Chemistry Pop-Quiz

Lucas10101

Activation Energy is the minimum energy which colliding particles need for a complete reaction to occur.
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Define:
(i) Heat of Formation.
(ii) Hess's Law
(iii) Law of Conservation of Mass

Your Man

heat of formation of is the heat change when a compound is formed from its elements.
Law of conservation of mass: energy cannot be created or destroyed, it can only be converted from one form to another,
Hess law: the heat change in the formation of a compound is the same if it takes place in one or several stages,

not sure about hess law, is that right?

State two differences between the modern periodic table and that devised by mendeleev.

theliam

Your Man wrote:

State two differences between the modern periodic table and that devised by mendeleev.

1-the actinides
2-the rare elements

nedward

Question? Feck it, he's logged off.

Give three industrial or natural uses of carboxylic acids.

bebop!

1.Food Perseratives e.g Benzoic Acid
2.Ethanoic Acid used to manufacture cellulose acetate which is used in making camera films.

^^ok after this one im bluffing

3.Methanoic acid used by ants and nettles to sting people!!!

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Q.Name 4 ways to increase the octane number of a fuel??

Lucas10101

(i) Adding Oxygenates i.e MTBE ( Methyl Tertiary Butyl Ether )
(ii) Catalytic Cracking
(iii) Isomerisation
(iv) Dehydrocyclisation

nedward

Dehydrocyclisation
Addition of oxygenates
Addition of lead compounds
Isomerisation


What produces the colours in fireworks?

EDIT Dammit!

Lucas10101

Sodium produces the yellow colour and potassium produces the lilac colour among other elements used in fireworks. These colours arise from these atoms gaining energy from the heat supplied. They jump from the ground to excited state and drop back after a short period to lose energy given by the equation e=hf, this energy is released in terms of a photon of light in the visible Balmer series. We see this light in the firework when the heat is supplied.

Explain the reasons in terms of delocalised electrons and sigma and pi bonds why Benzene is unreactive considering it's supposed to be exceptionally unsaturated?

nedward

Each carbon atom has one sigma and two pi bonds. Thus, Benzene has one "unpaired" electron, which joins with the electron cloud of the next Carbon atom to form a doughnut-shaped cloud above and below the carbon ring. These electrons do not belong to any particular atom, but are said to be delocalised, giving the benzene extra stability. etc.

Nice explanation Lucas.

Anyway, who invented the mass spectrometer and give the principle on which it operates.

Lucas10101

Francis William Aston

Works on the principal that atoms can be separated according to their masses when made a gas that passes through a magnetic field to produce a Mass Spectrum.

Explain why Carboxylic Acids have Higher Boiling points than Alcohols?

bebop!

There is a greater amount of hydrogen bonding in carboxylic acids than alcohols hence the higher boiling points.


Q.Name the scientist who identified cathode rays as sub atomic particles.

nedward

Carboxylic acids form dimers of two molecules, which raises their boiling points.
Hydrogen bonding between molecules.

Explain why carboxylic acids act as acids.

Lucas10101

Carboxylic Acids act as Acids for two main reasons:

1. Inductive Effect
The C which is a region of positive charge attracts the negative Oxygen from the -OH Group. This electron grabbing is called the Inductive Effect and draws electrons from the OH- group, this facilitates the ionisation of the H which shows that COOH can lose a proton readily. Hence, this means it's acting as an Acid.

2. Carboxylate Ion Stability
A Carboxylic Acid breaks up into RCOO- and H+, that former is called the Carboxylate Ion. Instead of negativity being localised on the Oxygen from the C-O-H group, it's spread across the three atoms. This structure is called a Resonance Hybrid and gives it extra stability. The fact it's so stable is the motive for it to lose a proton, and they lose protons readily thus are acting as acids.

Why does Ethanol act as an Acid?

Thomas_S_Hunterson

Lucas10101 wrote:

Why does Ethanol act as an Acid?

Inductive effect again I presume

Give an example of when water acts as an acid.

Give an example of when water acts as a base.

Substances such as water which exhibit both acidity and basicity are referred to as what?

Lucas10101

Third answer is Amphoteric or Amphiprotic.

The First answer is : In a reaction between HCL and Water, HCL donates a proton, and since Water accepts a proton, it's called a Base.
HCL + H2O -> H3O+ + CL-

The Second answer is : In a reaction between Ammonia and Water, Ammonia accepts a H+ ion to form NH4+. Thus Water acts as an Acid.
NH3 + H2O -> NH4+ + OH-

State Boyles and Chalres Law.

me2gud4u

what a horrible exam i was banking on A1 be lucky with a b1 now and i need every point i can get