Mod 6 Properties of acids and bases Flashcards
What are 3 properties of acids?
Acids have a sour taste
Acids can singe or burn your skin
In solution, acids conduct electricity
What are the 4 different reactions that acids can undergo?
Acid + metals –> salt + H2 gas
Acid + base –> salt + water
Acid + hydrogen carbonate/carbonate –> salt + water + carbon dioxide
Acid + ammonia –> ammonium salt
What are the 6 strong inorganic acids that should be remembered
HCl (hydrochloric acid)
HBr (Hydrogen bromide/ hydrobromic acid)
HI (Iodane/Hydroiodic acid)
HNO3 (Nitric acid)
H2SO4 (Sulfuric acid)
HClO4 (Perchloric acid)
What are the 7 weak inorganic acids that should be remembered
H3BO3 (monoprotic) (Boric Acid)
H2S (Hydrosulfuric acid)
HF (Hydrofluoric acid)
H3 PO4 (phosphoric acid)
HNO2 (nitrous acid)
H2SO3 (Sulphurous acid)
H2CO3 (Carbonic acid)
Is carbonic acid unstable?
Yes, it has the teendency to convert straight to carbon dioxide gas and water
What is an inorganic base?
This is an ionic compound which either contains an oxide or hydroxide ion (O2-, OH- ). Or which in solution, produces the hydroxide ion. Strong bases usually dissociate to form hydroxide ions in water
What are the 6 strong bases to remember?
LiOH (Lithium hydroxide)
NaOH (Sodium hydroxide)
KOH (Potassium hydroxide)
Ca (OH)2 (Calcium hydroxide)
Sr (OH)2 (Strontium hydroxide)
Ba (OH)2 (Barium hydroxide)
What are the 7 weak bases to remember?
NH3 (Ammonia)
NH4OH (Ammonium hydroxide)
Be(OH)2 (Beryllium hydroxide)
Mg (OH)2 (Magnesium hydroxide)
Al (OH)3 (Aluminium hydroxide)
NaHCO3 (Sodium hydrogen carbonate)
Na2CO3 (Sodium carbonate)
What is an alkali?
Generally defined as a soluble base or more specifically a soluble base made from the alkali metals (group 1 elements) as well as the alkaline earth metals (Group 2 elements)
An Alkali is a base
What ar some common properties of bases/alkalis?
Alkalis have a soapy feel
Alkalis have a bitter taste
In solution, alkalis are good conductors of electricity
Alkalis react with acids to form a salt and water
What is the pH scale?
A number between 0 to 14, which gives a numerical indicator of how acidic and how basic a substance is.
How do we measure pH, how does it work?
We measure pH using pH indicators which are solutions of weak acids that exist as natural dyes and indicate the concentration of H+/H3O+ ions in a solution via colour change
What is univeersal indicator
A vegetable dye that has the broadest spectrum of colours depending on the pH of the solution. Depending on the colour, this dye indicators the degree of acitity or basicity of a substance
What does a pH> 7 indicate?
Indicates a basic/alkaline solution
What does a pH = 7 indicate?
Indicates neutral solution
What does a pH <7 indicate?
Indicates an acidic solution
Can a pure liquid or gas be an acid or base?
No, only aqueous
What is the pH range of a strong acid?
-1 –> 2
What is the pH range of a weak acid
2 to 6
What is the pH range of a weak base
7+ to 11
What is the pH range of a strong base?
11 to 15
What is the mathematical relationship between pH and pOH?
pOH + pH = 14
What is Kw equal to?
10 ^ -14 = Conc of hydronium times conc of hydroxidee
What are the 4 indicators which are important to remember pH ranges?
Phenolphthalein
Methyl orange
Litmus
Bromothymol blue
What is the pH range of Phenolphthalein? As well as their corresponding colours
8.3 to 10.5. Colourless to magenta
What is the pH range of Methyl Orange? As well as their corresponding colours
3.1 - 4.4. Red to yellow
What is the pH range of litmus? As well as their corresponding colours
4.5 - 8.3. Pink to blue
What is the pH range of bromothymol blue? As well as their corresponding colours
6.0 - 7.5, yellow to blue
What happens between the pH range of a pH indicator?
There goes through colours called ‘transition colours’
Why are indicators important?
Can compare it to weak or strong acids or weak or strong bases
What is the general equation for pH indicators as equilibrium solutions of weak acids?
HIn (aq) + H2O (l) ⇌ H3O+ (aq) + In - (aq)
Where HIn is the weak acid indicator
How do pH indicators work? (Use methyl orange as an example) Use a relevant base equation as well
HIn (aq) + H2O (l) ⇌ H3O+ (aq) + In - (aq)
Considering HIn as the weak acid indicator, and using methyl orange as an example. The increase in H3O+ concentration will cause equilibrium reaction to shift to form more red HIn in accordance to LCP, conversely if methyl orange is placed in a basic solution, this decreases conc of H3O+ (through favouring the forward reaction below)
H3O(aq) + B (aq) ⇌ H2O(l) + BH+ (aq)
What is the difference between strong acids and bases compared to weak acids and basees?
If a strong acid such as H2SO4 is dissolved in water, the hydrogen ions completely dissociate. We can write this reaction with water:
H2SO4 (aq) + H2O (l) –> 2H3O+(aq) + SO4 2- (aq)
However, this is compared to a weak acid such as acetic acid, where some of the acetic acid molecules don’t dissociate, and some do, thus forming equilibrium reactions.
Is the neutralisation of an acid and a base exothermic or endothermic? What does this mean for the enthalpy of neutralisation?
Exothermic. Means that enthalpy is negative
What is the enthalpy of neutralisation?
Amount of heat energy released in kilojoules per mole of water formed (kJ mol^-1)
How is enthalpy of neutralisation measured?
Measured through using a calorimeter (a device which prevents transfer of heat energy from and to the reaction mixture)
What are the steps in calculating enthalpy of neutralisation?
Using ΔH = -mCΔT or q = mCΔT to calculate the change in energy. Note: if using q=mcΔt, remember need to make it negative. Just use delta h formula
After this, calculate the number of moles of water formed (using limiting reagents etc)
Divide ΔH by the number of moles of water
What are the 2 theories of acids prior to Arrhenius’ and B-L theory
Lavoisier’s oxygen theory of acid
Liebig/Davy’s theory of aacids
What was Lavoisier’s oxygen theory of acids?
Proposed that an acid is a substance that contains oxygen
What was Davy’s/ Liebigs theory of acid?
Davy suggested that an acid is a substance containing hydrogen as opposed to oxygen, yet he didn’t propose this officially and Liebig picked up on this and utilised this definition.
Stated that an acid is a substance that contains hydrogen that can bee repalced by a metal
What were the limitations of Liebig/Davy’s theory?
Based on macroscopic observations and was still limited to observing acid -metal reactions of hydrogen. No definition for bases, and bases were just regarded as any substance that reacts with acids to form salts
What are the two important theories of acids that we need to know?
Arrhenius and Bronsted Lowry Acid/base theories
How did Arrhenius come up with his theory?
During the electrolysis of aqueous solutions of acids, hydrogen gas is produced at the negative electrode this happens with all common acids, and Arrhenius applied his theories of electrolytes to this observation and proposed that the cause of hydrogen gas evolution at the cathode was the conversion of hydrogen ions in the water into hydrogen molecules.
What is an Arrhenius Acid?
A substance that produces hydrogen ions in water solution
What is an Arrhenius base
A substance that produces hydroxide ions in aqueous solution
What is a common formula to remember to prove Arrhenius acids? (example)
HCl (g) –> H+ (aq) + Cl- (aq)
Good to write H2O above arrow
Why was Arrhenius theory important in the development of th pH scale?
Recognised the importance of the concentration of hydrogen ions in water solution
What is a common formula to remember to prove Arrhenius bases? (example)
NaOH –> Na+ (aq) + OH- (aq)
Good to write H2O above arrow
What are 3 advantages of Arrhenius’ theory?
Classifies chemical substance as Arrhenius acids or Arrhenius bases depending on their properties in the aqueous solution
Explains neutralisation using a net ionic equation of H+ (aq_ + OH - (aq) –> H2O (l)
Explains thee relative strength of acids and bases in water
Does Arrhenius explain the process of neutralisation? If so how?
He proposed that when an acid neutralises a base, it is the hydrogen ions and hydroxide ions that react to form neutral water
Net ionic equation is: H+ (aq_ + OH - (aq) –> H2O (l)
What are the 4 main limitations of Arrhenius’ theory?
Only restricted to aqueous solutions
Couldn’t explain why some salts weren’t neutral; i.e., why are some salts acidic or basic rather than neutral
Couldn’t account for ammonia (ammonia reacts with water to form NH4OH which means its neither a base or acid)
Couldn’t explain why metallic oxides and carbonates are basic
Expand on Arrhenius theory being restricted to aqueous conditions. Give an examplee
Couldn’t define acids and bases that aren’t in water, meaning that the theory fails to explain behaviour of acids and bases in solutions like solid or gas phase.
For example, HCl gas can dissolve in organic solvents such as benzene, but doesn’t ionise in benzene as it does in water
Expand on Arrhenius theory being unable to explain non-neutral salts
Even though a solution of NaCl is neutral, the solution of zinc chloride is acidic. A solution of sodium sulfide is basic. Arrhenius couldn’t explain these observations
I.e. CH3COOH + NaOH –> NaCH3COO (basic)(aq) + H2O (l)
Expand on Arrhenius theory being unable to explain why metallic oxides and carbonates are basic, using examples.
Chemist know that acids can be neutralised by metallic oxides and carbonates. These compounds conain no hydroxide ions that can dissociate into water. Many carbonates are insoluble, yet they do react with acids and neutralise them.
CaCO3 (s) + 2HCl (aq) –> CaCl2 (aq) + H2O (l) + CO2(g) (IMPORTANT TO REMEMBR)
What is the equation associated with Arrhenius limitation of metal oxides and carbonates neutralising acids
CaCO3 (s) + 2HCl (aq) –> CaCl2 (aq) + H2O (l) + CO2(g)
What is thee bronsted lowry definition of acids?
Acids are proton donors
What is the bronsted lowry definition of bases?
Bases are proton acceptors
What was the difference between B-L theory and Arrhenius?
Recognised the importance of water as an ionising solvent.
It is also able to explain the basic property of substances that do not contain hydroxide ions.
It could also explain the basic nature of some basic compounds in solution
Species can be amphiprotic
Acid base reactions aren’t limiteed to aqueous solutions. For example:
NH3 (g) + HCl (g) –> NH4Cl (s)
Explain the concept of water as an ionising solvent
Molecular acids dissolve in water to produce ions. According to BL theory, this occurs because a proton is donated from thee molecular acid to the water molecule to produce a hydronium ion. In other words, water assists in being a proton donor or proton acceptor
What are the limitations of the B-L theory?
Can’t explain acidic oxidees (non-metal oxides such as CO2, SO2 and SO3 reeact with water to produce acidic solutions)
Can’t explain basic oxicdes (metal oxides such as CaO and MgO react with water to produce basic solutions)
Can’t explain Reactions of acidic and basic oxides can take place in the absence of a solvent that donates protons, such as:
SO3 (g) + CaO (s) –> Ca (SO4) (s)
What is the Lewis theory of acids and bases?
Lewis acid - an electron pair acceptor
Lewis base - an electron pair donor
What are some common household names for acids?
fizzy drinks; carbonic acid
vinegar; acetic acid
stomach acid; hydrochloric acid
Car battery acid; sulfuric acid
What are some common household names for bases
oven cleaner; sodium hydroxide
Baking soda; sodium bicarbonate ; NaHCO3
indigestion tablets; magnesium hydroxide or calcium carbonate
