77 Results
A Method of Visual Interactive Regression   
(Software, Instructional Material (1))
Over the past decade many colleges and universities have placed increased emphasis on having students develop statistical and data analysis skills in a range of disciplines. Some institutions now require that all students complete at least one course with a strong component of data analysis, whether the data are from chemical experiments, the census, or some other source. As chemists, one of our concerns should be to ensure that students view data analysis as an integral part of any quantitative experiment, and, as far as possible, do not treat this process as a black box. The authors of A Method of Visual Interactive Regression, a spreadsheet application, have developed a visual approach to linear least-squares curve fitting that drives home the idea of minimizing the sum of the squares of the deviations in order to find the best fit to a set of data that are being described by a linear relationship. For many students these visualizations are likely to persist a great deal longer than the mathematical derivations of the equation for the slope and the intercept. The visualizations will provide a useful connection between a set of equations and the buttons on a calculator or the insertion of a trendline in a spreadsheet.
Visualizing Numerical Methods (2)   
(Software, Instructional Material (1))
These movies are designed to help students visualize various numerical approaches to evaluating functions or solving equations. The methods themselves may be familiar to students from their mathematics courses, but they may have forgotten the material or never made the connection between a statement such as "the derivative of a curve at a given point is the slope of the line tangent to the curve at that point" and the way that one might evaluate such a derivative. All of the movies have VCR-style controls that enable the student to step through them one frame at a time and to move backwards as well as forwards.
Errors in Measurement   
(Other (1))
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Measurements, Quantities, and Unity Factors   
(Other (1))
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Handling Large and Small Numbers   
(Other (1))
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Thermochemistry : CalcMolarEnthalpy (5 Variations)   
(Assessment Material (1))
White phosphorus, P4, ignites in air to produce heat, light, and P4O10 according to the following reaction.

P4(s) + 5O2(g) P4O10(s)

If 67.2 g of P4 is burned,1620 kJ of energy is evolved. What is the molar enthalpy of combustion of P4 if the process was carried out under constant pressure?

Solutions : CalcMolarityFromPPT (10 Variations)   
(Assessment Material (1))
You are given a water sample to analyze from a lake contaminated with lead. It takes 24 mL of 0.020 M NaCl to exactly precipitate the Pb2+ ions from 61 mL of the water sample. What is the concentration of Pb2+ ions in the water?
Pb2+(aq) + 2NaCl(aq)PbCl2(s) + 2Na+(aq)
Thermodynamics : EntropyPhaseChange (13 Variations)   
(Assessment Material (1))
Aluminum can be evaporated in a vacuum to form highly reflective coatings. Aluminum boils at 2792K and has a heat of vaporization of 70.0 kcal/mol. Calculate the entropy change for the vaporization of one mole of aluminum.
Solutions : WtPercentToMolarity (4 Variations)   
(Assessment Material (1))
A common concentration unit used commercially is percent weight per volume (%W/V) which is the number of grams of solute in 100 mL of solution. A bottle of vinegar contains 5 %W/V acetic acid (CH3COOH). What is the molar concentration of acetic acid in the vinegar?
Solutions : GramsToMolalSoln (20 Variations)   
(Assessment Material (1))
How many grams of citric acid need to be added to 750 ml of ethanol to make a 0.50 m solution?

Density (g/ml)

Molecular Weight (g/mol)

Citric acid

1.665

192.14

Ethanol

0.7893

46.07

Solutions : ConvertConcUnits (10 Variations)   
(Assessment Material (1))
The maximum concentration of arsenic in drinking water that is allowed by the EPA is 0.050 mg/L. Express this as a weight percent. (You can assume the density of the water solution is 1.0g/mL.)
Thermochemistry : MassFromCalorimetry (2 Variations)   
(Assessment Material (1))
The table below lists the specific heat capacities of several metals and liquids.

SubstanceSpecific Heat Capacity
J/(g.oC)
SubstanceSpecific Heat Capacity
J/(g.oC)
Al0.902H2O4.18
Fe0.451C2H5 OH2.46
Cu0.383CCl40.861
Au0.128CCl2F2 0.598

In an experiment a block of aluminum was heated to 100oC and placed in 200 g of water at 25oC. If the final temperature of the system is 43oC, and no heat transfer to the surroundings occurred, what is the mass of the aluminum block?

Thermochemistry : CalcHHessLaw (8 Variations)   
(Assessment Material (1))
The industrial process for making sulfuric acid has three steps. Using the data given, calculate the enthalpy change for the overall reaction for the process (the equation is given below).

2S(s) + 3O2(g) + 2H2O(l)2H2SO4(l)

Data:

S(s) + O2(g) SO2(g) Hrxn = -296.83 kJ
2SO3(g)O2(g) + 2SO2(g) Hrxn = -198.2 kJ
SO3(g) + H2O(l)H2SO4(l) Hrxn = -227.72 kJ

Stoichiometry : SolnStoich (4 Variations)   
(Assessment Material (1))
You are working in a forensic lab and are given a blood sample from a suspected drunk driver and asked to determine the person's blood alcohol level. The legal limit is 0.08% by mass in most states. You use the following reaction in your determination, assuming only the ethanol (C2H5OH) in the blood sample will react with the dichromate.
16H+(aq) + 2Cr2O72-(aq) + C2H5OH(l)4Cr3+(aq) + 11H2(l) + 2CO2(g)

If 14.6 mL of 0.10 M K2Cr2O7 are needed to react completely with 28 g of blood, what is the blood alcohol level of the driver?

Stoichiometry : RxnTable (10 Variations)   
(Assessment Material (1))
Iron reacts with oxygen to form iron(III) oxide according to the following reaction.

4Fe(s) + 3O2(g)2Fe2O3(s)


Fe(s) O2(g) Fe2O3(s)
Initial Amount - - -
Change - - -
End Amount - - -

Complete the reaction table for a reaction mixture containing 12.0 moles of iron and 10.0 moles of oxygen, and select the true statement(s) from following list.

Stoichiometry : GivenMassCalcStMat (10 Variations)   
(Assessment Material (1))
Aspirin is a common analgesic. If you want to produce 250. mg of aspirin (C9H8O4) from the reaction of C7H6O3 and C4H6O3, what is the minimum amount of C7H6O3 that is needed?

2C7H6O3(s) + C4H6O3(l) 2C9H8O4(s) + H2O(l)

Thermodynamics : ATPFromGlucose (8 Variations)   
(Assessment Material (1))
When glucose is oxidized in the human body it releases a lot of Gibbs free energy. Rather than waste this free energy, the body stores much of it in the form of ATP. The following reaction shows this process of storing some of the energy from glucose in ATP. This is an example of coupled reactions in a biological system.

The label on a can of Coke says that it contains 39 g of sugar. Assume that all of the sugar is glucose (even though it isn't), and calculate how many moles of ATP can be produced theoretically by the oxidation of 39.0 g of glucose.
Stoichiometry : RxnMolsProduced (8 Variations)   
(Assessment Material (1))
Given the following balanced chemical reaction:
4A + 3B2 2A2B3
If 12 moles of A are reacted with excess B2, how many moles of A2B3 will be produced?
Very carefully enter the number below.
Stoichiometry : MolsO2ToReactFuel (10 Variations)   
(Assessment Material (1))
Butane can be used as a fuel. How many moles of oxygen are needed to completely react with 3.0 moles of butane?

The unbalanced reaction equation is given below:
C4H10(g) + O2(g) CO2(g) + H2O(g)

Stoichiometry : GivenYieldCalcStMat (4 Variations)   
(Assessment Material (1))
Calcium oxide and water are produced by heating calcium hydroxide. If the reaction has an expected yield of 60%, how much calcium hydroxide should be reacted to produce 115g of calcium oxide?

Ca(OH)2 CaO + H2O

Thermochemistry : EnthalpyEnergy (10 Variations)   
(Assessment Material (1))
2SO2(g) + O2(g)2SO3(g)
Horxn = -197.78 kJ
How much energy is transferred when 96.6 g of SO2 reacts to form SO3?
Matter_and_Measurement : ConversionFactor (4 Variations)   
(Assessment Material (1))
Which conversion factor is needed to complete the dimensional analysis for the following problem?

It costs $3 per package of 10 pairs of socks. How much does 2 pairs of socks cost?

Thermochemistry : CalcHCombustion (6 Variations)   
(Assessment Material (1))
Using the thermodynamic data given in , determine the enthalpy change for the combustion of ethane to produce carbon dioxide and water vapor.

2C2H6(g) + 7O2(g) 4CO2(g) + 6 H2O(g)

Kinetics : InitialRateMethod (16 Variations)   
(Assessment Material (1))
Use the experimental data below to determine the rate equation for the following reaction.


Thermochemistry : CalcHBondEnergy (14 Variations)   
(Assessment Material (1))
Use the bond energies given in to estimate the Ho for the reaction given below:

hint: both carbon dioxide and molecular oxygen have double bonds

Thermochemistry : FuelAmpWattHeat (4 Variations)   
(Assessment Material (1))
Gasoline has an enthalpy of combustion of approximately 24000 kJ/gallon. When gasoline burns in an automobile engine, approximately 30% of the energy released is used to produce mechanical work. The remainder is lost as heat transfer to the engine's cooling system and eventually the atmosphere. As a start on estimating how much heat transfer is required, calculate what mass of water could be heated from 25 to 100oC by the combustion of 1.0 gallon of gasoline in an automobile.
Thermochemistry : CoffeeCupCalorimeter (2 Variations)   
(Assessment Material (1))
A block of copper is heated to {x} °C and then is dropped into a coffee cup calorimeter containing {y} g of water at 25.0 °C. The final temperature of the system is 45.1 °C. What is the mass of the copper block to the nearest gram? (Assume all heat is transferred to the water). Write your answer in the box, and do NOT include units.

Specific heat capacity of copper = 0.383 J/(g*°C)

Specific heat capacity of water = 4.18 J/(g*°C)

Thermochemistry : CalcHStateChange (4 Variations)   
(Assessment Material (1))
Calculate the enthalpy change when 100. g of ice at 0.0 oC is heated to liquid water at 50.0oC. (The heat of fusion for water is 333 J/g.)
Thermochemistry : BombCalorimeter (4 Variations)   
(Assessment Material (1))
Stearic acid (CH3(CH2)16CO2H) is a fatty acid, the part of fat that stores most of the energy. 1.00 g of stearic acid was burned in a bomb calorimeter. The bomb had a heat capacity of 652 J/oC and a 500. g water reservoir. If the temperature rose from 25.0 to 39.3 oC, how much heat was released when the stearic acid was burned?
Stoichiometry : PrecipYield (3 Variations)   
(Assessment Material (1))
In a laboratory experiment to determine accurately the amount of barium in solution, aqueous sulfuric acid was added to the solution to precipitate barium sulfate, which was then filtered and weighed. In this experiment it is MOST important that ...
Stoichiometry : ExplainYldError (4 Variations)   
(Assessment Material (1))
Your TA gives you an aqueous solution containing an unknown quantity of AgNO3(aq) and an unknown quantity of Mg(NO3)2(aq). You are asked to determine the molarity of Ag+ in the solution. You add HCl(aq) to your unknown to precipitate the silver as AgCl(s), then filter out the precipitate, dry it, weigh it, and calculate the concentration of silver ion. However, your TA tells you that your calculated value of [Ag+(aq)] is lower than the actual value. Which of the following could account for your answer being too low? There may be more than one correct answer.
Solutions : SolnPrepByMass (4 Variations)   
(Assessment Material (1))
You are required to prepare 5 L of a solution containing 1.000 x 10-3 mol/L of Cu2+(aq). Which of the following procedures would produce an appropriate solution?
Solutions : SolnPrepByDilution (10 Variations)   
(Assessment Material (1))
For the analysis of trace metals it is necessary to prepare solutions of very low concentrations from a stock solution of higher concentration using a micropipet and a volumetric flask. What volume of a 0.0010 M solution of Zn(NO3)2 (aq) would be required to prepare a 5.0 nM solution of Zn2+ in a 250mL flask?
Solutions : SolnConcAfterMixing (4 Variations)   
(Assessment Material (1))
10 mL of 0.1 M BaCl2(aq) is mixed with 10 mL of 0.1 M AgNO3(aq). What are the concentrations of the ions in the final mixture?
Solutions : MassSoluteInSoln (10 Variations)   
(Assessment Material (1))
What is the mass of the solute in 500mL of 0.341M ammonium chloride?
Solutions : IonConcentration (4 Variations)   
(Assessment Material (1))
Which of the following solutions has the greatest concentration of Na+ ions?
Matter_and_Measurement : UseDensity (10 Variations)   
(Assessment Material (1))
If a 10.0 inch aluminum skillet weighs 3 pounds, how many cm3 of aluminum does it contain? The density of aluminum is 2.70 g/cm3.
Matter_and_Measurement : ConvertUnits (10 Variations)   
(Assessment Material (1))
Your textbook is approximately 8.75 inches by 10.25 inches. What are these measurements in centimeters?
Matter_and_Measurement : CompareFCTemps (10 Variations)   
(Assessment Material (1))
Which is the higher temperature, 350oC or 350oF?
Stoichiometry : CalcPercentPurity (4 Variations)   
(Assessment Material (1))
To test the purity of calcium sulfate, you dissolve a 4.56g sample in water and add oxalic acid to precipitate out calcium oxalate. If 3.45g of precipitate forms, what is the percent purity of the calcium sulfate?

CaSO4(aq) + H2C2O4(aq) CaC2O4(s) + H2SO4(aq)

Stoichiometry : CalcWtPercent (6 Variations)   
(Assessment Material (1))
A standard dose of antacid as a calcium supplement is two tablets. The active ingredient in many of these tablets is calcium carbonate. One tablet, having a weight of 1.415 g, is reacted with excess HCl(aq) to produce 0.22 g CO2. What is the weight percent of calcium in this tablet?

CaCO3(s) + 2HCl(aq)CaCl2(aq) + H2O(l) + CO2(g)

Equilibrium : MoreMolesAtEquil (19 Variations)   
(Assessment Material (1))
The following reaction has an equilibrium constant of 0.050 at a given temperature.

N2(g)+ O2(g) 2NO(g)

If you have 0.75 moles of N2(g) and 0.75 moles of O2(g) in a 2.0L container initially, how many moles of N2 will be present when the system reaches equilibrium?

Equilibrium : ConvertKcKp (6 Variations)   
(Assessment Material (1))
Nitrosyl bromide is formed from nitrogen oxide and bromine:

Kp for this reaction is {x} at {y}°C. Calculate Kc at this temperature. (R = 0.0821 L atm/mol K)

Note:
DO NOT use scientific notation
Use integers (no decimal places) even is this is not the correct number of significant figures.
DO NOT write in the units.
eg: 18

Equilibrium : CalcKc (4 Variations)   
(Assessment Material (1))
A container initially has {y} M ammonia at a certain temperature. When the system reaches equilibrium the concentration of ammonia is {x} M. Calculate Kc for the following reaction as written.

Note:
      Answers must be written using scientific notation with "e"
      DO NOT use spaces
      DO NOT write in the units.
      Be sure to use three significant figures.
          eg:       2.44e-5

Equilibrium : CalcKp (2 Variations)   
(Assessment Material (1))
In one experiment chemists studied the formation of phosgene, COCl2, by mixing {y} atm of carbon monoxide and {z} atm of Cl2 in a reaction vessel at 700K. After the system reached equilibrium, the total pressure was {x} atm. Calculate Kp for the reaction.

Hint: Remember that the total pressure is the sum of all the partial pressures.

Note:
      Do Not use scientific notation
      DO NOT use spaces
      DO NOT write in the units.
      Be sure to write your answer with only one decimal place even if this is not the correct number of significant figures.

Equilibrium : CalcRxnQuotient (13 Variations)   
(Assessment Material (1))
In an experiment, 4.44 mol of SO2, 7.93 mol of O2 and 4.03 mol of SO3 are placed in a 2.0L reaction vessel at a certain temperature. Calculate the reaction quotient, Q, for the reaction as written:

What is the calculated reaction quotient, Q? {2:NUMERICAL:=2.1e-1:1e-2#Correct! ~%50%2.1e-1:5e-2#Close but not quite right}

If Kc for this reaction at the temperature of the experiment is 3.7 x 103, will the reaction move toward the left or toward the right? {1:MULTICHOICE:left#Sorry, that's wrong.~=right#Correct!}

Stoichiometry : CalcTheorYield (10 Variations)   
(Assessment Material (1))
If you react 6.2g of phosphine with 8.30g of oxygen, what is the theoretical yield of phosphorous pentaoxide?

4PH3 + 8O2 P4O10 + 6H2O

Gases : GasRxnStoich (10 Variations)   
(Assessment Material (1))
One of the reactions in the process of obtaining very pure silicon for the microelectronics industry is shown below. If 24 g of SiO2 is reacted with an excess of carbon, what volume of gaseous carbon monoxide will be produced at a temperature of 17oC and a pressure of 735 mm Hg?

SiO2(s) + 2C(s)Si(S) + 2CO(g)

Equilibrium : EqConstConcData (4 Variations)   
(Assessment Material (1))
SbCl5(g) SbCl3(g) + Cl2(g)

You have 0.50 mol SbCl5 present initially in a 1.0L flask. The system is allowed to reach equilibrium at 450oC. There is 0.10 mol Cl2 present at equilibrium. What is the equilibrium constant, K?

Equilibrium : CalcMolesAtEquil (15 Variations)   
(Assessment Material (1))
The following reaction has an equilibrium constant of 0.083 at 900oC.

COCl2(g) CO(g) + Cl2(g)

If you have 1.00 mole of COCl2(g) in a 1.00L container initially, how many moles of COCl2 will be present when the system reaches equilibrium?

Equilibrium : EqConstRelationships (12 Variations)   
(Assessment Material (1))
The equilibrium constant for the reaction of hydrogen gas and ethene to produce ethane under certain conditions is 9.8 x 1018.
H2(g) + C2H4(g) C2H6(g) K = 9.8 x 1018

What is the equilibrium constant for the following reaction under the same conditions?
C2H6(g) H2(g) + C2H4(g) K = ?

Thermodynamics : GibbsFromHSandT (5 Variations)   
(Assessment Material (1))
On the space shuttle, the carbon dioxide produced by the astronauts is handled by an environmental control system that utilizes the following reaction.

H° = -138.4 kJ and S° = -139 J/K Calculate G° at 25°C for this reaction.
Thermodynamics : DetermineRxnFavored (8 Variations)   
(Assessment Material (1))
When industrial plants burn coal, sulfur dioxide is produced. Sulfur dioxide is a primary pollutant that contributes to both industrial smog and acid rain. Is this process of producing sulfur dioxide product-favored?

Using

Thermodynamics : CalcMinSpontTemp (9 Variations)   
(Assessment Material (1))
Calculate the minimum temperature above which the following reaction will be product-favored (spontaneous).


Thermodynamics : CalcDeltaS (9 Variations)   
(Assessment Material (1))
Using , calculate the entropy change for the reaction.
Thermodynamics : CalcDeltaG (14 Variations)   
(Assessment Material (1))
Using , calculate the Gibbs free energy change for the following reaction which produces the metal zinc from its ore zinc(II) oxide.
2 ZnO(s) 2 Zn(s) + O2(g)

Kinetics : ExpDataRateConst (16 Variations)   
(Assessment Material (1))
Use the experimental data below to determine the rate constant for the following reaction.


Stoichiometry : CalcWeightPercent (8 Variations)   
(Assessment Material (1))
What is the weight percent of oxygen in LiHCO3?
Stoichiometry : CalcPercentYield (8 Variations)   
(Assessment Material (1))
When copper is heated in air, copper(II) oxide is formed. In a given experiment, 1.50 g copper was heated to yield 1.76 g copper(II) oxide. What is the percent yield?
Kinetics : ArrheniusTemp (3 Variations)   
(Assessment Material (1))
The activation energy for the isomerization of cyclopropane to propene is 274 kJ/mol. By what factor does the rate of reaction increase as the temperature rises from 500oC to 550oC assuming all else remains constant? (R = 8.314 J/mol k)

Hint: This is asking for the ratio of rates which is proportional to the ratio of the rate constants, all else being equal.

Kinetics : ArrheniusRateConst (4 Variations)   
(Assessment Material (1))
CH3CH2NO2 C2H2 + HNO2

Using the graph below, calculate the rate constant for this reaction at 40.0oC.

Kinetics : ArrheniusActEnergy (4 Variations)   
(Assessment Material (1))
The rate constant for the first-order dehydration of tert-butyl alcohol at 500oC is 1.20 x 10 -4 s -1. The rate constant for this process at 600oC is 6.80 x 10 -3 s -1. Calculate the activation energy for this reaction in kJ/mol. (R = 8.314 J/mol K)
Gases : OzoneMolcsFromppm (10 Variations)   
(Assessment Material (1))
Although ozone is an important component of the upper atmosphere, long-term exposure to ozone in the air we breathe can cause inflammation of the lung, impairment of lung defense mechanisms, and irreversible changes in lung structure. The EPA has set an 8 hour limit for ozone of 0.08 ppm as an air quality standard for cities. At the EPA limit, how many ozone molecules are present in 5.0 liters of air at 25oC and 0.967 atm? (Hint: assume that air is an ideal gas and calculate the total number of molecules there are in 5.0 L. Then use the definition of ppm.)
Gases : IdealGasMolarMass (10 Variations)   
(Assessment Material (1))
A sealed flask contains 3.1 L of a gas at 2.4 atm and 22.7oC. If the density of the gas is 9.7 g/L, what is its molar mass? (You can assume that the gas behaves ideally.)
Gases : GasLaws (2 Variations)   
(Assessment Material (1))
Note: This is a calculation type question. If you exit the quiz without submitting it and you do not save an answer before exiting the quiz, the values in the question may change when you enter the quiz again.

You purchase a propane tank that can hold gas safely up to a pressure of {x} atm. When the tank contains 100. grams of propane at {y}°C, the gas exerts a pressure of {z}atm. What is the highest temperature to which the propane can be heated safely? (Report your answer in Kelvins.)

Gases : IdealGasLaw (11 Variations)   
(Assessment Material (1))
What volume is occupied by 2.60 moles of nitrogen at 1.70 atm and 14.9oC?
Gases : GasRxnVolumes (10 Variations)   
(Assessment Material (1))
A gas phase reaction takes place in a syringe at a constant temperature and pressure. If the initial volume before reaction is 30 mL and the final volume after the reaction is complete is 15 mL, which of the following reactions took place? (Note: You can assume that you start with stoichiometric amounts of the reactants, the reaction goes to completion and that the gases behave ideally.)
Gases : GasMoleMixPressure (5 Variations)   
(Assessment Material (1))
What is the pressure exerted by a mixture of gases in a 40.0 L container at 127oC if the mixture contains 0.100 mol O2, 0.400 mol CH4, and 0.500 mol SO2?
Gases : GasGramMixPressure (5 Variations)   
(Assessment Material (1))
4.80 g of CH4 is mixed with 17.6 g of CO2 in a 9.00 L flask at a temperature of 67.2oC. What is the total pressure of the flask? (Assume there is no reaction.)
Equilibrium : InterpretKsp (16 Variations)   
(Assessment Material (1))
Which of the following salts would give you the highest concentration of phosphate ions in solution if you placed 1 mole of the salt in a liter of water?
Equilibrium : ConcFromKsp (8 Variations)   
(Assessment Material (1))
The Ksp of BaF2 is 1.7 x 10-6 mol/L in water at 25oC. What is the concentration of barium ions in equilibrium with solid barium fluoride? (Assume that the only relevant reaction is the solubility-product equilibrium.)
Equilibrium : CommonIonEffect (9 Variations)   
(Assessment Material (1))
The molar solubility of lead(II) fluoride (PbF2) is 2.1 x 10-3 mol/L in pure water at 25oC. What is the molar solubility of lead(II) fluoride in 0.10 M NaF at 25oC? (Assume that the only relevant reaction is the solubility-product equilibrium.)
Matter_and_Measurement : NumOfSigFigs (4 Variations)   
(Assessment Material (1))
How many significant figures will the answer to the following problem contain?
Graphing   
(Activity, Instructional Material (7))
ACS Science for Kids activities explore the aspects of recording scientific data and presenting that data in useful graphs.
Motion & Energy   
(Activity, Instructional Material (13), Test, Assessment Material (2))
ACS Science for Kids activities and assessments that explore aspects of motion and energy.
Using Chemical Equations in Environmental Chemistry and Green Chemistry   
()
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Using Chemical Equations in Calculations in Biology   
()
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.