Unit 4: Topic 2 - Net Ionic Equations Flashcards
Describe qualitatively what happens in the reaction H2O(s) —> H2O(l).
H2O (s) is the reactant, and H2O (l) is the product. Reactants of a chemical reaction are substances that start a chemical reaction, and products are the substances produced by this chemical reaction. (s) represents a solid phase, and (l) represents a liquid phase. Solid water (ice) is a reactant, and liquid water is the product. This reaction represents when ice has been heated past its melting point to form water.
Determine the (unbalanced) chemical equation for the combustion of propane, C3H8.
Combustion of a hydrocarbon (a compound consisting of carbon and hydrogen), such as propane, occurs when the compound reacts with oxygen to produce carbon dioxide and water. The unbalanced equation for the combustion of propane is C3H8 + O2 —> CO2 + H2O (note that oxygen is a diatomic).
State the law of conservation of mass and explain how it applies to chemical
reactions.
The conservation of mass is a principle stating that mass cannot be created nor destroyed.
When applied to chemical reactions, if this reaction is closed off from the outside world (i.e. contained
in a closed jar or closed container), then the amount of mass before the reaction occurs should be
equivalent to the amount of mass after the reaction, and thus the number
of atoms of each element stays constant throughout the reaction.
Determine the balanced chemical equation for the combustion of propane, C3H8.
Above, the unbalanced equation is C3H8 + O2 —> CO2 + H2O. When we balance a chemical equation, we will minimize our choice of coefficients. For instance, if our coefficients are (2, 4, 8, 6), we can reduce them to (1, 2, 4, 3).
Therefore, using this, there will be 3 units of Carbon and 8 units of hydrogen: this calls for 3 units of CO2 (which has 3 units of carbon) and 4 units of H2O (which has 4* 2 = 8 units of hydrogen). From here, there are 3*2 + 4 = 10 units of oxygen, so the coefficient of oxygen should be 5 (since 5 * 2 = 10).
Final Answer: C3H8 + 5O2 —> 3CO2 + 4H2O.
Define what a chemical change is, and give an example of a chemical change represented by a chemical reaction
A chemical change, also known as a chemical reaction, is any process where one chemical substance
undergoes a transformation to form a different chemical substance. For example, in CaCl2 (aq)
+ Ag2CO3 (aq) —> 2AgCl (s) + CaCO3 (aq), the calcium chloride and silver carbonate, both soluble,
react and form a chemically different solid compound, insoluble in water.
Define what a balanced molecular equation is, and compare/contrast complete ionic and net ionic equations.
A molecular equation consists of reactants A and products B. The reactants come together, and
through some chemical reaction form the products B, denoted by A —> B.
A balanced molecular equation accounts for the conservation of mass, so for example, if there are 3
units of element X in the reactant bunch, the products should also consist of 3 units of element X, no
more and no less.
A complete ionic equation is a form of the balanced molecular equation, but every reactant and
product that can be broken up into separate ions (usually aqueous) is shown broken up. For example,
if AgNO3 (aq) is a reactant in the molecular equation, the complete ionic equation would have
Ag+ (aq) + NO3- (aq).
If a complete ionic equation has equivalent ions as both reactants and products, they can be
equivalently canceled to arrive at the net ionic equation.
The (unbalanced) reaction of Calcium Chloride and Silver Carbonate in water is CaCl2 + Ag2CO3 –> AgCl + CaCO3. Balance the equation, then determine the complete ionic and the net ionic equations.
The balanced reaction is CaCl2 (aq) + Ag2CO3 (aq) —> 2AgCl (s) + CaCO3 (aq). Based on this, silver chloride is insoluble. For everything that is aqueous (aq), we can break down into ions:
Ca 2+ (aq) + 2Cl- (aq) + 2Ag+ (aq) + CO3 2- (aq) —> 2AgCl(s) + Ca 2+ (aq) + CO3 2- (aq) is the
complete ionic equation.
To find the net ionic equation, cancel any pairs of ions that are on both sides of the equation;
the result should be 2Cl- (aq) + 2Ag+ (aq) —> 2AgCl(s), so we can even divide by 2:
Final Net Ionic: Cl- (aq) + Ag+ (aq) —> AgCl(s)
Barium sulfate is insoluble. The unbalanced reaction of hydrosulfuric acid with barium hydroxide in water is Ba(OH)2 + H2SO4 –> H2O + BaSO4. Balance the reaction, then write out the net ionic and complete ionic equations.
Barium sulfate is not soluble: this is memorization of the solubility rules. If we consider the balanced
equation for the reaction of hydrosulfuric acid with barium hydroxide, we have H2SO4 (aq) + Ba(OH)2
(aq) —> 2H2O (l) + BaSO4 (s) (note some nomenclature: H2SO4 could be considered hydrogen
sulfate, but when dissolved in water has acidic properties). To decompose this into the complete ionic
equation, we would have 2H+ (aq) + SO4 2- (aq) + Ba 2+ (aq) + 2OH- (aq) —> 2H2O(l) + BaSO4(s).
This also happens to be the net ionic equation, because there are no ions to cancel out (since in this
example H2O is now a liquid). BaSO4 is still a solid, and is insoluble.
