Which of the following describes a chemical change rather than a physical change?
Iron metal rusting to form iron oxide
Ice melting into liquid water
Salt dissolving in water
Water boiling into steam
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WhyIron rusting forms a new substance (iron oxide), so it is a chemical change. Melting, dissolving, and boiling only change physical state without forming new substances.
2Multiple choice · Easy
What is the oxidation number of sulfur in the sulfate ion, SO4^2-?
+6
+4
-2
+2
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WhyOxygen is -2 each, totaling -8. To give an overall charge of -2, sulfur must be +6 (since +6 + (-8) = -2).
3Multiple choice · Easy
Which type of reaction is represented by AgNO3(aq) + NaCl(aq) -> AgCl(s) + NaNO3(aq)?
Precipitation (double-replacement) reaction
Combustion reaction
Single-replacement reaction
Decomposition reaction
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WhyTwo ionic compounds exchange ions to form an insoluble solid (AgCl), which is a precipitation (double-replacement) reaction.
4Multiple choice · Easy
In the reaction HCl(aq) + NaOH(aq) -> NaCl(aq) + H2O(l), what type of reaction occurs?
Acid-base neutralization
Oxidation-reduction
Precipitation
Combustion
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WhyAn acid (HCl) reacts with a base (NaOH) to produce a salt and water, which is an acid-base neutralization reaction.
5Fill in the blank · Easy
In a redox reaction, the species that loses electrons is said to be .
Answer:
oxidized / oxidised
WhyLoss of electrons is oxidation (remember OIL RIG: Oxidation Is Loss). A species that loses electrons undergoes oxidation and acts as the reducing agent.
6Fill in the blank · Easy
For the net ionic equation, spectator ions are ions that appear unchanged on sides of the complete ionic equation and are therefore omitted.
Answer:
both
WhySpectator ions appear identically on both the reactant and product sides, so they cancel out and are left out of the net ionic equation.
7Multiple choice · Medium
What is the net ionic equation for the reaction between aqueous Pb(NO3)2 and aqueous KI?
Pb2+(aq) + 2 I-(aq) -> PbI2(s)
Pb2+(aq) + I-(aq) -> PbI(s)
K+(aq) + NO3-(aq) -> KNO3(s)
Pb(NO3)2(aq) + 2 KI(aq) -> PbI2(s) + 2 KNO3(aq)
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WhyPb2+ and I- combine to form insoluble PbI2; K+ and NO3- are spectator ions and are removed from the equation.
8Multiple choice · Medium
How many grams of CO2 are produced when 0.50 mol of C3H8 burns completely according to C3H8 + 5 O2 -> 3 CO2 + 4 H2O?
66 g
22 g
44 g
132 g
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Why0.50 mol C3H8 yields 3 x 0.50 = 1.5 mol CO2; multiplying by 44.0 g/mol gives 66 g CO2.
9Multiple choice · Medium
In the reaction Zn(s) + Cu2+(aq) -> Zn2+(aq) + Cu(s), which species is the oxidizing agent?
Cu2+
Zn
Zn2+
Cu
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WhyCu2+ gains electrons (is reduced) and therefore causes oxidation of Zn, making Cu2+ the oxidizing agent.
10Multiple choice · Medium
A 25.0 mL sample of HCl is exactly neutralized by 30.0 mL of 0.100 M NaOH. What is the molarity of the HCl?
0.120 M
0.100 M
0.0833 M
0.0600 M
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WhyMoles NaOH = 0.0300 L x 0.100 M = 0.00300 mol; HCl reacts 1:1, so M = 0.00300 mol / 0.0250 L = 0.120 M.
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Chemical Reaction: A process in which reactants are rearranged into new substances with different chemical identities.
Physical Change: A change in the form or appearance of matter that does not alter its chemical composition, such as melting or dissolving.
Chemical Change: A change that produces one or more new substances with different properties, evidenced by signs like gas formation, color change, or precipitate.
Reactant: A starting substance that is consumed during a chemical reaction.
Product: A substance that is formed as a result of a chemical reaction.
Chemical Equation: A symbolic representation of a reaction showing reactants, products, and their relative amounts.
Balanced Equation: A chemical equation in which the number of atoms of each element is equal on both sides, satisfying conservation of mass.
Coefficient: A number placed in front of a chemical formula to indicate how many units of that species participate in a reaction.