Химия на английском. Модуль 1
.pdf5.BALANCING CHEMICAL EQUATIONS
5.1.In laboratory, oxygen gas may be generated by decomposing potassium chlorate
(KClO3) into potassium chloride and oxygen gas. Write a balanced equation describing the reaction.
5.2.Water that contains dissolved calcium compounds is called "hard" water. One
way to "soften" such water is to add sodium carbonate, Na2CO3. It removes the calcium by forming calcium carbonate, which is insoluble in water. Balance the equation that illustrates the reaction.
5.3.Consider the combustion of amyl alcohol, C5H11OH.
a)How many moles of O2 are needed for the combustion of 1 mole of amyl
alcohol?
b)How many moles of H2O are formed for each mole of O2 consumed?
c)How many moles of CO2 are produced for each mole of amyl alcohol
burned?
5.4.Balance each of the following equations:
a)CH4 + Cl2 → CCl4 + HCl;
b)C2H6 + O2 → CO2 + H2O;
c)Al(OH)3 + H2SO4 → Al2(SO4)3 + H2O;
d)P2H4 → PH3 + P4;
e)Fe + H2O → Fe3O4 + H2;
f)S2Cl2 + NH3 → N4S4 + NH4Cl + S8;
g)Al4C3 + HCl → AlCl3 + CH4;
h)Ag + HNO3 → AgNO3 + NO + H2O.
5.5.Balance the following equations:
a)C2H4(OH)2 + O2 → CO2 + H2O;
b)Li + H2O → LiOH + H2;
c)Ba(OH)2 + AlCl3 → BaCl2 + Al(OH)3;
d)KHC8H4O4 + KOH → K2C8H4O4 + H2O;
e)(NH4)2Cr2O7 → N2 + Cr2O3 + H2O.
5.6.What is the molecular formula of the compound represented by X in the following balanced equation?
4 X + 5 O2 = 4 NO + 6 H2O
5.7. Determine the formula of X in the following balanced equations:
a) 9 Fe2O3 + 2 NH3 = 6 X + N2 + 3 H2O;
b) 2 MnO2 + 4 X + O2 = 2 K2MnO4 + 2 H2O;
c) 2 KMnO4 + 16 HCl = 2 MnCl2 + 2 KCl + 5 X + 8 H2O;
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d) Cr2O3 |
+ 3 X = 2 CrCl3 + 3 CCl2O; |
e) As2S3 |
+ 12 NaNO3 + 3 Na2CO3 = |
=X + 3 Na2SO4 + 3 CO2 + 12 NaNO2.
5.6.Predict the products of the following reactions and balance the equations: a) HCl + Mg(OH)2 → …
b)PbCl2 + K2SO4 → …
c)CH3CH2OH + O2 → …
d)Fe + AgNO3 → …
5.7.Given that the oxidation state of hydrogen is “+1”, of oxygen “–2”, and of
fluorine “–1”, determine the oxidation states of the other elements in:
a) NaF; |
b) H2SiO3; |
c) PH3; |
d) H2S; |
e) CrF3; |
f) H2SO4; |
g) H2SO3; |
h) Al2O3; |
i) HPO42–. |
5.8. Determine the oxidation number of the central atom in: |
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a) K4P2O7; |
b) NaAuCl4; |
c) Na5HV10O28; |
d) ICl; |
e) Ba2XeO6; |
f) Ca(ClO2)2. |
5.9. Find the oxidation number of each atom in the following molecules and ions:
a) CO2; |
b) AgNO3; |
c) BaO2; |
d) LiH; |
e) Ca2P2O7; |
f) C2O42–; |
g) PCl62–; |
h) B4O72–; |
i) UO22+. |
5.10. Find the oxidation number of each atom in the following molecules and ions:
a) SO3; |
b) H2SO3; |
c) Zn(IO3)2; |
d) Na2O2; |
e) (NH4)2PO4; |
f) V2O72–; |
g) BiO+; |
h) SiO32–; |
i) S2O32–. |
5.11. Write balanced ionic half-reactions for the oxidation of each of the following
reducing agents in acid solution: |
c) Br–; |
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a) Sn; |
b) H2C2O4; |
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d) Sn2+; |
e) H2S; |
f) Ba; |
g) Al; |
h) HNO2; |
i) Hg22+; |
j) I–; |
k) H3AsO3; |
l) H2O2. |
5.12. Write balanced ionic half-reaction equations for the reduction of each of the
following oxidizing agents in acid solution: |
|
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a) Co3+’ |
b) PbO2; |
c) ClO4–; |
d) F2; |
e) Ag+; |
f) NO3–; |
g) BrO–; |
h) Sn2+; |
i) MnO2; |
j) ClO2–; |
k) H2O2; |
l) Cr2O72–; |
m) IO3–; |
n) Br2; |
o) Fe2+; |
p) Cd2+. |
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5.13.Balance the oxidation-reduction equations:
a)NaBr + Cl2 → NaCl + Br2;
b)Sn + O2 + HCl → SnCl2 + H2O;
c)FeCl2 + H2O2 + HCl → FeCl3 + H2O.
5.14.Balance the oxidation-reduction equation for the oxidation of H2S by HNO3 to produce NO and S in aqueous acidic solution (thus H+ and H2O may be involved).
5.15.Balance the oxidation-reduction equation for the oxidation of FeCl2 by Na2Cr2O7 to give CrCl3 and FeCl3 in aqueous acidic solution.
5.16.Balance the oxidation-reduction equation for the oxidation of Zn by NaNO3 to produce Na2Zn(OH)4 and NH3 in basic aqueous solution.
5.17.Balance the following equations, describing oxidation by nitric acid:
a) Cu + HNO3 (conc.) → Cu(NO3)2 |
+ NO2 + H2O; |
b) Cu + HNO3 (dilute) → Cu(NO3)2 |
+ NO + H2O; |
c) Zn + HNO3 (dilute) → Zn(NO3)2 |
+ NH4NO3 + H2O; |
d) CuS + HNO3 → Cu(NO3)2 + S + NO + H2O;
e)As2S5 + HNO3 → H3AsO4 + H2SO4 + NO2.
5.18.Balance the following skeleton equations (acidic aqueous solutions), complete molecular reactions:
a)MnO + PbO2 → MnO4– + Pb2+;
b)C2O42– + MnO4– → CO2 + Mn2+;
c)H2O2 + MnO4– → Mn2+ + H2O.
5.19.Balance the following equations (basic aqueous solutions):
a)Bi2O3 + NaOH + NaOCl → NaBiO3 + NaCl;
b)Fe(CN)63– + Cr2O3 → Fe(CN)64– + CrO42–;
c)CrI3 + Cl2 → CrO42– + IO4– + Cl–;
d)Ag + CN– + O2 → Ag(CN)2– + OH–;
e)Co2+ + Na2O2 → Co(OH)3↓.
5.20.Balance the following equations (no water involved):
a)NaN3 → Na3N + N2;
b)Ca3PO4 + SiO2 + C → CaSiO3 + P4 + CO;
c)P2H4 → PH3 + P4H2.
5.21.Write balanced equations for the reaction that occurs between metallic zinc and dilute nitric acid to produce ammonium nitrate as one of the products.
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5.22.When sodium thiosulfate, Na2S2O3, interacts with iodine in quantitative analysis, one of the products is sodium tetrathionate, Na2S4O6. Write the complete equation and balance it.
5.23.A sample of potassium iodide contains some potassium iodate as impurity. When sulfuric acid is added to a solution of this sample, iodine is produced. Give the equation for the formation of the iodine.
5.24.When copper is heated in concentrated sulfuric acid, an odor of sulfur dioxide is noted. Write the chemical equation; balance it.
5.25.A classical operation in quantitative analysis is the use of a Jones reductor, a column of granulated zinc. A solution of ferric (Fe3+) salts is passed through this column prior to titration with potassium permanganate. Give the equation for the reaction in the column.
5.26.Pure hydroiodic acid (HI) cannot be prepared by adding concentrated sulfuric acid to sodium iodide and distilling off the hydroiodic acid, because of side reactions. One side reaction yields hydrogen sulfide, as noted by the odor. Give the equation for this side reaction.
5.27.Write the balanced equation for the reaction that occur when chlorine gas is bubbled through a solution of iron(II) bromide.
5.28.In the final step of producing bromine from sea water, a mixture of sodium bromide and sodium bromate is treated with sulfuric acid. Give the equation for the reaction; balance it.
5.29.A microchemical procedure uses a cadmium amalgam (cadmium dissolved in metallic mercury) to reduce iron salts to their lowest oxidation state prior to titration with standard solution. Give the equation for the reaction involving the cadmium.
5.30.When zinc is heated with concentrated sulfuric acid, hydrogen sulfide is evolved. Write the chemical reaction; balance it.
5.31.The Marsh test for the detection of arsenic depends on the reaction of an
arsenic compound, such as H3AsO4, with metallic zinc in acid solution. The arsenic is liberated as arsine, AsH3, which may be decomposed by heat to give an "arsenic mirror". Write the balanced equation for the reaction that occurs in the case of the arsenic-positive test.
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6.CALCULATIONS BASED ON CHEMICAL EQUATIONS
6.1.When mercury oxide, HgO, is heated, it releases mercury and oxygen gas. How many moles of oxygen gas will be produced from the decomposition of 4 mol of mercury oxide?
6.2.How many molecules of potassium chlorate are required in the preparation of 6 mol of oxygen gas?
6.3.When aluminum is heated with sulfur, aluminum sulfide is formed.
a)Write the balanced equation.
b)Calculate the number of moles of aluminum that combines with 6 mol of
sulfur.
c)Calculate the number of aluminum sulfide molecules produced from 0.4 mol of Al.
6.4.If 212 grams of sodium carbonate react with calcium hydroxide, how many grams of sodium hydroxide are formed?
6.5.How many grams of sodium hydroxide will react with 49 g of phosphoric acid?
6.6.How many liters of oxygen (at STP) are liberated by heating 490 g of potassium chlorate?
6.7.Consider the reaction
MnO2 + 4 HCl → MnCl2 + Cl2 + 2 H2O.
How many grams of MnO2 are required to produce 5.6 L of Cl2 at STP?
6.8.If 152 mL of liquid carbon disulfide (density 1.25 g/mL) are burned completely:
a)how many liters of SO2 at STP are formed?
b)how many liters of O2 are required at STP?
6.9.How many liters of carbon dioxide are formed from the combustion of 60 liters
of ethylene gas, C2H4? Recall that the combustion of any compound made from C and H elements produces carbon dioxide and water vapor.
6.10.Given the balanced equation N2 + 3 H2 = 2 NH3, calculate (assuming that all volume measurements are made under identical conditions):
a)the volume of H2 that reacts with 12 L of N2;
b)the volume of N2 that reacts with 12 L of H2;
c)the volume of NH3 produced from 4 L of N2;
d)the volumes of N2 and H2 to produce 60 L of NH3;
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6.11.Aluminum reacts with hydrochloric acid and produces aluminum chloride and hydrogen gas. Answer the following questions for 2.7 g of aluminum used in the reaction.
a)How many grams of AlCl3 will be produced?
b)How many moles of HCl are used?
c)How many molecules of H2 are formed?
6.12.The combustion of ammonia, NH3, produces NO and H2O.
a)Write the balanced equation representing the reaction.
b)How many moles of H2O are produced when 2 mol of NH3 is burned?
c)How many moles of O2 are required to react completely with 3 mol of
NH3?
d)How many grams of NO are produced when 16 grams of O2 are used?
e)How many grams of H2O are formed when 8.96 L of NH3 at STP is completely burned?
f)How many liters of NO at STP will be produced when 1.8x2023 NH3 molecules are burned?
g)How many liters of O2 and how many liters of air are required to burn
20 L of NH3?
(Assume the identical conditions. Recall that 1/5 of air is O2 by volume.)
6.13. A portable hydrogen generator utilizes the reaction:
CaH2 + 2 H2O → Ca(OH)2 + 2 H2↑. How many grams of H2 can be produced by 50 g of CaH2?
6.14. How much iron(III) oxide can be produced from 6.76 g of FeCl3·6H2O by the
following reactions? |
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FeCl3·6H2O + 3 NH3 = Fe(OH)3 |
+ 3 NH4Cl + 3 H2O; |
2 Fe(OH)3 = Fe2O3 |
+ 3 H2O. |
6.15.In a rocket motor fueled with butane, C4H10, how many kilograms of liquid oxygen should be provided with each kilogram of butane to provide for complete combustion?
6.16.Ethyl alcohol, C2H5OH, can be made by the fermentation of glucose, C6H12O6, as indicated by the (unbalanced) equation:
C6H12O6 → C2H5OH + CO2.
How many metric tons of alcohol can be made from 2.00 metric tons of glucose?
6.17. In the Mond process for purifying nickel, the volatile nickel carbonyl, Ni(CO)4, is produced by the reaction:
Ni + 4 CO = Ni(CO)4.
How much CO is used in volatilizing each kilogram of nickel?
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6.18.The mixture of 2 mol of H2 and 2 mol of O2 gases are ignited to obtain water. Which reactant is limiting? Which is the excess reactant? How much water will be produced?
6.19.A mixture of 100 g Al and 200 g MnO was heated to initiate the reaction:
2 Al + 3 MnO = Al2O3 + 3 Mn. Which initial substance remained in excess? How much?
6.20. Carborundum, SiC, is used as an abrasive. It is formed by the combination of SiO2 and carbon, according to the reaction:
SiO2 + 3 C = SiC + 2 CO.
What mass of SiC is formed from 6 grams of SiO2 and 6 grams of C?
6.21.How many grams of water are produced when 4 g of H2 and 8 g of O2 are
reacted?
6.22.Given: N2 + 3 H2 = 2 NH3. If 20 L of N2 and 15 L of H2 gases at the same conditions are reacted, which gas will be excess and how many liters?
6.23. Given: N2 + 3 H2 = 2 NH3. 3.01x1023 molecules of nitrogen and 3.36 L of H2 at STP are reacted. How many grams of NH3 are produced?
6.24. Aluminum and hydrogen bromide react according to the following reaction:
2 Al + 6 HBr = 2 AlBr3 + 3 H2. If 4 mol of Al and 9 mol of HBr are allowed to react,
a)which of the two reactants is the limiting one?
b)how many moles of the excess reactant are left at the end of reaction?
c)what is the maximum mole number of H2 obtained?
6.25.18 g of C and 8 g of oxygen are reacted to form CO2. Which element and how many grams remain behind?
6.26.Given: the reaction 2 H2S + 3 O2 = 2 H2O + 2 SO2. The quantities of reactants are given below. For each of the following, determine the excess reactant and the maximum grams of water produced.
a)2 mol of H2S and 4 mol of O2;
b)4 mol of H2S and 6 mol of O2;
c)8.5 g of H2S and 9.6 g of O2;
d)6.02x1022 H2S molecules and 6.72 L O2 at STP;
e)4.48 L H2S at STP and 19.2 g O2;
f)17.92 L H2S at STP and 13.44 L O2 at STP.
6.27.Given the reaction: As4O6 + 4 I2 + 4 H2O = 2 As2O5 + 8 HI. What is the maximum grams of HI produced if 2 mol of each of the reactants are reacted?
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6.28.Nitric oxide, NO, is prepared according to the following reaction in
laboratories: 3 KNO2 + KNO3 + Cr2O3 = 4 NO + 2 K2CrO4. Calculate the maximum liters of NO at STP produced by the reaction of 100 g of each of the reactants.
6.29.Equal weights of sodium and chlorine gas are reacted in a closed container to give 0.1 mol of sodium chloride. Which element will remain behind and how many grams?
6.30.Equal moles of aluminum and oxygen are reacted to give 20.4 g of aluminum oxide. Which one remains unreacted and how many moles?
6.31.Equal volumes of sulfur dioxide and oxygen gases are reacted to give 5 liters of sulfur trioxide at the same conditions. Which one remains unreacted and how many liters?
6.32.A mixture of 1 ton of CS2 and 2 tons of Cl2 is passed through a hot reaction tube, where the following reaction takes place:
CS2 + 3 Cl2 → CCl4 + S2Cl2.
a)How much CCl4 can be made by complete reaction of the limiting starting material?
b)Which starting material is in excess, and how much of it remains unreacted?
6.33.What mass of Cu2S can be produced from the reaction of 100 g copper with 50 g of sulfur?
6.34.What weight of HCl is produced when sulfuric acid reacts with 200 grams of 87.75% pure sodium chloride (assume that 12.25% of the sample is inert in the reaction)?
6.35.How many liters (at STP) of oxygen can be liberated from 1700 grams of a solution which is 3.0% hydrogen peroxide by mass? The equation is:
2 H2O2 → 2 H2O + O2↑.
6.36.How many grams of H2SO4 can be produced from 300 g of FeS2 which is 60 % pure by weight?
6.37.How many grams of sodium chloride that is 90 % pure are required to produce 73 g of HCl according to the reaction with H2SO4?
6.38.A 25 g sample of iron reacts with 200 g of 14.6 % HCl solution by mass. The
reaction is: Fe + 2 HCl = FeCl2 + H2. Calculate the percentage of iron in the sample. (Assume the impurities are inert to HCl.)
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6.39.When an unknown quantity of magnesium is reacted with HCl, 4.48 L of H2 at STP together with some magnesium chloride are formed.
a) What mass of magnesium chloride is formed?
b) If the sample of magnesium is 96 % pure, what mass of magnesium sample is used in the reaction?
c) What mass of HCl solution that is 20 % HCl by mass would it be required to produce 4.48 L of H2 at STP?
6.40.When 20 g of iron is reacted with oxygen, 20 g of iron(III) oxide is formed. What percentage of iron is reacted with oxygen?
6.41.The acetylene gas, C2H2, is an important raw material in the production of many chemicals, such as synthetic rubber, alcohol, etc. It may be prepared from
limestone (CaCO3), coke (C) and water according to the following reactions: I. CaCO3 → CaO + CO2;
II. CaO + 3 C → CaC2 + CO;
III. CaC2 + H2O → C2H2 + Ca(OH)2.
Assuming an excess of all other reactants, how many liters of C2H2 at STP can be obtained from 50 g CaCO3.
6.42. KBrO4 may be prepared by the following series of reactions: I. Br2 + 2 KOH → KBr + KBrO + H2O;
II. 3 KBrO → 2 KBr + KBrO3;
III. 4 KBrO3 → 3 KBrO4 + KBr.
Assuming the excess KOH, how much Br2 in grams is needed to prepare 109.8 g KBrO4 by the above sequence of reactions?
6.43. Given the reactions:
I. Al4C3 |
+ 12 H2O = 4 Al(OH)3 + 3 CH4; |
II. CH4 |
+ 2 O2 = CO2 + 2 H2O. |
The methane gas that is obtained from 50 g impure sample of Al4C3 is required 38.4 g of O2 to be completely burned. What is the percentage purity of Al4C3 in the impure sample?
6.44. Iron is prepared in the blast furnace according to the sequence of these reactions:
I. 2 C + O2 = 2 CO;
II. 3 CO + Fe2O3 = 2 Fe + 3 CO2.
Assuming the excess of O2, how many tons of iron can be obtained by the reaction of 5 tons of hematite or Fe2O3, that is 80 % pure, with 1 ton of coke?
6.45. To burn 30 liters of a mixture of C3H4 and C3H8 gases at STP, 140 liters of O2 are needed at the same conditions. Calculate the volume of C3H4 in the mixture.
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6.46.The complete combustion of a 13.44 L mixture of C2H4 and C3H4 gases at STP produces 31.36 L CO2 under the same conditions. Find the mole number of each gas in the mixture.
6.47.11.9 g of an alloy made from Al and Zn is reacted with sufficient amount of HCl and 8.96 L of H2 at STP are produced. What is the amount of Al in the alloy?
6.48.A 20 g alloy of Mg and Al elements is reacted with HCl and 24.64 L of H2 at STP are produced. Find the percentage by mass of Al in the mixture. Both metals react with HCl and produce metal chlorides and hydrogen gas.
6.49.Both sodium and calcium metals react with water to produce metal hydroxides
and H2 gas. If 4 moles of H2 are obtained from 5 moles of the mixture of sodium and calcium metals, calculate the mole percentage of sodium in the mixture.
6.50.When 2.2 g of a compound containing carbon and hydrogen is burned, 3.36 liters of CO2 at STP are produced. What is the empirical formula of the compound?
6.51.The complete combustion of 8 g of compound made from only C and H produced 26.4 g CO2. What is the empirical formula of the compound?
6.52.When 2.3 g of a compound containing C, H and O is burned completely, 4.4 g of CO2 and 2.7 g of H2O are produced. Find its empirical formula.
6.53.When 1.76 g of a compound containing C, H and O is burned completely in oxygen, 3.52 g of CO2 and 1.44 g of H2O are produced.
a)Calculate the empirical formula of the compound.
b)If 0.05 mol of the compound is 4.4 g, what is the molecular formula of the compound?
6.54.Copper(II) nitrate is prepared by dissolving a weighed amount of copper metal in a nitric acid solution:
3 Cu + 8 HNO3 → 3 Cu(NO3)2 + 2 NO↑ + 4 H2O.
What volume of 6.00 M HNO3 should be used to prepare 10.0 g of Cu(NO3)2?
6.55.The preparative task is to precipitate all the Ag+ from 50 mL of 0.12 M AgNO3 solution. Answer the following questions.
a)What weight of AgCl can be obtainedl?
b)What weight of NaCl is required to precipitate the AgCl?
c)What volume of 0.24 M HCl would be needed for the task?
6.56.How many milligrams of Na2CO3 will react with 45.00 mL of 0.2500 M HCl?
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