Acids and Bases Study Guide - Chemistry

If a solution has a pH of 4, what would be the pH of a solution that is 100 times less acidic?

• 2

• 6

• 8

• 10

Answer explanation

A pH of 4 indicates a certain acidity level. A solution that is 100 times less acidic has a pH increase of 2 units (since pH is logarithmic). Therefore, 4 + 2 = 6, making 6 the correct answer.

Which ion is produced when potassium hydroxide (KOH), a strong base, is added to water?

• K+ ions

• H+ ions

• OH− ions

• H3O+ ions

Answer explanation

When potassium hydroxide (KOH) dissolves in water, it dissociates into K+ and OH− ions. The strong base produces OH− ions, which increase the hydroxide concentration in the solution.

How does the hydrogen ion concentration in a solution with pH 5 compared to a solution with pH 6?

• It is 10 times greater

• It is 10 times smaller

• It is 100 times greater

• It is 100 times smaller

Answer explanation

The pH scale is logarithmic, meaning each whole number change represents a tenfold change in hydrogen ion concentration. Therefore, a solution with pH 5 has 10 times greater hydrogen ion concentration than one with pH 6.

What gas is produced when aluminum reacts with an acidic solution?

• Oxygen

• Chlorine

• Carbon dioxide

• Hydrogen

Answer explanation

When aluminum reacts with an acidic solution, it displaces hydrogen ions, resulting in the production of hydrogen gas. Therefore, the correct answer is hydrogen.

Tags

NGSS.MS-PS1-2

Why is a 3% solution of hydrochloric acid considering a strong acid despite its low concentration?

• It has a very low pH

• It completely dissociates in water

• It has a high concentration of chloride ions

• It reacts violently with metals

Answer explanation

A 3% solution of hydrochloric acid is considered a strong acid because it completely dissociates in water, releasing a high concentration of hydrogen ions, which results in its strong acidic properties despite the low concentration.

What is formed when a base reacts with an acid?

• Sodium chloride and water

• Sodium chloride and hydrogen gas

• Sodium hydroxide and chlorine gas

• Sodium hydride and oxygen gas

Answer explanation

When a base reacts with an acid, they undergo a neutralization reaction, producing salt and water. In this case, sodium chloride (salt) and water are formed, making 'Sodium chloride and water' the correct answer.

A 0.01 M solution of HCl has a pH of 2. What would be the pH of a 0.001 M HCl solution?

• A) 1

• B) 2

• C) 3

• D) 4

Answer explanation

The pH of a solution is calculated as -log[H+]. For 0.01 M HCl, pH = 2. For 0.001 M HCl, [H+] = 0.001 M, so pH = -log(0.001) = 3. Thus, the pH of the 0.001 M HCl solution is 3 (Choice C).

Which of the following pairs consists of a conjugate acid-base pair?

• HCl and NaOH

• H2SO4 and H2O

• NH4+ and NH3

• HNO3 and NO3−

Answer explanation

NH4+ (ammonium) is the conjugate acid of NH3 (ammonia), which acts as the base. This pair represents the transfer of a proton (H+), making them a conjugate acid-base pair. The other options do not fit this definition.

Which of the following would have the highest pH?

• 0.1 M HCl

• Pure water

Answer explanation

Pure water has a neutral pH of 7, while 0.1 M HCl is an acid with a pH less than 1. Therefore, pure water has the highest pH among the given options.

Explain the difference between the Arrhenius and Brønsted-Lowry definitions of acids and bases. Give an example of each.

• Arrhenius: Acid produces H+ ions in water, base produces OH- ions in water. Example: HCl (acid), NaOH (base). Brønsted-Lowry: Acid donates a proton (H+), base accepts a proton. Example: HCl (acid), NH3 (base).

• Arrhenius: Acid donates a proton, base accepts a proton. Example: H2SO4 (acid), NH3 (base). Brønsted-Lowry: Acid produces H+ ions in water, base produces OH- ions in water. Example: HCl (acid), NaOH (base).

• Arrhenius: Acid produces OH- ions in water, base produces H+ ions in water. Example: NaOH (acid), HCl (base). Brønsted-Lowry: Acid accepts a proton, base donates a proton. Example: NH3 (acid), HCl (base).

• Arrhenius: Acid produces H2O in water, base produces O2 in water. Example: H2O (acid), O2 (base). Brønsted-Lowry: Acid donates an electron, base accepts an electron. Example: Cl- (acid), Na+ (base).

Answer explanation

The correct choice defines Arrhenius acids as H+ producers and bases as OH- producers in water, exemplified by HCl and NaOH. Brønsted-Lowry defines acids as proton donors and bases as proton acceptors, with HCl and NH3 as examples.