Chapter 3
Structural formula
Shows the relative placement and connections of atoms in a molecule
Empirical formula
The simplest whole-number ratio of moles of each element in a compound
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
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
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 amount of product that could be formed from each reactant. 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.
The _____ formula of a compound is an integer multiple of the _____ formula.
molecular; empirical
Which one of the following options gives the correct procedure to calculate the mass of a substance given the number of moles?
moles x molar mass
Molecular formula
Actual number of atoms of each element in a molecule
Which convention is used in this textbook for rounding off atomic masses based on the periodic table?
Atomic masses are rounded to 4 significant figures.
Which of the following statements describe combustion analysis correctly? Select all that apply.
The mass of hydrogen in the compound is determined from the amount of H2O produced. Combustion analysis involves burning a compound in O2. Every 1 mole of carbon in the compound will produce 1 mole of CO2.
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
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.
A balanced chemical equation Change in the amounts of reactants and products during the reaction Initial amounts of reactants and products before reaction Final amounts of reactants and products remaining after the reaction
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 ratio of atoms of each element must be a ratio of integer numbers. 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 mass percentage of each element is converted to moles using the mass formula mass / molar mass
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.
Which of the following statements describe the information that can be gained from a balanced chemical equation? Select all that apply.
The relative quantities (moles) of substances involved. The identities of substances involved. The physical states of reactants and products, often.
A chemical equation must be balanced. This means that the same _____ and _____ of atoms must appear on both sides of the equation.
number; type
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.
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 equations 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
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.
1. Assume that the sample contains 100.0g of compound and express each mass percent as a mass in grams 2. convert the mass of each element to moles for each element 3. derive the emirical formula looking for the simplest whole-number ratio of moles 4. divide the molar mass of the compound by the mass of the empirical formula in order to find a multiple that is an integer 5. multiply each subscript of the empirical formula by the integer multiple
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.
There are 2.04 × 10-2 moles of H in the sample. The mass of C present is 0.123
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)
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.
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)
Which of the following actions are permitted in balancing a chemical equation? Select all that apply.
Multiplying all coefficients by a common factor Inserting coefficients in front of formulas of reactants and products
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.
The change in moles of H2 (a) is equal to -2.2. The change in moles of O2 (b) is equal to -1.1. Identify H2 as the limiting reactant.
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 final quantity of NH3 present is 3.0 mol. The change in moles of N2 (a) is equal to -1.5.
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 molar mass of the compound The number of moles of the element in one mole of the compound
In order to calculate the overall % yield for a multistep process ___________.
multiply the individual % yields by each other
A chemical equation is a statement using chemical <blank> that expresses both the identities and the relative <blank> of the reactants and products involved in a chemical or physical change.
formulas; proportions
Which one of the following options gives the correct procedure to calculate the number of moles of a substance given the mass?
given mass / molar mass
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.
1. Calculate the number of moles of each element of the sample using mass/(molar mass) 2. Write a 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 determine the molecular formula for a compound using combustion analysis data. Start with the first step at the top of the list.
1. Determine the masses of carbon and hydrogen from the masses of CO2 and H2O respectively. 2. Determine the mass of oxygen, if present, by subtracting the masses of carbon adn hydrogen from the total mass 3. Determine the number of moles of each element in the compound and hence the empirical formula 4. determine the molecular formula using the empirical formula and the molar mass
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 by its molar mass 2. Determine the amount of products that could be formed from each reactant using the appropriate moles ratios 3. identify the limiting reactant as the reactant that produces the least amount of product 4. To find mass, multiply the number of moles of product formed (from the limiting reactant) by the molar mass of the product
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.
