Topic 3 Acids and Alkalis Flashcards
Name some natural sources of indicators
red cabbage,
red rose petals,
beetroot,
red onion skin
What happens to red and blue litmus paper when placed in acid?
red paper remains red, blue litmus turns red
What happens to red and blue litmus paper when placed in alkali?
blue litmus remains blue, red litmus turns blue
What happens to red and blue litmus paper when placed in a neutral solution?
remain unchanged
Why is universal indicator better than litmus?
Litmus only tells if something is acid, alkali or neutral. Universal indicator indicates the strength of an acid or alkali.
What is pH and what should you remember?
pH is a measure of how acidic or alkaline a substance is. Remember it is small p capital H.
What pH do acids have?
Less than 7
What pH do neutral substance have?
7
What pH do alkalis have?
More than 7
What pH do strong acids have?
1-2 (low)
What pH do weak acids have?
3-6
What pH do neutral substances have?
7
What pH do weak alkalis have?
8-11
What pH do strong alkalis have?
12-14 (high)
What colour do strong acids turn universal indicator?
red
What colour do strong alkalis turn universal indicator?
purple
What colour do weak acids turn universal indicator?
orange at pH 3 to yellow at pH 6
What colour do weak alkalis turn universal indicator?
turquoise at pH 8 to blue at pH 11
What colour do neutral substances turn universal indicator?
green
Name some strong acids
stomach acid which is hydrochloric acid
Name some weak acids
lemon juice, vinegar, acid rain
Name a neutral substance
water
Name some weak alkalis
ammonia, toothpaste
Name some strong alkalis
oven cleaner, sodium hydroxide
What does too much stomach acid cause?
indigestion
How would you make a concentrated acid/alkali less hazardous
add it to water
Strong acids and alkalis can be…
corrosive
Alkalis feel…
soapy
Weak acids, like vinegar and lemon juice, taste…
sour
Acids are neutralised by…
alkalis
Alkalis are neutralised by…
acids
What is the name given to the reaction of an acid with an alkali and what is produced?
Neutralisation, neutral water is produced
Give some examples of neutralisation reactions
Treating (i) indigestion with an antacid, (ii) acid produced by mouth bacteria from sugary foods with tooth paste (alkali), (iii) nettle stings (acid) with juice of a dock leave (alkali), (iv) treating bee stings (acid) with baking soda (alkali), (v) treating wasp stings (alkali) with vinegar/lemon juice (acid)
What is universal indicator made from?
A mixture of dyes
What is an indicator?
A dye that changes colour depending on whether it is in an acid or alkali.
Describe how you would make an indicator solution from red cabbage.
Half fill a beaker of water and add some red cabbage.
Place the mixture on a tripod and gauze and heat using a Bunsen burner.
Boil for about 5 min then allow to cool.
Filter the cooled mixture, collecting the liquid in a conical flask.
The liquid can be used a an indicator.
