028 g of the second contains 2.6228 g of lead. a) Demonstrate that
These data illustrate the law of multiple proportions. b) According to this law
determine their formulas.
2.144.- Three nitrogen oxides contain 74.07%, 63.16%, and 36.36% of oxygen a) These
What is the molecular weight of the second oxide? c) Calculate the masses of nitrogen and oxygen.
What must be combined to produce 1 pound of the third oxide.
2.145.- A mass of 25.1 g of mercury combines with 2 g of oxygen to form a
oxide. Under other conditions, 0.402 g of mercury combines with 0.01 g of oxygen to
to form another oxide. Demonstrate the law of multiple proportions.
2.146.- Two oxides of the same metal M contain: Compound A: 20.13% oxygen and
Compound B: 11.18% oxygen. a) Show that these compounds agree with the
law of multiple proportions. b) What are the simplest formulas of the
compounds?. c) If the sum of the molecular weights of both compounds is 222.5. Find the
atomic weight of the metal.
A certain metal forms two chlorides that contain 85.2% and 65.80% of the metal.
respectively a) Demonstrate that these compounds conform to the law of the
multiple proportions. b) What are the simplest formulas of the compounds and what is
the atomic weight corresponding to the metal?
2.148.- Three nitrogen oxides contain 69.55%, 53.12%, and 36.35% of oxygen. a) These
Oxides are an example of multiple proportions. Demonstrate this statement.
Considering the oxide with 36.35% oxygen, calculate the weights of oxygen and nitrogen.
What must be combined to produce 200 g of this oxide? c) Determine which oxide it is.
in section b. Answer- b) 72.7 g of O, 127.3 g of N ;
COMBINATION VOLUMES
What volume of air is required to combust 40 liters of methane gas?
b) What volume of CO2 and water vapor is formed?
a) What is the resulting composition if the combustion has been complete?
2.150.- It is desired to obtain 1 m3 of hydrogen chloride under normal conditions, starting from the
gas phase reaction of hydrogen and chlorine. How many m3 of hydrogen and chlorine in the
The same conditions will be necessary if the reaction yield is 95%?
Resp.-0.53 m3 H20.53 m3 Cl2
2.151.- What volume of acetylene under normal conditions is obtained from the reaction between
water and 0.8 kg of CaC2? Resp.-0.28 m3
A sample of 50 ml of H2 and O2 was placed in a gas burette at the pressure
Atmospheric conditions caused a spark to jump in the sample, resulting in the formation of all the water.
possible. The resulting pure gas had a volume of 10 ml at barometric pressure. What was it?
the initial percentage in moles of the mixture? a) If the residual gas after the spark was
hydrogen? b) was it oxygen? 73%
2.153.- What volume of O2under normal conditions, combustion is required
complete from 28.6 g of propane gas?
2.154.- A certain volume of a mixture of hydrogen and oxygen is exploded. The gas
residual, which is oxygen, returns to the same conditions of pressure and temperature occupies
one quarter of the original volume. Calculate the composition of the mixture.
50% Hydrogen, 50% Oxygen.
BIBLIOGRAPHY
1.- Hein, Morris, CHEMISTRY, Iberoamericana Publishing, Mexico City 1992
2.- Colonel, Leonardo and others, CHEMISTRY, Official text for the pre-university course of
engineering. La Paz Bolivia. Impressions the friend. 1999
3.- QMC 99 Course Guide for Chemistry Teachers 1978
4.- Cardenaz, F., Gelvez, C. CHEMISTRY AND ENVIRONMENT. Ed. Mc Graw Hill
5.- Shaum. CHEMISTRY PROBLEMS. Ed. Mc Graw Hill
6.- Brown et al. CHEMISTRY, The Central Science. Prentice Hall Publishing. 1998
Note: Students should only solve the even exercises.

Prepared by: Moisés Calliconde A.

PROPOSED EXERCISES
CHAPTER IV
Multiple proportions
5.74.- Three common gaseous compounds of nitrogen and oxygen of different
elemental composition, (a) 63.65 % N, (b) 46.68 % N, and (c) 30.45 % N. Show how these
Data can illustrate the law of multiple proportions.
5.105.- Internal combustion engines produce nitrogen oxide (NO). When the NO is
it comes into contact with air, it quickly converts to nitrogen dioxide, NO₂2what is
a very corrosive and toxic gas. What mass of O combines with 1 g of N in a) NO, b) N02?.
Prove that the NOT and the NOT2they follow the law of multiple proportions. Answer - a) 1.14 g
of O., b) 2.28 g of O.

5.75.- a) Silver chloride consists of 75.3% silver and 24.7% chlorine. If they react
17.8 g of silver with 5.47 g of chlorine. What mass of silver chloride is formed?
Does the law of defined composition clarify this problem? Response: 22.1 g

GASES
5.34.- The centesimal composition of a compound formed by carbon and hydrogen is C =
92.3%: H = 7.7%: the weight of one liter of this gas at C.N. is 1.16g. What is the formula?
molecular?
Resp.- C2H2
5.108.- A sample of 100.0 mg of a pure metal M was treated with an excess of acid.
diluted sulfuric, producing M+3and 25.0 ml of H2(collected at water at 22.0°C and
715 torr. What is the chemical symbol of the metal? Resp.-Tb
5.42.- Find the volume of hydrogen gas measured over water at 25 °C and 750 mm, that is
they release when heating 1.52 g of Silicon with caustic soda solution. The vapor pressure
the vapor pressure of water at 25 ºC is 23.8 mmHg.
Resp.- 4.88 l of H2
3.91.- A hydrocarbon has the following composition: C=80%, H=20%. One liter of the gas at
0°C and 780 mmHg has 1.3420 g. What is the molecular formula? Resp.-C2H6

3.101.- A solid mercury chloride contains 84.97% mercury. The compound is

molecular formula of this mercury chloride. Resp.-Hg2Cl2
3.102.- When burning 0.739 g of toluene, 2.471 g of carbon dioxide and 0.578 g of
water. At 100 °C and 722 mm, a flask with a capacity of 325.6 ml contains 0.932g of substance.
in vapor state. Find the molecular formula of toluene. Resp.-C7H8
3.132.-5.1 g of previously oxidized magnesium powder was treated with HCl. In this case, it
They released 3.74 L of H.2measured in C.N. Find the mass percentage of magnesium that
it contained the sample. Resp.-79.6 %