Chemical Changes And Structure #4: Acids And Bases Flashcards
Acids have a pH of…
Less than 7
Pure Water + Neutral Solutions have a pH…
of 7
Alkalis have a pH of…
Greater than 7
Why do chemists use electronic pH probes to accurately measure the pH of a solution?
Because using a colour chart is subjective
What do chemists use to accurately measure the pH of a solution?
pH probes
Examples of Acids
- Vinegar
- Lemonade
- Soda Water
- Coke
Examples of Alkalis
- Baking Soda
- Dishwasher Powder
- Bleach
Acids are compounds that produce ____ when dissolved in water
H+ (aq) ions
Alkalis are compounds that produce ____ when dissolved in water
OH- (aq) ions
Formula of Hydrochloric Acid
HCl
Ions present in Hydrochloric acid (HCl)
H+ (aq) and Cl- (aq)
Formula for sulfuric acid
H2 SO4
Ions Present in Sulfuric Acid (H2SO4)
2H+ (aq) and SO4 2- (aq)
Formula for Nitric Acid
HNO3
Ions present in Nitric Acid (HNO3)
H+(aq) and NO3 - (aq)
Formula for sodium hydroxide
NaOH
Ions Present in Sodium Hydroxide (NaOH)
Na+ (aq) and OH- (aq)
Ions present in Potassium Hydroxide (KOH)
K+ (aq) and OH- (aq)
Formula of Potassium Hydroxide
KOH
Formula for Calcium Hydroxide
CaOH2
Ions present in Calcium Hydroxide (CaOH2)
Ca 2+ (aq) and 2OH-
How can you tell if something is an acid or alkali? ***
- It has the word acid in its name if it’s an acid
- It has the word hydroxide (OH-) in it if it’s an alkali
What is the concentration of H+ (aq) and OH- (aq) in neutral solutions?
It’s equal
Give an example of equal concentration in neutral solutions
H2O ⇌ H+ (aq) + OH- (aq)
What is a reversible reaction?
One which can proceed in both directions:
Reactant + Reactant ⇌ Product(s)
What is equilibrium? (2)
- Equilibrium is when the rates of the forward and reverse reactions are equal
- At equilibrium, the concentrations of reactants and products remain constant, although not necessarily equal
What happens to the concentrations of reactants and products at equilibrium?
They remain constant, although not necessarily equal
Equilibrium in water (5)
1 - Water molecules are constantly breaking up to form ions which in turn are constantly combining to reform water molecules
2 - This equilibrium exits in water and all aqueos solutions
3 - H20 ⇌ H+ (aq) + OH- (aq)
4 - Only 1 in 55million water molecules break up into ions
5 - Therefore, water is a poor conductor of electricity
What are water molecules constantly doing?
Breaking up to form ions which in turn are constantly combining to reform water molecules
What does the equilibrium of molecules breaking up to form ions and then combining to reform molecules exist in?
Water and all aqueos solutions
Why is water a poor conductor of electricity?
Only 1 in 55million water molecules break up into ions
What is pH a measure of?
The hydrogen ion concentration
p = potens (power)
H = Hydrogen (H+)
Acidic solutions contain more ___ than ___
H+ (aq) ions , pure water
Alkaline solutions contain more ___ than ___
OH- (aq) ions, pure water
Neutral solutions contain ___ concentrations of ___
H+ (aq) and OH- (aq) ions
What do concentrated acids and alkalis contain?
A lot of acid or alkali in a small volume of water
What do dilute acids and alkalis contain?
A small amount of acid or alkali in a large volume of water
The effects of dilution (adding water) to an acid?
It increases the pH of the solution as the concentration of H+ (aq) ions decreases
The effects of dilution (adding water) to an alkali?
It decreases the pH of the solution as the concentration of OH- (aq) ions decreases
What do non-metals burn in oxygen to produce?
Non-Metal Oxides.
C(s) + O2 (g) -> CO2 (g)
What do non-metal oxides dissolve in water to form? Give an example.
Acidic Solutions.
CO2 (g) + H2O (l) -> H2CO3 (aq)
What do metals burn in oxygen to produce? Give an example.
Metal oxides. (All of which are bases)
2Mg (s) + O2 (g) -> 2MgO (s)
All metal oxides are…
Bases
What happens if a metal oxide (metals burned in the presence of oxygen) is soluble in water? Give an example.
An alkali.
MgO (s) + H2O (l) -> Mg(OH)2 (aq)
What do all soluble metal hydroxides do?
Dissolve in water to produce alkaline solutions
What do insoluble oxides and hydroxides not do?
Affect the pH of water (because they don’t dissolve in it)
What page is the solubility of compounds found?
8
What is ammonia the common name for?
Nitrogen Hydride
What does ammonia do (as a gas)? What does this make it?
Neutralise acids, making it a base
What is ammonia (as a covalent molecule)?
It dissolves in water to produce an alkaline solution
Formula of ammonia dissolving in water to produce an alkaline solution
NH3 (g) + H2O ⇌ NH4 + (aq) + OH - (aq)
What is the formula of ammonium?
NH4
What is the formula of ammonia?
NH3
What is a neutralisation reaction?
The reaction of acids with bases
What happens to the pH in a neutralisation reaction?
It moves toward 7
What is a base? ***
Compounds which react with H+ (aq) ions to produce water
(A SOLUBLE ALKALI)
Bases include:
- Metal Oxides
- Metal Hydroxides
- Metal Carbonates
- Ammonia (kind of an exception but still a base)
What are the 4 main neutralisation reactions?
Acid + Metal hydroxide -> salt + water
Acid + Metal oxide -> salt + water
Acid + Metal carbonate -> salt + water + carbon dioxide
Acid + metal -> salt + hydrogen
What are salts?
Ionic compounds that are formed during neutralisation
What happens during neutralisation?
The hydrogen ions of the acid are replaced by metal ions or ammonium ions
What do salts contain?
- a positive metal ion (or ammonium ion) from the base
- a negative ion from the acid
How are salts named?
- positive metal ion of the base (ammonia becomes ammonium)
- negative ion present in the acid
(hydrochloric acid makes chloride salts)
(nitric acid makes nitrate salts)
(sulphuric acid makes sulfate salts)
What is the form for HCl (aq) + NaOH (aq) -> NaCl (aq) + H20
Acid + alkali -> salt + water
What is a spectator in?
An ion which appears on both sides of the ionic equation. It is present in the reaction mixture but takes no part in the reaction.
n =
CV
n stands for
Number of moles
C stands for
Concentration (l-1)
V stands for
Volume (l)
c =
n/v
v =
n/c
What is a standard solution?
One whose concentration is known accurately
Why is knowing the exact concentration in a standard solution important?
If you are going to carry out calculations involving that equation
Procedure of making standard solution
- Accurately weigh the substance in a small beaker
- Add a small volume of deionised water and stir to dissolve
- Transfer to a standard flask along with the washings from the beaker
- Make up to the mark carefully using distilled water
- Invert several times to mix thoroughly
What is a volumetric titration?
An experiment in which the volumes of reacting liquids are accurately measured
How is the alkali/acid measured in acid/alkali titrations?
Alkali = pipettes
Acid = bufete
How can we calculate the concentration of an acid or alkali?
If the concentration of the alkali is known or vice versa
Procedure of volumetric titration
- Pipette 25ml of alkali into the conical flask.
- Add universal indicator and swirl
- Fill the burette with acid, zero, and remove funnel
Then proceed to rough titration:
4. Add 1ml of acid at a time and swirl after each addition. Note the end-point volume
Proceed to Accurate Titration:
5. Add the acid until 1ml from the rough end point. Carefully add the acid drop-wise and swirl after each addition.
6. Continue titrating until you have 2 concordant results that agree within 0.2ml.
Soluble metal oxides form
Alkalis
Soluble non-metal oxides form
Acids
