SC4 - Acids and Alkalis Flashcards
What is concentration?
The amount of solute per unit volume. Concentrated acids have lots of H+ ions per unit volume, concentrated alkalis have lots of OH- ions per unit volume.
What is the pH scale?
A measure of the acidity or alkalinity of a substance.
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Acidic Neutral Alkaline
What are indicators?
Substances that change colour depending on the pH.
What colour is universal indicator in acids, alkalis and neutral?
Acids - red
Neutral - green
Alkalis - blue/purple
What colour is litmus in acids and alkalis?
Acids - red
Alkalis - blue
What colour is methyl orange in acids and alkalis?
Acids - red
Alkalis - yellow
What colour is phenolphthalein in acids and alkalis?
Acids - colourless
Alkalis - pink
What is the difference in concentration between an acid of pH1 and pH3?
Each time the pH of an acid increases by 1 it has been diluted by a factor of 10. So, pH1 is 10x10 more concentrated than pH3 (x100 difference).
How can you measure pH?
Universal indicator can be used then matched to a colour chart.
A pH probe can be used to measure the pH to to 2d.p. . This is better as it removes human error and gives the value to 2d.p. whereas universal indicator will only give a whole number.
What is a strong acid?
Strong acids fully dissociate (split up) when in solution. For example, all molecules of hydrochloric acid (HCl) are spilt into H+ and Cl- ions. This means that strong acids generally have lower pHs as all the molecules produce H+ ions, however this may not always be the case if it is very dilute.
What are weak acids?
Weak acids only partially dissociate (split up into ions) in solution. For example, only a few ethanoic acid molecules (CH3COOH) split up into CH3COO- and H+, the rest stay the same. Weak acids generally have higher pHs (closer to neutral) as only some molecules produce H+ ions, however this is not always the case as it may be very concentrated.
What is the equation for the reaction between an acid and a base?
Base + acid -> salt + water (BASH2O)
What is the equation for the reaction between an acid and a metal?
Metal + acid -> salt + hydrogen (MASH2)
What is the equation for the reaction between an acid and a metal carbonate?
Metal carbonate + acid -> salt + water + carbon dioxide (CASH2OCO2)
How would you prepare a soluble salt from an insoluble base?
Add an excess of the insoluble base to the acid (you know it’s in excess when it stops dissolving). Filter off the excess then crystallise the salt solution to form crystals of the soluble salt.