Quiz 7: Titrations and Redox Reactions

Titration

The end results of _______________ tells you what is present in a solution and how much titrant is present

Equivalence Point

The _______________ of a titration is the point where the titrant is chemically equivalent to the analyte

Endpoint

The ____________ is the point where the indicator changes color, signaling the completion of the titration

Exact concentration of analyte

The goal of performing acid-base titrations is to find the ___________________

Concentration (M) = moles of analyte / volume of solution in liters

How do you calculate the concentration of an analyte after a titration?

HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)

1. Moles of analyte

0.03746L NaOH x (0.0775 mol NaOH/ 1 L NaOH) x (1 mol HCl/ 1 mol NaOH)

= 2.908 x 10^-3 mol HCl

2. Concentration → molarity (mol/L)

(2.908 x 10^-3 mol/ 0.02500L) = 0.116 M HCl

Acid-base titration: Determine the concentration of the analyte

HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)

In a 25.00mL solution of HCl (analyte) the titration of 0.0775M NaOH (titrant) requires 3.46mL to reach the endpoint

Mass % = (mass analyte/ mass sample) x 100%

What equation is used to solve for mass percentage?

1. Moles of analyte

0.0068L x (0.450 mol I2/ 1 L I2) x (1 mol H2O/ 1 mol I2)

= 0.006192 mol H2O

2. Mass percentage = (mass analyte/mass sample) x 100%

(0.112g H2O/ 0.100g berries) x 100% = 11.2% H2O

Acid-base titration: Determine the mass percentage of the analyte

2H2O + SO2 + I2 → H2SO4 + 3 HI

I2 → 6.88mL of 0.450 M in 0.100g berries

- oxidized

- reduced

A redox reaction involves the transfer of electrons, where one substance is ___________ and another is _____________

LEO → Loss of Electrons is Oxidation

GER → Gain of Electrons is Reduction

Determine the significance of the phrase below:

LEO the lion says GER

Oxidizing agent

The ______________ is the reactant that causes oxidation and contains the element that is reduced

Reducing agent

The ________________ is the reactant that causes reduction and contains the element that is oxidized

True

True or False:

A redox reaction is present when the oxidation state changes (oxidation numbers change)

1. all oxidation numbers add up to zero in a neutral compound

2. all oxidation numbers add up to the ionic charge in an ion

3. free elements = 0

4. Fluorine = -1

5.

Group 1 = +1

Group 2 = +2

Al = +3

6.

H + nonmetal = +1

H + metal = -1

7. Oxygen = -2

8. If no rules apply,

Group 17 = -1

Group 16 = -2

Group 15 = -3

List the general rules of interpreting oxidation numbers in order (8)

O2 and CaCl2 are neutral - will add up to 0

MnO4 2- and NH4+ are ions - will add up to ionic charge

Will the oxidation numbers for the compounds below add up to 0 or will it add up to its ionic charge?

O2

CaCl2

MnO4 2-

NH4+

True

True or False:

The oxidation number of Oxygen is usually -2, except when in a compound with fluorine or peroxides

Charge = 1 +

Oxidation number = + 1

Determine the charge and oxidation number:

Na+

Charge = 2 -

oxidation number = - 2

Determine the charge and oxidation number:

O2-

Charge = 3 +

oxidation number = + 3

Determine the charge and oxidation number:

Fe3+

Si oxidation number = -2 x +2 = -4 → +4

O oxidation number = -2

Determine the oxidation numbers:

SiO2

Cl oxidation number = -2 x +3 = -6 + (+5) = - 1

O oxidation number = - 2

Determine the oxidation numbers:

ClO3-

not in a compound →

oxidation number = 0

Determine the oxidation numbers:

Mg

Cl2

Mg2+Cl-

Mg oxidation number = +2

Cl oxidation number = - 1

Determine the oxidation numbers:

MgCl2

K+ = + 1

Mn = -2(+4) = -8 + (+1) = +7

O42- = - 2

Determine the oxidation numbers:

KMnO4

Na1+ = + 1

N = -2(3) = -6 + (+1) = +5

O2 = -2

Determine the oxidation numbers:

NaNO3

O is combined with a peroxide

H = +1

O = +1

Determine the oxidation numbers:

H2O2

Mg = 0

Mg = +2 → oxidized (get more + or less -)

H = + 1

H = 0

Cl = - 1

Cl = - 1 → reduced (gets less + or more -)

oxidizing agent → HCl (aq)

Reducing agent → Mg(s)

Determine the oxidation numbers and identify the oxidizing and reducing agents:

Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)

C = - 4

C = + 4 → oxidized

H = +1

H = +1

O = 0

O = - 2 → reduced

Oxidizing agent → O2(s)

Reducing agent → CH4(g)

Determine the oxidation numbers and identify the oxidizing and reducing agents:

CH4(g) + 2O2(s) → CO2(g) + 2H2O(g)

N = -2 x 5 = -10 + (+5) = +5

N = +5

O = -2

O = -2

Na = +1

Na = +1

H = +1

H = +1

C = -2 x 3 = -6 + (+1) + (+1) = +4

C = +4

False: Not a redox reaction, no change in oxidation state

True or false: the reaction below is a redox reaction

Determine the oxidation numbers:

N2O5(g) + 2NaHCO3(aq) → 2NaNO3(aq) + 2CO2(g) + H2O (l)

Si = +4

Si = 0 → reduced

Cl = -1

Cl = -1

Mg = 0

Mg = +2 → oxidized

Oxidizing agent → SiCl4(l)

Reducing agent → Mg(s)

Determine the oxidation numbers and identify the oxidizing and reducing agents:

SiCl4(l) + 2Mg(s) → 2MgCl2(s) + Si(s)

Ag = +1

Ag = 0 → reduced

N = +5

N = +5

O = -2

O = -2

Cu = 0

Cu = +2 → oxidized

Oxidizing agent →AgNO3(aq)

Reducing agent → Cu(s)

Determine the oxidation numbers and identify the oxidizing and reducing agents:

2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2Ag(s)

True

True or False:

Oxidation numbers are not the same as an ionic charge

1) +2

2) 0

3) 0

4) C = +2 O = -2

5) -1

6) 0

7) O = +2 F = -1

8) 0

9) P = +5 F = -1

P → x + -1(5) = 0

x = +5

Determine the oxidation numbers:

1) Ca2+

2) P4

3) Au

4) CO

5) F-

6) N2

7) OF2

8) F2

9) PF5

1) N = +2 O = -2

2)

x + -2(3) = -1

x - 6 = -1

x = +5

N = +5 O = -2

3) 0

4)

x + -1(3) = 0

x -3 = 0

x = +3

Cl = +3 F = -1

5)

x + -2(4) = -2

x -8 = -2

x = +6

Mn = +6 O = -2

6) H = +1 O = -1

7)

x + -3 = -1

x = +2

C = +2 N = -3

8)

2x + -2(7) = -2

2x -14 = -2

2x = +12

x = +6

Cr = +6 O = -2

9)

2x + -2 = 0

2x = +2

x = +1

N = +1 O = -2

Determine the oxidation numbers:

1) NO

2) NO3-

3) O2

4) ClF3

5) MnO4 2-

6) H2O2

7) CN-

8) Cr2O7 2-

9) N2O

1)

x + -2(3) = -1

x - 6 = -1

x = +5

Cl = +5 O = -2

2)

x + -1(3) = 0

x -3 = 0

x = +3

Fe = +3 Cl = -1

3)

x + -3 = 0

x = +3

N = +3 Cl = -1

4)

x -2(2) = 0

x -4 = 0

x = +4

C = +4 O = -2

5)

x + -2(4) = -2

x - 8 = -2

x = +6

S = +6 O = -2

Determine the oxidation numbers:

1) ClO3-

2) FeCl3

3) NCl3

4) CO2

5) SO42-

1) Na = +1 Cl = -1

2) Na = +1 O = -1

3) Ca = +2 C = -1

4) H = +1 Cl = -1

5) H = +1 F = -1

6) Li = +1 H = -1

Determine the oxidation numbers:

1) NaCl

2) Na2O2

3) CaC2

4) HCl

5) HF

6) LiH