C8 Flashcards
What is relative acidity and alkalinity in terms of H+ and OH-?
Water -> neutral
When a substance is dissolved in water it becomes:
Acidic
More H+
Alkaline
More OH-
Neutral
Equal number of both
What is the pH scale?
A numerical scale which is used to show the acidity or alkalinity of a solution (1-14 and extra acidic can have values from 0-1)
Acidic -> less than 7 (lower)
Alkalis -> more than 7 (higher)
Neutral -> 7
pH measures concentration of H+ (inverse relationship)
Logarithmic -> change of 1 on scale is change in concentration by 10
What are indicators?
Shows if a solution is acidic or alkaline or neutral by a color change
What are the different types of indicators?
Two color indicators:
Distinguish acids and alkalis
Litmus paper (from lichen)
Synthetic indicators:
Organic compounds that are sensitive to changes in acidity
methyl orange-> used in acid-alkali titrations -> show endpoint ( point when color of solution changes completely with the addition of an indicator)
Universal indicator:
Mixture of different indicators which is used to measure pH
A drop is added to solution and the color is matched with color chart (look on docs for diagram)
Generally:
Warmer colors - acid
Greens - neutral or close
Cooler colors - alkali
What are some characteristic of acids?
pH value
___ when edible
___
Can neutralize __
Acid added to water->
Presence of ____
Proton ____
pH less than 7
Sour when edible
Corrosive
Can neutralise a base (forms a salt+water)
Acids added to water-> positively charged hydrogen ions
Presence of H+ makes it an acid
Proton donors (H+)
How can acids be arranged?
By amount of H+ per molecule
Monoprotic acid-> 1 H+ ion (hydrochloric acid, nitric acid)
Etc…
How ‘well’ they split into ions when put into water
Strong acid- completely dissociates into ions (hydrochloric, nitric)
Weak acid- partially dissociates into ions (ethanoic, carbonic)
How does the amount of H+ and strength of an acid relate to concentration?
(Dilute solution of HCl and concentrated solution of ethanoic acid)
Example:
A dilute solution of HCl (monoprotic) will be stronger than a concentrated solution of Ethanoic acid (monoprotic)
-> Most of HCl dissociate while very few of the ethanoic acid dissociate (but ethanoic is more acidic)
How are salts produced by acids?
When the H+ molecules in the acid are replaced by other positive ions (metal or ammonium ions) this creates salts
Hydrochloric acid → CHLORIDES
Sulphuric acid → SULPHATES/HYDROGEN SULPHATES
Nitric acid → NITRATES
What is created when metal reacts with acids?
Note: only metals above hydrogen in reactivity series will react to dilute acids
Acid + metal -> salt + hydrogen
Name of the salt related to acid (anion in acid) and metal
Ex:
Hydrochloric acid + magnesium -> magnesium chloride and hydrogen
Mg + 2 HCl -> MgCl2 + H2
Metal anion-ide and hydrogen
What is created when an acid is mixed with a base?
Water
Metal oxide + metal hydroxides (alkali) -> bases
React with acid -> neutralisation reaction
Acid + base -> salt + water (hydroxides or oxides)
Ex:
Hydrochloric acid -> magnesium chloride and water
Mg(OH)2 + 2HCl -> MgCl2 + 2 H2O
What is created when acid reacts with metal carbonates?
Forms corresponding metal salt, carbon dioxide and water
Acidic + metal carbonate -> salt + carbon dioxide + water
Ex:
Hydrochloric acid + magnesium carbonate -> carbon dioxide and water
MgCO3 + 2 HCl -> MgCl2 + CO2 + H2O
What is a neutralisation reaction?
Acid + base -> water
H+ + OH- => water
Ex:
HCl + NAOH -> H2O + NaCl
H+ + OH- => H2O
Na+ + Cl- => NaCl
What are the characteristics of bases?
pH value
What is alkali?
Can be neutralized by…
____ of metals
Alkali added to water->___
Presence of_____
pH value higher than 7
Alkali -> water soluble base
Can be neutralized by acid (form salt+water)
Usually oxides or hydroxides of metals
Alkali added to water -> OH-
Presence of OH- => base
What happens when alkalis and ammonium salts react?
Ammonium salts -> decomposition when warmed with alkali
Ammonia is weak base but volatile -> easy to displace from salt with another alkali
Alkali + ammonium salt -> salt, water, ammonia
NH4Cl + NaOH -> NaCl + H2O + NH3
What is the use of an alkali ammonium salt reaction?
Used to confirm presence of ammonium ions
Solution + alkali warmed
Damp red litmus paper will turn blue if ammonia is present
Why is it important to control acidity in soil?
If the soil is too alkaline or acidic, the crops won’t grow properly.
Usually soil is too acidic so a base (limestone, slaked lime, quicklime) can neutralize (usually sprayed in soil)
How can burning fossil fuel and factory waste be affected by acidity?
Air:
Burning fossil fuels release gases (nitrogen oxides and sulphuric dioxides) and react with the water and air -> acid rain
Build erode, harmful for soil, plants, water sources
Water:
Factory waste -> acidic and can leak into water
Usually treated with slaked lime
Define acids and bases in terms of proton (H+) transfer (aqueous solutions)
Acid are protons donors -> they ionise in solutions by producing protons (H+)
Bases are protons acceptors -> accept protons donated by acids
Why do alkali solutions and acidic solutions conduct electricity better?
They both have more H+ or OH- ions, allowing them to conduct electricity better
This can also be used to prove that the solution has ions
Why is water important to certain acids?
hydrogen chloride gas are dissolved in water and acidic solution is created
(Covalent molecules -> pure
Becomes acid when dissolved in water)
Define oxide
A compound made from one or more atoms of oxygen combined with one other element (MgO, ZnO, CO2 etc)
Define acidic oxide
A nonmetals element combines with oxygen
When dissolved in water forms an acidic solution
Define basic oxide
Metal element combines with oxygen
When dissolved in water produces basic solution (alkali)
Define neutral oxides
Oxides that do not react with either acids or bases and are ‘neutral’ (N2O, NO, CO, H2O etc)
