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7.E: Stoichiometry of Chemical Reactions (Exercises)

An equation is balanced when the same number of each element is represented on the reactant and product sides. Equations must be balanced to accurately reflect the law of conservation of matter.

What does it mean to say an equation is balanced? Why is it important for an equation to be balanced?

From the balanced molecular equations, write the complete ionic and net ionic equations for the following:

A novel process for obtaining magnesium from sea water involves several reactions. Write a balanced chemical equation for each step of the process.

Aqueous hydrogen fluoride (hydrofluoric acid) is used to etch glass and to analyze minerals for their silicon content. Hydrogen fluoride will also react with sand (silicon dioxide).

Fill in the blank with a single chemical formula for a covalent compound that will balance the equation:

Colorful fireworks often involve the decomposition of barium nitrate and potassium chlorate and the reaction of the metals magnesium, aluminum, and iron with oxygen.

Balance each of the following equations according to the half-reaction method:

Balance each of the following equations according to the half-reaction method:

Balance each of the following equations according to the half-reaction method:

Complete and balance each of the following half-reactions (steps 2–5 in half-reaction method):

Complete and balance each of the following half-reactions (steps 2–5 in half-reaction method):

Calcium cyclamate Ca(C 6 H 11 NHSO 3 ) 2 is an artificial sweetener used in many countries around the world but is banned in the United States. It can be purified industrially by converting it to the barium salt through reaction of the acid C 6 H 11 NHSO 3 H with barium carbonate, treatment with sulfuric acid (barium sulfate is very insoluble), and then neutralization with calcium hydroxide. Write the balanced equations for these reactions.

Write balanced chemical equations for the reactions used to prepare each of the following compounds from the given starting material(s). In some cases, additional reactants may be required.

Copper(II) sulfide is oxidized by molecular oxygen to produce gaseous sulfur trioxide and solid copper(II) oxide. The gaseous product then reacts with liquid water to produce liquid hydrogen sulfate as the only product. Write the two equations which represent these reactions.

Complete and balance the equations of the following reactions, each of which could be used to remove hydrogen sulfide from natural gas:

Calcium propionate is sometimes added to bread to retard spoilage. This compound can be prepared by the reaction of calcium carbonate, CaCO 3 , with propionic acid, C 2 H 5 CO 2 H, which has properties similar to those of acetic acid. Write the balanced equation for the formation of calcium propionate.

Lithium hydroxide may be used to absorb carbon dioxide in enclosed environments, such as manned spacecraft and submarines. Write an equation for the reaction that involves 2 mol of LiOH per 1 mol of CO 2 . (Hint: Water is one of the products.)

In a common experiment in the general chemistry laboratory, magnesium metal is heated in air to produce MgO. MgO is a white solid, but in these experiments it often looks gray, due to small amounts of Mg 3 N 2 , a compound formed as some of the magnesium reacts with nitrogen. Write a balanced equation for each reaction.

Great Lakes Chemical Company produces bromine, Br 2 , from bromide salts such as NaBr, in Arkansas brine by treating the brine with chlorine gas. Write a balanced equation for the reaction of NaBr with Cl 2 .

Write the molecular, total ionic, and net ionic equations for the following reactions:

The military has experimented with lasers that produce very intense light when fluorine combines explosively with hydrogen. What is the balanced equation for this reaction?

When heated to 700–800 °C, diamonds, which are pure carbon, are oxidized by atmospheric oxygen. (They burn!) Write the balanced equation for this reaction.

Complete and balance the equations for the following acid-base neutralization reactions. If water is used as a solvent, write the reactants and products as aqueous ions. In some cases, there may be more than one correct answer, depending on the amounts of reactants used.

Complete and balance the following oxidation-reduction reactions, which give the highest possible oxidation state for the oxidized atoms.

Complete and balance the following oxidation-reduction reactions, which give the highest possible oxidation state for the oxidized atoms.

Identify the atoms that are oxidized and reduced, the change in oxidation state for each, and the oxidizing and reducing agents in each of the following equations:

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acid-base; oxidation-reduction: Na is oxidized, H + is reduced; oxidation-reduction: Mg is oxidized, Cl 2 is reduced; acid-base; oxidation-reduction: P 3− is oxidized, O 2 is reduced; acid-base

Determine the oxidation states of the elements in the compounds listed. None of the oxygen-containing compounds are peroxides or superoxides.

Determine the oxidation states of the elements in the compounds listed. None of the oxygen-containing compounds are peroxides or superoxides.

Determine the oxidation states of the elements in the following compounds:

It is an oxidation-reduction reaction because the oxidation state of the silver changes during the reaction.

Silver can be separated from gold because silver dissolves in nitric acid while gold does not. Is the dissolution of silver in nitric acid an acid-base reaction or an oxidation-reduction reaction? Explain your answer.

Indicate what type, or types, of reaction each of the following represents:

Indicate what type, or types, of reaction each of the following represents:

Use the following equations to answer the next five questions:

The toxic pigment called white lead, Pb 3 (OH) 2 (CO 3 ) 2 , has been replaced in white paints by rutile, TiO 2 . How much rutile (g) can be prepared from 379 g of an ore that contains 88.3% ilmenite (FeTiO 3 ) by mass?

What mass of Ca(OH) 2 is required to react with the acetic acid in 25.0 mL of a solution having a density of 1.065 g/mL and containing 58.0% acetic acid by mass?

A mordant is a substance that combines with a dye to produce a stable fixed color in a dyed fabric. Calcium acetate is used as a mordant. It is prepared by the reaction of acetic acid with calcium hydroxide.

What volume of a 0.2089 M KI solution contains enough KI to react exactly with the Cu(NO 3 ) 2 in 43.88 mL of a 0.3842 M solution of Cu(NO 3 ) 2 ?

What volume of a 0.750 M solution of hydrochloric acid, a solution of HCl, can be prepared from the HCl produced by the reaction of 25.0 g of NaCl with an excess of sulfuric acid?

A compact car gets 37.5 miles per gallon on the highway. If gasoline contains 84.2% carbon by mass and has a density of 0.8205 g/mL, determine the mass of carbon dioxide produced during a 500-mile trip (3.785 liters per gallon).

In an accident, a solution containing 2.5 kg of nitric acid was spilled. Two kilograms of Na 2 CO 3 was quickly spread on the area and CO 2 was released by the reaction. Was sufficient Na 2 CO 3 used to neutralize all of the acid?

Urea, CO(NH 2 ) 2 , is manufactured on a large scale for use in producing urea-formaldehyde plastics and as a fertilizer. What is the maximum mass of urea that can be manufactured from the CO 2 produced by combustion of 1.00×10 3 kg of carbon followed by the reaction?

What mass of sodium azide is required to produce 2.6 ft 3 (73.6 L) of nitrogen gas with a density of 1.25 g/L?

Carborundum is silicon carbide, SiC, a very hard material used as an abrasive on sandpaper and in other applications. It is prepared by the reaction of pure sand, SiO 2 , with carbon at high temperature. Carbon monoxide, CO, is the other product of this reaction. Write the balanced equation for the reaction, and calculate how much SiO 2 is required to produce 3.00 kg of SiC.

What mass of silver oxide, Ag 2 O, is required to produce 25.0 g of silver sulfadiazine, AgC 10 H 9 N 4 SO 2 , from the reaction of silver oxide and sulfadiazine?

Silver is often extracted from ores as K[Ag(CN) 2 ] and then recovered by the reaction

I 2 is produced by the reaction of 0.4235 mol of CuCl 2 according to the following equation: (ce{2CuCl2 + 4KI rightarrow 2CuI + 4KCl + I2}).

Gallium chloride is formed by the reaction of 2.6 L of a 1.44 M solution of HCl according to the following equation: (ce{2Ga + 6HCl rightarrow 2GaCl3 + 3H2}).

H 2 is produced by the reaction of 118.5 mL of a 0.8775-M solution of H 3 PO 4 according to the following equation: (ce{2Cr + 2H3PO4 rightarrow 3H2 + 2CrPO4}).

Determine the number of moles and the mass requested for each reaction in Exercise .

Write the balanced equation, then outline the steps necessary to determine the information requested in each of the following:

Determine the number of moles and the mass requested for each reaction in Exercise .

Write the balanced equation, then outline the steps necessary to determine the information requested in each of the following:

This amount cannot be weighted by ordinary balances and is worthless.

Would you agree to buy 1 trillion (1,000,000,000,000) gold atoms for $5? Explain why or why not. Find the current price of gold at http://money.cnn.com/data/commodities/ (mathrm{(1: troy: ounce=31.1: g)})

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The phosphorus pentoxide used to produce phosphoric acid for cola soft drinks is prepared by burning phosphorus in oxygen.

How many molecules of the sweetener saccharin can be prepared from 30 C atoms, 25 H atoms, 12 O atoms, 8 S atoms, and 14 N atoms?

How many molecules of C 2 H 4 Cl 2 can be prepared from 15 C 2 H 4 molecules and 8 Cl 2 molecules?

Determine the limiting reactant and the percent yield of this reaction.

Uranium can be isolated from its ores by dissolving it as UO 2 (NO 3 ) 2 , then separating it as solid UO 2 (C 2 O 4 )·3H 2 O. Addition of 0.4031 g of sodium oxalate, Na 2 C 2 O 4 , to a solution containing 1.481 g of uranyl nitrate, UO 2 (NO 2 ) 2 , yields 1.073 g of solid UO 2 (C 2 O 4 )·3H 2 O.

What is the limiting reactant when 1.50 g of lithium and 1.50 g of nitrogen combine to form lithium nitride, a component of advanced batteries, according to the following unbalanced equation?

The conversion needed is (ce{mol: Cr rightarrow mol: H2PO4}). Then compare the amount of Cr to the amount of acid present. Cr is the limiting reactant.

Outline the steps needed to determine the limiting reactant when 0.50 g of Cr and 0.75 g of H 3 PO 4 react according to the following chemical equation?

Outline the steps needed to determine the limiting reactant when 30.0 g of propane, C 3 H 8 , is burned with 75.0 g of oxygen.

Convert mass of ethanol to moles of ethanol; relate the moles of ethanol to the moles of ether produced using the stoichiometry of the balanced equation. Convert moles of ether to grams; divide the actual grams of ether (determined through the density) by the theoretical mass to determine the percent yield; 87.6%

What is the percent yield of ether if 1.17 L (d = 0.7134 g/mL) is isolated from the reaction of 1.500 L of C 2 H 5 OH (d = 0.7894 g/mL)?

Outline the steps needed to solve the following problem, then do the calculations. Ether, (C 2 H 5 ) 2 O, which was originally used as an anesthetic but has been replaced by safer and more effective medications, is prepared by the reaction of ethanol with sulfuric acid.

In a laboratory experiment, the reaction of 3.0 mol of H 2 with 2.0 mol of I 2 produced 1.0 mol of HI. Determine the theoretical yield in grams and the percent yield for this reaction.

Toluene, C 6 H 5 CH 3 , is oxidized by air under carefully controlled conditions to benzoic acid, C 6 H 5 CO 2 H, which is used to prepare the food preservative sodium benzoate, C 6 H 5 CO 2 Na. What is the percent yield of a reaction that converts 1.000 kg of toluene to 1.21 kg of benzoic acid?

What mass of citric acid is produced from exactly 1 metric ton (1.000 × 10 3 kg) of sucrose if the yield is 92.30%?

Citric acid, C 6 H 8 O 7 , a component of jams, jellies, and fruity soft drinks, is prepared industrially via fermentation of sucrose by the mold Aspergillus niger. The equation representing this reaction is

Freon-12, CCl 2 F 2 , is prepared from CCl 4 by reaction with HF. The other product of this reaction is HCl. Outline the steps needed to determine the percent yield of a reaction that produces 12.5 g of CCl 2 F 2 from 32.9 g of CCl 4 . Freon-12 has been banned and is no longer used as a refrigerant because it catalyzes the decomposition of ozone and has a very long lifetime in the atmosphere. Determine the percent yield.

A sample of 0.53 g of carbon dioxide was obtained by heating 1.31 g of calcium carbonate. What is the percent yield for this reaction?

A student isolated 25 g of a compound following a procedure that would theoretically yield 81 g. What was his percent yield?

Which of the postulates of Dalton’s atomic theory explains why we can calculate a theoretical yield for a chemical reaction?

What is the limiting reactant in a reaction that produces sodium chloride from 8 g of sodium and 8 g of diatomic chlorine?

The following quantities are placed in a container: 1.5 × 10 24 atoms of hydrogen, 1.0 mol of sulfur, and 88.0 g of diatomic oxygen.

4.5: Quantitative Chemical Analysis

Q4.5.1

What volume of 0.0105-M HBr solution is be required to titrate 125 mL of a 0.0100-M Ca(OH)2 solution?

[ce{Ca(OH)2}(aq)+ce{2HBr}(aq) rightarrow ce{CaBr2}(aq)+ce{2H2O}(l)]

Q4.5.2

Titration of a 20.0-mL sample of acid rain required 1.7 mL of 0.0811 M NaOH to reach the end point. If we assume that the acidity of the rain is due to the presence of sulfuric acid, what was the concentration of sulfuric acid in this sample of rain?

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S4.5.2

3.4 × 10−3 M H2SO4

Q4.5.3

What is the concentration of NaCl in a solution if titration of 15.00 mL of the solution with 0.2503 M AgNO3 requires 20.22 mL of the AgNO3 solution to reach the end point?

[ce{AgNO3}(aq)+ce{NaCl}(aq)rightarrow ce{AgCl}(s)+ce{NaNO3}(aq)]

Q4.5.4

In a common medical laboratory determination of the concentration of free chloride ion in blood serum, a serum sample is titrated with a Hg(NO3)2 solution.

[ce{2Cl-}(aq)+ce{Hg(NO3)2}(aq)rightarrow ce{2NO3-}(aq)+ce{HgCl2}(s)]

What is the Cl− concentration in a 0.25-mL sample of normal serum that requires 1.46 mL of 5.25 × 10−4 M Hg(NO3)2(aq) to reach the end point?

S4.5.4

9.6 × 10−3 M Cl−

Q4.5.5

Potatoes can be peeled commercially by soaking them in a 3-M to 6-M solution of sodium hydroxide, then removing the loosened skins by spraying them with water. Does a sodium hydroxide solution have a suitable concentration if titration of 12.00 mL of the solution requires 30.6 mL of 1.65 M HCI to reach the end point?

Q4.5.6

A sample of gallium bromide, GaBr2, weighing 0.165 g was dissolved in water and treated with silver nitrate, AgNO3, resulting in the precipitation of 0.299 g AgBr. Use these data to compute the %Ga (by mass) GaBr2.

S4.5.6

22.4%

Q4.5.7

The principal component of mothballs is naphthalene, a compound with a molecular mass of about 130 amu, containing only carbon and hydrogen. A 3.000-mg sample of naphthalene burns to give 10.3 mg of CO2. Determine its empirical and molecular formulas.

Q4.5.8

A 0.025-g sample of a compound composed of boron and hydrogen, with a molecular mass of ~28 amu, burns spontaneously when exposed to air, producing 0.063 g of B2O3. What are the empirical and molecular formulas of the compound.

S4.5.8

The empirical formula is BH3. The molecular formula is B2H6.

Q4.5.9

Sodium bicarbonate (baking soda), NaHCO3, can be purified by dissolving it in hot water (60 °C), filtering to remove insoluble impurities, cooling to 0 °C to precipitate solid NaHCO3, and then filtering to remove the solid, leaving soluble impurities in solution. Any NaHCO3 that remains in solution is not recovered. The solubility of NaHCO3 in hot water of 60 °C is 164 g L. Its solubility in cold water of 0 °C is 69 g/L. What is the percent yield of NaHCO3 when it is purified by this method?

Q4.5.10

What volume of 0.600 M HCl is required to react completely with 2.50 g of sodium hydrogen carbonate?

[ce{NaHCO3}(aq)+ce{HCl}(aq)rightarrow ce{NaCl}(aq)+ce{CO2}(g)+ce{H2O}(l)]

S4.5.10

49.6 mL

Q4.5.11

What volume of 0.08892 M HNO3 is required to react completely with 0.2352 g of potassium hydrogen phosphate?

[ce{2HNO3}(aq)+ce{K2HPO4}(aq)rightarrow ce{H2PO4}(aq)+ce{2KNO3}(aq)]

Q4.5.12

What volume of a 0.3300-M solution of sodium hydroxide would be required to titrate 15.00 mL of 0.1500 M oxalic acid?

[ce{C2O4H2}(aq)+ce{2NaOH}(aq)rightarrow ce{Na2C2O4}(aq)+ce{2H2O}(l)]

S4.5.12

13.64 mL

Q4.5.13

What volume of a 0.00945-M solution of potassium hydroxide would be required to titrate 50.00 mL of a sample of acid rain with a H2SO4 concentration of 1.23 × 10−4 M.

[ce{H2SO4}(aq)+ce{2KOH}(aq)rightarrow ce{K2SO4}(aq)+ce{2H2O}(l)]

S4.5.13

1.30 mL

Q4.5.14

A sample of solid calcium hydroxide, Ca(OH)2, is allowed to stand in water until a saturated solution is formed. A titration of 75.00 mL of this solution with 5.00 × 10−2 M HCl requires 36.6 mL of the acid to reach the end point.

[ce{Ca(OH)2}(aq)+ce{2HCl}(aq)rightarrow ce{CaCl2}(aq)+ce{2H2O}(l)]

What is the molarity?

S4.5.14

1.22 M

Q4.5.15

What mass of Ca(OH)2 will react with 25.0 g of propionic acid to form the preservative calcium propionate according to the equation?

Q4.5.16

How many milliliters of a 0.1500-M solution of KOH will be required to titrate 40.00 mL of a 0.0656-M solution of H3PO4?

[ce{H3PO4}(aq)+ce{2KOH}(aq)rightarrow ce{K2HPO4}(aq)+ce{2H2O}(l)]

S4.5.16

34.99 mL KOH

Q4.5.17

Potassium acid phthalate, KHC6H4O4, or KHP, is used in many laboratories, including general chemistry laboratories, to standardize solutions of base. KHP is one of only a few stable solid acids that can be dried by warming and weighed. A 0.3420-g sample of KHC6H4O4 reacts with 35.73 mL of a NaOH solution in a titration. What is the molar concentration of the NaOH?

[ce{KHC6H4O4}(aq)+ce{NaOH}(aq)rightarrow ce{KNaC6H4O4}(aq)+ce{H2O}(aq)]

Q4.5.18

The reaction of WCl6 with Al at ~400 °C gives black crystals of a compound containing only tungsten and chlorine. A sample of this compound, when reduced with hydrogen, gives 0.2232 g of tungsten metal and hydrogen chloride, which is absorbed in water. Titration of the hydrochloric acid thus produced requires 46.2 mL of 0.1051 M NaOH to reach the end point. What is the empirical formula of the black tungsten chloride?

S4.5.19

The empirical formula is WCl4.

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