C8- Acids And Alkalis Flashcards
How are hazards of acids or alkalis shown
By international symbols - they indicate the precautions needed to be taken when handling them
How is the acidity or alkalinity of a solution measured
With a ph scale of 0 - 14 7 = neutral
Indicators can be used - that change colour
Universal indicator is made from a mixture of different indicators
Tell me about the indicator litmus
Blue in alkaline solution
Red is acid
Tell about methyl orange indicator
Yellow in alkali
Red in acid
Tell me about the indicator phenolphthalein
Pink in alkali
Colourless in acid
What happens when an atom loses electrons
Positive ion is formed
What are polyatomic ions
Former when small groups of atoms held by covalent bonds lose or gain electrons - eg OH
When happens to ions in acids
They produce an excess of hydrogen ions (H+) when they dissolve in water
What happens to ions in alkalis
Alkalis produce exceed hydroxide ions in water
How does concentration change
The higher the number of hydrogen ions in a certain volume, the higher a concentration
Same with alkalis with hydroxide ions
Neutral solutions - eg pure water have low and equal concentrations of hydrogen ions and hydroxide ions
What are bases
Substances that neutralise acids to form a salt and water only
All metal oxides are based
What happens in neutralisation
Hydrogen ions in the acid combine with oxide ions to form water
This removes hydrogen ions and so the ph increases to become neutral
The salts are produced by replacing the hydrogen ions with metal ions
Why is an excess of base always added
To make sure that all the acid is used up
How do you make sure the prepared salt is pure
The mixture is filtered to remove the residue (unreactive metal oxide) from the filtrate, leaving only the salt and water
How do crystallisation of the salt occur
Allowing the water to evaporate - leaving crystals
What’s a base that can dissolve in water
A soluble base is called an alkali wooow
Ph values above 7
Tell me about group 1 hydroxides - alkali bases
Eg NaOH - balance out
But group 2 tend to be like Ca(OH)_2 as more hydroxide needed to produce a neutral complex
What happens to temperature when the neutralisation reaction
The mixture becomes warmer
What’s a balanced equations
The number of atoms of each element must be the same on both sides
What happens if you try get some soluble salts from alkalis with the solution NOT being neutral
Otherwise you will contaminate the salt with an excess of one reactant
How can you obtain a neutral solution with only water and salt
Titration
What happens in a titration
Acid is added from a burette to a fixed volume of alkali in a conical flask
Use a measuring cylinder to measure out the alkali but a pipete is more accurate for repeatable measurements
A few drops of indicator are added to the alkali so you can follow the reaction
The end point is when the indicator changes colour
Methyl orange or phenolphthalein are used Becuase their obvious colour changes give you a sharp end point
What’s a burette
A tall peice of glassware with 0.1cm^3 graduations
Tell me the steps to make a pure dry salt
Carry out a titration
Note the exact volume of acid neutralise the alkali
Use the burette to add the correct volume of acid without the indicator
Evaporate the water from the solution formed
