Reactivity 3.1 Acids/Bases

Acids

100

What is the conjugate base of water when water acts as an acid?

OH^-

200

What is both the Bronsted-Lowry Definition and Arrhnius definition of an acid?

Proton donor

or

Releases H⁺ ions into solution

300

Which side of the pH scale is the acidic side? 

Give a number range.

Less than 7.

0-7

400

Describe the bond holding the hydrogen ion to the bromate ion.

HBrO₃

_{Acid strong/weak? Bond strong/weak?}

Weak acid, so it has a stronger bond.

In solution, all the H⁺ ions will NOT all fall off and could reattach

<-->  use double headed arrows

500

Identify the acid/base/conjugate acid/conjugate base

HPO₄^2- + H₂O <--> H₂PO₄^- + OH^-

Acid: H₂O              Conjugate Base: OH^-

Base:  HPO₄^2-        Conjugate Acid: H₂PO₄^-

Bases

100

What is the conjugate acid of water when water acts as an base?

H₃O⁺

200

What is the Arrhenius definition of a base?

What is the Bronsted Lowry definition of a base?

Can't remember which one is which? Say them both at least.

A: Releases OH^- ions

BL: H⁺ acceptor; takes H⁺ out of solution

300

What side of the pH scale is basic? Give a range.

More than 7.

7-14

400

Describe the bond holding the hydroxide ion to the sodium ion.

NaOH

_{base strong/weak? Bond strong/weak?}

Strong base, so it has a weaker bond.

In solution, all the OH^- ions will fall off and NOT reattach

-->  use single headed arrows

500

Identify the acid/base/conjugate acid/conjugate base

H₃PO₄ + NH₃ <--> NH₄⁺ + H₂PO₄^-

Acid: H₃PO₄    Conjugate Base: H₂PO₄^-

Base: NH₃       Conjugate Acid: NH₄⁺

Acid Base Reactions

100

1) predict the products 

2) balance the equation

Na + H₂SO₄ --> ?

2Na + H₂SO₄   -->  Na₂SO₄ + H₂

Metal + Acid --> Salt + H₂

Single replacement reaction

200

1) Predict the products

2) balance the equation

HCl + BaCO₃ --> ?

2HCl + BaCO₃ --> BaCl₂ + H₂O + CO₂

Acid + carbonate --> salt + H₂O + CO₂

300

1) Predict the Products

2) Balance the equation

H₃PO₄ + Ca(OH)₂ --> ?

2 H₃PO₄ + 3 Ca(OH)₂ --> Ca₃(PO₄)₂ + 6 H₂O

Acid + Base --> Salt + H₂O

400

When do you use normal arrows?       -->

When do you use equilibrium or double-headed arrows? <-->

normal - when the A/B does not reattach (STRONG acids/bases)

double headed - when the H⁺ or OH^- could reattach (WEAK acids/bases)

500

What is one way you can distinguish between strong and weak acids or bases?

reaction rate: strong = faster reaction

conductivity: strong = more conductive

pH: strong will be more acidic or more basic

pH Scale

100

The pH of a solution changes from 8 to 9.

A. the concentration of OH- decreases by 1 mole/L

B. the concentration of OH- decreases by 10 mol/L

C. the concentration of OH- increases by 1 mole/L

D. the concentration of OH- increased by 10 mole/L

D

The pH of a solution changes from 8 to 9.

The pH scale is logarithmic. every increase is a 10x change in concentration

8 --> 9 is getting more basic. [OH-] INCREASED

200

What is the concentration of H⁺ is in a solution that has a pH of 9.4?

UNITS ON YOUR ANSWER

3.98 x 10^-10     M    or   mol H⁺/L

[H⁺] = 10^-pH

300

What is the concentration of H+ in a solution with a pOH of 3.2?

1.58 x 10^-11

14 = pH + pOH

if pOH = 3.2, pH = 10.8

[H⁺] = 10^-pH

400

You have 50 mL of HCl at a pH of 5. 

You dilute it with 100 mL of water. 

What is the pH of your new diluted solution?

1) how much H+ did you start with?

[H+] = 10^-5 = 1x10^-5 mol H⁺/L

1x10^-5 mol H⁺/L  *   0.05 L =    5*10^-7 mol H⁺

2) We diluted the solution with 100mL, so the new solution has a total volume of 150 mL, or 0.15L

3) find new [H+]. Take moles H+, divide by L solution       [H+] =  5*10^-7 / 0.15L = 3.33*10^-6 M

4) Find pH     pH = -log[H+] = -log[3.33*10^-6 M]

pH = 5.48 

500

What does the pH scale actually measure?

How much H⁺ is in a solution.

[H+]

Titrations

100

Describe the color of phenolphthalein in different conditions.

Acidic - clear

Basic - prettiest pink around

200

WHY did we stop titrations at a pale pink color? Describe what is happening at the molecular level at that exact point in time.

At the equivalence point. 

H⁺ ions equal to OH^- ions;  pH 7

300

2HCl + Ca(OH)₂ --> H₂O + CaCl₂

When HCl is titrated with Ca(OH)2, it releases 0.034 moles of H⁺ ions. How many moles of OH^- ions are in the solution when it turns pale pink?

0.034 moles of OH- ions

It will take 2 moles of HCl to neutralize 1 mole of Ca(OH)₂, but the H⁺ ions still = OH^- ions at equivalence

400

What is the molarity of a KOH solution if 25 mL of it is neutralized by 31.7 mL of a 0.1 M HNO₃ solution?

M_aV_a=M_bV_b     Since 1:1 H⁺ to OH^- ratio

(0.1)(31.7)=M_b(25)

M_b = 0.13 M

500

H₂SO₄  + 2KOH --> 2H₂O + K₂SO₄

A 25mL sample of H₂SO₄ is neutralized by 27.4 mL of 1M KOH. What is the concentration of the acid?

Cannot use M_aV_a=M_bV_b  

Start calculations with 27.4 mL KOH.... 

0.0274 mol OH^- and H⁺

0.0137 mol H₂SO₄ / 0.025 L H₂SO₄ = 0.548 M H₂SO₄