Chemistry 2nd Semester Exam Review 2025

The characteristic properties of acids are:

• Sour taste, turn blue litmus red, react with metals to produce hydrogen gas

• Bitter taste, turn red litmus blue, feel slippery

• Sweet taste, do not affect litmus paper, do not react with metals

• No taste, turn blue litmus blue, react with non-metals

Answer explanation

The correct choice describes acids accurately: they have a sour taste, turn blue litmus red, and react with metals to produce hydrogen gas, distinguishing them from bases and neutral substances.

Which of the following statements correctly defines an amphoteric substance and provides two reactions that prove water is amphoteric?

• An amphoteric substance can act as both an acid and a base; water reacts with HCl to form H3O+ and with NH3 to form OH−.

• An amphoteric substance can only act as a base; water reacts with NaOH to form H2O2 and with HCl to form Cl2.

• An amphoteric substance can only act as an acid; water reacts with NaOH to form Na2O and with NH3 to form N2.

• An amphoteric substance is neutral and does not react; water does not react with acids or bases.

Answer explanation

The correct choice defines an amphoteric substance as one that can act as both an acid and a base. Water reacts with HCl to form H3O+ (acting as a base) and with NH3 to form OH− (acting as an acid), proving its amphoteric nature.

Calculate the [H+] for a solution with a pH of 5.2.

Answer explanation

To find [H+], use the formula [H+] = 10^(-pH). For pH = 5.2, [H+] = 10^(-5.2) = 6.31 x 10^(-6) M, which matches the first answer choice.

Name the following acid: HNO2

• Nitrous acid

• Nitric acid

• Hydrochloric acid

• Sulfuric acid

Answer explanation

HNO2 is known as nitrous acid. It is distinct from nitric acid (HNO3), which has a different structure and properties. Hydrochloric acid (HCl) and sulfuric acid (H2SO4) are entirely different compounds.

Predict the products of this neutralization reaction: H2SO4 + Ca(OH)2 →

• CaSO4 + 2H2O

• CaO + H2SO4

• Ca(OH)2 + SO2

• CaSO3 + H2O

Answer explanation

In this neutralization reaction, sulfuric acid (H2SO4) reacts with calcium hydroxide (Ca(OH)2) to produce calcium sulfate (CaSO4) and water (H2O). The balanced equation is H2SO4 + Ca(OH)2 → CaSO4 + 2H2O.

• 11

• 3

• 7

• 9

Answer explanation

To find the pH from the hydroxide ion concentration, use the formula pOH = -log[OH-]. Here, pOH = 3. Therefore, pH = 14 - pOH = 14 - 3 = 11. Thus, the correct answer is 11.

Write the formula for perbromic acid.

• HBrO4

• HBrO3

• HBrO2

• HBrO

Answer explanation

Perbromic acid is a strong acid derived from bromine and has the highest oxidation state of bromine. Its formula is HBrO4, indicating it contains four oxygen atoms bonded to bromine, making it the correct choice.

• 5.5

• 4.5

• 7.5

• 9.5

Answer explanation

To find pOH, first calculate pH using pH = -log[H+]. For [H+] = 3.2 x 10^-9 M, pH ≈ 8.5. Then, pOH = 14 - pH = 14 - 8.5 = 5.5. Thus, the correct answer is 5.5.

Identify the conjugate base of HCO3−.

• H2CO3 (carbonic acid)

• OH− (hydroxide ion)

• HCOO− (formate ion)

Answer explanation

The conjugate base of HCO3− (bicarbonate) is formed when it donates a proton (H+), resulting in CO3^{2−} (carbonate ion). Thus, the correct answer is CO3^{2−}.

What is the [OH-] in a solution with a pH of 10.5?

Answer explanation

To find [OH-], first calculate pOH: 14 - 10.5 = 3.5. Then, use the formula [OH-] = 10^{-pOH} = 10^{-3.5} = 3.16 × 10^{-4} M. Thus, the correct choice is the first option.