Chapter 4 Acids And Redox Flashcards
What is an acid?
A proton (H+) donor
What is a strong acid?
An acid which fully dissociates/ ionises in water.
For example, HCl, HNO3, H2SO4
Eg, HCl —> H+ + Cl-
H2SO4 —> 2H+ + SO4 2-
What is a weak acid?
An acid which partially dissociates/ ionises in water
For example, carboxylic acids
CH3COOH ⇌ CH3COO- + H+
The equilibrium sign ⇌ is used to show that the forward reaction is incomplete.
What is a base?
A proton acceptor (H+)
NH3 + H+ —-> NH4 +
H2O + H+ —-> H3O+
What is an alkali?
A soluble base which produces OH- ions in water
NaOH + (aq) —-> Na+ + OH-
What is a salt?
When the H+ ion of an acid is partially or completely replaced by a metal ion or an ammonium ion
What salt would Hydrochloric acid form?
____________ chloride
What salt would Sulfuric acid form?
___________ sulfate
What salt would Nitric acid form?
_________ nitrate
What salt would Phosphoric acid form?
___________ phosphate
What salt would Ethanoic acid form?
_____________ ethanoate
What is the neutralisation reaction of an acid + metal oxide?
Acid + metal oxide —> salt + water
What is the neutralisation reaction of an acid + metal hydroxide?
Acid + metal hydroxide —> Salt + water
What is the neutralisation reaction of an acid + ammonium hydroxide?
Acid + Ammonium hydroxide —-> salt + water
What is the neutralisation reaction for an acid + metal carbonate?
Acid + metal carbonate —-> Salt + water + carbon dioxide
What is the neutralisation reaction of an acid + base?
Acid + Base —-> Salt + water
Write the ionic equation of this neutralisation reaction.
HCl(aq) + NaOH(aq) —-> NaCl(aq) +H2O(l)
H+ (aq) + OH- (aq) ——> H2O (l)
What does reduction mean?
Reduction is the removal of oxygen or the addition of hydrogen.
Reduction is also the gain of electrons.
What does oxidation mean?
Oxidation is the addition of oxygen or the removal of hydrogen.
Oxidation is also the loss of electrons
What does reduction mean in terms of oxidation number?
Reduction is the decrease in oxidation number
What does oxidation mean in terms of oxidation number?
Oxidation is the increase in oxidation number
What is oxidation number?
A measure of the number of electrons involved in bonding to a different element.
What does the sum of the oxidation number equal to?
The sum of the oxidation number is equal to the overall charge of the species.
What are the rules of oxidation numbers?
Uncombined elements= always 0
Group 1= always +1
Group 2= always +2
Fluorine= -1
Hydrogen is always +1 except with Group 1 when it becomes -1
Oxygen is always -2 except in a peroxide- H2O2 when it is -1
Or when it is with Fluorine it = +2
Chlorine is always -1 except when bonded to either Oxygen or Fluorine when the oxidation number is positive.
What is the oxidation number of uncombined elements?
Always zero
What is the oxidation number of Fluorine?
-1
What is the oxidation number of Group 1?
+1
What is the oxidation number of Group 2?
+2
What is the oxidation number of Hydrogen?
+1
What is the oxidation number of hydrogen when with a Group 1 element?
-1
When does the oxidation number of hydrogen change?
When hydrogen is with a Group 1 element.
What is the oxidation number of Oxygen?
-2
What is the oxidation number of oxygen when with a peroxide?
-1
What is the oxidation number of oxygen when it is with Fluorine?
+2
When does the oxidation number of oxygen change?
The oxidation number of oxygen changes when it is with a peroxide or with Fluorine.
What is the molecular formula of hydrogen peroxide?
H2O2
What is the oxidation number of Sulfur in Sulfuric Acid?
H2SO4
H= +1 +1 —>(+1 x 2)= +2
O= -2 -2 -2 -2 —> (-2 x 4)= -8
The sum of the oxidation numbers should equal the total charge which is zero.
(+2) + (S) + (-8)=0
Oxidation number of Sulfur =+6
What is the oxidation number of nitrogen in NO3-?
NO3-
N= ?
O= -2 -2 -2 (-2 x 3) = -6
The sum of oxidation number should equal the total charge which equals -1 because of NO3- ion.
(N) + (-6) = -1
Oxidation number of Nitrogen= +5
Identify the systematic name of Na2SO4
Na2SO4
Na= +1 +1 (+1 x 2) = +2
S= +6
O= -2 -2 -2 -2 (-2 x 4)= -8
Total charge = 0
Systematic name uses the charge of the Sulfur atom (the atom in which you had to find the oxidation number for)
Name: Sodium Sulfate (VI)
Identify the Systematic name of ClO-
ClO-
Cl=+1
O= -2
Total charge = -1
Name: Chlorate (I)
What has been reduced and oxidised?
Mg + Cl2 —> MgCl2
Mg + Cl2 —-> MgCl2
0 0 +2 -1
Mg= 0
Cl2= 0
Mg in MgCl2= +2
Cl2 in MgCl2= -1 because -2/2=-1
Therefore,
Oxidised Mg (because there was an increase in oxidation number). From 0 in Mg to +2 in MgCl2
Reduced Cl2 (because there was a decrease in oxidation number). From 0 in Cl2 to -1 in MgCl2.
What is a titration?
A titration is a technique used to accurately measure the volume of one solution that reacts exactly with another solution.
What can titrations be used for?
Finding the concentration of a solution
Identification of unknown chemicals
Finding the purity of a substance
What is the procedure of an acid-base titration?
Add a measured volume of one solution to a conical flask using a pipette and place the conical flask under a white tile.
Add the other solution to a burette and record the initial burette reading to the nearest 0.05cm^3
Add a few drops of methyl orange indicator to the solution of the conical flask
Run the solution in the burette into the solution in the conical flask, swirling the flask throughout to mix the solutions. Once the indicator has changed colour from yellow to orange in an acid, the end point of the titration has been reached, this indicates the volume of one solution that exactly reacts with the volume of the second solution.
Record the final burette reading to two decimal points. The volume of solution added from the burette is known as the titre- this is calculated by subtracting the initial from the burette reading.
A quick, trial titration is carried out first to find the approximate titre
The titration is then repeated accurately, until two accurate titres are concordant (within 0.10cm^3)
What is important to do when working out the mean titre?
It is important to only include concordant titres when calculating the mean.
What is the oxidation number of Chloride?
-1
What is the oxidation number of Chlorine when bonded to Fluorine or Oxygen?
When bonded to Fluorine or Oxygen the oxidation number of Chlorine will always be positive because Fluorine and Oxygen are more electronegative.
What is disproportionation?
When an element undergoes both oxidation and reduction in the same reaction.
For example:
Cl2 + H2O —> HCl + HClO
Cl is oxidised from 0 in Cl2 to +1 in HClO
Cl is reduced from 0 in Cl2 to -1 in HCl
What are the roman numerals used for when naming?
The roman numerals show the oxidation state (oxidation number) of elements that forms ions with different charges.
What is the redox reaction in terms of electrons of
2Fe + 3Cl2 —> 2FeCl3
FeCl3 contains positive and negative ions Fe3+ and Cl-
Iron loses electrons and is oxidised
2Fe —-> 2Fe3+ + 6e-
Chlorine gains electrons and is reduced
3Cl2 + 6e- —> 6Cl-
How do acids undergo redox reactions?
Dilute acids can undergo redox reactions with some metals to produce salts and hydrogen gas.
Explain the redox reaction of:
Zn(s) + 2HCl(aq) —> ZnCl2(aq) + H2(g)
Reactants- Zn= 0 oxidation number
Products-Zn in ZnCl2 = +2 oxidation number
Reactants- H in HCl= +1 oxidation number
Products- H2= 0 oxidation number
Zn is oxidised because it increases from 0 in Zn to +2 in Zn of ZnCl2
H is reduced because it decreases from +1 in HCl to 0 in H2.
What is a redox reaction?
A reaction involving reduction and oxidation
What is a reducing agent?
An electron donor (gets oxidised in the process)
What is an oxidising agent?
An electron acceptor (gets reduced in the processed)
What are Monobasic/ Monophonic acids?
One acid molecule donates one proton.
Eg, HCl, HNO3, CH3COOH
What are Diabasic/ Diprotic acids?
One acid molecule donates two protons.
Eg, H2SO4
What are Tribasic/ Triprotic acids?
One acid molecule donates three protons.
Eg, H3PO4
What are examples of bases?
Metal oxides
Metal hydroxides
Ammonium hydroxides
Metal carbonates
Ammonia
What is the redox reaction of an acid + metal?
Acid + metal —> salt + hydrogen
Work out the formula of the systematic names
iron (II) oxide and iron (III) oxide?
Iron (II) oxide
Fe O
+2 -2
=FeO
Iron (III) oxide
Fe O
+3 -2
=Fe2O3
What is a standard solution?
A solution of known concentration made in a volumetric flask.
Calculate the mass of sodium hydroxide needed to make 250cm^3 of 0.125 moldm^-3 standard solution.
Concentration= mole/volume
250cm^3/1000= 0.25dm^3
0.25 x 0.125 = 0.03125 moles
Moles=mass/Mr
NaOH- (23.0 + 16.0 + 1.0)= 40.0
0.03125 x 40.0 = 1.25g of Sodium Hydroxide
How would you prepare a Standard Solution?
Zero a 2 d.p balance and weigh the solid accurately.
Dissolve the solid using a small volume of distilled water
Using a funnel, transfer the solution to a 250cm^3 volumetric flask
Rinse out the beaker with distilled water into the volumetric flask.
Make the solution up with distilled water to the meniscus of the graduation mark
Place a stopper on the volumetric flask and invert slowly several times to thoroughly mix.
A student suggested that the same salt could also be made by reacting potassium metal with sulphuric acid,
Suggest why this is not the preferred method.
Potassium is highly reactive with acid
