Exercises

What is the total mass of hydrogen in each of the molecules?

(a) CH₄

(b) CHCl₃

(c) C₁₂H₁₀O₆

(d) CH₃CH₂CH₂CH₂CH₃

Determine the molecular mass of the following compounds:

(a)

(b)

(c)

(d)

Which molecule has a molecular mass of 28.05 amu?

(a)

(b)

(c)

Compare 1 mole of H₂, 1 mole of O₂, and 1 mole of F₂.

(a) Which has the largest number of molecules? Explain why.

(b) Which has the greatest mass? Explain why.

Which contains the greatest number of moles of oxygen atoms: 1 mol of ethanol (C₂H₅OH), 1 mol of formic acid (HCO₂H), or 1 mol of water (H₂O)? Explain why.

Calculate the molar mass of each of the following compounds:

(a) hydrogen fluoride, HF

(b) ammonia, NH₃

(c) nitric acid, HNO₃

(d) silver sulfate, Ag₂SO₄

(e) boric acid, B(OH)₃

Calculate the empirical or molecular formula mass and the molar mass of each of the following minerals:

(a) limestone, CaCO₃

(b) halite, NaCl

(c) beryl, Be₃Al₂Si₆O₁₈

(d) malachite, Cu₂(OH)₂CO₃

(e) turquoise, CuAl₆(PO₄)₄(OH)₈(H₂O)₄

Determine the number of moles of compound and the number of moles of each type of atom in each of the following:

(a) 25.0 g of propylene, C₃H₆

(b) 3.06 $\times$ 10⁻³ g of the amino acid glycine, C₂H₅NO₂

(c) 25 lb of the herbicide Treflan, C₁₃H₁₆N₂O₄F (1 lb = 454 g)

(d) 0.125 kg of the insecticide Paris Green, Cu₄(AsO₃)₂(CH₃CO₂)₂

(e) 325 mg of aspirin, C₆H₄(CO₂H)(CO₂CH₃)

Determine the number of moles of the compound and determine the number of moles of each type of atom in each of the following:

(a) 2.12 g of potassium bromide, KBr

(b) 0.1488 g of phosphoric acid, H₃PO₄

(c) 23 kg of calcium carbonate, CaCO₃

(d) 78.452 g of aluminum sulfate, Al₂(SO₄)₃

(e) 0.1250 mg of caffeine, C₈H₁₀N₄O₂

The approximate minimum daily dietary requirement of the amino acid leucine, C₆H₁₃NO₂, is 1.1 g. What is this requirement in moles?

A 55-kg woman has 7.5 $\times$ 10⁻³ mol of hemoglobin (molar mass = 64,456 g/mol) in her blood. How many hemoglobin molecules is this? What is this quantity in grams?

Determine which of the following contains the greatest mass of hydrogen: 1 mol of CH₄, 0.6 mol of C₆H₆, or 0.4 mol of C₃H₈.

Diamond is one form of elemental carbon. An engagement ring contains a diamond weighing 1.25 carats (1 carat = 200 mg). How many atoms are present in the diamond?

One 55-gram serving of a particular cereal supplies 270 mg of sodium, 11% of the recommended daily allowance. How many moles and atoms of sodium are in the recommended daily allowance?

A tube of toothpaste contains 0.76 g of sodium monofluorophosphate (Na₂PO₃F) in 100 mL.

(a) What mass of fluorine atoms in mg was present?

(b) How many fluorine atoms were present?

What information do we need to determine the molecular formula of a compound from the empirical formula?

Determine the following to four significant figures:

(a) the percent composition of hydrazoic acid, HN₃

(b) the percent composition of TNT, C₆H₂(CH₃)(NO₂)₃

(c) the percent of SO₄^2– in Al₂(SO₄)₃

Determine the percent water in CuSO₄∙5H₂O to three significant figures.

Determine the empirical formulas for compounds with the following percent compositions:

(a) 43.6% phosphorus and 56.4% oxygen

(b) 28.7% K, 1.5% H, 22.8% P, and 47.0% O

Dichloroethane, a compound that is often used for dry cleaning, contains carbon, hydrogen, and chlorine. It has a molar mass of 99 g/mol. Analysis of a sample shows that it contains 24.3% carbon and 4.1% hydrogen. What is its molecular formula?

Polymers are large molecules composed of simple units repeated many times. Thus, they often have relatively simple empirical formulas. Calculate the empirical formulas of the following polymers:

(a) Lucite (Plexiglas); 59.9% C, 8.06% H, 32.0% O

(b) Saran; 24.8% C, 2.0% H, 73.1% Cl

(c) polyethylene; 86% C, 14% H

(d) polystyrene; 92.3% C, 7.7% H

(e) Orlon; 67.9% C, 5.70% H, 26.4% N

Explain what changes and what stays the same when 1.00 L of a solution of NaCl is diluted to 1.80 L.

What does it mean when we say that a 200-mL sample and a 400-mL sample of a solution of salt have the same molarity? In what ways are the two samples identical? In what ways are these two samples different?

Determine the molarity of each of the following solutions:

(a) 1.457 mol KCl in 1.500 L of solution

(b) 0.515 g of H₂SO₄ in 1.00 L of solution

(c) 20.54 g of Al(NO₃)₃ in 1575 mL of solution

(d) 2.76 kg of CuSO₄·5H₂O in 1.45 L of solution

(e) 0.005653 mol of Br₂ in 10.00 mL of solution

(f) 0.000889 g of glycine, C₂H₅NO₂, in 1.05 mL of solution

Consider this question: What is the mass of solute in 200.0 L of a 1.556-M solution of KBr?

(a) Outline the steps necessary to answer the question.

(b) Answer the question.

Calculate the number of moles and the mass of the solute in each of the following solutions:

(a) 325 mL of 8.23 $\times$ 10⁻⁵ M KI, a source of iodine in the diet

(b) 75.0 mL of 2.2 $\times$ 10⁻⁵ M H₂SO₄, a sample of acid rain

(c) 0.2500 L of 0.1135 M K₂CrO₄, an analytical reagent used in iron assays

(d) 10.5 L of 3.716 M (NH₄)₂SO₄, a liquid fertilizer

Consider this question: What is the molarity of HCl if 35.23 mL of a solution of HCl contain 0.3366 g of HCl?

(a) Outline the steps necessary to answer the question.

(b) Answer the question.

Calculate the molarity of each of the following solutions:

(a) 293 g HCl in 666 mL of solution, a concentrated HCl solution

(b) 2.026 g FeCl₃ in 0.1250 L of a solution used as an unknown in general chemistry laboratories

(c) 0.001 mg Cd²⁺ in 0.100 L, the maximum permissible concentration of cadmium in drinking water

(d) 0.0079 g C₇H₅SNO₃ in one ounce (29.6 mL), the concentration of saccharin in a diet soft drink.

What volume of a 1.00-M Fe(NO₃)₃ solution can be diluted to prepare 1.00 L of a solution with a concentration of 0.250 M?

If 4.12 L of a 0.850 M-H₃PO₄ solution is be diluted to a volume of 10.00 L, what is the concentration of the resulting solution?

What is the concentration of the NaCl solution that results when 0.150 L of a 0.556-M solution is allowed to evaporate until the volume is reduced to 0.105 L?

What is the final concentration of the solution produced when 225.5 mL of a 0.09988-M solution of Na₂CO₃ is allowed to evaporate until the solution volume is reduced to 45.00 mL?

An experiment in a general chemistry laboratory calls for a 2.00-M solution of HCl. How many mL of 11.9 M HCl would be required to make 250 mL of 2.00 M HCl?

The US Environmental Protection Agency (EPA) places limits on the quantities of toxic substances that may be discharged into the sewer system. Limits have been established for a variety of substances, including hexavalent chromium, which is limited to 0.50 mg/L. If an industry is discharging hexavalent chromium as potassium dichromate (K₂Cr₂O₇), what is the maximum permissible molarity of that substance?

What mass of a 4.00% NaOH solution by mass contains 15.0 g of NaOH?

What mass of HCl is contained in 45.0 mL of an aqueous HCl solution that has a density of 1.19 g cm^–3 and contains 37.21% HCl by mass?

The level of mercury in a stream was suspected to be above the minimum considered safe (1 part per billion by weight). An analysis indicated that the concentration was 0.68 parts per billion. Assume a density of 1.0 g/mL and calculate the molarity of mercury in the stream.

A throat spray is 1.40% by mass phenol, C₆H₅OH, in water. If the solution has a density of 0.9956 g/mL, calculate the molarity of the solution.

A cough syrup contains 5.0% ethyl alcohol, C₂H₅OH, by mass. If the density of the solution is 0.9928 g/mL, determine the molarity of the alcohol in the cough syrup.

Find the molarity of a 40.0% by mass aqueous solution of sulfuric acid, H₂SO₄, for which the density is 1.3057 g/mL.