The Components of Matter

A 1000  m solution of chloroacetic acid $\left({\text{ClCH}}_{\text{2}}\text{COOH}\right)$ freezes at $\mathbf{1}\mathbf{.}\mathbf{93}\mathbf{°}\mathbf{C}$  . Find the Ka of chloroacetic acid. (Assume the molarities equal the molalities.)

Sodium stearate $\left({\text{C}}_{\text{17}}{\text{H}}_{\text{35}}\text{COONa}\right)$ is a major component of bar soap. The Ka of the stearic acid is $\mathbf{\text{1.3}}\mathbf{\times }{\mathbf{\text{10}}}^{\mathbf{\text{ - 5}}}$. What is the pH of 0.42  mL of a solution containing 0.42 g of sodium stearate?

(a) If ${\mathbf{\text{K}}}_{\mathbf{\text{w}}}\mathbf{\text{ = 1.139}}\mathbf{\times }{\mathbf{\text{10}}}^{\mathbf{\text{ - 15}}}$at $\mathbf{0}\mathbf{°}\mathbf{C}$ and $\mathbf{\text{5.474}}\mathbf{\times }{\mathbf{\text{10}}}^{\mathbf{\text{ - 14}}}$at $\mathbf{50}\mathbf{°}\mathbf{C}$, find and pH of water at $\mathbf{0}\mathbf{°}\mathbf{C}$and $\mathbf{50}\mathbf{°}\mathbf{C}$. 

(b) The auto ionization constant for heavy water (deuterium oxide, ${\mathbf{\text{D}}}_{\mathbf{\text{2}}}\mathbf{\text{O}}$) is $\mathbf{\text{3.64}}\mathbf{\times }{\mathbf{\text{10}}}^{\mathbf{-}\mathbf{16}}$ at $\mathbf{0}\mathbf{°}\mathbf{C}$and $\mathbf{\text{7.89}}\mathbf{\times }{\mathbf{\text{10}}}^{\mathbf{\text{ - 15}}}$at $\mathbf{50}\mathbf{°}\mathbf{C}$ . Find $\left[{\text{D}}_{\text{3}}{\text{O}}^{\text{ + }}\right]$and pD of heavy water at $\mathbf{0}\mathbf{°}\mathbf{C}$and $\mathbf{50}\mathbf{°}\mathbf{C}$. 

(c) Suggest a reason for these differences.

What is the key difference between an element and a compound?

List two differences between a compound and a mixture.

Why was it necessary for separation techniques and methods of chemical analysis to be developed before the laws of definite composition and multiple proportions could be formulated?

(a) Does the percent by mass of each element in a compound depend on the amount of compound? Explain.

(b) Does the mass of each element in a compound depend on the amount of compound? Explain.

State the mass law(s) demonstrated by the following experimental results, and explain your reasoning: 

Experiment 1: A student heats 1.27 g of copper and 3.50 g of iodine to produce 3.81 g of a white compound; 0.96 g of iodine remains.

Experiment 2: A second student heats 2.55 g of copper and 3.50 g of iodine to form 5.25 g of a white compound, and 0.80 g of copper remains.

State the mass law(s) demonstrated by the following experimental results, and explain your reasoning: 

Experiment 1: A student heats 1.00 g of a blue compound and obtains 0.64 g of a white compound and 0.36 g of a colourless gas. 

Experiment 2: A second student heats 3.25 g of the same blue compound and obtains 2.08 g of a white compound and 1.17 g of a colourless gas.

What is the key difference between an element and a compound?

List two differences between a compound and a mixture.

The tap water found in many areas of the United States leaves white deposits when it evaporates. Is this tap water a mixture or a compound? Explain.

Explain the following statement: The smallest particles unique to an element may be atoms or molecules.

Can the relative amounts of the components of a mixture vary? Can the relative amounts of the components of a compound vary? Explain.

Explain the following statement: The smallest particles unique to a compound cannot be atoms.

Each scene below represents a mixture. Describe each one in terms of the number of elements and/or compounds present.

Does the percent by mass of each element in a compound depend on the amount of that element used to make the compound? Explain.

Which of the following are pure substances? Explain. 

(a) Calcium chloride, used to melt ice on roads, consists of two elements, calcium and chlorine, in a fixed mass ratio. 

(b) Sulfur consists of sulfur atoms combined into octatomic molecules. 

(c) Baking powder, a leavening agent, contains 26% to 30% sodium hydrogen carbonate and 30% to 35% calcium dihydrogen phosphate by mass.

(d) Cytosine, a component of DNA, consists of H, C, N, and O atoms bonded in a specific arrangement.

Classify each substance in Problem 2.3 as an element, compound, or mixture, and explain your answers.

Explain the following statement: The smallest particles unique to an element may be atoms or molecules.

Explain the following statement: The smallest particles unique to a compound cannot be atoms.

Can the relative amounts of the components of a mixture vary? Can the relative amounts of the components of a compound vary? Explain.

The tap water found in many areas of the United States leaves white deposits when it evaporates. Is this tap water a mixture or a compound? Explain.

Each scene below represents a mixture. Describe each one in terms of the number of elements and/or compounds present.

Samples of illicit “street” drugs often contain an inactive component, such as ascorbic acid (vitamin C). After obtaining a sample of cocaine, government chemists calculate the mass of vitamin C per gram of drug sample, and use it to track the drug’s distribution. For example, if different samples of cocaine obtained on the streets of New York, Los Angeles, and Paris all contain 0.6384 g of vitamin C per gram of sample, they very likely come from a common source. Do these street samples consist of a compound, element, or mixture? Explain.

Why was it necessary for separation techniques and methods of chemical analysis to be developed before the laws of definite composition and multiple proportions could be formulated?

In our modern view of matter and energy, is the law of mass conservation still relevant to chemical reactions? Explain.

Identify the mass law that each of the following observations demonstrates, and explain your reasoning:

(a) A sample of potassium chloride from Chile contains the same percent by mass of potassium as one from Poland.

(b) A flashbulb contains magnesium and oxygen before use and magnesium oxide afterward, but its mass does not change. 

(c) Arsenic and oxygen form one compound that is 65.2 mass % arsenic and another that is 75.8 mass % arsenic.

Which of the following scenes illustrate(s) the fact that compounds of chlorine (green) and oxygen (red) exhibit the law of multiple proportions? Name the compounds.

(a) Does the percent by mass of each element in a compound depend on the amount of compound? Explain.

(b) Does the mass of each element in a compound depend on the amount of compound? Explain.

Does the percent by mass of each element in a compound depend on the amount of that element used to make the compound? Explain.

State the mass law(s) demonstrated by the following experimental results, and explain your reasoning: 

Experiment 1: A student heats 1.00 g of a blue compound and obtains 0.64 g of a white compound and 0.36 g of a colour less gas. 

Experiment 2: A second student heats 3.25 g of the same blue compound and obtains 2.08 g of a white compound and 1.17 g of a colour less gas.

State the mass law(s) demonstrated by the following experimental results, and explain your reasoning: 

Experiment 1: A student heats 1.27 g of copper and 3.50 g of iodine to produce 3.81 g of a white compound; 0.96 g of iodine remains.

Experiment 2: A second student heats 2.55 g of copper and 3.50 g of iodine to form 5.25 g of a white compound, and 0.80 g of copper remains.

What is the key difference between an element and a compound?

Which of Dalton’s postulates about atoms are inconsistent with later observations? Do these inconsistencies mean that Dayton was wrong? Is Dalton’s model still useful? Explain.

Thomson was able to determine the mass/charge ratio of the electron but not it's mass. How did Millikan’s experiment allow the determination of the electron’s mass?

When Rutherford's coworkers bombarded gold foil with particles, they obtained results that overturned the existing (Thomson) model of the atom. Explain.

The mass percent of sulfur in a sample of coal is a key factor in the environmental impact of the coal because the sulfur combines with oxygen when the coal is burned and the oxide can then be incorporated into acid rain. Which of the following coals would have the smallest environmental impact?

Choose the correct answer. The difference between the mass number of an isotope and its atomic number is (a)directly related to the identity of the element; (b) the number of electrons; (c) the number of neutrons; (d) the number of isotopes.

Describe Thomson’s model of the atom. How might it account for the production of cathode rays?

Define atomic number and mass number which can vary without changing the identity of the element?

Magnesium oxide (MgO) forms when the metal burns in the air. How many grams of Mg are in534 g of MgO?

Zinc sulfide (ZnS) occurs in the zinc blend crystal structure. How many kilograms of Zn are in 3.82 kg of ZnS?

A compound of iodine and cesium contains 63.94 g of metal and 61.06 g of nonmetal. How many grams of cesium are in38.77 g of compound? How many grams of iodine?

Show, with calculations, how the following data illustrate the law of multiple proportions:Compound 1: 77.6 mass % xenon and 22.4 mass % fluorineCompound 2: 63.3 mass % xenon and 36.7 mass % fluorine

Galena, a mineral of lead, is a compound of the metal with sulfur. Analysis shows that a 2.34-g sample of galena contains2.03 g of lead. Calculate the mass percent of lead and sulfur in galena.

Fluorite, a mineral of calcium, is a compound of the metal with fluorine. Analysis shows that a 2.76-g sample of fluorite contains 1.42 g of calcium. Calculate the (a) mass of fluorine in the sample; (b) mass fractions of calcium and fluorine in fluorite; (c) mass percents of calcium and fluorine in fluorite.

Show, with calculations, how the following data illustrate thelaw of multiple proportions:Compound 1: 47.5 mass % sulfur and 52.5 mass % chlorineCompound 2: 31.1 mass % sulfur and 68.9 mass % chlorine

Dolomite is a carbonate of magnesium and calcium. Analysisshows that 7.81 g of dolomite contains 1.70 g of Ca. Calculate themass percent of Ca in dolomite. On the basis of the mass percentof Ca, and neglecting all other factors, which is the richer sourceof Ca, dolomite or fluorite (see Problem 2.20)?

Use Dalton’s theory to explain why potassium nitrate from India or Italy has the same mass percents of K, N, and O.