Acids and Bases - Acids and Bases Flashcards
What are acids?
Acids are substances which composes of one or more HYDROGEN atoms chemically bonded to one, or a group of, non-metal atoms. eg H2SO4 is made up of 2 H atoms bonded to the sulphate group SO4 ^2-
What happens to an acid in water?
It will dissociate into its ions, meaning that it will separate into its IONS. Eg HCl in water -> H ions, and Cl ions
How do strong acids differ from weak acids?
Strong acids will COMPLETELY dissociate, releasing ALL Hydrogen ions when in contact with water.
Weak acids do not completely dissociate and only release SOME of their hydrogen ions in water, some remain as neutral particles.
Examples of strong and weak acids
Laboratory acids like HCl, H2SO4, HNO3
Organic acids like acetic (in vinegar), citric acids are weak acids.
What do bases do?
Remove Hydrogen ions from a solution
What are bases usually?
Metal oxides, metal hydroxides, metal carbonates or metal hydrogen carbonates.
What is a base called if it does dissolve in water?
An alkali
What ions do alkali dissociate into?
Hydroxide ions.
What is the difference between strong alkalis and weak alkalis?
Strong alkalis COMPLETELY dissociate in water.
Weak alkalis do not completely dissociate and only release a small number of hydroxide ions. Some remain as neutral particles.
Which group of the periodic table are strong alkalis?
Any of the group 1 metals eg Na, Li…
What is the difference between weak/strong and concentrated/diluted acids or bases?
The STRENGTH of an acid/alkali does not change depending on concentration. Concentration is HOW MANY acid/alkali particles in per unit volume of water.
The REACTIVITY of an acid/alkali is determined by the concentration of ions in the solution.
What is the pH scale used to represent?
The concentration of acids and bases
What is the pH a measure of?
The concentration of hydrogens in a SOLUTION. The more hydrogen ions present, the more acidic the solution.
Each unit on the pH scale represents a _____ change in acidity
The pH scale is logarithmic so each unit on the pH scale represents a TENFOLD change in acidity. ie pH of 4 is 10x more acidic than pH of 5, and 100x more acidic than pH of 6
What are the indicators for pH?
-Litmus: Litmus indicator SOLUTION turns red in acidic solutions and blue in alkaline solutions.
Blue litmus paper turns red in an acidic solution and remain blue in neutral/alkali solution. Red litmus turns blue when in alkali but stays red in acidic/neutral solutions.
-Universal indicator: many different colour changes, from red for strong acids to dark purple for strong bases. Green is neutral
What is the important difference between litmus and universal indicator?
Litmus DOES NOT tell you HOW STRONG the acid or alkali is whereas the universal indicator does.
Describe the neutralisation reaction
It is when a base cancels out the effects of the acid because a neutral solution is made if the right amount of acid and base is added together.
When hydrogen ions collide with hydroxide ions what is produced?
Water!!
How are salts formed?
When an acid is neutralised by a base (metals, bases or carbonates).
Acid + base -> salt + water
What are salts?
Ionic substances composed of a positively charged metal ions and a negatively charged non-metal ion.
Properties of salts
- relatively High melting points
- many are soluble in water
How are salts made? (Soluble salts)
- Heat acid til 70°C. Do not boil acid.
- Add insoluble base until saturated.
- Allow beaker to cool.
- Fold filter paper and place in funnel. Place funnel into beaker
- Pour down in filter paper and allow to filter through
- Place beaker full of water on to tripod
- Place evaporating dish on top of this beaker and pour solution from other beaker into evaporating basin
- Gently heat until solution has reduced by half
- Leave dish to cool. Move to a warm place and observe over a few days.
How to make salts using soluble bases or soluble carbonates
If the base or carbonate is soluble, then you cannot tell if the acid has been used up because excess solids will dissolve even after the acid has been neutralised, of if a colourless liquid base or carbonate is used, it will just form a colourless solution with the acid.
Therefore, an indicator must be used to determine when neutralisation occurs.
NEUTRAL SOLUTION/EQUAL AMOUNTS
Reaction between an acid and a metal hydroxide?
Acid + metal hydroxide –> metal salt + water
Reaction between an acid and a metal oxide?
Acid + metal oxide –> metal salt + water
Reaction between an acid and a metal carbonate?
Acid + metal carbonate –> salt + carbon dioxide + water
Reaction between an acid and a metal?
Acid + metal –> salt + hydrogen
Reaction between an acid and a metal hydrogen-carbonate?
Acid + metal carbonate –> salt + carbon dioxide + water
Properties of salts (2)
- High melting points
- Generally soluble in water
Properties of alkalis
Alkalis turn fats and oils into soluble soap
- feel soapy
- taste bitter.
How do we know if CO2 is produced?
Bubbles
use limewater test.
