If two elements in their standard states are going to be reacted together, what type of reaction must be occurring?
Ex: N2 and H2 are mixed in a catalytic environment. What product results?
Combination reactions are the only possible result of two standard elements being mixed.
Ex: N2 + 3H2 ⇒ 3NH3
In general, make sure you are keeping track of the standard states of the elements involved and their standard oxidation numbers in order to predict the product and write a balanced equation.
Solid sulfur is burned in an oxygen atmosphere. What product results? What is the balanced equation for this reaction?
SO2 is the product.
S + O2 ⇒ SO2
Note: A combination reaction where molecular oxygen is one of the reactants is also known as a combustion reaction.
Solid sulfur is burned in an oxygen atmosphere. What are the starting and finishing oxidation numbers for the atoms in the reaction?
S + O2 ⇒ SO2
This reaction is both a combustion and a redox reaction. Both S and O are in their standard states, hence must start with oxidation number 0. S is then oxidized to +4, and O is reduced to -2.
What is the name for any reaction where a material is combined with oxygen and heat is applied?
A combustion reaction.
Ex: The equation for the combustion of glucose is:
C6H12O6 + 6O2 ⇒
6CO2 + 6H2O
If one substance is the only reactant, what type of reaction must be occurring?
Ex: CaCO3 is heated and a reaction occurs creating multiple products?
Decomposition reactions are the only possible reactions with only one reactant.
Ex: CaCO3 ⇒ CaO + CO2
Note: one of the products of a decomposition reaction is almost always an oxide gas. General practice is to figure out possible oxide gas products first, then proceed to other products.
Hydrogen peroxide, H2O2, is exposed to UV light and a chemical reaction occurs. What products result? What is the balanced equation for this reaction?
O2 and H2O are the products.
2H2O2 ⇒ O2 + 2H2O
Note: even though it's conceptually possible for H2 to be produced here; H2 is NOT an oxide gas hence is not expected.
Carbonic acid, H2CO3, is heated and a chemical reaction occurs. What products result? What is the balanced equation for this reaction?
CO2 and H2O are the products.
H2CO3 ⇒ CO2 + H2O
CO2 is the common oxide gas expected to be produced, and H2O is the only possible remaining product.
If two solutions are mixed, and a solid compound results, what sort of reaction occurred?
When a solid appears out of solution, a precipitation reaction has occurred.
Ex: AgNO3(aq) + NaCl(aq) ⇒
AgCl (s) + NaNO3 (aq)
Note: solubility rules help to predict the products of precipitation reactions. In this case, alkali metal salts are soluble, as are nitrate salts, so AgCl is the only expected precipitation product.
Solutions of sodium hydroxide and iron (III) chloride are mixed. What will the precipitate, if any, be?
Iron (III) hydroxide, Fe(OH)3, will be the precipitate.
The balanced reaction is:
3NaOH (aq) + FeCl3 (aq) ⇒
3NaCl (aq) + Fe(OH)3 (s)
Note: the only soluble hydroxide salts are alkali metal or ammonium hydroxides.
Solutions of calcium nitrate and sodium sulfate are mixed. What will the precipitate, if any, be?
Calcium sulfate, CaSO4, will be the precipitate.
The balanced reaction is:
Ca(NO3)2 (aq) + Na2SO3 (aq) ⇒
NaNO3 (aq) + CaSO4 (s)
Note: the insoluble sulfate salts are Ag+, Ca+2, Sr+2, Ba+2, Pb+2, and Hg2+2 sulfates.
If a pure metal is added to water, what will the resultant products be?
Metals react with water to produce a base and hydrogen gas.
Ex: 2K (s) + 2H2O ⇒
2KOH (aq) + H2 (g)
Note: In the case of alkali metals, this reaction is sufficiently exothermic that it can ignite the hydrogen released, setting it on fire.
If a metal hydride is added to water, what will the resultant products be?
Metal hydrides react with water to produce a base and hydrogen gas.
Ex: CaH2 + 2H2O ⇒
Ca(OH)2 (aq) + 2H2 (g)
Note: because the reaction of metal hydrides with water is less vigorous than that of bare metals, metal hydrides are sometimes seen being used as desiccants (drying agents) on many chemistry tests like the AP Chem exam.
Equal moles of NaOH and HNO3 are combined in water. Will the pH of the resultant solution be acidic, neutral, or basic?
The pH will be neutral.
When identical molar equivalents of strong base and strong acid are combined, they neutralize each other perfectly and the resultant solution will be neutral.
Equal moles of NaOH and CH3COOH are combined in water. Will the pH of the resultant solution be acidic, neutral, or basic?
The pH will be basic.
When identical molar equivalents of strong base and weak acid are combined, the strong base has a dominant effect and the pH of the resultant solution will be basic.
Equal moles of NH3 and HCl are combined in water. Will the pH of the resultant solution be acidic, neutral, or basic?
The pH will be acidic.
When identical molar equivalents of weak base and strong acid are combined, the strong acid has a dominant effect and the pH of the resultant solution will be acidic.
A strip of solid zinc is placed in a solution of copper(I) sulfate. Will there be a chemical reaction? If so, what will happen?
Eored (Cu+⇒Cu) = +0.52 V
Eored(Zn+2⇒Zn) = -0.76 V
Zn will be oxidized to Zn+2, while the Cu+ ions will be reduced to solid Cu and precipitate out of solution.
Cu's positive reduction potential indicates that Cu(I) ions will favorably reduce, while Zn's negative reduction potential indicates that Zn(s) will preferentially oxidize.
The net voltage gain from this process is +1.28V.
A strip of solid silver is placed in a solution of copper(II) sulfate. Will there be a chemical reaction? If so, what will happen?
Eored (Ag+⇒Ag) = +0.80 V
Eored(Cu+2⇒Cu) = +0.34 V
No reaction will occur.
The fact that Ag's reduction potential is more positive than that of Cu(II) means that Ag will preferentially stay in its solid, reduced state. The amount of energy liberated by reducing the Cu is insufficient to oxidize the Ag.
There is no voltage gain, but if .46V were applied (the difference) a reaction could be generated.
What reaction, if any, will occur when magnesium is burned in an atmosphere of chlorine gas?
Eored (Cl2⇒2Cl-) = +1.36 V
Eored(Mg+2⇒Mg) = -2.37 V
Mg(s) + Cl2(g) ⇒ MgCl2(s)
Cl2's positive reduction potential indicates that Cl2 will prefer to reduce to Cl-, while Mg+2's negative reduction potential indicates that Mg(s) will preferentially oxidize to Mg+2, and the net reaction will be formation of the ionic salt.
The net voltage gain is 3.73V through this process.
What properties will a colored chemical compound have?
Colored chemical compounds will contain either transition metals with positive oxidation numbers or large, conjugated systems.
In either case, the color comes from the absorption of visible photons when electrons change energy levels.
What will be the color of an aqueous copper(II) sulfate solution?
A copper(II) sulfate solution will be blue-green.
Most solutions of copper ions will be blue or green in color. Unprotected copper left outside will develop a green patina on its surface as it oxidizes.
What will be the color of an iron(III) oxide solution?
An iron(III) oxide solution will be red-brown in color.
Red-brown is the indicative color of oxidized iron (also known as rust).
What is the color of solutions containing free Co+2 ions?
Solutions containing free Co+2 ions tend to be pink in color.
Most Co+2 salts are blue or purple in the solid phase, but turn pink when dissolved in water.
What is the color of titanium dioxide salt?
Titanium dioxide salt is bright white in color.
Titanium dioxide is used in white paint and sunscreen for its reflective qualities.
What is the color of silver chloride salt?
Silver chloride salt is white in color.
Nearly all ionic salts of small, simple ions are white crystalline solids.
What is the color of potassium chromate salt?
Potassium chromate salt is yellow-orange in color.
Many complex ions, which feature a transition metal and other ligands, are colored. Chromium-containing complexes tend to be yellow and orange in color.
What color do these alkali metals impart when heated in a flame?
Li makes a red flame
Na makes an orange flame
K makes a purple flame
Cs makes a blue flame
These metals are responsible for the colors in many fireworks.
What color do these alkali earth metals impart when heated in a flame?
Be imparts no color
Mg imparts no color
Ca makes a red-orange flame
Sr makes a deep red flame
Ba makes a green-yellow flame
The latter three are responsible for the colors in many fireworks.
What is the IUPAC name for the below molecule, C4H10?
This molecule is called butane.
A molecule with nothing but carbons and hydrogens, combined with single bonds, is known as an alkane. The prefix for carbon chains of one through six carbons are meth-, eth-, prop-, but-, pent-, and hex-.
What is the IUPAC name for the below molecule, C4H8?
This molecule is called 1-butene.
A molecule with nothing but carbons and hydrogens, with a carbon-carbon double bond, is known as an alkene.
The carbon chain is numbered from one end. The end that is chosen as carbon #1 is the end that results in the double bond being attached to the lower numbered carbon. In this case, the chain is numbered from the right.
This molecule would never be called 3-butene.
What is the IUPAC name for the below molecule, C4H6?
This molecule is called 1-butyne.
A molecule with nothing but carbons and hydrogens, with a carbon-carbon triple bond, is known as an alkyne. The carbon chain is numbered using the lowest possible numbering/order for the carbon chain.
This molecule would never be called 3-butyne.