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A Level Chemistry (OCR B Salters) > The Chemical Industry > Flashcards

The Chemical Industry Flashcards

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1
Q

What type of chemistry do many nitrogen compounds + ions play an important role in?

A

Soil chemistry

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2
Q

What is the systematic name, appearance, and oxidation state of nitrogen in the compound N2O?

A

Dinitrogen oxide

+1

Colourless gas

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3
Q

What is the systematic name, appearance, and oxidation state of nitrogen in the compound NO?

A

Nitrogen oxide

+2

Colourless gas

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4
Q

What is the systematic name, appearance, and oxidation state of nitrogen in the compound NO2?

A

Nitrogen dioxide

+4

Brown gas

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5
Q

How is nitrogen (II) oxide formed from nitrogen?

A

N2 (g) + O2 (g) → 2NO (g)

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6
Q

How is nitrogen (IV) oxide formed from nitrogen (III) oxide?

What colour is the product?

A

2NO(g) + 2O2 (g) → 2NO2 (g)

Brown gas formed

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7
Q

Which nitrate do anaerobic bacterua reduce during respiration?

A

Nitrate (V)

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8
Q

What is the equation/sequence for anaerobic respiration in nitrogen-respiring bacteria?

A

NO2-(aq) → NO(g) → N2O(g) → N2 (g)

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9
Q

Why is ammonia able to act as a base?

A

Lone pair is able to accept H+ to become ammonium ion

NH3 + H+ → NH4+

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10
Q

What is nitrate (V) often known as?

A

Just nitrate

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11
Q

What is the molecular formula, bond angle, and diagram for nitrate (V) ions?

A

NO3-

120º - Triangular Planar

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12
Q

What are the properties of nitrate (V) ions?

A

Lone pairs form dative covalent bonds to O therefore increases oxidation no.

Very soluble in water

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13
Q

What is the molecular formula, bond angle, and diagram for nitrate (III) ions?

A

NO2-

120º - Triangular planar

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14
Q

What are the properties of nitrate (III) ions?

A

Very soluble in water.

Can use lone pair to form dative covalent bonds

2 ressonance forms

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15
Q

What are the properties of diatomic nitrogen?

A

Very strong triple bond - low reactivity.

High bond enthalpy.

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16
Q

Why is it not possible to test for compounds containing nitrate (V) or ammonium ions using precipitation?

What type of tests must be used instead?

A

They are all soluble

Must use tests involving formation of ammonia gas instead

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17
Q

What is the oxidation state of nitrogen, dot-and-cross diagram, molecular shape, and bond angle for ammonia?

A

-3

Trigonal pyrimidal

107º

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18
Q

What is the oxidation state of nitrogen, dot-and-cross diagram, molecular shape, and bond angle for ammonium?

A

-3

Tetrahedral

109.5º

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19
Q

Describe the test for ammonium ions

A

Substance being tested warmed with added NaOH.

If ammonium present, ammonia gas formed + will turn damp red litmus blue

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20
Q

What is the equation for the test for ammonium ions?

A

NH4+(aq) + OH-(aq) → NH3 (g) + H2O(l)

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21
Q

What is the test for nitrate (V) ions?

A

Added NaOH + spatula of Devarda’s alloy (mis of Cu, Al, Zn) + heat gently

Ammonia gas formed + will turn damp red litmus blue

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22
Q

Other than using damp red litmus, how can you test for ammonia gas?

A

Using conc. HCl as when fumes mixed produces white ammonium chloride gas

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23
Q

What are the interconversions of nitrogen compounds important in maintaining?

A

The balance of nutrient ions (e.g. nitrate (V)) in the soil

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24
Q

Give the definition of a catalyst

A

Substance that speeds up the rate of reaction by providing an alternate reaction pathway with a lower Ea

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25
What is the equation for Kc?
[C]c[D]d [A]a[B]b AKA **P**roducts over **R**eactants
26
If the **concentration** of reactant(s) is changed, how is the **position of equilibrium**, **Kc**, and **rate** affected?
The **position** of equlibium is **changed** to **oppose change** - favours side with lower conc. **Kc** is **unchanged** The **rate** is **changed** as only rate at which equilibrium reached changed.
27
If the total pressue of a reaction is changed, how is the **position** of equilibrium, **Kc**, and **rate** affected?
**Position** of equilibrium **may change** in order to keep ratio of reactants + products same ## Footnote **Kc unchanged** **Rate may change**
28
If the the temperature of a reaction is changed, how is the **position** of equilibrium, **Kc**, and **rate** affected?
The **position** of equilibrium will **change** to favour the endo/exo side depending on if temp increased/decreased **Kc** will **change** (temp only factor that changes it) **Rate changed** due to position changing
29
How does a **catalyst** affect the **position** of equilibrium, **Kc**, and **rate**?
**Position** of equlibrium is **unchanged** **Kc unchanged** Only **rate** at which equilibrium reached **changed**, **not composition** (Kc)
30
What is the only factor that affects the magnitude of Kc?
Temperature
31
How can the units of Kc be found?
By substituting them into the equilibrium equation
32
What is it important to remember when calculating the units for Kc?
Must be calcuted in every case (won't necessarily be the same) May have **no units**
33
How may mol-2dm6 also be written?
1/(moldm-3)2
34
What techniques can be used to determine equilibrum constants/how?
First necessary to **determine the conc. substances involved** e.g. by **titration** if one substance is **acidic** **Conc other substances** can then be **deduced from molar ratio**
35
Aside from titration, what other experimental techniques can be used to determine equilbrium constants?
**Spectroscopic** or **calorimetric** methods
36
What is stoichiometry?
**Molar ratio** of **reactants + products** in a chemical equation
37
What general equation can be used to calculate rate of reaction?
change in property (e.g conc reactant) / Time taken
38
What are the units for rate of reaction usually?
**moldm-3s-1** (applies if change in conc. of smth being measured)
39
What **characteristics**/changes in a reaction can be monitored to identify/**measure rate directly**? **How** can they be monitored?
**Vol. gas** evolved from a **gas syringe** **Mass change** using a **balance** **pH change** using a **pH meter** **Colour changes** using a **colorimeter**
40
Complete the sentence: Quenching uses ____ \_\_\_\_\_ as conc. reactants/products determined via titration
Chemical analysis
41
What quenching is and how it can be used to determine rate?
Effectively stops progress of reaction by **slowing rate down suddenly**. Allows composition/progress of reaction to be analysed (e.g. by titration) Can be done by adding large amounts **water** or **neutralising**
42
Describe how colorimetry can be used to determine the concentration of an unknown sample
* Make up series of **standard solutns** of **known conc** * Select **filter** with **complimentary colour** to test solutns * **Zero** the colorimeter with **pure solvent** (e.g water) * Measure the absorbance of the standard solution + plot a **calibration curve** showing conc vs. abs. * Measure the **absorbance** of the **test solutn** + read off the conc from the calibration curve
43
Describe the structure of a colorimeter
Narrow bean of light Filter/diffraction grating selects light of wavelengths absorbed by solutn (is complimentary colour) Solution under test Photocell Sensitive meter
44
What is the overall order of reaction?
The sum of orders of reaction for each individual reactant
45
What is the rate equation?
Mathmatical equation which enables the rate of reaction to be calculated In the form: rate = k[A]m[B]n
46
What cannot be used to determine the rate equation? What must be used instead?
Cannot predict rate equation from **balanced equation** Must use **experimental data**
47
If a reactant is **zero order**, what is the effect of doubling the conc of the reactant on the rate of reaction?
No effect rate ∝ [A]0
48
If a reactant is first order, what is effect does doubling its conc have on the rate of reaction?
**Rate doubled** when conc doubled rate ∝ [A]1
49
If a reactant is second order, what happens to the rate of reaction when its conc is doubled?
**Rate quadrupled** when conc doubled rate ∝ [A]2
50
If a substance is zero order, what doesn't it appear in/befre?
The rate determining step
51
How can k be calculated from the rate equation?
By rearranging to give: rate / [A]m[B]n *Must also calculate **units***
52
Increasing temp. of a reaction increases its rate. Which part of the rate equation does this effect and why?
Effects k as doesn't effect [A]/[B]
53
What are the units for a zero order reaction?
k = moldm-3s-1
54
What are the units for a first order reaction?
k = s-1
55
What are the units for a second order reaction?
k = mol**-1**dm**3**s-1
56
Other than reactants and k, what might appear in the rate equation?
Catalysts
57
What is the formula of the Arrhenius equation?
k = A-Ea/RT
58
What can be used to determine the value of k in the rate equation?
The Arrhenius equation
59
What equation do you get if you take natural logs of the Arrhenius equation? How can this be rearranged to be in the form y = mx + c?
lnk = lnA - Ea/RT In the form y = mx + c: **lnk = -Ea/RT x 1/T + lnA**
60
What does **T** stand for in the Arrhenius equation? What are its units? Is it variable or constant?
Temperature **K**elvin **Variable**
61
What does **Ea** stand for in the Arrhenius equation? What are its units? Is it variable or constant?
Activation enthalpy ## Footnote **Jmol-1** **Variable**
62
What does **e** stand for in the Arrhenius equation? What are its units? Is it variable or constant?
Mathmatical constant (the exponential constant) No units Constant...
63
What does **A** stand for in the Arrhenius equation? What are its units? Is it variable or constant?
The **frequency factor** No units **Constant**
64
What is the frequency factor/A in the Arrhenius equation?
Include factors such as **frequency of collisions** + **orientation** of molecules
65
How can you plot a graph using the Arrhenius equation experimentally? What values can this graph be used to work out?
Can be used to calculate **Ea** + **A** To plot, must **calculate k at different temperatures** Then convert these values to **lnk** & **1/T** to plot graph using **lnk = -Ea/R x 1/T = lnA**
66
By how much does a catalyst roughly decrease the value of Ea? Why?
By roughly **10kJmol-1** As it significantly increases the **number of collisions with energy \> E**a therefore **increases rate**
67
When determining the rate equation experimentally, what must be kept constant? What will change if it is not kept constant?
**Temperature** Otherwise **k** will change
68
How can you determine the rate of reaction using the initial rate method?
Graphs drawn plotting **change in property over time**. **Tangent** drawn to **t=0** giving initial rate. Can also draw another graph with **conc2 vs time** to check if **second order**. Once several graphs drawn for different concs of reactant used in experiment, must draw final graph with **initial rate vs conc**.
69
How can you use the progress curve method to determine the rate of reaction?
Graph showing change in **conc reactant over time** plotted **Series of tangents** drawn at **different concs**, giving **rate of reaction at different times** Can then use **initial rate** method to find order by plotting **initial rate over conc**.
70
What does a graph of initial rate over concentration look like for a zero order reaction?
Straight line
71
What does a graph of initial rate over concentration look like for a first order reaction?
Initial rate + conc. directly proportional
72
What does a graph of initial rate over concentration look like for a second order reaction?
Can either be shown as **initial rate and conc2** being directly proportional (straight line) or as rate quadrupling when conc doubled (shown in pic)
73
How can you use the reciprocal to measure initial rate?
Done by measuring **how long to produce a small, fixed amount** e.g. how long for enough precipitate to form to obscure cross Avg rate = amount of product formed to reach end point / Reaction time for product to form Means that **avg rate ∝ 1/t**. Can then **plot 1/t over concs** (after using several different concs in experiments) Must keep **volume constant**
74
What is half life?
The time taken for the concentration of a reactant to half also shown by **t1/2**
75
How can half life be used to determine the order of reaction?
Uses a graph showing **conc reactant over time** Work out how long it takes for conc. reactant to **half** then half again, etc. If half life **constant = first order**. **Not constant = second/zero order**
76
77
What does a graph showing conc. reactant over time look like for a zero order reaction?
Inversely proportional
78
What does a graph showing conc. reactant over time look like for a first order reaction?
79
What does a graph showing conc. reactant over time look like for a second order reaction?
Decreases more than first order
80
What is the rate determining step?
The slowest step of a reaction mechanism therefore determines the rate + speed of the overall reaction
81
What does the rate equation tell you about the RDS?
Which compounds (in the reaction) are involves in the RDS Can include catalysts
82
What does the order of reaction of each substance tell you about the RDS?
Tells you the no. **moles** involved in the RDS
83
What is an intermediate?
Chemical formed and then destroyed during the course of the reaction

A Level Chemistry (OCR B Salters) (12 decks)

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