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An 8.65-g sample of an unknown group 2a metal hydroxide is dissolved in 85.0 ml of water. an acid-base indicator is added and the resulting solution is titrated with 2.50 m hcl(aq) solution. the indicator changes color signaling that the equivalence point has been reached after 56.9 ml of the hydrochloric acid solution has been added.

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Answer;

The molar mass of metal hydroxide = 121.66 g/ mole

The formula is Sr(OH)2

Explanation;

M(OH)2 + 2 HCl = MCl2 + 2 H2O  

Moles of the acid = 2.5 x 56.9 / 1000 = 0.14225  

Therefore; moles of hydroxide at the eq point = 0.0711 moles  

These have a mass of 8.65g

Thus; mass of 1 mole = 8.65 / 0.0711

         = 121.66 g / mole  

That means the compound is Sr (OH)2 ..

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If 63.8 grams of aluminum metal (Al) react with 72.3 grams of sulfur (S) in a synthesis reaction, how many grams of the excess reactant will be left over when the reaction is complete? Be sure to write out the balanced equation for this reaction and to show all of your work.

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The balanced chemical reaction would be:

16Al + 3S8 = 8Al2S3

We need to determine which reactants are the limiting and the excess. To determine this, we use the initial amounts of the reactants given above. We need to convert them into units of moles and use the balanced reaction to relate the substances calculating the amount needed to react all of the reactants. We do as follows:

63.8 g Al ( 1 mol Al / 26.98 g Al ) ( 3 mol S8 / 16 mol Al ) (256.48 g S / 1 mol S )= 113.72 g S8 needed to completely react
72.3 g S8 ( 1 mol S8 / 256.48 g S8) ( 16 mol Al / 3 mol S8 ) ( 26.98 g / mol ) = 40.56 g Al needed to completely react

Therefore, the excess would be Al and the limiting would be sulfur. The amount excess would be 63.8 g Al  – 40.56 g Al = 23.24 g Al

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Describe two ways he could change the metal physically and two ways he could change the metal chemically to try to identify it.

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Answered by answersmine AT 22/10/2019 – 03:18 AM

Physical change is a change that occurs in a substance that does not change the identity of the substance. It does not alter the chemical structure of the molecules ehile chemical change involves the breaking of the bonds in the substance forming new substance. To identify a metal physically, we can use properties like their boiling and melting points. We can determine at what temperatures these metals melt or boil then from literature we compare the values. Another properties that can be looked upon to are hardness, color and density. For chemical methods, we can allow it to react with substances, that will produce precipitates containing the metal in question. Also, we can use other methods like titration method. All chemical methods involves the use of chemical reactions.

Post your answer

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A metal washer is made by cutting out a circle 13.2 mm in diameter from a larger circle. To the nearest tenth, what is the area of the washer?

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A metal washer is made by cutting out a circle 13.2 mm in diameter from a larger circle. To the nearest tenth, what is the area of the washer?

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You have two pieces of wire that allow electrons to pass through them when they arfe connected to each other. if you insert cable betwee the wires, electrons will flow easily. the metal cable is?

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You have two pieces of wire that allow electrons to pass through them when they arfe connected to each other. if you insert cable betwee the wires, electrons will flow easily. the metal cable is?

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A recipe for candy requires that the liquid ingredients be stirred constantly until the liquid reaches a temperature of 140°C. What type of spoon – wood or metal – will prevent burns to a person’s hand while stirring the hot liquid? Explain your choice.

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Sample Response: A wooden spoon will prevent the person’s hand from burning because wood is an insulator. An insulator slows the transfer of thermal energy so that very little thermal energy from the hot liquid will transfer to the person’s hand. 

include:

-A wooden spoon will prevent the person’s hand from burning.

-Wood is an insulator.-An insulator slows the transfer of thermal energy.-The wooden spoon will transfer very little thermal energy to the person’s hand.

you’re welcome lol

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In order to observe a ______ property of a substance, the substance must interact with another substance , such as when gasoline burns or when sodium metal reacts with water

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This problem is to apply Roult’s Law.

Roult’s Law states that the vapor pressure, p, of a solution of a non-volatile solute is equal to the vapor pressure of the pure solvent, Po solv, times the mole fraction of the solvent, Xsolv

p = Xsolv * Po sol

X solv = number of moles of solvent / number of moles of solution

The solvent is water and the solute (not volatile) is glycerin.

Number of moles = mass in grams / molar mass

mass of water = 132 ml * 1 g/ml = 132 g

molar mass of water = 18 g/mol

=> number of moles of water = 132 g / 18 g/mol = 7.33333 mol

mass of glycerin = 27.2 g

molar mass of glycerin:, C3H8O3: 3 * 12 g/mol + 8 * 1 g/mol + 3*16 g/mol = 92 g/mol

number of moles of glycerin = 27.2g / 92 g/mol = 0.29565

total number of moles = 7.33333 moles + 0.29565 moles = 7.62898 moles

=> X solv = 7.33333 / 7.62898 = 0.96125

=> p = 0.96125 * 31.8 torr ≈ 30.57 torr ≈ 30.6 torr.

Answer: 30.6 torr

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Silver tarnishes as silver metal reacts with hydrogen sulfide, H2S, in the air. In this reaction, dark silver sulfide, Au2S, covers the surface of silver. When silver is polished, this coating of silver sulfide can be removed from the surface. This makes the silver shiny again. Enter the coefficients that balance the tarnishing reaction equation. (Type 1 for no coefficient.)Ag(s) + H2S(g) → Ag2S(s) + H2(g)

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Explanation :

In the net ionic equations, we are not include the spectator ions in the equations.

Spectator ions : The ions present on reactant and product side which do not participate in a reactions. The same ions present on both the sides.

(a) The given balanced ionic equation is,

Ni(NO_3)_2(aq)+Na_2S(aq)rightarrow NiS(s)+2NaNO_3(aq)

The ionic equation in separated aqueous solution will be,

Ni^{2+}(aq)+2NO_3^-(aq)+2Na^+(aq)+S^{2-}(aq)rightarrow NiS(s)+2Na^+(aq)+2NO_3^-(aq)

In this equation, Na^+text{ and }NO_3^- are the spectator ions.

By removing the spectator ions from the balanced ionic equation, we get the net ionic equation.

The net ionic equation will be,

Ni^{2+}(aq)+S^{2-}(aq)rightarrow NiS(s)

(b) The given balanced ionic equation is,

NaNO_3(aq)+KBr(aq)rightarrow KNO_3(s)+NaBr(aq)

The ionic equation in separated aqueous solution will be,

Na^+(aq)+NO_3^-(aq)+K^+(aq)+Br^-(aq)rightarrow KNO_3(s)+Na^+(aq)+Br^-(aq)

In this equation, Na^+text{ and }Br^- are the spectator ions.

By removing the spectator ions from the balanced ionic equation, we get the net ionic equation.

The net ionic equation will be,

NO_3^-(aq)+K^+(aq)rightarrow KNO_3(s)

(c) The given balanced ionic equation is,

Li_2SO_4(aq)+BaCl_2(aq)rightarrow BaSO_4(s)+2LiCl(aq)

The ionic equation in separated aqueous solution will be,

2Li^+(aq)+SO_4^{2-}(aq)+Ba^{2+}(aq)+2Cl^-(aq)rightarrow BaSO_4(s)+2Li^+(aq)+2Cl^-(aq)

In this equation, Li^+text{ and }Cl^- are the spectator ions.

By removing the spectator ions from the balanced ionic equation, we get the net ionic equation.

The net ionic equation will be,

SO_4^{2-}(aq)+Ba^{2+}(aq)rightarrow BaSO_4(s)

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How many milliliters of sodium metal, with a density of 0.97 g/mL, would be needed to produce 34.5 grams of sodium hydroxide in the single replacement reaction below? Unbalanced equation: Na + H2O —> NaOH + H2

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The balanced chemical reaction is as shown below,

                 N₂ + 3H₂  –> 2NH₃

The equation shows that every 3 moles of hydrogen, H2, there would be 2 moles of ammonia, NH3, that is going to be formed. Using this concept, we solve for the unknown in this item. 

Since we are restricted only of the number of hydrogen, it becomes our limiting reactant. 

          (6 moles H2) x (2 moles NH3/3 moles H2) = 4 moles NH3

Therefore, given enough amount of N2, the amount of NH3 that can be formed out of the 6 moles of H2 is equal to 4 moles. 

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A metal sample is heated and placed into the water in a calorimeter at room temperature. Which statement best describes how the calorimeter can be used to determine the specific heat capacity of the metal sample? Energy transfers to the metal from the water and calorimeter until they are all at room temperature. Energy transfers from the metal to the water and calorimeter until they are all at room temperature. Energy transfers to the metal from the water and calorimeter until they all reach a single temperature. Energy transfers from the metal to the water and calorimeter until they all reach a single temperature.

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This problem is to apply Roult’s Law.

Roult’s Law states that the vapor pressure, p, of a solution of a non-volatile solute is equal to the vapor pressure of the pure solvent, Po solv, times the mole fraction of the solvent, Xsolv

p = Xsolv * Po sol

X solv = number of moles of solvent / number of moles of solution

The solvent is water and the solute (not volatile) is glycerin.

Number of moles = mass in grams / molar mass

mass of water = 132 ml * 1 g/ml = 132 g

molar mass of water = 18 g/mol

=> number of moles of water = 132 g / 18 g/mol = 7.33333 mol

mass of glycerin = 27.2 g

molar mass of glycerin:, C3H8O3: 3 * 12 g/mol + 8 * 1 g/mol + 3*16 g/mol = 92 g/mol

number of moles of glycerin = 27.2g / 92 g/mol = 0.29565

total number of moles = 7.33333 moles + 0.29565 moles = 7.62898 moles

=> X solv = 7.33333 / 7.62898 = 0.96125

=> p = 0.96125 * 31.8 torr ≈ 30.57 torr ≈ 30.6 torr.

Answer: 30.6 torr

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Zinc and magnesium metal each reacts with hydrochloric acid to make chloride salts of the respective metals, and hydrogen gas. a 11.20-g mixture of zinc and magnesium produces 0.6854 g of hydrogen gas upon being mixed with an excess of hydrochloric acid. determine the percent magnesium by mass in the original mixture.

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The balanced chemical reaction is as shown below,

                 N₂ + 3H₂  –> 2NH₃

The equation shows that every 3 moles of hydrogen, H2, there would be 2 moles of ammonia, NH3, that is going to be formed. Using this concept, we solve for the unknown in this item. 

Since we are restricted only of the number of hydrogen, it becomes our limiting reactant. 

          (6 moles H2) x (2 moles NH3/3 moles H2) = 4 moles NH3

Therefore, given enough amount of N2, the amount of NH3 that can be formed out of the 6 moles of H2 is equal to 4 moles. 

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A record label surveyed 150 random visitors to its website to discover whether they prefer metal, rock, hip-hop, or jazz. The survey showed that 27 visitors preferred metal, 78 preferred rock, 21 voted for hip-hop, and 24 liked jazz. If the company estimates sales of 6,000 copies a week at its online store, how many will likely be from the rock genre? 1,040 3,000 3,120 4,200

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A record label surveyed 150 random visitors to its website to discover whether they prefer metal, rock, hip-hop, or jazz. The survey showed that 27 visitors preferred metal, 78 preferred rock, 21 voted for hip-hop, and 24 liked jazz. If the company estimates sales of 6,000 copies a week at its online store, how many will likely be from the rock genre? 1,040 3,000 3,120 4,200

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Find the area of the metal sheet below that is requires to make this square – shaped traffic sign. 5x – 3.

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Answer:  The correct option is (C). 10 = square root of the quantity of x minus 8 all squared plus y minus 9 all squared

Step-by-step explanation:  Given that the segment AB has point A located at (8, 9). The distance from A to B is 10 units.

We are to select the correct option that could be used to calculate the coordinates for point B.

Let, (x, y) be the co-ordinates of point B.

According to distance formula, the distance between two points (a, b) and (c, d) is given by

d=sqrt{(c-a)^2+(d-b)^2}.

Therefore, the distance between the points A(8, 9) and B(x, y) is given by

d=sqrt{(x-8)^2+(y-9)^2}.

Since, distance between A and B is 10 units, so

d = 10.

Therefore,

10=sqrt{(x-8)^2+(y-9)^2}.

Thus, the correct statement is

10 = square root of the quantity of x minus 8 all squared plus y minus 9 all squared.

Option (C) is correct.

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Elecrical wiring is commonly composed of metal covered in plastic ir rubber coating which of these materials is an insulator and which is a conductor

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The equation for how temperature changes the resistance R is: 

R=R₀(1+α(T-T₀)), where R₀ is the resistance at T₀=20°C, T is the temperature for which we want to calculate the resistance and α is the temperature coefficient for resistance. 

The resistance of the copper wire increases by 18% or by 0.18, so the new value for the resistance is R=1.18*R₀.

T₀=20°C
=0.0068
R=1.18*R₀

Now we need to input that into the equation for resistance change and solve for temperature T.  

1.18R₀=R₀(1+α(T-20)), R₀ cancels out,

1.18=1+α(T-20),

1.18-1=α(T-20), we divide by α,

0.18/α=T-20, we put 20 on the left side,

26.47+20=T

T=46.47°C

So the temperature on which the resistance of copper wire will increase by 18% is T=46.47°C. 

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A metal smith pours 3.00 kg of lead shot at 99oc into 1.00 kg of water at 25oc in an isolated container. what is the final temperature of the mixture?

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The equation for how temperature changes the resistance R is: 

R=R₀(1+α(T-T₀)), where R₀ is the resistance at T₀=20°C, T is the temperature for which we want to calculate the resistance and α is the temperature coefficient for resistance. 

The resistance of the copper wire increases by 18% or by 0.18, so the new value for the resistance is R=1.18*R₀.

T₀=20°C
=0.0068
R=1.18*R₀

Now we need to input that into the equation for resistance change and solve for temperature T.  

1.18R₀=R₀(1+α(T-20)), R₀ cancels out,

1.18=1+α(T-20),

1.18-1=α(T-20), we divide by α,

0.18/α=T-20, we put 20 on the left side,

26.47+20=T

T=46.47°C

So the temperature on which the resistance of copper wire will increase by 18% is T=46.47°C. 

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Aluminum metal reacts with iron(ii) sulfide to form aluminum sulfide and iron metal. what is the stoichiometric coefficient for aluminum when the chemical equation is balanced using the lowest, whole-number stoichiometric coefficients?

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Explanation :

In the net ionic equations, we are not include the spectator ions in the equations.

Spectator ions : The ions present on reactant and product side which do not participate in a reactions. The same ions present on both the sides.

(a) The given balanced ionic equation is,

Ni(NO_3)_2(aq)+Na_2S(aq)rightarrow NiS(s)+2NaNO_3(aq)

The ionic equation in separated aqueous solution will be,

Ni^{2+}(aq)+2NO_3^-(aq)+2Na^+(aq)+S^{2-}(aq)rightarrow NiS(s)+2Na^+(aq)+2NO_3^-(aq)

In this equation, Na^+text{ and }NO_3^- are the spectator ions.

By removing the spectator ions from the balanced ionic equation, we get the net ionic equation.

The net ionic equation will be,

Ni^{2+}(aq)+S^{2-}(aq)rightarrow NiS(s)

(b) The given balanced ionic equation is,

NaNO_3(aq)+KBr(aq)rightarrow KNO_3(s)+NaBr(aq)

The ionic equation in separated aqueous solution will be,

Na^+(aq)+NO_3^-(aq)+K^+(aq)+Br^-(aq)rightarrow KNO_3(s)+Na^+(aq)+Br^-(aq)

In this equation, Na^+text{ and }Br^- are the spectator ions.

By removing the spectator ions from the balanced ionic equation, we get the net ionic equation.

The net ionic equation will be,

NO_3^-(aq)+K^+(aq)rightarrow KNO_3(s)

(c) The given balanced ionic equation is,

Li_2SO_4(aq)+BaCl_2(aq)rightarrow BaSO_4(s)+2LiCl(aq)

The ionic equation in separated aqueous solution will be,

2Li^+(aq)+SO_4^{2-}(aq)+Ba^{2+}(aq)+2Cl^-(aq)rightarrow BaSO_4(s)+2Li^+(aq)+2Cl^-(aq)

In this equation, Li^+text{ and }Cl^- are the spectator ions.

By removing the spectator ions from the balanced ionic equation, we get the net ionic equation.

The net ionic equation will be,

SO_4^{2-}(aq)+Ba^{2+}(aq)rightarrow BaSO_4(s)

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A capacitor consists of two metal surfaces separated by an electrical insulator

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A capacitor consists of two metal surfaces separated by an electrical insulator

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I PLEASE HELP! How many liters of a 2.25 molar hydrobromic acid (HBr) solution would be needed to react completely with 100.0 grams of calcium metal? Ca (s) + 2HBr (aq) CaBr2 (aq) + H2 (g)

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The balanced chemical reaction is as shown below,

                 N₂ + 3H₂  –> 2NH₃

The equation shows that every 3 moles of hydrogen, H2, there would be 2 moles of ammonia, NH3, that is going to be formed. Using this concept, we solve for the unknown in this item. 

Since we are restricted only of the number of hydrogen, it becomes our limiting reactant. 

          (6 moles H2) x (2 moles NH3/3 moles H2) = 4 moles NH3

Therefore, given enough amount of N2, the amount of NH3 that can be formed out of the 6 moles of H2 is equal to 4 moles. 

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Boats typically have several metal fittings where ropes can be fastened. What is the name for these metal fittings?

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Boats typically have several metal fittings where ropes can be fastened. What is the name for these metal fittings?

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Describe one chemical property of Group 1 metals that results from the atoms of each metal having only one valence electron.

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The balanced chemical reaction is as shown below,

                 N₂ + 3H₂  –> 2NH₃

The equation shows that every 3 moles of hydrogen, H2, there would be 2 moles of ammonia, NH3, that is going to be formed. Using this concept, we solve for the unknown in this item. 

Since we are restricted only of the number of hydrogen, it becomes our limiting reactant. 

          (6 moles H2) x (2 moles NH3/3 moles H2) = 4 moles NH3

Therefore, given enough amount of N2, the amount of NH3 that can be formed out of the 6 moles of H2 is equal to 4 moles. 

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Determine the identity of a cube of metal that measures 1.5 cm on each side and has a mass of 35.45 g

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Explanation:

  • For 1: protons plus neutrons.

Atomic mass is the sum of number of neutrons and protons present in an element.

Hence, the correct answer is atomic number

Atomic number is defined as the number of protons or electrons present in an element.

Hence, the correct answer is atomic number.

Photographic film is used as an imaging detector and thus detects the radiation.

Hence, the correct answer is photographic film.

Solid state is defined as the state which have fixed shape and volume.

Hence, the correct answer is solid.

Neutrons are a subatomic particle which is present in the nucleus and does not carry any charge.

Hence, the correct answer is neutron.

Protons are a subatomic particle which is present in the nucleus and carry positive charge.

Hence, the correct answer is proton.

  • For 7: occupies the whole container

Gaseous state is defined as the state which does not have any fixed shape or volume. It occupies the shape of the container.

Hence, the correct answer is gas

  • For 8: measures intensity of radiation

Geiger counter is defined as an instrument that is used for detecting and measuring the ionization radiation.

Hence, the correct answer is Geiger counter,

  • For 9: Smallest particle to retain characteristics.

Atom is defined as the smallest unit of matter which cannot be further broken down and thus retain its properties.

Hence, the correct answer is Atom.

Electrons are a subatomic particle which are located around the nucleus in orbits and carry negative charge.

Hence, the correct answer is electron.

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Three students measured the height of a lab table, each using a different meter stick. One student reported a height of 98 cm, another reported a height of 99 cm, and the last student reported a height of 70 cm. The most likely explanation for the difference in the reported heights is that one A. student improperly read the meter stick. B. meter stick was metal and the other meter stick was wood. C. student viewed the meter stick from a different angle. D. meter stick was constructed with nonstandard cm marks.

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Pampas and Patagonia

The Pampas are prolific South American marshes that comprise more than 750,000 km2 and combine the Argentine territories of Buenos Aires, La Pampa, Santa Fe, Entre Ríos and Cordoba. The vast fields are a common region, suspended only by the low Ventana and Tandil hills, near Bahia Blanca and Tandil Argentina, with an elevation of 1,300 m (4,265 ft) and 500 m (1,640 ft), sequentially.

Patagonia is a sparsely populated area at the southerly end of South America, administered by Argentina and Chile. The district encompasses the southerly segment of the Andes hills and the sands, pampas, and meadows to the east. Patagonia is one of the rare areas with shores on three oceans, with the Pacific Ocean to the westward, the Atlantic Ocean to the east, and the Southern Ocean to the South land.

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Single-replacement reactions A. Consists of two reactants producing two products B. Involve a single product C. Occur when any metal can replace any other metal D. Are restricted to metals

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The answer 

the main rule
A  —– B
A is the reactants  and B the products of a reaction
the number of atome of the elements of A must be equal to the number of atome of the elements of B
in our case
to balance the equation
a0 KI + a1 Pb(NO3)2 → a2 PbI2 + a3 KNO3
 2KI      +   Pb(NO3)2  →     PbI2 +     2KNO3
proof

A (reactants ) ——————– B (products)

 2KI means  2K,   2I             PbI2 :   2I,  2KNO3:  2K ( K and I are balanced) 
 Pb(NO3)2:
1 Pb, 2 NO3                         PbI2 and 2KNO3:  
                                             1Pb and  2 NO3 (Pb and NO3 are balanced)

finally 
 a0= 2,  a1= 1, a2= 1, a3=2                            
            

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Daniel is adding a metal border to a company’s lawn to stop the grass growth. The length of the lawn is 42 yards and the width is 27 yards. How much metal border will Daniel need?

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Answer:

Length is : x^{2} -3x+2

Step-by-step explanation:

The width of the rectangular playground is given as = x+3

The area of the playground is given as = x^{3} -7x+6

We have to find the length.

The area of the rectangle is given as :

A= length*width

So, length can be found as : length=frac{area}{width}

=> frac{x^{3}-7x+6 }{x+3}

Solving this we get,

Factoring frac{x^{3}-7x+6 } we get (x-1)(x-2)(x+3)

Using the rational root theorem and assuming a0=6 and a(n)=1

Divisors of a0 = 1,2,3,6

Divisor of a(n) = 1

1/1 is the root of equation. So, factoring out x-1 we get

(x-1)frac{x^{3}-7x+6 }{x-1}

frac{x^{3}-7x+6 }{x-1}

x^{2} +frac{x^{2}-7x+6 }{x-1}

x^{2} +x+frac{-6x+6}{x-1}

dividing frac{-6x+6}{x-1} we get -6

So, result becomes x^{2} +x-6

Factoring this we get: (x-2)(x+3)

frac{(x-1)(x-2)(x+3)}{(x+3)}

Cancelling x+3

We get the length as = (x-1)(x-2) or x^{2} -3x+2

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What was the history of the heavy metal?

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Chronological thinking is at the heart of historical reasoning.  Students should be able to distinguish between past, present, and future time.  Students should be able to identify how events take place over time.  Students should be able to use chronology in writing their own histories.  Students should be able to interpret data presented in time lines.  Students should be able to analyze patterns of historical duration or continuity as well as to recognize historical change.  Finally, students should begin to understand how the periodization of history is culturally constructed.  Europeans tend to see historical change and periodization as a gradual move to modernity and divide history into the history of the Ancient World, the Medieval (or Middle) period, the Early Modern Period (we’re no longer middle but we haven’t gotten into modernity yet), the Modern Period, and the Contemporary Period (generally history in the post-World War II period).  Moreover, our current system of dating events depends upon a Christian conception of time even though historians now believe Jesus was alive at the time A.D. begins.  B.C.  means “before Christ.”  A.D. means “Anno Domini,” or after the birth of our lord.  Historians now are more like to name these two patterns of dating B.C.E. (“before the common era”) and C.E. (“after the common era”) to secularize periodization.  Other civilizations, including the Nahuas, understood history quite differently, understood time in a more cyclical way.  Their history and sense of time, too, was culturally constructed.  Their notion of time contributed to the Mexica understanding of their history.  The Toltecs, who dominated ancient Mexico from the city of Tula long before the Mexica took power, worshipped Quetzalcoatl, an ancient god of the sky and wind.  According to oral traditions, an ancient Toltec ruler, Topiltzin, became merged with the god.  After a battle, Toplitzin/Quetzalcoatl left or was forced out of Tula.  The Mexica subsequently embraced Topiltzin/Quetzalcoatl to persuade others that they were the legitimate successors of the Toltecs, and they constructed a temple to the god in Tenochititlán.  Legend taught that Quetzalcoatl would return to reclaim his title.  Adding to the legend, Quetzalcoatl was born in the year Ce Acatl one-Reed and left in the year one-Reed.  This corresponded to fifty-two years, which would be one cycle in the Mexica calendar.  According to sources, Cortés appeared in what would have been one-Reed in the Mexica calendar, hence the reason why Moctezuma might have assumed that Cortés was Topiltzin/Quetzalcoatl.  This makes a good story, but there is no way to know if this story was constructed before or after the conquest.  What is important to understand is how much our history and construction of time contribute to our understanding of ourselves and shape our actions in the present world.   Other great civilizations had their own periodization, and even European historians argue with each other about how history should be divided up.  As you do the assigned reading in the textbook, you should think about how its authors have organized historical eras.  Can you think of different ways they might have ordered events?   Many of your study questions are designed to stimulate chronological thinking and an understanding of how things changed over time.

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