Indicators Video Lecture | Science Class 10

0:0:0: what are indicators
0:0:3: suppose you are in a laboratory and I
0:0:6: give you to test tubes one has an acid
0:0:8: in it and the other has a base and asks
0:0:11: you to identify them
0:0:13: now how will you do that
0:0:15: you cannot taste or touch them as the
0:0:18: acids and bases present in Laboratories
0:0:21: are very corrosive in nature they can
0:0:23: even burn your mouth or skin
0:0:25: so what will you do
0:0:27: the best and easiest way to identify the
0:0:30: difference is by using an indicator
0:0:33: an indicator is a substance that changes
0:0:36: its color when it comes in contact with
0:0:38: an acid or a base
0:0:40: the two most common types of indicators
0:0:42: are natural and synthetic indicators
0:0:46: let's discuss natural indicators first
0:0:49: a natural indicator is a type of
0:0:52: indicator that can be found naturally
0:0:54: and can determine whether the substance
0:0:56: is an acidic substance or a basic
0:0:58: substance
0:1:0: one of the most common examples of
0:1:2: natural indicators is litmus
0:1:5: litmus is a purple dye that is extracted
0:1:7: from plants called lichens
0:1:10: the natural color of litmus is purple
0:1:13: now this purple color dye is mixed with
0:1:16: water and this becomes the litmus
0:1:18: solution which is obviously purple in
0:1:20: color
0:1:21: what will happen if we add acid like
0:1:23: hydrochloric acid to this solution
0:1:26: well the solution will turn red
0:1:29: but on the other hand if we add a base
0:1:31: like soap solution to this solution it
0:1:34: will turn blue
0:1:36: so to summarize litmus turns red when in
0:1:39: contact with acids and blue with bases
0:1:42: but the litmus is most commonly used as
0:1:45: an indicator in the form of litmus
0:1:47: papers
0:1:49: we have three types of litmus paper
0:1:52: one is blue litmus paper other is red
0:1:55: litmus and lastly the purple litmus
0:1:57: paper
0:1:58: these litmus papers are made by soaking
0:2:1: filter papers with red purple and blue
0:2:3: Solutions mentioned before
0:2:6: now coming back to the question we asked
0:2:8: you in the beginning of the video
0:2:11: how will you identify which test tube
0:2:13: has an acid and which one has a base
0:2:16: yes
0:2:17: we will use the litmus papers to do so
0:2:21: so let's discuss it in detail
0:2:24: in the first test tube we will add a red
0:2:26: litmus paper
0:2:28: we will see that there is no change and
0:2:30: the color of the litmus paper remains
0:2:32: red
0:2:33: then we will put a blue litmus paper in
0:2:36: the same test tube and we will notice
0:2:38: that the color will change to red
0:2:40: similar thing will happen with the
0:2:42: purple litmus paper
0:2:44: it will turn red
0:2:46: the conclusion we can make is that the
0:2:48: first test tube consists of acid
0:2:51: we will follow the similar process with
0:2:53: the second test tube
0:2:55: the red and purple litmus paper will
0:2:58: turn blue and the blue litmus paper will
0:3:0: not change its color indicating that the
0:3:2: second test tube consists of a base
0:3:5: so always remember be it any colored
0:3:8: litmus as it changes it to red and base
0:3:11: changes the litmus to Blue
0:3:13: now are you wondering how the color of
0:3:16: litmus papers will change in a neutral
0:3:18: solution which is neither acidic nor
0:3:20: basic
0:3:21: let's try putting the different litmus
0:3:24: paper in a neutral solution and see what
0:3:26: happens
0:3:27: the color of all the papers will remain
0:3:30: the same
0:3:31: that means there is no change in the
0:3:33: color of litmus paper due to the neutral
0:3:35: solution
0:3:37: the next natural indicator that we are
0:3:39: going to discuss is a common household
0:3:41: item
0:3:43: it is turmeric
0:3:44: yes turmeric which is so commonly used
0:3:47: in Indian households especially for
0:3:49: cooking
0:3:51: now we all know that turmeric is yellow
0:3:53: in color but have you observed one thing
0:3:55: that when you wash a stain of Curry on a
0:3:58: cloth with soap it turns reddish brown
0:4:1: that is because turmeric is working like
0:4:3: an indicator here
0:4:5: soap is basic in nature
0:4:8: so as soon as it comes in contact with
0:4:11: turmeric turmeric changes to reddish
0:4:13: brown
0:4:14: but what happens to turmeric in acid
0:4:17: can you think of an acid which is used
0:4:19: in cooking that comes in contact with
0:4:21: turmeric
0:4:23: well you may have observed that when we
0:4:25: use turmeric in food and we squeeze
0:4:27: lemon in it which is acidic in nature
0:4:29: the color of turmeric Remains the Same
0:4:32: that means turmeric and acidic medium
0:4:35: remains yellow whereas in basic medium
0:4:37: it changes to reddish brown
0:4:40: there is one more natural indicator
0:4:42: which is red cabbage and it looks a
0:4:44: little purple
0:4:46: the extract of red cabbage is used as an
0:4:49: indicator
0:4:50: in acid the extract turns red whereas in
0:4:53: base the extract turns bluish green
0:4:56: even Petals of some flowers like
0:4:58: hydrangea petunia and geranium can be
0:5:1: used as indicators
0:5:3: for example if we take hydrangea the
0:5:6: flowers of hydrangea will appear blue if
0:5:8: the soil from which they grow is acidic
0:5:10: and they will appear pink if the soil
0:5:12: from which they grow is basic
0:5:14: so the Petals of the flowers of these
0:5:17: plants can be used as indicators
0:5:20: so until now we have discussed various
0:5:23: examples of natural indicators
0:5:25: to retreat we have discussed litmus
0:5:28: turmeric red cabbage and Petals of
0:5:31: flowers like hydrangea petunia and
0:5:33: geranium
0:5:35: now let us move on to synthetic
0:5:38: indicators
0:5:39: synthetic indicators are those which are
0:5:42: man-made the first one we are going to
0:5:45: discuss is methyl Orange
0:5:47: the name itself tells that it is orange
0:5:50: in color
0:5:51: when acid is added in methyl or in
0:5:54: solution it turns red whereas in base it
0:5:56: turns yellow the second synthetic
0:5:59: indicator that we will be discussing is
0:6:1: phenolphthalein
0:6:3: phenolphthalein is colorless
0:6:6: in acid it remains colorless whereas in
0:6:8: a base it turns pink
0:6:10: if it is a very strong base it may also
0:6:13: turn purple
0:6:15: so the two colors of phenol fetaline are
0:6:18: colorless and pink now we have discussed
0:6:20: ample examples of natural and synthetic
0:6:23: indicators
0:6:25: but wait there is one more interesting
0:6:27: way of testing whether a substance is
0:6:30: acidic or basic
0:6:32: let's discuss it with an example
0:6:34: let's say we have to beakers
0:6:37: Beacon a and Beaker B have acid and
0:6:39: basic Solutions but we don't know which
0:6:42: Beaker has what
0:6:44: so we add onion slices in both the
0:6:47: beakers
0:6:48: you heard it right
0:6:50: we are going to add onion slices in both
0:6:52: the beakers
0:6:54: what will happen
0:6:56: are you waiting for the colors of onions
0:6:58: to change
0:7:0: well let's check Beaker a it will have
0:7:2: the smell of onions
0:7:4: nothing new here
0:7:6: now let's check Beaker B the smell of
0:7:9: onions will vanish
0:7:10: this indicates that Beaker a has acid in
0:7:13: it whereas Beaker B has base in it
0:7:16: when such substances like onions would
0:7:19: change their smell in acidic and basic
0:7:22: medium are called olfactory indicators
0:7:25: actually olfactory nerve is responsible
0:7:27: for the sense of smell
0:7:29: so such indicators which change their
0:7:32: odor in acidic and basic medium are
0:7:34: called olfactory indicators
0:7:37: so an onion is an olfactory indicator
0:7:40: which changes its smell and base
0:7:43: we can try the same activity with
0:7:45: vanilla essence
0:7:47: we put two drops of vanilla Essence in
0:7:49: Beaker which has acid and Beaker B which
0:7:52: has a base
0:7:53: in Beaker a the smell Still Remains
0:7:55: whereas in Beaker be the smell of
0:7:58: vanilla Essence has vanished
0:8:0: that means Beaker B is a base
0:8:3: so always remember that in acids the
0:8:6: smell of olfactory indicator remains as
0:8:9: it is whereas in bases the odor goes off
0:8:12: this thing can also be repeated with
0:8:14: clove oil
0:8:16: so in this video we have discussed what
0:8:18: are indicators and the three types of
0:8:21: indicators natural synthetic and
0:8:23: olfactory indicators
0:8:26: now indicators are an important topic
0:8:28: for class 10 board exams
0:8:31: let's discuss a previous year question
0:8:33: from indicators
0:8:35: the question from 2019 board exam is how
0:8:39: is the presence of an asset tested with
0:8:41: the strip red litmus paper
0:8:43: this question is a bit tricky because an
0:8:45: asset will have no effect on the red
0:8:47: litmus paper
0:8:49: similarly a neutral solution does not
0:8:51: change the color of red litmus paper
0:8:54: so how can we differentiate between an
0:8:57: acid and a neutral solution with the
0:8:59: help of a red litmus paper
0:9:1: so firstly we will dip the red litmus
0:9:4: paper into a basic solution
0:9:6: the basic solution will turn the red
0:9:9: litmus paper blue
0:9:10: then we will dip this blue litmus paper
0:9:13: into the unknown solution
0:9:15: if the solution turns the blue part of
0:9:17: the red litmus red that means the
0:9:19: solution is acidic otherwise it is
0:9:21: neutral or basic
0:9:23: now it's time to practice more questions
0:9:26: related to this topic
0:9:28: eduriff provides practice tests for all
0:9:31: the topics of science along with chapter
0:9:33: notes videos ncrt Solutions py cues and
0:9:37: so much more
0:9:39: hope you have enjoyed this video
0:9:41: thank you