CHEM1510 Exam 1

The _____ formula of a compound is an integer multiple of the _____ formula.

molecular; empirical

In order to calculate the overall % yield for a multistep process ___________.

multiply the individual % yields by each other

The mass % of Ca in CaSO4 is 29.45%. To calculate the mass of Ca present in a 25.6-g sample of this compound, the correct procedure is given by _____.

(29.45/100)*25.6

Percent yield

(actual yield/theoretical yield) × 100

Correctly order the steps necessary to calculate the empirical formula of a compound, assuming that the masses of each element of the compound are provided. Start with the first step at the top of the list.

- Calculate the number of moles of each element of the sample using (mass/molar mass) -Write a chemical formula containing subscripts -divide each subscript by the smallest subscript -If integers are not obtained, multiply each subscript by the smallest integer that gives all integer subscripts -verify that the integer subscripts cannot be divided by a common factor

Which of the following statements correctly describe the percent yield in a chemical reaction? Select all that apply.

-% yield = (actual yield/theoretical yield) × 100 -The actual yield is almost always less than the theoretical yield.

Given the balanced equation Ag2S(s) + 2HCl(aq) → 2AgCl(s) + H2S(g), determine the moles of HCl required and the mass of AgCl formed from the complete reaction of 18.3 g of Ag2S.

-0.148 mol HCl are required. -21.2 g of AgCl are formed.

Which of the following statements correctly describe the information conveyed by the balanced equation 16Cu (s) + S8 (g) → 8Cu2S (s)? Select all that apply.

-16 moles of Cu react with 1 mole of S8 to form 8 moles of Cu2S. -Cu and S8 are reactants and Cu2S is the product. -16 atoms of Cu react with 1 molecule of S8 to form 8 formula units of Cu2S.

Given the balanced equation 2Al(s) + 3Cl2(g) → 2AlCl3(s), select all the conversion factors that correctly represent the molar relationships in this equation.

-2mol Al/3 mol Cl2 -2 mol AlCl3/3 mol Cl2

Calculate the correct number of moles AND formula units in 7.3 x 10^-3 g of CaSO4. Avogadro's number is 6.022 x 10^23.

-3.2 x 1019 formula units of CaSO4 -5.4 x 10-5 moles of CaSO4

Arrange the necessary steps in order for finding the molecular formula of an unknown compound from mass percent data. Place the first step at the top of the list.

-Assume that the same contains 100.0 g of compound and express each mass percent as a mass in grams -Convert the mass of each element to moles of each element -Derive the empirical formula looking for the simplest whole-number ratio of moles -Divide the molar mass of the compound by the mass of the empirical formula in order to find a multiple that is an integer -Multiply each subscript of the empirical formula by the integer multiple

Which of the following statements correctly describe the steps used to determine which reactant in a given reaction is limiting? Select all that apply.

-Calculate the molar masses of any reactants for which a mass has been given. -Calculate the amount of product that could be formed from each reactant. -The reactant that produces the least amount of possible product is the limiting reactant.

Which of the following statements correctly describe the empirical formula for a compound? Select all that apply.

-Different compounds can have the same empirical formula. -The empirical formula of a compound gives the smallest whole number ratio of atoms in a compound.

A useful method for keeping track of quantities in a chemical reaction is a reaction table. Which of the following are components of a reaction table? Select all that apply.

-Final amounts of reactants and products remaining after the reaction -A balanced chemical equation -Initial amounts of reactants and products before reaction -Change in the amounts of reactants and products during the reaction

Which of the following statements correctly interpret the balanced chemical equation 4HCl (aq) + MnO2 (s) → MnCl2 (aq) + 2H2O (g) + Cl2 (g)? Select all that apply.

-HCl is a reactant in this equation. -The MnCl2 produced is dissolved in water.

Hydrogen and oxygen react to form water according to the balanced equation 2H2 (g) + O2 (g) → 2H2O (l). In a particular reaction vessel, 2.2 mol of H2 are reacted with 2.2 mol of O2. Which of the following options correctly describe how to complete the reaction table given? Select all that apply.

-Identify H2 as the limiting reactant. -The change in moles of O2 (b) is equal to -1.1. -The change in moles of H2 (a) is equal to -2.2.

Which of the following actions are permitted in balancing a chemical equation? Select all that apply.

-Inserting coefficients in front of formulas of reactants and products -Multiplying all coefficients by a common factor

Which of the following statements correctly describe isomers? Select all that apply.

-Isomers are compounds with the same molecular formula. -Isomers are compounds with the same molar mass. -Isomers are compounds with the same empirical formula.

Which of the following statements correctly describe the molecular formula for a compound? Select all that apply.

-It is possible that the molecular formula for a compound is the same as its empirical formula. -A molecular formula may give little or no information about the structure of the compound. -The molecular formula gives the actual number of each type of atom in a compound.

Which of the following steps are necessary to calculate the mass percent of oxygen in acetic acid (CH3COOH)? Select all that apply.

-Multiply the moles of oxygen in the molecular formula by the molar mass of oxygen and then divide by the mass of one mole of acetic acid. -Calculate the molar mass of acetic acid from its formula. -Multiply the answer by 100 to find the mass percent of oxygen in acetic acid.

Hydrogen and nitrogen react to form ammonia according to the balanced equation 3H2 (g) + N2 (g) → 2NH3 (g). In a particular reaction vessel, 4.5 mol of H2 are reacted with 4.5 mol of N2. Which of the following options correctly describe how to complete the reaction table given? Select all that apply.

-The change in moles of N2 (a) is equal to -1.5. -The final quantity of NH3 present is 3.0 mol.

Which items of information are necessary to calculate the mass percent of an element in a given compound? Select all that apply.

-The formula of the compound -The number of moles of the element in one mole of the compound -The molar mass of the compound

Which of the following choices describe the steps required to determine the empirical formula of a compound from the mass percent? Select all that apply.

-The mass percentage of each element is converted to moles using the mass formula -If a compound contains 52% of mass of C, it can be assumed that there are 52 g of C in 100 g of the compound. -The ratio of atoms of each element must be a ratio of integer numbers.

Which of the following statements describe the information that can be gained from a balanced chemical equation? Select all that apply.

-The physical states of reactants and products, often. -The relative quantities (moles) of substances involved. -The identities of substances involved.

Which of the following options identify the correct coefficients required to balance the reaction illustrated? In the illustration, carbon is black and oxygen is red. Select all that apply.

-The reactant CO must have the coefficient 2. -CO2 is a product and has the coefficient 2.

Iodine trichloride is produced in a two-step process, represented by the following balanced equations: I2 (s) + Cl2 (g) → 2ICl (s)I2 (s) + Cl2 (g) → 2ICl (s); and ICl (s) + Cl2 (g) → ICl3 (s)ICl (s) + Cl2 (g) → ICl3 (s). Select all the statements that correctly describe how to write a complete balanced equation for the overall process.

-The second equation must be multiplied by 2. -The overall equation is given by I2 (s) + 3Cl2 (g) → 2ICl3 (s)I2 (s) + 3Cl2 (g) → 2ICl3 (s).

Under certain conditions, the reaction of propane and water will produce carbon dioxide and hydrogen gas. The reaction may be represented as a two-step process: C3H8 (g) + 3H2O (g) → 3CO (g) + 7H2 (g) CO (g) + H2O (g) → CO2 (g) + H2 (g) Select the statements that correctly describe how to write a complete balanced equation for the overall process.

-The second equation must be multiplied by 3. -The overall equation is given by C3H8 (g) + 6H2O (g) → 3CO2 (g) + 10H2 (g)

Which of the following options correctly describe the symbols used to write a balanced equation? Select all that apply.

-The symbol (g) indicates a substance in the gas phase. -A liquid is indicated by the symbol (l).

Which of the following steps would be required to convert between the masses of any two substances involved in the same chemical reaction? Select all that apply.

-Write a conversion factor using the coefficients from the balanced equation, and convert to moles of the second substance. -Convert from the given mass to moles of the same substance. -Write a balanced chemical equation for the reaction.

Correctly order the steps necessary to determine the molecular formula for a compound using combustion analysis data. Start with the first step at the top of the list. Position 1 of 4 Determine the masses of carbon and hydrogen from the masses of CO2 and H2O, respectively. correct toggle button unavailable Determine the masses of carbon and hydrogen from the masses of CO2 and H2O, respectively.

-determine the masses of carbon and hydrogen from the masses of CO2 and H2O -determine the mass of oxygen, if present, by subtracting the masses of carbon and hydrogen from the total mass -determine the number of moles of each element in the compound and hence the empirical formula -determine the molecular formula using the empirical formula

In a limiting-reactant problem, the final quantities in a reaction table will show ______.

-the amount of the reactant in excess -one of the reactants totally consumed (final amount is zero)

Correctly order the steps necessary to solve for the mass of a product, or second reactant required, given the mass of one of the reactants in a chemical process. Start with the first step at the top of the list.

1) a balanced equation for the reaction 2) Convert the given mass into moles using molar mass. Convert moles of A to moles of B

Correctly order the steps necessary to calculate the mass of product formed in a chemical reaction, given the masses of all reactants. Start with the first step at the top of the list.

1) determine the moles of each reactant present by dividing its mass bu its molar mass 2) Determine the amount of product that could be formed from each reactant using the appropriate mole ratios 3) identify the limiting reactant that produces the least amount of product 4) to find the mass, multiply the number of moles of product formed (from the limitoing reactant) by the molar mass of the product

Correctly order the steps necessary to balance a chemical equation. Start with the first step at the top of the list.

1) write a skeleton equation 2) balance the atoms 3) adjust the coefficients such that they are the smallest whole-number coefficients 4) Do a final check to make sure the equation is balanced

B2 reacts with AB to form AB2 according to the balanced equation B2 + 2AB → 2AB2. If 1.5 moles of B2 are reacted with 1.5 moles of AB, the maximum amount of AB2 that can form is equal to _____ moles.

1.5

The balanced equation 2S(s) + 3O2(g) → 2SO3 (g) is given. The number of moles of SO3 that will form from the complete reaction of 1.5 mol of O2 is given by _____. Multiple choice question.

1.5 mol O2 x (2mol SO3/3mol O2)

What is the mass of Cs present in 15.0 g of cesium acetate, formula CsCH3COO?

10.4 g

What is the mass of nitrogen in 43.7 g of ammonium carbonate, (NH4)2CO3?

12.7 g

KrF2

121.8 g/mol

Given the balanced equation 3H2(g) + N2(g) → 2NH3(g), calculate the mass of NH3 produced by the complete reaction of 2.55 g of H2.

14.4 g

SF6

146.1 g/mol

CCl4

153.8 g/mol

Identify the whole number coefficients required to balance the chemical equation SO2(g) + O2(g) → SO3(g) correctly. (Enter ALL numbers, including the digit 1 if required, and make sure you have the simplest ratio of coefficients.)

2 SO2 1 O2 2 SO3

Which of the following provides the correct mathematical operation to calculate the number of molecules in 2.0 mol of CH4?

2.0 mol × 6.022 × 1023 molecules/mol

1.52 × 1024 atoms of Au correspond to_______ mol of Au atoms. Report your answer to 3 significant figures, using decimal notation (NOT scientific notation). (Avogadro's number is 6.022 × 10^23.)

2.52

The molecular formula of a compound having an empirical formula NH2 (ℳ = 32.05 g/mol) is N_________H________

2;4

Which of the following options give the correct number of moles AND the correct number of atoms in a 3.54-g sample of copper (Cu)? Avogadro's number is 6.022 × 1023. Select both correct answers. 3.35 × 1022 atoms of Cu 5.57 × 10-2 mol of Cu 9.25 × 10-26 atoms of Cu 2.25 × 102 mol of Cu

3.35 × 1022 atoms of Cu 5.57 × 10-2 mol of Cu

CH2O

30.03 g/mol

When hydrogen gas is passed over powdered iron(III) oxide, iron metal and water vapor are formed. Which of the following is the correct balanced equation for this process?

3H2(g) + Fe2O3(s) → 2Fe(s) + 3H2O(g)

What is the mass percent of oxygen in aluminum oxide (Al2O3)?

47.075%

A reaction is expected to produce 83.5 g of CaCO3. The percent yield is recorded as 62.5%. What is the actual mass of CaCO3 obtained?

52.2 g

Combustion analysis of a 0.3756 g sample containing only C and H yields 1.1385 g of CO2 and 0.5805 g of H2O. What is the molecular formula given its molar mass is 58.12 g/mol?

C4H10

How many grams of KMnO4 correspond to 3.13 x 10^22 formula units of KMnO4? Avogadro's number is 6.022 x 10^23.

8.21 g of KMnO4

A particular reaction is expected to yield 125 g of calcium. The actual amount of calcium obtained is equal to 105 g. Calculate the percentage yield for the reaction.

84.0%

Molecular formula

Actual number of atoms of each element in a molecule

Balance the unbalanced equation given and match each substance to the correct coefficient as indicated. Al2S3(s) + H2O(l) → Al(OH)3(aq) + H2S(g)

Al2S3 1 H2O 6 Al(OH)3 2 H2S 3

Actual yield

Amount of product obtained experimentally from a chemical reaction

Compound B2 (represented by the red spheres) reacts with AB, as shown in the illustration. From the illustration, the reagent in excess is _____, and the limiting reagent is _____.

B2; AB

A compound has the empirical formula CH2O. What are the possible options for the molecular formula of this compound? Select all that apply.

C6H12O6 CH2O C2H4O2

match each compound with the correct mass percentage of hydrogen C6H6 CH3OH CH2O

C6H6: 7.7% CH3OH: 12.6% CH2O: 6.71%

1 mole of this substance contains 1 mole of carbon and 4 moles of chlorine.

CCl4

1 mole of this substance contains 12.01 g of carbon, 2.016 g of hydrogen, and 70.90 g of chlorine.

CH2Cl2

What is the empirical formula of a hydrocarbon containing 79.9% carbon by mass?

CH3

This molecule contains 12.01 amu of carbon, 1.008 amu of hydrogen, and 106.35 amu of chlorine.

CHCl3

Which step is INCORRECT to determine the molecular formula for a compound using combustion analysis data?

Determine the mass of a third element, if present, from the mass of its oxide produced in the combustion.

True or false: In order to balance the reaction of hydrogen gas (H2) with oxygen gas (O2) to form liquid water (H2O), a student adds a subscript of 2 after the oxygen in H2O. This is an acceptable method of balancing the above reaction.

False

True or false: To calculate the overall percent yield for a multistep process, add the individual percent yields together.

False

What is the empirical formula of a compound that consists of 0.039 moles of iron atoms combined with 0.052 moles of oxygen atoms?

Fe3O4

Which of the following compounds has the largest molar mass? SO2 C6H6 CH2Cl2 H2SO4

H2SO4

A nitrogen oxide contains 30.45% N mass. If the molar mass of the compound is 90. ± 5 g/mol, what is its molecular formula?

N2O4

Structural formula

Shows the relative placement and connections of atoms in a molecule

Combustion analysis is commonly used to determine the empirical formula of unknown compounds containing principally C and H. For a compound containing C, H, and O only, which of the following statements is INCORRECT?

The amount of oxygen is determined from the mass of H2O produced.

Theoretical yield

The amount of product calculated from the molar ratio in the balanced chemical equation

Which of the following pieces of information is/are necessary to calculate the molar mass of a compound? Select all that apply.

The formula of the compound The atomic masses of each of the elements that make up the compound

Menthol (molar mass = 156.3 g/mol) is a compound of carbon, hydrogen, and oxygen. When 0.1595 g of menthol underwent a combustion analysis, 0.449 g of CO2 and 0.184 g of H2O were produced. Select all the statements that correctly interpret these data.

The mass of C present is 0.123 g. There are 2.04 × 10-2 moles of H in the sample.

What is the only additional information needed to calculate the empirical formula of a compound if the masses of each element of the compound are provided?

The molar mass of each element

empirical formula

The simplest whole-number ratio of moles of each element in a compound

Which of the following statements correctly describe CH3COOH (acetic acid)? Select all that apply.

There are 4 moles of hydrogen atoms per mole of acetic acid. There are 2 atoms of carbon in one molecule of acetic acid.

In order to calculate the mass of an element in a given sample of a compound, the mass of the compound is multiplied by the mass __________of the element in the compound.

fraction

The _______ gives the smallest whole number ratio of moles of each element in a compound. Therefore, multiple compounds may have it in common.

empirical formula

A chemical equation is a statement using chemical __ that express both the identities and the relative __ of the reactants and products involved in a chemical or physical change

formulas; quantity

Molecular formulas ______.

give the actual number of each element in a compound

The ______ mass of a substance is the mass per mole of its entities, where the term "entities" can describe________, ions, molecules, or formula units.

molar;atoms

Which of the following provides the correct mathematical operation to convert the number of atoms of a sample to the number of moles?

number of atoms/Avogadro's number

A chemical equation must be balanced. This means that the same _____ and _____ of atoms must appear on both sides of the equation.

number; type

The compounds depicted are _________ isomers because they have the same ____________formula but have different _____________formulas.

structural;molecular;structural