Test Review #8

Which compounds are classified as Arrhenius acids?

• HCl and NaOH

• HNO₃ and NaCl

• NH₃ and H₂CO₃

• HBr and H₂SO₄

Answer explanation

Look at Table K. Recall that Arrhenius acids break apart to give H⁺ or H₃O⁺ ions in water. Most acids start with an H in their formula (Except for H₂O). HBr and H₂SO₄ both start with H.

Which substance is an electrolyte?

• C₆H₁₂O₆

• C₂H₅OH

• NaOH

• H₂

Answer explanation

An electrolyte is any substance that dissolves in water to form ions. These ions can then move around in the water to allow the flow of electric current. All soluble ionic compounds are electrolytes. Arrhenius acids and bases are also good electrolytes because they also produce ions in water.

Recall that Arrhenius Bases break apart in water and release OH^- ions. All Arrhenius bases contain a metal bonded to an OH. Look at Table L.

According to one acid-base theory, a water molecule acts as a base when it

• Donates H⁺

• Accepts H⁺

• Donates OH^-

• Accepts OH^-

Answer explanation

The Bronsted-Lowry acid-base theory is an alternate theory from Arrhenius. The alternate theory states that:

Acids Donate H⁺ in a reaction

Bases Accept H⁺ in a reaction

Given the balanced equation representing a reaction:

H₂PO₄^-(aq) + H₂O(l) --> H₃PO₄(aq) + OH^-(aq)

According to one acid-base theory, the H₂O(l) molecules act as

Answer explanation

Recall that Acids donate H⁺ in a reaction

Bases accept H⁺ in a reaction

In the given reaction, the H₂O is an acid because it loses an H:

H₂O --> OH^-

The H₂SO₄ acts as a base because it gains an H:

H₂SO₄^- --> H₃PO₄

When the pH of an aqueous solution is changed from 1 to 2, the concentration of hydronium ions in the solution is

• decreased by a factor of 2

• decreased by a factor of 10

• increased by a factor of 2

• increased by a factor of 10

Answer explanation

Recall that the pH scale measures the amount of H⁺ or H₃O⁺ ions in solution.

Low pH = More H⁺ (More acidic)

High pH = Less H⁺ (Less acidic)

The pH scale goes by factors of 10.

pH = 1, H⁺ = 10^-1 M or 0.1 M

pH= 2. H⁺ = 10^-2 M or 0.01 M

A pH of 2 is ten times less acidic than a pH of 1.

The H₃O⁺ concentration of a solution is 1 x 10^-12 mole per liter. This solution is

• Acidic and has a pH of 12

• Basic and has a pH of 10

• Acidic and has a pH of 10

• Basic and has a pH of 12

Answer explanation

Recall that pH measures the amount/concentration of H⁺ or H₃O⁺ ions.

The pH = the exponent of the H⁺ concentration.

H⁺ = 10^-12 , pH = 12

This pH is more than 7 so it is basic.

Which indicator is yellow in a solution with a pH of 9.8?

• methyl orange

• bromthymol blue

• bromcresol green

• thymol blue

Answer explanation

Look at Table M. The pH range for methyl orange is:

3.1-4.4 goes from red to yellow.

A pH of 9.8 is above 4.4 thus it will be yellow.

Anything below 3.1 would be red.

If equal volumes of 0.1 M NaOH and 0.1 M H₂SO₄ are mixed, the resulting solution will contain

Answer explanation

Recall that a strong acid and base will react with each other to produce water and a salt.

In this case:

Acid + Base ---> Water + Salt

H₂SO₄ + 2 NaOH --> 2H₂O + Na₂SO₄

Tags

NGSS.HS-PS1-7

In a neutralization reaction, an aqueous solution of an Arrhenius acid reacts with an aqueous solution of an Arrhenius base to produce

• an ether and water

• an ether and an alcohol

• a salt and water

• a salt an an alcohol

Answer explanation

A Neutralization reaction is a double replacement reaction between a strong acid and base that forms water and a salt.

A student neutralized 16.4 mL of HCl by adding 12.7 mL of 0.620 M KOH. What was the concentration of the HCl acid?

• 0.168 M

• 0.480 M

• 0.620 M

• 0.801 M

Answer explanation

This is an acid-base titration. Use the equation on the back of the reference table:

M_A x V_A = M_B x V_B

Note that HCl is the acid

Note that KOH is the base

M_A x 16.4 mL = 0.620 M x 12.7 mL

16.4 M_A = 7.874

M_A = 0.480 M

Tags

NGSS.HS-PS1-7