Topic 3 Chemical Change Flashcards
What are acids and alkalis?
Acids=
-the pH is less than 7
- they are a source of hydrogen ions, H+
- hydrochloric acid releases H+ ions
- the higher the concentration of H+ ions, the lower the pH of the acidic solution
Alkalis=
- the pH is more than 7
- they are a source of OH- ions
- sodium hydroxide releases OH- ions
- the higher the concentration of OH- ions, the higher the pH of the alkaline solution
What are strong and weak acids?
A concentrated solution has a greater amount of dissolved solute particles than a dilute solution.
Strong acid= acids that fully dissociate into ions in solution. All the molecules release H+ ions
Weak acid= acids that partially dissociate into ions in solution. Only a few molecules release H+ ions
What are bases and alkalis?
An alkali is a soluble base- one that will dissolve in water
A base is any substance that reacts with an acid to form a salt and water only
A salt forms when hydrogen ions in an acid are replaced by metal ions or ammonium ions
What is the test for hydrogen?
A lighted splint ignites hydrogen with a squeaky pop
What is the test for carbon dioxide?
Carbon dioxide turns limewater milky or cloudy white
What is neutralisation?
Neutralisation is the reaction between an acid and a base. In an acid-alkali neutralisation, hydrogen ions from the acid react with hydroxide ions from the alkali to form water.
How do you make a soluble salt from a soluble base?
-use an acid base titration to find the exact volume of the soluble base that reacts with the acid
- mix the acid and soluble base in the correct proportions, producing a solution of the salt and water
- warm the salt solution to evaporate the water-this will leave crystals behind
How do you carry out a typical titration?
Method:
- put acid into a burette
- use a Pipette to put known volume of alkali into a conical flask
- put a few drops of suitable indicator solution such as phenolphthalein or methy orange into the alkali
- record there burette start reading
- add acid to the alkali until the colour changes- the end point
- record the burette end reading
How do you make insoluble salts?
Method:
- mix solutions of two substances that will form the insoluble salt
- filter the mixture. The insoluble salt will be trapped in the filter paper
- wash the salt with distilled water
- leave the salt to dry on the filter paper. It could be dried in an oven.
What is electrolysis?
Electrolysis is used to decompose ionic compounds in the molten state or dissolved in water.
Electrolyte- an ionic compound in the molten state
Anions- negatively charged ions that move to the positive electrode
Cations- positively charged ions that move to the negative electrode
What happens at the anode and cathode?
Cathode:
Negative electrode
Hydrogen is produced
The compound contains ions from a metal less reactive than hydrogen
The metal is produced instead
Anode:
Positive electrode
Oxygen is produced
The compound contains Halide ions
What are the colours in a acidic and alkaline solution whilst using litmus and phenolphthalein?
Litmus- acidic= red alkaline= blue
Phenolphthalein- acidic= colourless alkaline= pink
Reactions of acids with metals and metal carbonates?
Metals= a salt and hydrogen only
Metal carbonates= salt, water and carbon dioxide
How do find the mean titres?
Mean titre= sum of concordant titres/ number of concordant titres
What is electrolysis of molten lead bromide?
Produces lead and bromine
Negative electrode = electrons are gained and lead is formed
Positive electrode= electrons are lost and bromine is formed
