Gen Chem Lesson 3
The amount of oxygen is determined from the mass of H2O produced.
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?
one of the reactants totally consumed (final amount is zero) the amount of the reactant in excess
In a limiting-reactant problem, the final quantities in a reaction table will show ______.
Empirical formula The simplest whole-number ratio of moles of each element in a compound Molecular formula Actual number of atoms of each element in a molecule Structural formula Shows the relative placement and connections of atoms in a molecule
Match each term with its correct definition.
Theoretical yield The amount of product calculated from the molar ratio in the balanced chemical equation Actual yield Amount of product obtained experimentally from a chemical reaction Percent yield actual yield/theoretical yield × 100
Match each type of reaction yield to the correct description.
mole atoms
The is the SI unit that expresses the amount of substance. Specifically, it is defined as the amount of substance containing the same number of entities as the number of in exactly 12 g of carbon-12.
2 4
The molecular formula of a compound having an empirical formula NH2 (ℳ = 32.05 g/mol) is N H .
6.022 23
The number of entities in a mole (to 4 significant figures) is equal to 6.02 multiplied by 10 to the power of 23 and is called Avogadro's number..
The molar mass of each element
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?
Atomic masses are rounded to 4 significant figures.
Which convention is used in this textbook for rounding off atomic masses based on the periodic table?
Multiplying all coefficients by a common factor Inserting coefficients in front of formulas of reactants and products
Which of the following actions are permitted in balancing a chemical equation? Select all that apply.
The mole contains 6.022 x 1023 entities. The number of entities in a mole is called Avogadro's number.
Which of the following correctly reflect Avogadro's number? Choose all that apply.
formulas, quantity
A chemical equation is a statement using chemical that expresses both the identities and the relative of the reactants and products involved in a chemical or physical change.
CH2O C2H4O2 C6H12O6
A compound has the empirical formula CH2O. What are the possible options for the molecular formula of this compound? Select all that apply.
1.5
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.
Al2S3 -> 1 H2O -> 6 Al(OH)3 - > 2 H2S -> 3
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)
B2; AB
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 _____.
- Determine the moles of each reactant present by dividing its mass by its molar mass - Determine the amount of product that could be formed from each reactant using the appropriate mole ratios - I identify the limiting reactant as the reactant that produces the least amount of product - To find the mass, multiply the number of moles product formed (from the limiting reactant) by the molar mass of the product.
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.
2mol Al/3mol Cl2 2mol AlCl3/3mol Cl2
Given the balanced equation 2Al(s) + 3Cl2(g) → 2AlCl3(s), select all the conversion factors that correctly represent the molar relationships in this equation.
2 -> SO2 1 -> O2 2 -> SO3
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.)
molecular; empirical
The _____ formula of a compound is an integer multiple of the _____ formula.
1.5 mol O2 x (2mol SO3)/(3mol O2)
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 _____.
constitutional molecular structural
The compounds depicted are isomers because they have the same formula but have different formulas.
mol 40.08 mol or mole or mol of Ca
The molar mass of a monatomic element is the numerical value listed on the periodic table expressed in units of g/. For example, the molar mass of calcium (Ca) is with units of g/. (Remember to round to 4 significant digits.)
2.0 mol × 6.022 × 1023 molecules/mol
Which of the following provides the correct mathematical operation to calculate the number of molecules in 2.0 mol of CH4?
number of atoms/Avogadro's number
Which of the following provides the correct mathematical operation to convert the number of atoms of a sample to the number of moles?
Isomers are compounds with the same empirical formula. Isomers are compounds with the same molecular formula. Isomers are compounds with the same molar mass.
Which of the following statements correctly describe isomers? Select all that apply.
The molar mass of a substance is the mass per mole of its entities The periodic table can be used to calculate the molar mass of any substance When referring to the mass per mole of an entity, the term "entities" could refer to atoms, ions, molecules, or formula units.
Which of the following statements correctly describe molar mass? Select all that apply.
% yield = actual yield/theoretical yield × 100 The actual yield is almost always less than the theoretical yield.
Which of the following statements correctly describe the percent yield in a chemical reaction? Select all that apply.
The MnCl2 produced is dissolved in water. HCl is a reactant in this equation.
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.
number type
A chemical equation must be balanced. This means that the same _____ and _____ of atoms must appear on both sides of the equation.
C6H6 -> 7.74% CH3OH ->12.6% CH2O -> 6.71%
Match
ℳof H2SO4= (2 ×ℳof H) + (ℳof S) + (4 ×ℳof O) ℳ of H2SO4= (2 × 1.008 g/mol) + (32.07 g/mol) + (4 × 16.00 g/mol) ℳof H2SO4= 98.09 g/mol
Place the following calculations in the correct order to determine the molar mass of H2SO4. Start with the first step at the top of the list.
Identify that nitrogen exists as N2 and find the atomic mass of nitrogen on the periodic table Multiply the atomic mass of nitrogen by 2 in order to calculate its molecular mass. Report the molar mass of nitrogen as 28.02 g/mol. correct toggle button unavailable Report the molar mass of nitrogen as 28.02 g/mol.
Place the steps in order for calculating the molar mass of nitrogen gas, starting with the first step at the top of the list.
False
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.
47.08%
What is the mass percent of oxygen in aluminum oxide (Al2O3)?
The ratio of atoms of each element must be a ratio of integer numbers. The mass percentage of each element is converted to moles using the mass formula mass/molar mass. 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.
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.
6.022 × 10^23 entities x 1 mol
Which of the following correctly reflects Avogadro's number?
The atomic mass of each element contained in the compound The formula of the compound
Which of the following pieces of information is/are necessary to calculate the molar mass of a compound? Select all that apply.
16 atoms of Cu react with 1 molecule of S8 to form 8 formula units of Cu2S. 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.
Which of the following statements correctly describe the information conveyed by the balanced equation 16Cu (s) + S8 (g) → 8Cu2S (s)? Select all that apply.
molar atoms or particles or objects or compounds or units
The __ mass of a substance is the mass per mole of its entities, where the term "entities" can describe __, ions, molecules, or formula units.
moles x molar mass
Which one of the following options gives the correct procedure to calculate the mass of a substance given the number of moles?
given mass/molar mass
Which one of the following options gives the correct procedure to calculate the number of moles of a substance given the mass?
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 items of information are necessary to calculate the mass percent of an element in a given compound? Select all that apply.
Calculate the molar masses of any reactants for which a mass has been given. The reactant that produces the least amount of possible product is the limiting reactant. Calculate the amount of product that could be formed from each reactant.
Which of the following statements correctly describe the steps used to determine which reactant in a given reaction is limiting? Select all that apply.
Combustion analysis involves burning a compound in O2. Every 1 mole of carbon in the compound will produce 1 mole of CO2. The mass of hydrogen in the compound is determined from the amount of H2O produced.
Which of the following statements describe combustion analysis correctly? Select all that apply.
The identities of substances involved. The physical states of reactants and products, often. The relative quantities (moles) of substances involved.
Which of the following statements describe the information that can be gained from a balanced chemical equation? Select all that apply.
Multiply the answer by 100 to find the mass percent of oxygen in acetic acid. 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.
Which of the following steps are necessary to calculate the mass percent of oxygen in acetic acid (CH3COOH)? Select all that apply.
- Assume that the sample 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
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.
4 1.008 12.01
Atomic masses are commonly read from the periodic table to significant figures. The atomic mass of H is therefore equal to amu, whereas the atomic mass of C is equal to amu. Use the periodic table given in your textbook to answer the question.
Write a skeleton equation. Balance the atoms. Adjust the coefficients such that they are the smallest whole-number coefficients. Do a final check to make sure the equation is balanced.
Correctly order the steps necessary to balance a chemical equation. Start with the first step at the top of the list.
1. Calculate the number of moles of each element of the sample using (mass/ molar mass) 2. Write chemical formula containing fractional subscripts 3. Divide each subscript by the smallest subscript 4. If integers are not obtained, multiply each subscript by the smallest integer that gives all integer subscripts 5. Verify that the integer subscripts cannot be divided by a common factor
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.
N2O4
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?
84.0%
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.
52.2 g
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?
Change in the amounts of reactants and products during the reaction A balanced chemical equation Initial amounts of reactants and products before reaction Final amounts of reactants and products remaining after the reaction
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.
