CHEM 1000 Lecture Notes - Lecture 7: Magnesium Hydroxide, Logarithmic Scale, Conjugate Acid

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peachreindeer167

6 Apr 2016

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Document Summary

Acids and bases are a specific set of compounds that react together in predictable ways. There are a few different ways to consider acids and bases, but we will use the so-called br nstead-lowry. According to this theory, acids and bases work via the transfer of a proton (h+). Since this proton transfer must occur in some medium, all acid/base reactions that we will examine are taking place in an aqueous environment (the compounds are dissolved in water). We can see above that acids produce the hydronium ion (h3o+) in water while bases produce the hydroxide ion (oh-). When an acid gives up its proton, it turns into its conjugate base. The compound that accepted the proton becomes a conjugate acid. Most often in this course we will assume that acids/bases undergo proton transfer with h2o molecules, as seen above. Example - for each of the species below, create the required chemical equation and label the conjugate pairs. a) b)

Related Questions

For conjugate acid-base pairs, how are Ka and Kb related?

Consider the reaction of acetic acid in water:

CH₃CO₂H (aq) + H₂O (l) ⇌ CH₃CO₂⁻ (aq) + H₃O⁺ (aq) where Ka = 1.8 × 10⁻⁵

Which two bases are competing for the proton?
Which is the stronger base?
In light of your answer to part b. why do we classify the acetate ion (CH₃CO₂⁻) as a weak base? Use an appropriate reaction to justify your answer.
In general, as base strength increases, conjugate acid strength decreases. Explain why the conjugate acid of the weak base NH₃ is a weak acid.

To summarize, the conjugate base of a weak acid is a weak base and the conjugate acid of a weak base is a weak acid (weak gives you weak). Assuming Ka for a monoprotic strong acid is 1× 10⁶, calculate Kb for the conjugate base of this strong acid.

Why do conjugate bases of strong acids have no basic properties in the water?

List the conjugate bases of the six common strong acids.

To tie it all together, some instructors have students think of Li⁺, K⁺, Rb⁺, Cs⁺, Ca²⁺, Sr²⁺, and Ba²⁺ as the conjugate acids of the strong bases LiOH, KOH, RbOH, CsOH, Ca(OH)₂, Sr(OH)₂, and Ba(OH)₂. Although not technically correct, the conjugate acid strength of these cations is similar to the conjugate base strength of the strong acids. That is, these cations have no acidic properties in water; similarly, the conjugate bases of strong acids have no basic properties (strong gives you worthless). Fill in the blanks with the correct response. The conjugate base of a weak acid is a_____base. The conjugate acid of a weak base is a_____acid. The conjugate base of a strong acid is a_____base. The conjugate acid of a strong base is a_____ acid. ( Hint: Weak gives you weak and strong gives you worthless.)

periwinklegoat463

QUESTION 1

Which of the following substances is most acidic?

		Cowâs milk - pH 6.6
		Apple juice - pH 3.0
		Tomato juice - pH 4.5
		Distilled water - pH 7.0

2 points

QUESTION 2

A buffer is a substance that converts:

Alkaline solutions to neutral solutions.

Acidic solutions to alkaline solutions.

Strong bases or acids to weak bases or acids.

Acidic solutions to neutral solutions.

QUESTION 3

How does a solution of pH 7 compare to a solution of pH 10?

		pH 7 has more OH^- ions
		pH 7 is more basic
		pH 7 has a higher pH
		pH 7 has more H⁺ ions

2 points

QUESTION 4

According to the Arrhenius Theory of acids and bases, a base is:

A substance that decrease the amount of hydroxide ions present.

A substance that increases the amount of hydroxide ions present when it is dissolved in water.

A substance that increase the amount of hydrogen ions present.

A substance that increases the amount of hydrogen ions present when it is dissolved in water.

QUESTION 5

Which of the following are true regarding acid-base titrations?

		They are used to determine the concentration of an unknown acid or base.
		The acid or the base must be a standard solution with a known concentration
		The standard solution is titrated into the chemical with the unknown concentration.
		All of the above are true regarding acid-base titrations.

2 points

QUESTION 6

Which of the following is not an example of a neutralization reaction?

HCl + NaOH NaCl +H₂O

2 NaOH + H₂CO₃ Na₂CO₃ +2 H₂O

H₂SO₄ + 2 NH₄OH (NH₄)₂SO₄ + 2 H₂O

2 AgNO₃ + Zn 2Ag +Zn(NO₃)₂

QUESTION 7

Which acid base theory defines an acid as a proton donor and a base as a proton acceptor?

		Arrhenius Theory
		Bronsted-Lowery Theory
		Conjugate Pairs Theory
		Lewis Theory

2 points

QUESTION 8

The Arrhenius Theory states that acid-base reactions create a solution composed of a water and a salt. This is because mixing an acidic and basic solution together yields:

A neutral solution

A solution with a pH at or near 7

Both A and B are correct

QUESTION 9

Which of the following correctly defines a standard solution?

		A solution which always has the same molecular geometry.
		A solution in which the concentration is precisely known.
		A solution in which the volume is precisely known.
		A solution which always has different levels of solutes and solvents.

2 points

QUESTION 10

Acids naturally present in food are generally safe to eat because they are usually:

		Concentrated
		Dilute
		Weak
		Strong

None of the above are correct

1. Identify the following substances as a Brønsted-Lowry base, a Brønsted-Lowry acid, or neither.

2.Enter the formulas of the conjugate bases of the following Brønsted-Lowry acids.

$H C l O_{4}$ Express your answer as a chemical formula.

- $({C H}_{3})_{2} {N H}_{2}^{+}$ Express your answer as a chemical formula.

- $H_{2} S$ Express your answer as a chemical formula.

- $H S e O_{3}^{-}$ Express your answer as a chemical formula.

3.Based on the $K_{a}$ values in the table, rank the following solutions in order of decreasing $p H$ : 0.10 $M$ $H C O O H$ , 0.10 $M$ $H F$ , 0.10 $M$ $H_{2} {C O}_{3}$ , 0.10 $M$ ${H S O}_{4}^{-}$ , and 0.10 $M$ ${N H}_{4}^{+}$ .