Acid & Bases Flashcards
What are ssome common acids and their uses?
Acetic acid - flavouring; preservative
Citric acid: flavouring
Phosphoric acid: rest remover
Boric acid: ,o;d amtosptic/insecticide
Hydrochloric acid: Brick / ceramic tile cleaner
Sodium hydroxide: oven cleaner
Ammonia: Household cleaner
Sodium carbonate: Water softener, grease remover
sodium hydrogen carbonate: Fire extinguisher, backing powder
What does Arrhenius define an acid as?
H+ producer in aqueous solution
What does Arrhenius define a base as?
OH- produced in aqueous solution
What does Bronsted Lowry define an acid as?
Proton (H+) donor
What does Bronsted Lowry define a base as?
Proton (H+) acceptor
What is H+?
H+ is short for H3O+ in the reaction which is hydronium
What is a strong acid/base?
A strong acid or base has equilibrium to the right (I.e. it is fully ionised/dissociatied). (Complete dissociation)
What is a weak acid/base?
A weak acid or base has equilibrium to the left (partial ionisation/dissociation)
What is Ka and Kb?
The acid dissociation constant (Ka) is a quantitative measure of the strength of an acid in solution while the base dissociation constant (Kb) is a measure of basicity—the base’s general strength.
Uses the same formula as in Keq, and ignore liquid and solid states
What is a conjugate acid
A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid gives a proton (H +) to a base—in other words, it is a base with a hydrogen ion added to it, as it loses a hydrogen ion in the reverse reaction.
I.e. NH4+ is the conjugate acid of NH3
What is a conjugate base
A conjugate base is basically an acid that lost its hydrogen ion. Its formula is the acid formula, minus the hydrogen ion.
I.e. NH3 is the conjugate base of NH4+
What is meant by the autoionisation of water?
It is the ability of water to react with itself and form a hydronium and hydroxide ion. The ability of water to react with itself is known as autoionisation.
What is the ionisation/equilibrium constant for autoionisation of water?
Kw = 10^-14 = [H3O+][OH-]
What is [H+] in a neutral solution?
[H+] = [OH-] = 1.0 x 10^-7
What is [H+] in a acidic solution?
[H+] > 1.0 x 10^-7
What is [H+] in a basic solution?
[H+] < 1.0 x 10^-7
What is the pH equation?
-log[H+]
What is the pOH equation?
-log[OH-]
What is the relationship between pH and pOH?
pH + pOH = 14
What pH is acidic?
pH < 7
What pH is neutral?
pH = 7
What pH is basic?
pH > 7
What is a strong acid or base?
these completely ionise in water
Equilibrium is completely to the right –> Ka or Kb = infinity
What are some examples of strong acids (6)
H2SO4 (Sulfuric acid)
HCl (Hydrochloric acid)
HBr(Hydrobromic acid)
HI ( Hydroiodic acid)
HNO3 (Nitric acid)
HClO4 (Perchloric acid)
What are some examples of strong bases?
All hydroxides of groups 1 and 2 except for Be
If there is 0.1M of a strong acid/base, what would the concentration of the hydroxide or hydronium ions be after dissociation (assuming it is monoprotic)
0.1M as well
What is a weak acid/base?
If they are weak, they don’t completely ionise in water (partially ionise/dissociate)
How do we calculate pKa?
-log(Ka)
How do we calculate pKb?
-log(Kb)
What is the relationship between Ka and pKa?
The larger the value of Ka, the stronger the acid and the lower the value of pKa
Can we assume small change? What is the condition (rarely needed)
Yes we can assume small change, however, the general accepted rule is that small change needs to be maximum 5% of the original subtraction (i.e. 0.1-x, it can be a maximum of 0.005)
What is the relationship between Ka, Kb and Kw?
Ka x Kb = Kw = 10^-14
What is the relationship between pKa and pKb?
pKa + pKb = 14
Why does Ka decrease as we remove hydrogens?
because ionization happens in steps because as protons are removed, the remaining negatively charged ions experience increased repulsion, making it harder to remove additional protons
Harder to remove charge against increased negative charge
How can you tell if a salt is an acidic, neutral or basic given that it is a salt of a weak acid or base?
We look at what creates the salt. If there is a strong acid/base, the salt will be a acid/basic depending on which one was strong in creating the salt. I.e. for NH4Cl, it is a salt of NH4OH (weak base) and HCl (strong acid)
As the acid “wins”, the pH < 7 –> the salt is acidic
However, the more refined:
What are the general rules for acidic, neutral or basic salts?
Whenever an acid and a base react, they have the potential to form a salt. For example, when sodium hydroxide reacts with hydrochloric acid in water, they form sodium chloride, a salt. Salts come in three different forms: basic salts, neutral salts and acid salts. When a strong base reacts with a strong acid, a neutral salt is formed. When a strong base reacts with a weak acid, a basic salt is formed. When a strong acid reacts with a weak base, an acidic salt is formed.
What is the school’s method of classifying a certain salt as either acidic, neutral or basic?
- State what the salt ionises to form
- State which ion is neutral (which can be determined by which came from a strong acid or base), and state that it cant hydrolyse further
- State that the other ion (which came from a weak acid or base) comes from a certain weak acid or base, and that it will undergo hydrolysis in water
- Concluding statement: Excess OH- or H+ in solution makes solution (basic/acidic). Thus pH is greater or less than or equal to 7 (depending)
What is the common ion effect?
Used to describe the effect on an equilibrium when one or more species in the reaction is shared with another reaction –> results in shifting equilibrium properties
I.e. when an ion is the same as ions already existing in the equilibrium reaction
Adding a common ion prevents the weak acid or weak base from ionizing as much as it would without the added common ion. The common ion effect suppresses the ionization of a weak acid by adding more of an ion that is a product of this equilibrium.
What is a buffer system?
It is a solution containing both a weak acid/base and its conjugate acid/base on opposite sides of the reaction. Buffer systems are able to withstand changes in pH when acid or base (limited amounts) are added
How do we do buffer system and pH change questions, where a random substance is added?
Technically we use two ice tables, where the thing that is added is used up, and the system shifts to adjust for this, and each reactant and product is adjusted for this (check example in ppt 31)
And then solve the next ice table kind of thing
What is the Henderson hasselbach equation?
pH = pKa + log ([initial base] / [initial acid])
What is the condition for the ideal buffer capacity?
pH = pKa
What is buffer capacity?
It is the amount of strong acid or base that can be added without causing a significant pH change
What can optimise buffer capacity?
Highest when [HA] and [A-] are large
Highest when [A] = [A-]
Most effective buffers have acid/base ratio less than 10 and more than 0.1 –> pH range is +- 1
Why are buffers important in natural systems?
Biological systems such as blood contain buffers:
pH control is essential because biochemical reactions are very sensitive to pH
What is the ideal pH of human blood?
It is slightly basic, pH = 7.39 - 7.45
What are dangerous levels of pH in the human blood?
pH < 7.2 = acidosis
pH > 7.6 = alkalosis
Death occurs for pH less than 6.8 or greater than 7.8
What are the buffer systems involved in the blood?
Extracellular buffer:
H+ (aq) + HCO3 (aq) ⇌ H2CO3 (aq)
H2CO3 (aq) ⇌ H2O (l) + CO2 (g)
pH can be reduced by:
H2CO3 (aq) + OH- (aq) ⇌ HCO3- (aq) + H2O (l)
CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-
Explain the blood buffer system
As cells in our bodies produce the carbon dioxide as a form of waste, it dissolves in blood forming carbonic acid, through the following equilibrium system
CO2 (g) + H2O (l) ⇌ H2CO3 (aq)
The carbonic acid is an unstable and weak acid, which dissociates to form the hydronium ion and bicarbonate polyatomic ion (HCO3-)
H2CO3 (aq) + H2O (l) ⇌ HCO3− (aq) + H3O+ (aq) (IMPORTANT TO RMBR)
When there is an acid increase H+, the equilibrium shifts to the left (favours the reverse reaction) forming carbonic acid (H2CO3) molecules. For example, a common way the pH of blood can decrease is due to the presence of lactic acid (C3H6O3). Lactic acid
is produced in muscle cells when oxygen levels in the body is low
When there is an increase in bicarbonate (HCO3
−) in the blood, as bicarbonate is another cellular waste product from metabolism, the buffer system reacts to the presence of extra bicarbonate in the blood and causes a shift to the left of the equilibrium system (favours the reverse reaction).
How do we prepare buffers given some options, the desired pH and trying to find some ratio of concentrations
We can look at the Ka/Kb values and then convert them into pKa/pKb. We then pick the value which is closest to pH value, and then sub those values into the henderson-hesselbach equation to discover the ratio of concentrations of acid and base which are needed
Assume complete dissociation of polyprotic acids?
Need to double check
What are some useful pH indicators to know?
Methyl orange
Methyl purple
Bromothymol blue
Phenolphthalein
What is the pH range of methyl orange
3.2-4.4
Red - orange
what is the pH range of methyl purple
4.8 - 5.4
purple - green
what is the pH range of bromothymol blue
6.0-7.6
yellow - blue
What is the pH range of phenolphthalein
8.2-10.0
colourless - pink
What is an endpoint
It is when a colour change in the indicator is observed.
We need to choose an indicator which has an endpoint close to the equivalence point of the titrationW
What is equivalence point?
When number of moles of base = original moles of acid
What are the equivalence points (pHs) of strong acid/strong base, weak acid/strong base and strong acid/weak base
strong acid/strong base –> pH = 7
weak acid/strong base –> pH > 7
strong acid / weak base –> pH < 7
How do we calculate the pH of the solution at different parts of a strong acid/strong base titration or a strong base/strong acid titration
1) strong acids/bases completely dissociate in solution. This allows us to calculate the pH or pOH by doing -log(concentration of acid/base)
2) if strong base is added, it reacts with H3O+, so H3O+ is reduced as it forms more water. Then we can calculate the pH with the remaining concentration of strong acid/strong base because of the complete dissociation
3) Equivalence point: when amount of added base/acid = amount of acid/base. Here the pH would be 7, as all that is left is neutral water
4) After equivalence, any excess OH or H3O from the added solution will increase the concentration of that given molecule and ultimately influence the pH to be calculated later.
What are the key areas to note when looking at the titration curve for a weak acid/strong base titration?
1) Initial pH is high compared to strong acid
2) There is the buffering region right after which encompasses around pH = pKa. This line is curved and shows a slowdown in the increase in pH.
3) There is the equivalence point
4) There is the region where excess base is added
How is pH calculated initially at step 1?
We can use the Ka or Kb expression because it is a weak acid/weak base
How is pH calculated during the buffering region (step 2)?
it is calculated using the henderson hasselbach equation:
pH = pKa + log([base]/[acid])
How is the pH at the equivalence point calculated? (step 3)
Here, the salt formation of the original reaction (i.e the other thing when the acid is initially there would be base, or same vice versa) undergoes equilibrium and we calculate either concentration of OH or H3O from there using Kb or Ka values and then calculate pH or pOH
i.e. if it was CH3COOH reacting with HCl, we would be doing the CH3COO- + H2O (equilibrium sign) OH- + CH3COOH. This is because at equivalence the CH3COOH has all reacted out to form CH3COO-
How is the pH calculated in the region where excess acid/base is added? (step 4)
We just see how much excess acid/base there is and then calculate the pH from there because thats the only ‘active component’
Describe the 4 steps in more detail?
Check the book and lecture 32 for more info on the process of calculating it
How are the titration curves for polyprotic acids or bases figured out?
There will be multiple equivalence points, with each equivalence point corresponding to one disssociation. I.e. a triprotic acid would have 3 equivalence points and so on
Why are carboxylic acids important?
They can act as painkillers (aspirin)
exist in grapes and wine (tartaric acid)
Important for hormones, induces labour
Drugs, such as those which lower cholestrol
Why are carboxylic acids more acidic than alcohols?
Because the conjugate base of a carboxylic acid (carboxylate) is better stabilised than conjugate base of an alcohol (alkoxide) –> allows for better acidic properties
Can carboxylic acids participate in acid-base reactions?
Yes they do, typically to form a salt and water
What are the main properties of amino acids?
Amino acids contain carboxylic acids
There exists ‘L’ and ‘D’ stereoisomers of the general form of amino acids
What is the general form of amino acids?
It has a carboxylic acid functional group, which also contains an amine functional group next to it
What are zwitterions?
Zwiterrions are molecules having separable equal number of positive and negatively charged groups in the molecule, giving an overall neutral charge.
I.e. on the left side of the molecule it could be negatively charged whereas the right side of the molecule it is positively charged
a molecule or ion having separate positively and negatively charged groups.
What is an isoelectric point?
The pH at which a sample of an amino acid will carry no net charge (i.e. the pH that the amino acid becomes a zwitterion). At any other pH, the amino acid will carry a charge
What are fatty acids?
Fatty acids are long chain carboxylic acids (C8-C20)
What are saturated fatty acids
These have alkane chains (i.e. coconut oil, animal fats, butter)
What are monosaturated fatty acids
Contains one double bond (e.g. olive, canola, sesame oils)
What are polysaturated fatty acids
Contains two or more double bonds (e.g. sunflower, soyabean)
What is the difference between fats and oils?
They are both esters of a fatty acid and an alcohol
However, fats are solid whereas oils are liquid
What is the process of esterification?
Involves forming esters by reacting a carboxylic acid and an alcohol directly.
However, this needs a catalyst (H+) (acidification), and sometimes heat to speed up the reaction. The H+ deprotonates the carboxylic acid for the thingo to continue.
This process then forms water as a byproduct
Basically the OH on the carboxylic acid reacts with the H from the OH on the alcohol, which together forms water. Then the O from the OH bonds to the C=O to create an ester. The whole OH goes along with the H
If we can do the process of esterification, why cant we form amides from amines reacting with carboxylic acids? (as in follow the same process)
This is because an amine is basic whereas a carboxylic acid is acidic. Ultimately the amine only reacts with the H from the OH on the carboxylic acid, creating the highly unreactive carboxylate ion , and also the NH2 wants to just keep the H as it is basic, thus it wont do a similar process
What is the main function of esters?
esters in nature are the ones that give fruity flavours
What are fats?
Fats are esters of long chain fatty acids and glycerol.
Glycerol has 3 alcohol groups –> forms a triester, so fats are also called triglycerides
Why are saturated fats solids at room temperature?
Because they have only alkanes and thus pack together well, enabling them to adopt a solid formation at room temperature
Why are unsaturated fats liquid at room temperature?
Because they have some double bonds. This means that they pack less well, and are thus liquid at room temperature
What is a soap? How are they made?
Combination of a hydrophobic hydrocarbon tail and polar hyrdophillic carboxylate group, which work together to pull grease into water
They are made from heating fats with concentrated NaOH
How do soaps work?
Its components; the hydrophilic head and hydrophobic tail work together to pick up dirt particles and allow for cleaning action.
The way it works is that then soaps are introduced, the hydrophobic tails want to get away from the water, so it implants itself into dirt particles, while the hydrophilic head sticks out. Once enough of these hydrocarbons attach to the dirt particle, it is able to be ‘lifted away’ in a spherical looking shape called a micelle, which allows for the dirt particle to be washed away
What are ddetergents?
These are synthetic analogues of fatty acid salts which can be also used instead of soaps.
They are cheaper to make + stronger grease pentrating power
They also have a hydrophilic head but instead of it being the carboxylate ion on the head, it is actually replaced with another ion, typically sulfur
Do OH groups engage in hydrogen bonds? If so, how does this explain some observable features of the alcohol functional group
Yes they do. As such, these alcohols have high boiling points and increased solubility in water
Are alcohols acidic or basic?
They are neither acidic or basic. It doesn’t readily accept H+ and also takes a very strong base to remove the H (i.e. to become acidic)
What are phenols
It is when a hydroxyl group is attached to a carbon atom which is part of an aromatic ring
Describe the nature of phenols(i.e. acidic or basic?)
They display weak acidic behaviour, especially compared to OH functional groups
Phenol is more acidic than ethanol because after losing a proton (H+), phenol forms phenoxide ion which is stabilised by resonance whereas ethoxide ion is not.
Explain why phenols are acidic
Because the negative charge in a phenoxide ion is localised only on the oxygen atoms, but delocalised by a number of carbon atoms in the bbenzene ring
Stabilisation of phenoxide ion through presence of electron withdrawing group –> increased acidicty of phenol by stabilising phenoxide ion while presence of electron releasing group decrease acidict of phenol by destabilising phenoxide ions
This is sus explanation look above.
What is conjugation?
When there are alternating single and double bonds
What does aromaticity require?
1) Aromatic systems must be conjugated
2) Conjugated systems is cyclic
3) Conjugated system must contain 4n + 2 pi electrons (where n = 0, 1, 2, 3,…. - so 2,6, 10 …etc pi electrons <– 2 electrons in each pi bond) (Huckel’s Rule)
What is the difference between aliphatic and aromatic compounds?
Aliphatic - these are non-aromatic structures which contains hydrogens and carbons linked together in a chain via single, double or triple bonds
Aromatic - These are compounds in an aromatic structure following the criteria as above
Can amines form hydrogen bonds?
Yes they form hydrogen bonds (FON)
What are amines?
Contain > 1 organic group(s) bonded to nitrogen
are amines acidic or basic?
Amines are basic. This is because they can adopt a proton, especially when exposed to dilute acids
What important compounds contain amines?
A lot of neurotransmitters and hormones (adrenalin, serotonin, dopamine and acetylcholine)
Also, a lot of psychoactive drugs exist through amines (nicotine, MDMA, cocaine, heroine)
What are some examples of carboxylic acid derivatives?
Aldehydes, ketones, acid chlorides, esters, thioesters, amides
How can we achieve the carboxylic acid derivatives?
We can achieve them by ‘activating’ the carboxylic acids for further reaction with other compounds.
WHy is ‘activating’ a carboxylic acid important?
Because carboxylic acids by themselves are relatively unreactive, and thus can’t form some of the acid derivatives without ‘activation’
What does ‘activating’ a carboxylic acid involve?
Involves converting carboxylic acids to acyl chlorides (or acid chlorides) with a specific chlorinating reagent; thionyl chloride (SOCl2)
Acyl chlorides are very reactive and easily transformed into a range of other things; e.g. esters and amides
Overall reaction:
carboxylic acid +n thionyl chloride –> acyl chloride + HCl + SO2
How can we make esters and amides from acyl chlorides (activated form of carboxylic acid)
acyl chloride + an alcohol –> ester + HCl
acyl chloride + an amine –> amide + HCl
Why doesn’t reacting carboxylic acids directly with amines work?
Because amines are basic whereas the carboxylic acid is acidic –> acts as a ‘neutralisation’ –> not working
How can we make esters from carboxylic acids?
Carboxylic acids in the acidified conditions and add an alcohol –> ester + H2O
Why are amides important?
Because they are used in various pharmaceuticals:
Penicillin, lidocaine, paracetamol, prilocaine
What are hydrolysis reactions?
Reacting with water which involves breaking apart the bonds and replacing them with new ones
In a hydrolysis reaction, a larger molecule forms two (or more) smaller molecules and water is consumed as a reactant. Hydrolysis (“hydro” = water and “lysis” = break) involves adding water to one large molecule to break it into multiple smaller molecules.
What reactions are we concerned with for hydrolysis?
Reactions of acid chlorides, esters, thioesters, and amines
Explain the products and reactants of the hyydrolysis of acid chlorides
acid chloride + h2o –> carboxylic acid + HCl
Ester + H2O –> (using H+ as a catalyst) carboxylic acid + R’OH
Thioester + H2O –> (using H+ as a catalyst) carboxylic acid + R’SH
Amine + H2O –> (using HCl and heat as catalysts) carboxylic acid + R’NH3+Cl- (amine becomes protonated with HCl)
Amine + H2O –> (using NaOH and heat as catalysts) carboxylate ion with Na+ (salt formation) + R’NH2 (carboxylic acid is deprotonated when using NaOH)
What is an important thioester in nature?
Acetyl coenzyme A
delivers acetate and other groups in biosynthetic processes
What does oxidation of organic molecules involve?
Involves increasing either the O content or decreasing the H content.(Reduction is the opposite)
What conditions do you need for oxidation?
Typically need KMn)4 or Na2Cr2O7 as oxidising agents
What happens if you oxidise a primary alcohol?
Turns into an aldehyde (which is quite reactive) which further oxidises into a carboxylic acid
What happens if you oxidise a secondary alcohol
Forms a ketone
WHat happens if you oxidise a tertiary alcohol
Nothing happens
Can you oxidise an alkane?
Yes we can oxidise an alkane into an alcohol
What is reduction?
Reverse reaction of oxidation and involves the reduction of carboxylic acids back to its basic form
What conditions/reagents do you need for reduction?
Need lithium aluminium hydride (LiAlH4) and also H3O+?
NaBH4 can also be used as its cheaper and easier to handle. Not reactive enough to reduce carboxylic acids but it can work with ketones and aldehydes. LiAlH4 is a lot stronger and is more reactive –> can do it better
What does reduction do?
Carboxylic acid –> (use of reagents/catalysts) alcohol
OR it could be the relevant functional group which isnt just carboxylic acid, such as ketones and aldehydes
