A balanced chemical equation has the same number of atoms of each element on both sides.
Correct Answer
True
True. Atoms are neither created nor destroyed in a chemical reaction, so a balanced equation must show the same number of each kind of atom among the reactants and the products. This is the law of conservation of mass applied to equations.
Category: Balancing Equations
Question 2
In a balanced chemical equation, the sum of the coefficients on the reactant side must equal the sum on the product side.
Correct Answer
False
False. Atoms must balance, but the total number of molecules need not. In 2H2 + O2 -> 2H2O, the reactant coefficients add to 3 while the product coefficient is 2.
Category: Balancing Equations
Question 3
Spectator ions appear unchanged on both sides of a complete ionic equation and are left out of the net ionic equation.
Correct Answer
True
True. Spectator ions stay dissolved throughout the reaction and take no part in the chemical change. Removing them leaves the net ionic equation, which shows only the species that actually react.
Category: Ionic Equations
Question 4
In a complete ionic equation, a dissolved ionic compound such as KNO3(aq) is written as an intact formula unit.
Correct Answer
False
False. Soluble ionic compounds dissociate in water, so in a complete ionic equation KNO3(aq) is written as separate ions, K+(aq) and NO3-(aq). Only solids, liquids, gases, and weak electrolytes are written as intact formulas.
Category: Ionic Equations
Question 5
Compounds containing the ammonium ion, NH4+, are soluble in water.
Correct Answer
True
True. Ammonium compounds, like those of the Group 1 cations, are soluble with no common exceptions. This makes ammonium salts useful as sources of dissolved anions.
Category: Precipitation
Question 6
Carbonates of Group 2 metals, such as CaCO3, are soluble in water.
Correct Answer
False
False. Carbonates are generally insoluble, and the only exceptions are compounds of Group 1 cations and ammonium. Calcium carbonate is insoluble, which is why it forms limestone and scale in kettles.
Category: Precipitation
Question 7
Hydrochloric acid reacts completely with water to form hydronium ions and chloride ions.
Correct Answer
True
True. HCl is a strong acid, so essentially every dissolved HCl molecule transfers H+ to water, forming H3O+ and Cl-. Strong acids are written as ions in complete ionic equations.
Category: Acids and Bases
Question 8
Acetic acid, HC2H3O2, is a strong acid that ionizes completely in water.
Correct Answer
False
False. Acetic acid is a weak acid; only a small fraction of its molecules transfer H+ to water at any moment. The common strong acids are HCl, HBr, HI, HNO3, HClO4, and H2SO4.
Category: Acids and Bases
Question 9
When a strong acid such as HCl reacts with a hydroxide base such as NaOH, the products are a salt and water.
Correct Answer
True
True. H+ from the acid combines with OH- from the hydroxide base to form water, and the remaining ions make up a salt. HCl and NaOH, for example, form NaCl and H2O.
Category: Acids and Bases
Question 10
In a precipitation reaction, the reactants are solids that dissolve to form an aqueous product.
Correct Answer
False
False. A precipitation reaction runs the other way: dissolved reactants combine to form an insoluble solid product. Mixing solutions of AgNO3 and NaCl, for example, produces solid AgCl.
Category: Precipitation
Question 11
Oxygen has an oxidation number of -2 in hydrogen peroxide, H2O2.
Correct Answer
False
False. Oxygen is usually -2, but in peroxides each oxygen is -1. In H2O2 the two hydrogens are +1 each, so the two oxygens must total -2, or -1 apiece.
Category: Oxidation Numbers
Question 12
Fluorine has an oxidation number of -1 in all of its compounds.
Correct Answer
True
True. Fluorine is the most electronegative element, so in every compound it is assigned -1. Other halogens are usually -1 but can take positive values when combined with oxygen or a more electronegative halogen.
Category: Oxidation Numbers
Question 13
In the reaction 2Na + Cl2 -> 2NaCl, chlorine is oxidized.
Correct Answer
False
False. Chlorine goes from 0 in Cl2 to -1 in NaCl, a decrease in oxidation number, so it is reduced. Sodium goes from 0 to +1 and is the element that is oxidized.
Category: Redox Reactions
Question 14
The complete combustion of a hydrocarbon in excess oxygen produces carbon dioxide and water.
Correct Answer
True
True. In complete combustion, all of the carbon in the fuel ends up as CO2 and all of the hydrogen ends up as H2O. Methane, for example, burns as CH4 + 2O2 -> CO2 + 2H2O.
Category: Redox Reactions
Question 15
The limiting reactant can be identified simply as the reactant present in the smallest mass.
Correct Answer
False
False. The limiting reactant is the one that is used up first, which depends on moles and on the mole ratio in the balanced equation, not on mass alone. A reactant with a small mass can still be in excess if little of it is needed.
Category: Reaction Yields
Question 16
The theoretical yield is the amount of product calculated from the complete reaction of the limiting reactant.
Correct Answer
True
True. Theoretical yield is the maximum product predicted by stoichiometry when all of the limiting reactant reacts. The amount actually collected, the actual yield, is usually less.
Category: Reaction Yields
Question 17
The coefficients in a balanced equation give the mass ratio in which the reactants combine.
Correct Answer
False
False. Coefficients give the ratio of moles, or of molecules, not of masses. To find a mass ratio, each mole amount must be multiplied by the molar mass of that substance.
Category: Reaction Stoichiometry
Question 18
Titrating an acid with a base solution of known concentration can be used to determine the concentration of the acid.
Correct Answer
True
True. Measuring the volume of base needed to reach the equivalence point gives the moles of base, and the mole ratio from the balanced equation converts that to moles of acid. Dividing by the acid sample's volume gives its concentration.
Category: Chemical Analysis
Question 19
In gravimetric analysis, the amount of analyte is determined by measuring the volume of titrant needed to react with it.
Correct Answer
False
False. Gravimetric analysis relies on mass measurements: the analyte is isolated, often as a precipitate that is filtered and dried, and then weighed. Measuring a volume of titrant describes a titration.
Category: Chemical Analysis
Question 20
In combustion analysis, the mass of hydrogen in a sample is found from the mass of water produced.
Correct Answer
True
True. All of the hydrogen in the burned sample is converted to H2O, which is trapped by an absorber and weighed. Multiplying the water's mass by the mass fraction of hydrogen in H2O gives the hydrogen in the original sample.
Category: Chemical Analysis