College Chemistry : College Chemistry

Study concepts, example questions & explanations for College Chemistry

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Example Questions

Example Question #81 : Reactions

Which of the following is a weak base?

Possible Answers:

Correct answer:

Explanation:

Strong acids and bases are those that ionize completely in solution. In contrast, weak acids and bases ionize only partially in solution.

, hydrogen fluoride, is an example of a very strong acid. In solution, it dissolves completely to form  and 

, sodium hydroxide, is an example of a very strong base. In solution, it dissolves completely to form  and .

, acetic acid, is an example of a weak acid. In solution, it dissolves partially to form  and .

, ammonia, is an example of a weak base. In solution, it accepts a proton to form  and .

Example Question #31 : Acid Base Reactions

 reacts with  in aqueous solution according to the chemical equation provided. If it took  of a   solution to titrate  of an  solution, what was the concentration of original  solution?

Possible Answers:

Correct answer:

Explanation:

Using the concentration of  as a conversion factor, we can convert the volume of  to moles by dimensional analysis:

At the equivalence point of the titration:

Example Question #171 : College Chemistry

Determine the acid dissociation constant expression for the given reaction.

Possible Answers:

Correct answer:

Explanation:

Acid dissociation constant which is denoted as  is the equilibrium constant for the ionization of an acid. Therefore, the numerator contains the product of the concentrations of the substances on the product side of the chemical equation. The denominator contains the product of the concentrations of the substances on the reactant side of the chemical equation.   is omitted in the acid dissociation constant expression because as the solvent it is in excess and therefore the change in its concentration is negligible in comparison to the other substances in solution.

Example Question #31 : Acid Base Reactions

Identify the Bronsted-Lowry acid in the following equation:

Possible Answers:

Correct answer:

Explanation:

Recall that a Bronsted-Lowry acid donates a proton. From the equation, we can see that  becomes , which it lost an , or a proton. Thus, water must be the Bronsted-Lowry acid.

Example Question #1 : Lewis, Brønsted Lowry, And Arrhenius Definitions

Identify the Lewis Base in the following reaction:

Possible Answers:

Correct answer:

Explanation:

Recall that a Lewis base accepts a proton, while a Lewis acid donates a proton. Looking at the equation, we can see that  becomes . Since  accepted a proton, it must be the Lewis base.

Example Question #3 : Lewis, Brønsted Lowry, And Arrhenius Definitions

Which type of acid is defined by its ability to produce hydrogen ions in aqueous solution?

Possible Answers:

Bronsted-Lowry acid

None of these

Lewis acid

Arrhenius acid

Correct answer:

Arrhenius acid

Explanation:

There are three main definitions for acids and bases: the Lewis acids and bases, Bronsted-Lowry acids and bases, and Arrhenius acids and bases.

A Lewis acid is a species which can accept an electron pair from a donor. An example of a Lewis acid is ; as a cation, it can accept an electron pair. A Lewis base is a species which can donate an electron pair. An example of a Lewis base is ; as an anion, it can donate an electron pair.

A Bronsted-Lowry acid is a species which can donate a proton. An example of a Bronsted-Lowry acid is , which can donate its hydrogen ion. A Bronsted-Lowry base is a species which can accept a proton from a donor. An example of a Bronsted-Lowry base is , which can accept a hydrogen ion in order to become water.

An Arrhenius acid is a species which releases hydrogen ions into solution. An example of an Arrhenius acid is . When this compound dissolves in aqueous solution, it produces  and . An Arrhenius base is a species which releases hydroxide ions into solution. An example of an Arrhenius base is . When this compound dissolves in aqueous solution, it produces  and .

Example Question #34 : Acid Base Reactions

What is the pH of a   solution?

Possible Answers:

Correct answer:

Explanation:

PH is defined as , where  is hydronium concentration). In order to do this we simply take :

=

Example Question #1 : Lewis, Brønsted Lowry, And Arrhenius Definitions

 

According to the Brønsted-Lowry definition of acids and bases, which species in the reaction are acids?

Possible Answers:

There are no acids in the reaction

Correct answer:

Explanation:

Remember a Brønsted-Lowry acid is defined as a proton donor.

In the forward reaction,  is a proton donor. In the backward reaction,  is the proton donor.

The acids in this reaction are  and .

Example Question #171 : College Chemistry

The literature value for the melting point of a given compound is 240 degrees Celsius. A scientist uses the melting point apparatus to experimentally measure the compound's melting point at 230 degrees Celsius. What is the scientist's percent error? 

Possible Answers:

Correct answer:

Explanation:

The percent error is given by the following formula:

 

In this case, the theoretical value is 240 degrees Celsius, and the actual value is 230 degrees Celsius. The percent error is thus calculated to be 4.16 %. The calculation is as follows:

Example Question #172 : College Chemistry

A scientist wants to separate and purify a small, positively charged protein. Which of the following techniques might be employed to accomplish this task?

Possible Answers:

Reverse phase chromatography

Normal phase chromatography

Size exclusion chromatography and cation exchange chromatography

None of these

Thin layer chromatography

Correct answer:

Size exclusion chromatography and cation exchange chromatography

Explanation:

Size exclusion chromatography is a good technique for separating proteins based on size due to tiny pores in the beads in the column (the smaller proteins will elute out last). Cation exchange chromatography is a good technique for separating proteins based on charge due to negatively charged beads in the column (the positively charged molecules will elute out last). Normal and reverse phase chromatography are methods of separation based on a molecule's polarity; in normal phase chromatography, a nonpolar mobile phase is employed so that polar, hydrophilic molecules elute last. The opposite is true for reverse phase chromatography - a polar, aqueous mobile phase is used and any nonpolar molecules tend to adsorb to the hydrophobic beads, causing them to elute out last. Thin layer chromatography is not a good method of purifying substances, rather, it is a better indicator of reaction progress via elucidation of the retardation factor, .

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