High School
SAT
ACT
University
MCAT
LSAT
DAT

Practice: Mass Percentage

Related Topics

Wize University Chemistry Textbook > Stoichiometry

Empirical and Molecular Formulae Problems

4 Activities

Wize University Chemistry Textbook > Stoichiometry

Stoichiometry

6 Activities

checklist
Mark Yourself Question
  1. Grab a piece of paper and try this problem yourself.
  2. When you're done, check the "I have answered this question" box below.
  3. View the solution and report whether you got it right or wrong.
A compound containing sodium, chlorine, and oxygen is 25.42% sodium by mass. A 3.25 g sample gives 4.33 x 1022 atoms of oxygen. What is the empirical formula?



Hint: This is a tricky problem but start by writing the variables that you know.....what can you solve for?
If you're still not sure, my hint is to start with O! We can calculate moles of O, then mass of O, then % mass of O! What should we do next??

More Empirical and Molecular Formulae Problems Questions:
Mass Percentage
A compound containing sodium, chlorine, and oxygen is 25.42 % sodium by mass. A 3.25 g sample gives 4.33 x 1022 atoms of oxygen. What is the empirical formula?
MW Na: 23 g/mol
MW Cl: 35.45 g/mol
Empirical formula
A compound has the following mass composition: C 86.59%, H 8.36% and N 5.05%. What is the empirical formula of this compound?
Gas Stoichiometry
Cyanogen is 46.2 % C and 53.8 % N by mass. 1.00 g cyanogen gas occupies 0.476 L at 25 °C and 750 Torr. Determine the empirical and molecular formula of cyanogen.
Mass Percentage II
A certain metal hydroxide with the formula M(OH)2 is 17.22 % oxygen by mass. What is the identity of the metal, "M" ?
Spring 2017, Practice Exam 1 (CHM2045/UF)
A 7.21 g sample of a LiClO4 · xH2O was heated to drive off the water. The mass was reduced to 4.78 g. What is the formula of the hydrate?
Mass Percentage
A compound containing sodium, chlorine, and oxygen is 25.42 % sodium by mass. A 3.25 g sample gives 4.33 x 1022 atoms of oxygen. What is the empirical formula?
Hint: This is a tricky problem but start by writing the variables that you know.....what can you solve for?
If you're still not sure, my hint is to start with O! We can calculate moles of O, then mass of O, then % mass of O! What should we do next??
Practice: Empirical and Molecular Formula
A sample of a compound contains 1.52 g of N atoms and 3.47 g of O atoms. The molar mass of the compound is between 90.0 g and 95.0 g. Determine the empirical and molecular formulas.
Elements: Mass Percentage
A metal oxide with the formula M2O3 is 21.2 % oxygen by mass. What is the identity of the metal, "M"?
Empirical formula: Hydrates
A 15.67 g sample of a hydrate of magnesium carbonate (MgCO3) was heated, without decomposing the carbonate, to drive off the water. The mass was reduced to 7.58 g. What is the formula of the hydrate?
Empirical Formulae
A compound has an empirical formula of C2H5O. Its molar mass is 225.305 g/mol. Determine its molecular formula.
Empirical Formulae
7. A compound has an empirical formula of CH2O. Its molar mass is 180.01 g/mol. Determine its molecular formula.
Chemical formula: Molecular formula
Part 1: What's the empirical formula for a molecule containing 65.5% C, 5.5% H, and 29.0% O?
Part 2: It was found that the atomic mass of the molecule is 110g/mol. What is the molecular formula?
Molecular Formula from Empirical Formula
p-dichlorobenzene (mM = 147.00 g/mol) is a common disinfectant and deodorant used in industrial applications. It has an empirical formula of C3H2Cl. Determine its molecular formula. You do not need subscripts for your submission. For example, if you answer is the empirical formula, enter it as: C3H2Cl.
Chemical Reactions: Finding an Unknown Empirical Formula from Mass Percentages
A compound containing sodium, chlorine, and oxygen is 25.42% sodium by mass. A 3.25 g sample gives 4.33 x 1022 atoms of oxygen. What is the empirical formula?
Chemical Reactions: Hydrate Question
A 15.67 g sample of a hydrate of magnesium carbonate (MgCO3) was heated, without decomposing the carbonate, to drive off the water. The mass was reduced to 7.58 g. What is the formula of the hydrate?
Chemical Formula: Mass Percentage Problem
A compound is found to contain 50.05 % sulfur and 49.95 % oxygen by weight. What is the empirical formula for this compound? The molecular weight for this compound is 64.07 g/mol. What is its molecular formula?
Note: Empirical formula is the formula that expresses the SMALLEST whole number ratio of atoms present whereas the molecular formula expresses the same ratio as the empirical formula but is the actual number of atoms present in a molecule.
Empirical and Molecular Formula: Molar Mass
A sample of a compound contains 1.52 g of N atoms and 3.47 g of O atoms. The molar mass of the compound is between 90.0 g and 95.0 g. Determine the empirical and molecular formulas. Also, calculate the actual molar mass of this compound.
More Stoichiometry Questions:
Consider the reaction between hydrogen gas (H2\rm H_2) and carbon monoxide (CO\rm CO) which produces methanol gas (CH3OH\rm CH_3OH).
2H2(g)+CO(g)→CH3OH(g)\rm 2H_2(g)+CO(g)\rightarrow CH_3OH(g)
The scheme above represents the initial content of a flask before any reaction took place. Which of the schemes below would correspond to the content of this flask once the reaction has reached completion?
Precipitation
A 4.23 g sample of a mixture of BaCl2 and Ba(NO3)2 is treated with excess AgNO3(aq). The precipitate is filtered off and then dried. If the dry precipitate weighs
5.27 g, what is the percentage by mass of BaCl2 in the original mixture?
Molar masses:
A piece of zinc is allowed to react with an excess quantity of sulfuric acid, and the hydrogen gas produced is collected in a gas burette by displacement of water. Neglecting the effect of the vapor pressure of water on the system, calculate how many milligram (mg) of zinc would generate 92.0 mL of the gas at a temperature of 25.0 °C and a pressure of 1.00 atm.
Stoichiometry: Mole Ratios
How many moles of H2 and N2 can be formed by the decomposition of 12.7mol of ammonia, NH3? Do not include units in your answer.
2NH3→N2+3H22NH_3\rightarrow N_2+3H_2
Stoichiometry: Limiting Reagent
What is the maximum mass of Ca(CN)2 that can be obtained from 1.56 g of HCN and 2.58 g of Ca(OH)2? The balanced chemical equation is shown below.
2HCN(aq)+Ca(OH)2(aq)→Ca(CN)2(aq)+2H2O(ℓ)27.03g/mol74.10g/mol92.12g/mol18.02g/mol \def\arraystretch{1.5}\begin{array}{ccccccc} 2 HCN(aq) &+ &Ca(OH)_2(aq)&→& Ca(CN)_2(aq) &+& 2 H_2O(\ell) \\ 27.03g/mol && 74.10g/mol && 92.12g/mol&& 18.02g/mol \end{array}
Stoichiometry
The thermite reaction is used for welding railroad rails. The reaction is:
Fe3O3(s)+2Al(s)→3Fe(s)+Al2O3(s){Fe}_3{O}_3({s})+2{Al(s)}\rightarrow 3{Fe(s)}+{Al}_2{O}_3\text{(s)}
If 25g of iron, Fe(s), are produced from a reaction how many grams of aluminum oxide are generated?
Stoichiometry: Yield
What is the maximum amount of iodine gas (in moles) that can be formed if 1.00 mole of manganese (IV) oxide was allowed to react with 2.00 moles of hydroiodic acid to from manganese(II) iodide, iodine gas, and water?
Gases (Ideal) IIII
Today, most ammonia is produced by the Haber Process, which combines nitrogen from the air with hydrogen to produce ammonia gas. At 400oC and 2.00 atm, what volume of nitrogen gas is required to react completely with 50.0 L of hydrogen gas to produce ammonia gas?
Precipitation
Given the following reaction:
Na2SO4(s) + 2 C(s) → Na2S(s) + 2 CO2(g)
How many grams of carbon are required to produce 18.4 g Na2S(s)?
Limiting Reagent
What is the maximum mass of Ca(CN)2 that can be obtained from 1.56 g of HCN and 2.58 g of Ca(OH)2? The balanced chemical equation is shown below. The molar masses are given in gmol−1. (Choose the closest answer.)
2 HCN(aq) + Ca(OH)2(aq) → Ca(CN)2(aq) + 2 H2O(l)
27.03 74.10 92.12 18.02
Precipitation
A 4.23 g sample of a mixture of BaCl2 and Ba(NO3)2 is treated with excess AgNO3(aq). The precipitate is filtered off and then dried. If the dry precipitate weighs
5.27 g, what is the percentage by mass of BaCl2 in the original mixture?
Molar masses:
Stoichiometry
How many moles of H2 and N2 can be formed by the decomposition of 12.7 mol of ammonia, NH3?
When coal is burned, sulfur that is present within coal is converted to sulfur dioxide(SO)2{\small \text{(SO)}_2}. This results in the acid ran phenomenon.
S(s)+O2(g)→SO2(g)\text{S(s)}+\text{O}_2\text{(g)}\rightarrow\text{SO}_2\text{(g)}
If 3.75 kg of S are reacted with oxygen, calculate the volume ofSO2{\small \text{SO}_2} gas (in L) formed at 25.0°C{\small \degree\text{C}} and 1.10 atm.
The following gaseous reaction takes place at 473 K and 101.3 kPa:
N2(g)+O2(g)→NO2(g)N_{2(g)}+O_{2(g)}\to NO_{2(g)}
If 80.0 g of 02 are available to react, how many litres of N2 will be required to completely consume the oxygen supply?
Br2 and F2 can react to form BrF5(g) according to the following unbalanced reaction: R=0.08206atmL/molK
Br2(g)+ F2(g)→BrF5(g)Br_{2\left(g\right)}+\ F_{2\left(g\right)}\to BrF_{5\left(g\right)}
How many litres of BrF5 can be produced at 43 °C and 1.0 atm if 18 mols of F2 are reacted with an excess quantity of Br2?
Stoichiometry 3
What mass of C5H12 produces 9.033 ⋅\cdot 1022 CO2 molecules upon complete combustion?
What volume of 3.16 M H3PO4 solution is necessary to react with 27 mL of 0.18 M Mg(OH)2?
Consider the two following reactions:
CS2 + 3Cl2 → CCl4 (l)+ S2Cl2 (l) 60% yield
3 CCl4 (l) + 2 SbF3 (s) → 3 CCl2F2 (g) + 2SbCl3 (s) 80% yield
Redox Reactions and Calculation Using the Mole Method
Cu2+ reacts with Na2S2O3 by the following reaction:
Cu2+ + I− + S2O32− → CuI (s) + S4O62−
A 4.115 g sample containing CuSO4 and excess KI is treated with 32.55 mL of 0.2214 M Na2S2O3 solution to titrate Cu2+. What is the % CuSO4 in the sample?
Sulfur, S8, reacts with O2 at high temperature to produce SO2. If 160 molecules of O2 are used up:
a. How many molecules of sulfur react?
b. How many molecules of SO2 form?
Consider the following two step reaction:
TeO2 + 2 OH- = TeO32- + H20
TeO32- + 2H+ = H2TeO3
What mass of KClO3 is required to produce proper amount of O2 needed to achieve complete combustion of 78.88 g CH4?
2 KClO3 → 2 KCl + 3 O2
Gas Stoichiometry
The oxidation of phosphine is shown below:
2 PH3(g) + 3 O2(g) → P2O3(s) + 3 H2O(g)
What volume of O2(g), measured at 101 kPa and 50 oC, is consumed in the formation of 20.0 g of P2O3 by this reaction?
Mole method
What is the maximum number of moles of CCl2F2 that can be obtained from 6.5 mol SbF3 and 5.2 mol CCl4?
3 CCl4 + 2 SbF3 → 3 CCl2F2 + 2 SbCl3
Gas Stoichiometry
A 1.8 g mixture of KClO3 and KCl was heated until the complete decomposition of KClO3. The released O2 has a volume of 405 mL at 25 ⁰C and 745 Torr. What was the percent of KClO3 present in the mixture?
Calculating Molarity from Mass
In a reaction described by the equation below (unbalanced), excess calcium carbonate is added to 70.0 mL of hydrochloric acid. The theoretical yield of this reaction produces 20.0 g of carbon dioxide. Assuming the reaction proceeds with 100% yield and the volume of the solution does not change upon addition of solid, calculate the molairty, in mol/L, of the hydrochloric acid solution. The units for your answer should be in M or mol/L, but no units are required in your answer.
CaCO3 (s)    +    HCl (aq)    →    CaCl2 (aq)    +    CO2 (g)    +    H2O (l)CaCO_3\ \left(s\right)\ \ \ \ +\ \ \ \ HCl\ \left(aq\right)\ \ \ \ \rightarrow\ \ \ \ CaCl_2\ \left(aq\right)\ \ \ \ +\ \ \ \ CO_2\ \left(g\right)\ \ \ \ +\ \ \ \ H_2O\ \left(l\right)
Chemical Reactions: Limiting Reagent
Based on the unbalanced chemical reaction below:
NaNO2 (s)    +    O2 (g)    →    NaNO3 (s)NaNO_2\ \left(s\right)\ \ \ \ +\ \ \ \ O_2\ \left(g\right)\ \ \ \ \rightarrow\ \ \ \ NaNO_3\ \left(s\right)
a) Calculate the mass of sodium nitrate if 10.25 g of sodium nitrite is reacted with 7.55 g of oxygen gas.
Chemical Reactions: Limiting Reagent & Percent Yield Practice
Iron oxidizes when exposed to oxygen to form iron oxide according to the following equation:
Fe + O2 ​→Fe2​O3​
352g of pure iron is exposed to 12.0 mols of O2, and after a period of time 46.7 g of iron oxide (rust) is collected.
What volume of hydrogen (STP) is produced by dissolving one-half mole of aluminum in sulfuric acid?
2Al(s)+3H2SO4(aq)→Al2(SO4)3(aq)+3H2(g)2Al_{(s)}+3H_2SO_{4(aq)} \to Al_2(SO_4)_{3(aq)}+3H_{2(g)}
Br2 and F2 can react to form BrF5(g) according to the following unbalanced reaction:
Br2(g)+ F2(g)→BrF5(g)Br_{2\left(g\right)}+\ F_{2\left(g\right)}\to BrF_{5\left(g\right)}
How many litres of BrF5 can be produced at 43 °C and 1.0 atm if 18 mols of F2 are reacted with an excess quantity of Br2?
Stoichiometry: Limiting reagents
Ammonia, NH3, and borane, BH3, react to form a Lewis adduct, ammonia borane as shown below.
NH3(sol)+BH3(sol)→NH3BH3(s)NH_{3(sol)} + BH_{3(sol)} \rightarrow NH_3BH_{3(s)}
If 24 mL of a 0.74 M solution of ammonia is mixed with 12 mL of a 1.8 M solution of borane what is the maximum mass of ammonia borane that can be produced?
Stoichiometry: Mass Percentage
How many grams of PCl3 are needed to produce 10g of POCl3 using an excess of hydrogen peroxide assuming a typical reaction yield of 78%?
PCl3+H2O2→POCl3+H2OPCl_3+H_2O_2\rightarrow POCl_3+H_2O
Stoichiometry: Percent yield
Consider the following unbalanced reaction:
C4H8O2+O2→CO2+H2O\rm C_4H_8O_2 +O_2 \to CO_2 + H_2O
If 36.00 g of C4H8O2\rm C_4H_8O_2 is burned, what mass of water would be collected if the reaction yield was 76%?
Chemical Reactions: Limiting Reagent
15mL of a 1.2M solution of HCl reacts with 22mL of a 1.4M solution of NaOH. How many moles of NaOH are left after the reaction is complete?
HCl(aq)+NaOH(aq)→H2O(l)+NaCl(aq)HCl_{(aq)}+NaOH_{(aq)}\rightarrow H_2O_{(l)}+ NaCl_{(aq)}
Stoichiometry: Mass of product calculation
16.0 mL of Hg (mp = -38.8oC, density = 13.56 g/mL) reacts with Fluorine gas and the reaction goes to completion as shown below in the unbalanced chemical reaction.
Hg(l)+F2(g)→HgF2(s)Hg_{(l)}+F_{2(g)}\rightarrow HgF_{2(s)}
Once the reaction has gone to completion, what mass of Mercury Fluoride, HgF2, is produced?
Chemical Reactions: Hydrate Question
A 15.67 g sample of a hydrate of magnesium carbonate (MgCO3) was heated, without decomposing the carbonate, to drive off the water. The mass was reduced to 7.58 g. What is the formula of the hydrate?
Stoichiometry: Percent Yield
A compound with the formula C7H8O3\text{C}_7\text{H}_8\text{O}_3 is burned to completion in excess O2\text{O}_2. If 18.0g of the organic compound was consumed in the reaction, how many grams of H2O\text{H}_2\text{O} will be collected if the yield was 85%?
In dilute nitric acid, HNO3, copper metal dissolves according to the following equation. How many grams of HNO3 are needed to dissolve 11.45 g of Cu according to this equation?
3Cu+8HNO3→3Cu(NO3)2+2NO+4H2O3Cu+8HNO_3→3Cu(NO_3)_2+2NO+4H_2O
When coal is burned, sulfur that is present within coal is converted to sulfur dioxide (SO2). This results in the acid rain phenomenon. If 3.75 kg of S are reacted with oxygen, calculate the volume of SO2 gas (in L) formed at 25.0 °C and 1.10 atm.
The potassium salt of benzoic acid, potassium benzoate (KC7H5O2, MM=160 g/mol) can be made by the action of potassium permanganate on toluene (C7H8, MM=92 g/mol). If the yield of potassium benzoate cannot realistically be expected to be more than 71%, what is the minimum number of grams of toluene needed to produce 11.5 g of potassium benzoate?
C7H8+2KMnO4→KC7H5O2+2MnO2+KOH+H2OC_7 H_8+2KMnO_4→KC_7 H_5 O_2+2MnO_2+KOH+H_2 O
Stoichiometry: Percent Yield
How many grams of PCl3 are needed to produce 10g of OPCl3 using an excess of hydrogen peroxide assuming a typical reaction yield of 78%?
PCl3​ + H2​O2 ​→ OPCl3​ + H2​O
Stoichiometry
The thermite reaction is used for welding railroad rails. The reaction is:
Fe3O3(s)+2Al(s)→3Fe(s)+Al2O3(s)\text{Fe}_3\text{O}_3\text({s})+2\text{Al(s)}\rightarrow 3\text{Fe(s)}+\text{Al}_2\text{O}_3\text{(s)}
If 25. grams of iron, Fe(s), are produced from a reaction how many grams of aluminum oxide are generated?
Chemical Reactions: Limiting Reagent & Percent Yield Practice
Iron oxidizes when exposed to oxygen to form iron oxide according to the following equation:
Fe + O2 ​→Fe2​O3​
352g of pure iron is exposed to 12.0 mols of O2, and after a period of time 46.7 g of iron oxide (rust) is collected.
Stoichiometry and Ideal Gas Law Practice
The combustion of methanol (CH3OH) is shown below. If 16g of methanol is burned in oxygen, what volume of CO2 is produced if the pressure is 101.3kPa, T=25C, and R=8.314kPaL/molK? Round to the nearest whole number.
CH3OH + O2 --> CO2 + H2O
Is the equation balanced?
No
A piece of zinc is allowed to react with an excess quantity of sulfuric acid, and the hydrogen gas produced is collected in a gas burette by displacement of water. Neglecting the effect of the vapor pressure of water on the system, calculate how many milligram (mg) of zinc would generate 92.0 mL of the gas at a temperature of 25.0 °C and a pressure of 1.00 atm.
Consider the reaction between hydrogen gas (H2\rm H_2) and carbon monoxide (CO\rm CO) which produces methanol gas (CH3OH\rm CH_3OH).
2H2(g)+CO(g)→CH3OH(g)\rm 2H_2(g)+CO(g)\rightarrow CH_3OH(g)
The scheme above represents the initial content of a flask before any reaction took place. Which of the schemes below would correspond to the content of this flask once the reaction has reached completion?
A 2.56 g sample of ZnSO4 ⋅ 7H2O is heated to dryness. Determine the anhydrous mass remaining after all the water has been driven off. (provide an answer with 2 decimal places and correct unit)
Stoichiometry: Molar mass and Avogadro's Number
How many hydrogen atoms are in exactly 2 g of hydrazinium sulfate, N2H6SO4?
Ideal Gas Law: Stoichiometry
What volume of hydrogen (STP) is produced by dissolving one-half mole of aluminum in sulfuric acid?
2Al(s)+3H2SO4(aq)→Al2(SO4)3(aq)+3H2(g)2Al(s)+3H_2SO_4(aq)→Al_2(SO_4)_3(aq)+3H_2(g)
A piece of zinc is allowed to react with an excess quantity of sulfuric acid, and the hydrogen gas produced is collected in a gas burette by displacement of water. Neglecting the effect of the vapor pressure of water on the system, calculate how many milligram (mg) of zinc would generate 92.0 mL of the gas at a temperature of 25.0 °C and a pressure of 1.00 atm.
Gas Laws: Practice
A student decides to do a more controlled version of the hydrogen balloon explosion. The unbalanced chemical equation for this reaction is shown below:
H2(g)+O2(g)→H2O(g)H_2(g)+O_2(g)→H_2O(g)
(a) Write the balanced chemical equation for this reaction.
Chemical Reactions: Limiting Reagent
Potassium carbonate, K2CO3, will react with acetic acid, CH3CO2H, to produce carbon dioxide gas, as per the following unbalanced reaction:
K2CO3(s)+CH3CO2H(aq)→KCH3CO2(aq)+CO2(g)+H2O(l)K_2CO_3(s)+CH_3CO_2H(aq)\rightarrow KCH_3CO_2(aq)+CO_2(g)+H_2O(l)
If 4 moles of K2CO3 reacted with an excess of CH3CO2H, how many moles of CH3CO2H reacted?
Stoichiometry
Br2 and F2 can react to form BrF5(g) according to the following unbalanced reaction: R=0.08206atmL/molK
Br2(g)+ F2(g)→BrF5(g)Br_{2\left(g\right)}+\ F_{2\left(g\right)}\to BrF_{5\left(g\right)}
How many litres of BrF5 can be produced at 43 °C and 1.0 atm if 18 mols of F2 are reacted with an excess quantity of Br2?
Stoichiometry
The following gaseous reaction takes place at 473 K and 101.3 kPa:
N2(g)+O2(g)→NO2(g)N_{2(g)}+O_{2(g)}\to NO_{2(g)}
If 80.0 g of 02 are available to react, how many litres of N2 will be required to completely consume the oxygen supply?
Like Spring 2019 Exam 2
At 100oC and 1.00 atm, what volume of nitrogen gas is required to react completely with 10.0 L of hydrogen gas to produce ammonia gas?