10.1 10.1 Acids and alkalis in Acids and alkalis in daily life daily life
Dec 27, 2015
10.1 10.1
Acids and alkalis in Acids and alkalis in
daily lifedaily life
The orange juice tastes
sour!
The orange juice tastes
sour!
The baking powder tastes
bitter!
The baking powder tastes
bitter!
Why do some substances taste sour
and some substances taste bitter? Why do some substances taste sour
and some substances taste bitter?
p.2p.2The detergent works well in removing dirt.
The detergent works well in removing dirt.
Tony! Be careful! The detergent is
very slippery!
Tony! Be careful! The detergent is
very slippery!
Why does the dish become slippery after cleaned with
the detergent?
Why does the dish become slippery after cleaned with
the detergent?
In Unit 6, we have learnt how to classify substances as solids, liquids and gases.
In fact, there are many different ways to classify substances.
In fact, there are many different ways to classify substances.
p.3p.3
Scientists can classify substances as below:
acid(酸 )
acid(酸 )
alkali(鹼 )
alkali(鹼 )
neutral substance(not an acid or alkali)
neutral substance(not an acid or alkali)
SubstancesSubstances
- Many substances in daily life contain acids or alkalis.
- Some foodstuffs taste sour because they contain acids.
p.4p.4
orangeorange
lemonlemontangerinetangerine
grapefruitgrapefruit
contain citric acidcontain
citric acidCitrus Citrus
fruitsfruits
AppleApple contain containss
malic acid malic acid (( 蘋果酸蘋果酸 ))
GrapeGrape contains containstartaric acidtartaric acid
(( 酒石酸酒石酸 ))
whitewhitevinegarvinegar
ketchupketchupred vinegarred vinegar
containcontain etha ethanoic acidnoic acid((or called or called aceacetic acidtic acid))
tomatotomato
Some soft Some soft
drinksdrinks contain containcarbonic acidcarbonic acid
Some Some
drinksdrinks and and
candiescandies
containcontainascorbic acidascorbic acid((vitamin Cvitamin C))
containcontainascorbic acidascorbic acid((vitamin Cvitamin C))
Milk Milk and and yogyoghurthurt
containlactic acidcontain
lactic acid
SpinachSpinach and and
somesome
shampoosshampoos
contain oxalic acid
( 草酸 )
contain oxalic acid
( 草酸 )
Toilet cleanserToilet cleanser containscontains
hydrochloric hydrochloric acidacid
AspirinAspirin also also contains contains acidacid
- Acids taste soursour, but alkalis generally taste bitter.
Did you taste the following alkaline drugs or foodstuff before?Did you taste the following alkaline drugs or foodstuff before?
almondalmond
antacidantacid
How do they taste?
p.4p.4
- Many household cleansers contain alkalis.
Alkalis are good for removing greases. They react with the greases so that the resulting substances can be washed away with water easily.
Alkalis are good for removing greases. They react with the greases so that the resulting substances can be washed away with water easily.
Slippery! Be careful!
After the toilet has just been cleaned, there is often a cautionary notice. Why?
After the toilet has just been cleaned, there is often a cautionary notice. Why?
- Alkalis are generally slippery.p.4p.4
Acids and alkalis can also be found in our body.
stomastomachch
stomastomachch
produceshydrochloric acidthat helps break
down the foodjuicesjuices
inside arealkaline
small small intestinintestin
ee
small small intestinintestin
ee
salivsalivaasalivsalivaa
p.4p.4
- Many household cleansers contain alkalis.
but this toilet cleanser toilet cleanser contains acid instead.
=>=> cannot distinguish between acids and alkalis by their uses
Should we distinguish an acid from an alkali by tasting by tasting it?
Natural acid-alkali indicatorNatural acid-alkali indicator p.5p.5
- We should distinguish between acids and alkalis by using indicators ( 指示劑 ).
- Indicators Indicators contain pigmentspigments
=>=> change colour in acids and alkalis.
- Some natural materials contain pigments and can be used as natural indicators.
Using red cabbage extract as indicator
p.5p.5Experiment Centre 10.1Experiment Centre 10.1
1 Cut the red cabbage into pieces and boil them in hot water to get the red cabbage extract.
2 Examine the red cabbage extract. What colour is it?
______________________________Reddish purple/purple.
3 Add a few drops of the extract into two test-tubes containing lemon juice lemon juice and soap solution soap solution respectively.
4 Write down the colour of the mixtures in the following table.
Substance Colour of the mixture
lemon juice
soap solution
red
green
The colour of red cabbage extract The colour of red cabbage extract is ____________ i
n acids acids and ______________ in alkalis.
redred
greengreen
Indicator magicIndicator magicIndicator magicIndicator magic
You can also make your own indicator in your kitchen by using the red cabbage.
Try to use the indicator to test whether the baking powder solution is acidic or alkaline. baking
powder
p.6p.6Little ScientistLittle Scientist
You can also use the extracts from the following plants as acid-alkali indicators!
onion
grape
Boyle found that pigments in some plants can be used as indicators.
Boyle found that pigments in some plants can be used as indicators.
p.6p.6
a British scientist (1627–1691) One day, when Boyle was working in the laboratory, he put some violet
into a beaker…
The flower is beautiful!
When he did some experiments on acids…
Oh! The acid splashes on the petals.
Boyle washed the flower with water immediately…
The colour of the flower changes from
purple to redred.
Boyle discovered that some flower or plant extracts showed different colours in acids and alkalis.
Boyle’s discovery demonstrates that both luck and careful
observationare required for scientific
discovery.
Boyle’s discovery demonstrates that both luck and careful
observationare required for scientific
discovery.
Making your own acid-alkali indicator
p.7p.7Experiment Centre 10.2Experiment Centre 10.2
1 Put some petals into the mortar.
2 Crush the petals with the pestle.
mortar
mortar
pestle
pestle
4 Add some distilled water so that the volume is enough for three tests.
3 Add a few drops of ethanol, mix it with the petals.
petals mixed with ethanol and distilled
water
petals mixed with ethanol and distilled
water
5 Pour the coloured extract into three test-tubes.
6 Add 2 to 3 drops of lemon juice to one test-tube, soap solution to the second one. The last test-tube contains the extract in distilled water only.
7 Shake the test-tubes and observe the colour of the mixtures.
8 Record your results in the table below.
9 Wash the apparatus. Repeat steps 1 to 8 with petals of other flowers.
1 Why do we need to have a test-tube containing the extract in distilled water?
______________________________ ______________________________
QuestionsQuestions
2 What extract gives the most clear-cut colour changes?
______________________________
p.8p.8
For comparison of colour when there
is no acid or alkali.