Acids And Bases Flashcards
What is the pH scale?
It is a scale that measures how acidic or alkaline a solution is. A neutral substance is pH 7. Acids are less than 7 and form H+ ions in water. Alkalis are more than 7 and form OH- ions.
How to measure the pH of a solution?
You use indicators:
- universal indicator changes the colour of the solution to match the scale.
- litmus turns red in acidic, purple in neutral and blue in alkaline.
- methyl orange turns red in acidic,yellow in neutral and alkaline.
- phenolphthalein is colourless in acidic or neutral but pink in alkaline.
What does a neutralisation reaction produce?
It produces water
Base + acid –> salt + water
OH- + H+ –> H2O
What is the difference between strong and weak acids?
Strong acids ionise completely in water and tend to have low pHs whereas weak acids do not fully ionise in solution and have pHs around 3-6, Also the ionisation of a weak acid is a reversible reaction.
Difference between strong acids and concentrated acids?
Acid strength tells you what proportion of the acid molecules ionise with water whereas concentration tells you how much acid there is in a litre of water, how watered down it is.
How does concentration affect pH?
If the concentration of H+ ions increases by a factor of 10, the pH decreases by 1.
What reacts with acids to produce salt + hydrogen?
Metal
M + A -> S + H
What reacts with acid to make salt + water + carbon dioxide?
Metal carbonate
M C + A -> S + H2O + CO2
How do you make a salt?
You make a salt depending on its solubility, if it is insoluble you use precipitation and if it is soluble you use an acid and insoluble base.
How do you tell if a substance is insoluble or not?
Usually common chlorides,sulfates and salts of sodium,potassium and ammonium are soluble. Whereas common carbonates and hydroxides are insoluble
What is electrolysis?
It is the breaking down of a substance using electricity. An electronic current is passed through an electrolyte causing it to decompose.
What is OIL RIG?
Oxidation Is Loss (of electrons) Reduction Is Gain (of electrons)
What is the name for the positive and negative ion? What is the name for the positive and negative electrode?
Cation is a positive ion
Anion is a negative ion
Cathode is a negative electrode
Anode is a positive electrode
The positive ion moves to the negative electrode (it reduced)
The negative ion moves to the positive electrode (it oxidised)
Why can’t an ionic solid be electrolysed?
Because the ions are in a fixed position and can’t move whereas molten ionic compounds can as they have can move freely and conduct electricity.
Why is it different in aqueous solutions?
Because as well as ions there will be hydrogen ions and hydroxide ions from the water. The hydrogen ions will go to the cathode and the hydroxide will go to the anode.
