In a balanced chemical equation, the numbers written in front of formulas to show the relative amounts of each substance are called coefficients.
Missing Word
coefficients
Coefficients multiply every atom in the formula that follows them and give the mole ratios used in stoichiometry. They are the only numbers changed when balancing an equation.
Category: Balancing Equations
Question 2
An insoluble solid that forms when two solutions are mixed is called a precipitate.
Missing Word
precipitate
A precipitate forms when the ions from two solutions combine into a compound that does not dissolve, such as AgCl from AgNO3 and NaCl. The solubility guidelines predict whether one will form.
Category: Precipitation
Question 3
The extent to which a substance dissolves in a given solvent is called its solubility.
Missing Word
solubility
Solubility describes how much of a substance can dissolve in a given amount of solvent. Compounds of very low solubility are called insoluble and are the ones that precipitate.
Category: Precipitation
Question 4
An acid dissolved in water transfers H+ to water molecules, forming the hydronium ion, H3O+.
Missing Word
hydronium
The hydronium ion, H3O+, forms when a water molecule accepts a hydrogen ion from an acid. An acidic solution is one in which the concentration of H3O+ is greater than that of OH-.
Category: Acids and Bases
Question 5
A base dissolved in water increases the concentration of the hydroxide ion, OH-.
Missing Word
hydroxide
Hydroxide is the OH- ion. Ionic hydroxides such as NaOH release it directly, while weak bases such as ammonia produce it by taking H+ from water.
Category: Acids and Bases
Question 6
The half of a redox process in which an element's oxidation number decreases is called reduction.
Missing Word
reduction
Reduction is the gain of electrons. It always occurs together with oxidation, because the electrons gained by one species must be lost by another.
Category: Redox Reactions
Question 7
Burning a fuel such as methane in oxygen, releasing heat and light, is an example of the reaction type called combustion.
Missing Word
combustion
Combustion is a redox reaction in which a fuel, often a hydrocarbon, reacts with an oxidant, usually oxygen. Burning methane in a gas stove is a familiar example.
Category: Redox Reactions
Question 8
The oxidation number of nitrogen in the nitrate ion, NO3-, is +5.
Missing Word
5
Each oxygen is -2, and the oxidation numbers must add up to the ion's charge of -1, so N + 3(-2) = -1 and N = +5. Nitrogen shows a wide range of oxidation numbers, from -3 in ammonia to +5 in nitrate.
Category: Oxidation Numbers
Question 9
An atom in an elemental substance, such as Fe or N2, has an oxidation number of 0.
Missing Word
0
Atoms in a pure element share electrons equally or not at all, so each is assigned an oxidation number of zero. This is the first rule for assigning oxidation numbers.
Category: Oxidation Numbers
Question 10
The quantitative relationship between the amounts of reactants and products in a chemical reaction is called stoichiometry.
Missing Word
stoichiometry
Stoichiometry uses the mole ratios from a balanced equation to relate amounts of reactants and products. It is the basis for calculating masses, yields, and concentrations from reactions.
Category: Reaction Stoichiometry
Question 11
A reactant that is left over after the limiting reactant has been used up is said to be present in excess.
Missing Word
excess
A reactant in excess is supplied in a greater amount than the stoichiometry requires, so some of it remains unreacted. The amount of product depends only on the limiting reactant.
Category: Reaction Yields
Question 12
In a titration, the solution of known concentration that is added to the sample is the titrant.
Missing Word
titrant
The titrant is delivered in measured volumes until the reaction with the sample is complete. Its known concentration and measured volume give the moles that reacted.
Category: Chemical Analysis
Question 13
The substance whose amount or concentration is being determined in a chemical analysis is the analyte.
Missing Word
analyte
The analyte is the target of the measurement, such as the acid in a sample being titrated. Every quantitative method, from titration to gravimetric analysis, is designed around it.
Category: Chemical Analysis
Question 14
A dye that changes color at or very near the equivalence point of a titration is an indicator.
Missing Word
indicator
An indicator signals when a titration is complete by changing color. The volume at which the color change is seen is the end point, which in a good method lies very close to the equivalence point.
Category: Chemical Analysis
Question 15
Every redox reaction involves the transfer of electrons from the species that is oxidized to the species that is reduced.
Missing Word
electrons
Oxidation and reduction always occur together because the electrons lost by one species are gained by another. Tracking changes in oxidation numbers is a bookkeeping method for following this electron transfer.
Category: Redox Reactions