4 - Acids and Redox Flashcards
What’s is the Equation for a Metal + Acid?
Metal + Acid —> Metal Salt + Hydrogen
What’s is the Equation for a Metal Oxide + Acid?
Metal Oxide + Acid —> Salt + Water
What’s is the Equation for a Metal Hydroxide + Acid?
Metal Hydroxide + Acid —-> Salt + Water
What’s is the Equation for a Metal Carbonate + Acid?
Metal Carbonate + Acid —-> Metal Salt + Carbon Dioxide + Water
What ions do Acids produce in a aqueous solutions?
+
H
What ions do Alkalis produce in a aqueous solutions?
-
OH
What is the formula for Hydrochloric Acid and it’s ending for Salts?
HCl
Chloride
What is the formula for Sulfuric Acid and it’s ending for Salts?
H SO
2 4
Sulphate
What is the formula for Nitric Acid and it’s ending for Salts?
HNO
3
Nitrate
What is the formula for Ethanoic Acid and it’s ending for Salts?
CH COOH
3
Ethanoate
What are common bases?
Metal Oxides, Metal Hydroxide and Metal Carbonates.
What is the formula for Sodium Hydroxide?
NaOH
What is the formula for Potassium Hydroxide?
KOH
What is the formula for Ammonia?
NH
3
What are Acids and what happens when they are mixed with water?
A species that releases H+ ions in aqueous solution. Acids are proton donors.
What do bases do?
Bases do the opposite of acids, Proton acceptors and want to grab H+ ions.
What are Alkalis and what do they release?
Bases that are soluble in water known as alkalis, they release OH- ions in the solution.
What are strong acids?
The acid completely dissociate/ionise in water, all H+ ions are released.
What are Weak Acids?
An acid that dissociates only partially in solution. Only few H+ ions are released.
What is a Base?
A compound that neutralises an acid to form a salt.
What is Neutralisation?
The reaction between an acid and a base to produce a salt.
What is a Salt?
The product of a reaction in which the H+ ions from the acid are replaced by metal or ammonium ions.
What is the difference between strong bases and weak bases?
In a strong base nearly all OH- are released whereas a weak base only a few OH- ions are released.
What is an oxidation number?
A measure of the number of electrons that an atom uses to bonds with atoms of another element. Oxidation numbers are derived from a set of rules.
What is the oxidation state?
The oxidation number.
What is oxidation?
Loss of electrons or an increase in oxidation number.
What is redox reaction?
A reaction involving reduction and oxidation.
What is Reduction?
Gain of electrons or a decrease in oxidation number.
What is the reducing agent?
A reagent that reduces (adds electron to) another species.
What is an oxidising agent?
A reagent that oxides (takes electrons from) another species.
What is the oxidation number of Hydrogen in H2?
0
What is the oxidation number of Na+?
+1
What is the oxidation number of Sulfur and Oxygen in [SO4]2-?
(-2 x 4) + (+6) = -2
Oxygen = -2
Sulfur = +6
What is the oxidation number of each element in K2Cr2O7?
(+1 x 2) + (+6 x 2) + (-2 x 7) = 0
K = (+1)
Cr = (+6)
O = (-2)
What is oxygen normal oxidation number and the exception in peroxides?
Oxidation Number = -2
Peroxides = -1
What is the equation for oxygen in peroxides?
2-
O2
What is hydrogens normal oxidation number and the exception in metal hydrides?
Normal Oxidation Number = +1
Metal Hydrides = -1
What is the equation metal hydrides?
MHx (M = Metal)
Why are Roman numerals used for oxidation state?
It shows an elements oxidation number when it is not in its normal oxidation state?
What is the corresponding oxidation number for the Roman numerals: (I) , (II) , (III)?
(I) = +1
(II) = +2
(III) = +3
What is the oxidation number of Iron and formula in Iron(II) Sulphate?
ON = +2
Formula = FeSO4
What do compounds ending in -ate contain?
Oxygen and another element
(Exp. Sulphate - Sulphur and oxygen)
What is the formula of Iron(III) Sulphate?
Iron’s oxidation number is +3 and SO4 2- has an overall charge of -2.
(+3 x 2) + (-2 x 3) = 6 + -6 = 0 as the overall charge of Iron(III) Sulphate is 0.
Therefore Ratio of Fe:SO4 is 2:3
So the formula is Fe2(SO4)3
What is the systematic name for ClO2-?
Formula contains oxygen and chlorine, so chlorate.
Oxygen has ON of -2.
There for Chlorine must have a charge of +3 as it has an overall charge of -1 and Oxygen has a charge of (-2 x 2)= -4
Therefore it is Chlorate (III). As +3 ON.
What elements are oxidised and reduced in a reaction between a metal and an acid?
Metal atoms oxidised to form positive metal ions.
Hydrogen ions are reduced.
What elements oxidised and reduced in the equation Mg + 2HCl —> MgCl2 + H2?
Mg goes from 0 to +2 oxidation number so is oxidised.
H goes from +1 to 0 oxidation number so is reduced.
What are the 6 steps for writing half equations?
- Calculate oxidation states on each side of the equation.
- Balance the element changing oxidation state.
- Sort out electrons. If oxidation state becomes more negative then it gains electrons. If the oxidation state becomes more positive then electrons are lost.
- Sort out Os. For every O gained/lost, add/remove one H2O molecule.
- Sort out Hs. For every H gained/lost, add/remove one H+ ion.
6, Check- if the charge on the left equal the same as the right.
Create the half equation for BrO3- —> Br2?
- Br Oxidation Number goes from (+5) to (0).
- 2 Br on the right so need 2 BrO3- on left.
- Electrons - 5e- x 2 = 10e- (2x Br become 5 more negative so 10 electrons gained).
- 6 more O on left so need 6 H2O on the right.
- 12 less H on left so add 12 H+ to left.
Half Equation is 2 BrO3- + 10e- + 12 H+ —> Br2 + 6 H2O
Create the half equation for Pb 4+ —> Pb 2+?
Pb 2+ —> Pb 4+ + 2e-
Create the half equation Br- —> Br2?
2Br- —> Br2 + 2e-
Create the half equation Cr2O7 2- —> Cr 3+ ?
2 Cr 3+ + 7 H2O —> Cr2O7 2- + 6e- + 14 H+
Combine the two half equations so the electrons cancel out of:
MnO4- + 8 H+ + 5e- —> Mn 2+ + 4 H2O
2 Cl- —> Cl2 + 2e-
x 2 = 2 MnO4 - + 16 H+ + 10e- —> 2 Mn 2+ + 8 H2O
x 5 = 10 Cl- —> 5 Cl2 + 10e-
Combining = 2 MnO4- + 16 H+ + 10e- + 10 Cl- —> 2Mn 2+ + 8 H2O + 5 Cl2 + 10e-
Final Answer = 2 MnO4- + 16 H+ + 10 Cl- —> 2Mn 2+ + 8 H2O + 5 Cl2
Combine the two half equations so the electrons cancel out of:
H2O2 —> 2 H+ + O2 + 2e-
FeO4 2- + 8 H+ + 3e- —> Fe 3+ + 4 H2O
Combined = 2 FeO4 2- + 16 H+ + 6e- + 3 H2O2 —> 2Fe 3+ + 8 H2O + 6 H+ + 3 O2 + 6e-
-6 H+ -6 H+
Final Answer = 2 FeO4 2- + 10 H+ + 3 H2O2 —> 2Fe 3+ + 8 H2O + 3 O2
Determine the mole ratio for when MnO4 - reacts with Fe 2+ to form Mn 2+ and Fe 3+?
MnO4 - + 5e- —> Mn 2+
Fe 2+ —> Fe 3+ + e-
Mole ratio is 1:5
Determine the mole ratio for when MnO4 - reacts with SO3 2- to form Mn 2+ and SO4 2- ?
MnO4 - + 5e- —> Mn 2+
SO4 2- + 2e- —> SO3 2-
The mole ratio is 2:5
What do Titrations allow you to find out?
Exactly how much acid is needed to neutralise a quantity of alkali.
How does a titration work?
You measure out some alkali using a pipette and put in a flask, along with indicator.
Explain the practical for a titration.
- Do a rough titration to get an idea were the end point is, where the alkali is exactly neutralised. To do this, take an initial reading of how much acid is in the burette to start off. Then add acid to the alkali constantly swirling the flask. Stop when the indicator shows a permanent colour change, and record the final reading of your burette.
- Now do an accurate titration. Run the acid until till close to the end point and then add the acid drop by drop until the solution change colour.
- Work out the amount of acid needed by the final reading minus the initial reading, known as the titre.
- Repeat the test to find a mean titre, readings should be within 0.1 cm3 of each other.
What is known as the titre and how is it calculated?
The volume of acid used to neutralise the alkali.
Initial reading - Final reading
Difference between a pipette and burette?
Pipette - Measures only one volume of solution.
Burette - Measures different volumes, and let’s you add solution drop by drop.
How do you take a reading from the burette?
Read from the bottom of the meniscus. Taking the reading to the nearest 0.05 cm3
In between two lines would have a reading of X.X5
On the line the reading would be X.X0
What are the two indicators for acid/alkali reactions (Titrations)?
Methyl orange - turns YELLOW to RED when adding acid to alkali
Phenolphthalein - turns PINK to COLOURLESS when adding acid to alkali
Why is universal indicator not used and methyl orange/phenolphthalein used instead?
Universal inductor it’s colour change is too gradual/slow.
These indicators change colour quickly over a very small pH range.
What is a standard concentration?
A solution of a known concentration.
What are the steps to make up a standard solution?
- Using a balance, weigh out the required mass of a solid.
- Transfer to a beaker, use distilled water to wash any bits of solid into the beaker.
- Add distilled water to the beaker to completely dissolve the solid using a glass rod to stir the solution.
- Transfer solution into a volumetric flask, rinse the glass rod and beaker with water into this aswell.
- Use water to fill volumetric flask up to the graduation line. Use a pipette to add final drops so it is accurate.
- Put the lid on the flask and turn the flask over to mix the solution.
How many dm3 in a litre?
1 dm3
25.0 cm3 of 0.500 mol dm-3 HCl was used to neutralise 35.0 cm3 of NaOH solution. Calculate the concentration of the sodium hydroxide solution in mol dm-3.
- First write a balanced equation.
HCl + NaOH —> NaCl + H2O - No. of moles of HCl = 0.500 x (25.0/1000) = 0.0125 moles
- From the equation, you know 1 mole of HCl neutralises 1 mole of NaOH. So 0.0125 moles of HCl must neutralise 0.0125 moles of NAOH.
Conc. of NaOH = n / volume = 0.0125 / (35.0/1000) = 0.36 mol dm-3
What is reaction stoichiometry?
This is how many moles of one reactant react with how many moles of another reactant.
In titration calculation what must you remember to do?
Use the balanced equation when working out the concentrations.
This equation shows the reaction between sodium hydroxide and sulfuric acid:
2 NaOH + H2SO4 —> Na2SO4 + 2 H2O
Given that it takes 19.1 cm3 of 0.200 mol dm-3 NaOH to completely neutralise 25.0 cm3 of the acid, calculate the concentration of the sulfuric acid.
n (NaOH) = conc. x volume = 0.200 x (19.1/1000) = 0.00382 moles
Ratio 2:1 for NaOH:H2SO4, so for every 2 moles of NaOH you need 1 mole of H2SO4.
n (H2SO4) = 0.00382 / 2 = 0.00191 mol
Concentration of H2SO4 = 0.00191 / (25.0/1000) = 0.0764 mol dm-3
What are polyprotic acids?
Acids that donate more than one proton.
Types of Polyprotic acids?
Sulfuric acid (H2SO4), Carbonic acid (H2CO3), hydrogen Sulfide (H2S).
What is the different in moles need for a monoprotic acid, diprotic acid and triprotic acid?
You’ll need double the number of moles of base to neutralise a diprotic acid compared to a monoprotic acid.
You’ll need to triple the number of moles of base to neutralise a tripotic acid compared to monoprotic acid.
20.4 cm3 of a 0.500 mol dm-3 solution of sodium carbonate reacts with 1.50 mol dm-3 nitric acid. Calculate the volume of nitric acid required to neutralise the sodium carbonate.
- Write a Balanced Equation.
Na2CO3 + 2 HNO3 ——> 2 NaNO3 + H2O + CO2
20.4 cm3 ?
0.5 mol dm-3 1.5 mol dm-3 - n (Na2CO3) = 0.500 x (20.4/1000) = 0.0102 mol
- Molar ratio of 1:2 for Na2CO3 : HNO3
Volume (HNO3) = 0.0204 / 1.50 = 0.0136 dm3 = 13.6 cm3
