Full transcript
0:02all right let's get started with our
0:03first chapter now this first chapter is
0:06not anything too crazy we're just going
0:08to kind of look at a little bit of an
0:11overview an introduction to
0:13understanding what it is we're going to
0:14be looking at in chemistry okay
0:19so when you think chemistry everybody
0:21starts thinking oh chemicals so what are
0:25chemicals here we have a picture that
0:28has got uh
0:30um picture of a kitchen and a bunch of
0:32things that you find in a kitchen Okay
0:35so we've got your refrigerator which is
0:39a metal alloy if you have a gas burning
0:42stove you'll have some natural gas there
0:45uh usually it's the same gas that we use
0:47in our bunts and burners and lab a lot
0:49of fruits they're grown with pesticides
0:52fertilizers uh I don't know if you've
0:54ever when you buy a piece of fruit
0:56hopefully you wash them but a lot of
0:58times there might be some sort of
0:59residue on on them okay um there's
1:02polymers everywhere if you have glass in
1:04your kitchen usually that silicon
1:06dioxide our water it's treated with lots
1:09of different chemicals so um for a long
1:12time we've had fluoride added to our
1:14water and there's a lot of other
1:16dissolved stuff in our water what
1:18dissolves stuff and how much dissolves
1:20stuff usually varies from region to
1:23region in San Diego we have a whole
1:25bunch of different areas um of town
1:27where we get you know water sources from
1:29and so if you test test water at my
1:30house uh versus testing water downtown
1:33at school they might be a little bit
1:35different with their dissolved stuff but
1:38the main point is that there's nothing
1:41that we touch or hold that is not made
1:43of chemicals so they are all around us
1:46and so hopefully this semester you'll
1:48gain a better understanding of some of
1:50these various different chemicals that
1:52we have around
1:53us so what is
1:56chemistry so here's a textbook
1:58definition for you chemistry chemistry
2:00is the science of the properties
2:01composition and behavior of materials
2:05what we like to do in chemistry is we
2:06like to describe and explain these
2:08different forms of matter and the
2:10reactions that we have um so in this
2:13picture right here you can see that
2:16there is um an ocean and a beach and a
2:19whole bunch of buildings so probably
2:22some sort of city here on the West
2:24Coast but it's all kind of gross looking
2:28the air doesn't look real gross great
2:30well one of the things is an
2:31environmental chemist might try to
2:34understand well what's in that air in
2:36air that's gross like this we have some
2:38NO2 okay NO2 is known as
2:44nitrogen
2:47dioxide and it's part of a class of
2:49chemicals that we put as n x where that
2:53X can represent any number of oxygen
2:56there's a lot of different nitrogen
2:57oxygen compounds out there there that
3:00have various different numbers of
3:01oxygens that are uh involved as
3:04pollutants in the air okay and so again
3:08we like to describe explain different
3:10forms of matter and our chemical
3:12reactions in this semester we are going
3:14to learn why did that NO2 uh get named
3:17nitrogen dioxide we'll learn about
3:20looking here why that kind of has a
3:23little bit of um an angled shape to it
3:27we'll learn how everything bonds
3:29together we'll learn about some
3:31reactions that occur and maybe
3:33understand a little bit more of what's
3:35going on behind that nitrogen dioxide
3:38and what it does in our atmosphere and
3:40all sorts of other types of
3:42reactions now when we talk about
3:44chemistry we can subclassify it okay we
3:48have applied chemistry so applied
3:50chemistry is a lot of what you're going
3:51to see in Industry where we're looking
3:53for something that's useful maybe in
3:54Pharmaceuticals our search there is
3:57we're trying to find some sort of drug
4:00that works really well to treat a
4:02disease or to battle cancer or to have
4:07better pain relief okay then we have our
4:10theoretical chemistry a lot of what
4:13happens at a University campus ends up
4:15being theoretical chemistry and so what
4:18we're trying to do in theoretical
4:19chemistry is we're trying to explain
4:22nature we're trying to explain these
4:24natural processes within theoretical
4:26chemistry we have a few other branches
4:28uh there's organic chemistry
4:30there's inorganic chemistry biochemistry
4:33physical chemistry okay and so we have
4:36subclassifications there and then we can
4:38even classify further than that okay so
4:40we can take chemistry and our inorganic
4:43chemistry we're looking at elements
4:45properties preparation applications of
4:47compounds um inorganic chemistry usually
4:51a lot of it's really colorful U
4:53especially work that's done with
4:54transition metals we can get some really
4:56cool colored stuff organic chem
4:59chemistry that's looking at Carbon and
5:01its compounds if you're taking this
5:02class because you are hoping to go into
5:05nursing someday um you should end up
5:08having to take chem 130 um after chem
5:11100 and that is going to be an organic
5:13chemistry course physical chemistry um
5:18it crosses over a lot with physics and
5:21there's a lot of theoretical and
5:23mechanical things we'll do we'll talk a
5:25little bit about physical chemistry this
5:27semester we don't do a whole lot with it
5:29um personally a little bit of my
5:32background I am not a physical chemist
5:34physical chemistry was probably the most
5:36difficult of my chemistry courses um for
5:40me when I was in
5:42school uh biochem we're looking at
5:45reactions within living systems and then
5:47there's my Branch analytical chemistry
5:51so the textbook definition here says
5:54study of constituents and identification
5:57in chemical substances but there's a lot
5:59of things that we can do with analytical
6:02chemistry so I happen to work all on
6:05organic molecules um I did something
6:08called redo dependent hydrogen bonding
6:11that may sound like complete gibberish
6:13to you now by the end of the semester
6:15you will understand what redo means and
6:17you will understand what hydrogen
6:19bonding means what was interesting about
6:21what I did is we were looking at very
6:24basic very tiny molecular recognition
6:27systems host guest systems trying to
6:29figure out um whether or not we could
6:33make sensor technology better make
6:35things better on an onoff switch at that
6:38molecular level um electrochemical
6:40sensors are used in a lot of different
6:42places if you know anybody that is
6:43diabetic that has to test their blood
6:45sugar okay those meters are a type of
6:48electrochemical
6:50sensor now most people when they
6:53specializ on something they get kind of
6:55full of themselves and they get very
6:57into well this is my thing and it is
6:59more important than everything else and
7:00so chemists like to say that chemistry
7:02is the central science and that all
7:05other Sciences tie into us and some of
7:07them are super obvious like medicine
7:10ties into chemistry in a lot of ways
7:12Pharmaceuticals that's all chemistry
7:14there trying to understand reactions
7:16that happen in the body nutrition very
7:19very based on chemistry biology okay
7:22same thing we start to get you know all
7:24those reactions in Biochemistry with
7:26living systems so then we Branch into
7:28biochemistry s where you get even more
7:30into the chemistry angle and less into
7:32the biology angle physics um ties into
7:36chemistry we look at uh the structure of
7:38an atom and what happens with an an atom
7:41when we look at spectroscopy when we
7:44talk about material science uh
7:46environmental science we had a little
7:48bit of an example there a couple slides
7:50ago when we looked at that gross smoggy
7:52sky and now we have to start to
7:55understand what's making it all smoggy
7:56what molecules are in the air how did
7:58they get there what are they doing once
8:00they are in the air plant science okay
8:04there's some really interesting stuff
8:06when it comes to plants there's a flower
8:10that the color of the flower is
8:13different depending on the pH so how
8:16acidic or how basic the soil is so if
8:19the soil's more acidic it's one color if
8:21the soil is more basic it's another
8:23color okay there's
8:25astronomy what's really cool is we can
8:29using spectroscopic techniques figure
8:31out what elements are in distant stars
8:35and or around distant planets okay and
8:39then geology all of our rocks and
8:41minerals those are all composed of
8:44chemicals one of the things that
8:47hopefully you'll get out of the semester
8:50is thinking like a chemist so when we
8:52look at an image like this okay I'm a
8:55chemist my parents are not chemists my
8:58husband is not a chemist okay they all
9:01might think of things a little bit
9:02different my mom or my husband they
9:05might look at this and go oh we see you
9:07know a nice lake or Beach there's some
9:10sand there um my three-year-old would
9:14immediately look at this and get very
9:16excited because the um adult and the
9:19child are both wearing pink and sitting
9:21on a pink blanket all right so that's
9:23how a lot of other people think but as a
9:27chemist I look at this little different
9:29okay first thing that comes to my mind
9:32is well is this a freshwater lake or is
9:34this a body of water like at the ocean
9:38what's in there are there salts are
9:40there minerals um what sorts of things
9:43are floating around in there and so I
9:45start to picture in my head what might
9:48be in that Lake like this right here
9:52that's a a water molecule water if you
9:54don't already know is
9:56H2O okay when we have symbols we have
9:59drawings like this oxygen is very
10:01frequently almost always represented by
10:03a red dot water um has one oxygen in it
10:07so we've got that red dot there hydrogen
10:09is represented by white or grayish dots
10:12there's two hydrogens so we've got the
10:14two white dots there um so this would be
10:17O2 that would be an oxygen molecule okay
10:20and there's other stuff floating around
10:22in there and so as a
10:24chemist I start to think like that the
10:27sand what's the sand composed of
10:29okay so that's how we want to start
10:31thinking is looking at things on more
10:33than just a surface level and starting
10:36to probe within them to understand what
10:40they're composed
10:41of okay when we study chemistry there
10:45are some things to keep in mind be
10:47curious this is science we ask a lot of
10:50questions like with that think like a
10:51chemist okay ask those questions be
10:55curious probe deeper okay in fact I even
10:59put on the slide ask questions ask
11:01yourself questions what is interesting
11:03about something and try to delve deeper
11:05than that if you don't understand
11:07something ask me okay I have office
11:10hours I have email we have canvas lots
11:13of ways to get a hold of me learn your
11:16vocabulary and nomenclature when we get
11:18to it um so you got to understand the
11:23language behind chemistry uh just
11:25because we run the class in English
11:27doesn't mean there's not a a lot of
11:29terminology to learn keep current with
11:31the class don't wait for tests this is
11:33why I have you turn your notes in
11:36especially with an online class this is
11:39so important to keep current it's so
11:43easy in an online class just be like
11:46yeah yeah yeah whatever I'm not going to
11:47worry about the lectures and then you
11:48get to getting ready for a test and you
11:50go oh huh I have four weeks of material
11:53I have barely looked at okay so I do
11:56have you turn your notes in to make sure
11:59that you are actually keeping up with
12:00and pacing yourself properly in the
12:03course study groups are great I had lots
12:06of study groups in college um my
12:08favorite one we had a group of us that
12:10were taking um calculus and physics
12:14together and we used to meet at a
12:17Denny's near San Diego State University
12:20and we would study there till like 2: in
12:23the morning and it wasn't just great for
12:26making sure we understood the material
12:28but it was great to have group that was
12:30going through the same classes together
12:33so we could all kind of commiserate with
12:35each other um and when things got really
12:37frustrating we could help bolster each
12:39other up and then delve into our course
12:43material and work problems don't just
12:46copy down what I do in slides okay after
12:50you finished a lecture maybe pull the
12:52blank slides and try the example problem
12:55again and see if you can do what I did
12:59on your own before going back to your
13:01notes okay so working the same problem
13:04over and over again to make sure that
13:05you understand how that problem is done
13:09is really
13:10crucial okay now when we go through
13:15science we also need to understand the
13:17scientific method all right so we have
13:20some sort of an observation this
13:23observation will describe something that
13:25we see that we hear that we taste that
13:28we feel smell okay now what I can do is
13:32let's say it is the first week of
13:34classes and I walk into my office and I
13:37comment to one of my colleagues oh my
13:40goodness the parking lot is really
13:42crowded today there is my observation
13:46okay I can see that the parking lot is
13:48crowded now I can come up with some sort
13:52of conclusion to myself okay I can make
13:57some sort of hypothesis I can make an
13:58educated guess based upon this
14:01observation oh well there's a lot of
14:03people in the parking lot today oh I
14:06think there's something going on on
14:08campus well maybe I need more than one
14:10observation okay because notice here I
14:12have series of observations maybe I take
14:15you know a few things in consideration
14:16like one lots of PE lots of
14:26cars okay maybe number two is lots of
14:33people on
14:36campus and maybe number three is I see
14:41large
14:43crowds
14:45outside
14:49classrooms okay so then maybe my
14:53hypothesis here is that classes started
14:57all of a sudden there's tons of people
14:58people parking there's tons of people on
15:00campus and there's lots of students
15:02waiting outside classrooms so my
15:05hypothesis is that classes have started
15:07so then I can turn to the scientific
15:09method okay so there's my observations
15:12my empirical facts okay now sometimes we
15:15have scientific laws so we have some
15:17things that we've tested already based
15:18on consistent observations I can put
15:21things together in a hypothesis and then
15:23I can test that explanation I can test
15:27um my observations
15:29and make sure that I come up with
15:30something cohesive okay so I can expand
15:33my scientific method into this right
15:35here so my observations I made three
15:37observations okay I did that part
15:40hypothesis I did my hypothesis now my
15:43prediction okay I predict that if I go
15:48and query people that are standing
15:51outside classrooms they will tell me
15:52that they are there because classes have
15:54started okay so I have predicted what's
15:57going to happen now I can go run my my
15:58test okay now I can actually go talk to
16:01all of these students and say hey why
16:04are you here and they might say I'm here
16:06because class has started today and I'm
16:08waiting for my class to start okay if
16:11that works woohoo my hypothesis is
16:15tested I can make my theory I can do
16:17some more tests maybe I travel to a
16:19different classroom and I ask those
16:21students they corroborate what the
16:23previous one said bada bing done okay it
16:28worked out well now what happens though
16:30if
16:31I strike out
16:33here what happens if I go ask this crowd
16:37outside the classroom and they tell me
16:39that they are there for a special event
16:43not for classes okay well then I have to
16:45reject my hypothesis now I have to come
16:48up here and go and make a new hypothesis
16:52okay maybe all these increased people
16:54are on campus because we are hosting a
16:56conference not classes with just started
16:58but San Diego City College is hosting
17:01some sort of conference okay make my new
17:04prediction I go ask people and they
17:07start tell me yeah I'm here for this
17:09special event yeah we're having you know
17:12um a conference for high school students
17:15that want to major in stem subjects and
17:18now we're all here for this or maybe
17:20we're hosting a conference for fellow
17:23Educators and we've all traveled to San
17:25Diego and now we're waiting for our
17:26different sessions and so
17:29so it's an iterative
17:32process we don't always get it right the
17:35first time okay we use what we have to
17:38make the best prediction
17:41possible but we don't always get it
17:43right so I want you to ask yourself
17:45where do we learn more okay do we learn
17:48more if we've supported our hypothesis
17:50right away or do we learn more if we
17:53reject our hypothesis and we have to go
17:56back up
17:57here and rethink it so think about that
17:59to yourself where do you think we might
18:01learn more okay now before we finish off
18:04this chapter just so we start getting
18:06some of that terminology down
18:10um just going to briefly go over a
18:13couple more things okay one thing to
18:16understand is that scientific
18:17discoveries uh you don't have to
18:19memorize any of this I just think this
18:20is really interesting um if we look at
18:23this the law of gravity was back in
18:261687 we figured out oxygen and
18:291774 we figured out an electric battery
18:31in 1800 and then in the 1800s you can
18:34see there were a whole bunch of
18:36discoveries but then when we get to the
18:391900s we get even more discoveries so
18:42it's really cool about science is like
18:44it took a long time to start to discover
18:47things but then as we started being able
18:49to do more and we started developing
18:51better Technologies and better tests and
18:53things we were able to start really
18:56exponentially ramping up all of our
18:59discoveries okay and then now in the
19:022000s what else are we going to discover
19:06okay just a few more here just
19:09understand some of our terminology when
19:11we rely to matter so what is matter okay
19:16anything that occupies space and has
19:18mass what is mass we want to think of
19:21mass okay it's the amount of matter that
19:23an object contains so when we Mass
19:26something we usually use gram or
19:30kilogram okay so that's a little
19:32different than
19:34weight mass is related to inertia so a
19:37tendency of a body at rest to be at rest
19:39so Mass again is just the amount of
19:41matter that an object contains my mass
19:43on planet Earth is going to be exactly
19:46the same as my mass on the moon my
19:48weight however changes between Earth and
19:52the Moon because what is different about
19:54Earth and the moon gravity weight is
19:56simply the effect of gravity on matter
19:58so the amount of mass you contain does
20:01not change from one place to another but
20:05your weight might change based upon
20:08gravity we have three different states
20:10of matter we have gas we have liquid and
20:14we have solids gases we will go over in
20:17more detail toward the end of the
20:19semester um I have a slated to start
20:22talking about gases in week 13 so we'll
20:25learn more about gases then but one
20:27thing about gases they expand okay um so
20:30they have no definite shape no definite
20:33volume they fill their container they
20:34Bounce Around
20:36randomly liquids constant volume they
20:39take the shape of the container well the
20:41tape of the container bottom because
20:43they rest at the bottom there is random
20:45particle motion but it
20:47is a fixed volume and our solid constant
20:51volume constant shape what's interesting
20:53is the particles still vibrate in place
20:56um which I will try to show you example
20:58of that um
21:00later okay and so here is kind of a
21:04fuzzy image but you can see our gas
21:07expands to fill the container the liquid
21:09has a definite volume there and then the
21:11solid definite volume definite shape we
21:14can go between states of matter um by
21:17cooling or heating when we talk about
21:19solids there's a couple different types
21:21there's crystallin and amorphous solids
21:25so this is the most common is
21:27crystalline so salt quartz Etc we'll
21:30look more at this later this
21:32semester Cryin solids they're crystallin
21:35because they exist in regular repeating
21:37three-dimensional patterns Amorphis
21:40things like Plastics glass gels okay
21:44they do not have a regular
21:46pattern and so here is a picture so
21:50silicon dioxide we can get two different
21:52forms of it quartz or glass okay and so
21:55our quartz is crystalline we've got that
21:57regular pattern
21:59our glass is amorphous we get a
22:01non-regular pattern that's why if you
22:03drop a piece of glass it shatters into
22:06very random pieces it's because it's a
22:08morphus okay and then we can go between
22:11our states of
22:13matter all right we can take a solid and
22:17heat it up and get a liquid and we can
22:18take that liquid and heat it up further
22:20and get a gas we can take gas and we can
22:25uh condense it cool it down and get a
22:26liquid again you can take that liquid
22:28and freeze it and end up getting a
22:31solid some substances will allow us to
22:34go directly between solid and gas and
22:36gas and solid if you've ever dealt with
22:39uh dry ice um dry ice does this we go
22:42directly from the solid to the gas and
22:44then if we were able to trap that gas
22:46and cool it back down again we would go
22:47directly from the gas to the
22:50solid in your labs this semester you
22:54will get to see a demo of something um
22:57undergoing sublimation
22:59iodine mostly sublimes there's a a
23:02little bit of liquid but you don't
23:04really see it so it it appears as though
23:05it Sublime so when you watch it it'll go
23:07directly from the solid to the gas and
23:10then uh directly from the gas back to
23:13the solid so it's a really cool demo
23:14that you'll get to
23:16see when we do this further
23:19classification of matter we can get a
23:21pure substance so one substance only
23:24it's got a definite composition definite
23:25properties are we get a mixture where we
23:27have two or more substances and so the
23:30properties are going to depend on the
23:32composition there and what's interesting
23:34about mixtures is when we talk about
23:36liquids and solutions later this
23:38semester we'll talk about something
23:40called colligative properties and when I
23:42make a mixture like let's say I dissolve
23:45uh something in water well it changes
23:47those properties so water would be a
23:48pure substance and then whatever
23:50solution I make would be a mixture and
23:53so um we can exploit these properties
23:56too if you've ever lived somewhere where
23:58it gets super cold you might have had to
24:00put antifreeze in your carage radiator
24:02well antifreeze is a mixture of water
24:04and ethylene glycol and what happens in
24:06that mixture is the presence of the
24:08ethylene glycol lowers the freezing
24:11point of the water so instead of
24:13freezing at 0° C it freezes at a lower
24:16temperature thus hopefully preventing
24:19the water in the radiator from freezing
24:21and then cracking the radiator
24:23block with pure substances we can get an
24:26element so we cannot separate those
24:28chemically into simpler substances or we
24:31can get a compound like water which we
24:34can separate into simpler substances so
24:36water would be a compound h2o because we
24:39have more than one element there and
24:41then there are chemical methods to
24:42separate that into oxygen gas and
24:44hydrogen gas okay mixture we get a
24:48homogeneous mixture or a heterogeneous
24:50mixture so
24:51homogeneous um uniform appearance we
24:54can't tell one particle apart from the
24:56other like if you make coffee
24:58in the morning and you put sugar in your
25:00coffee you can't tell the difference
25:01between the coffee the caffeine and the
25:04sugar it all looks like one uniform
25:07thing heterogeneous we can see the
25:10different parts in there so like let's
25:12say you make hot chocolate and you put
25:13marshmallows in your hot chocolate that
25:15would be a heterogeneous mixture because
25:18you can absolutely with your naked eye
25:20visibly see the difference between the
25:22hot chocolate and the marshmallows
25:24floating
25:25there okay
25:29so when we start to do this we like to
25:32you know classify things so like
25:34aluminum all right based on what we had
25:37here aluminum is going to be an element
25:40we cannot separate it chemically into
25:41simpler substances okay so it's going to
25:46be matter it's going to be pure and then
25:50it'll be an element all right so we
25:53can't decompose it into simpler
25:54substances by chemical reactions so
25:56therefore it is an element okay now
25:59aluminum can make compounds so oxides of
26:02aluminum occur naturally um rubies and
26:05sapphires are oxides of aluminum oxide
26:08means it has oxygen with it we can also
26:12alloy okay um into mixtures so an alloy
26:17you take one metal you take another
26:19metal you melt them down you mix them
26:21together and usually then they
26:22resolidify okay so these would be
26:25compounds
26:26here
26:29this is an
26:31element okay and then our different
26:33Alloys would be
26:35mixtures so we can do a lot with our
26:38different
26:39elements we can do a lot of different
26:41things with mixtures and a lot of
26:42different things with
26:43compounds now as we start going through
26:49um the
26:50semester okay you will get familiar with
26:53a lot of the periodic table but the
26:55elements I have highlighted here in
26:58yellow these are elements that we will
27:01start working with a lot more that you
27:03will see more frequently than some of
27:05the other ones so these are ones to
27:07start getting familiar with now if
27:09you've never used the periodic table
27:11before you are not going to be very
27:13familiar with what the symbols and the
27:15names are um let's see here your
27:18textbook does have a copy of the
27:21periodic table that does have the
27:23symbols with their names so you can
27:25start to learn that Something Like H
27:29this is
27:32hydrogen okay or B this is
27:37boron okay or maybe this HG this is a
27:41weird one HG the symbol for this element
27:45comes from the Latin name okay HG is
27:51mercury okay and so now versus later is
27:57a good time to start getting familiar
27:59with these don't wait until we get to
28:02chapter 6 um in week five when we do our
28:05nomenclature to start learning all of
28:08these start learning to pair the
28:11elements and the symbols now that way
28:14you get familiar with them and as we
28:18start going through everything you will
28:19be able to speak that language of
28:22chemistry sooner rather than later all
28:25right so this was our first chapter our
28:27subsequent chapters will be broken into
28:30some smaller videos I'm not going to
28:32make you set through an hour and a half
28:34long video for a longer chapter I will
28:37break the videos into smaller pieces so
28:39that way um you can focus on specific
28:41topics this first chapter though it's
28:43just kind of an overview of things so I
28:46just use it all lumped together in one
28:49lecture so make sure that you have your
28:52notes ready to go I don't mind if your
28:55notes are handwritten and then you scan
28:57them or take pictures of them I don't
28:59mind if you have done your notes on an
29:02iPad like I'm using here to do these
29:05lectures just as long as you have taken
29:07notes you will make some sort of image
29:09of your notes and then you will upload
29:11your notes to Canvas to receive credit
29:15for having basically attended class
29:18watching the lecture videos and taking
29:19CL taking notes on them that is your
29:21course attendance for an online class so
29:24make sure you do get those notes
29:26uploaded make sure that when you upload
29:28things they are in the correct
29:30orientation if you have written it in a
29:32vertical form and then it shows up
29:34horizontal I get a horizontal image and
29:37I can't really do a whole lot with that
29:39because the canvas app does not allow me
29:41to rotate images within the app for
29:44grading purposes so make sure that your
29:47files are oriented correctly um I do
29:50have unlimited submissions enabled that
29:53way you are able to fix something once
29:55you have reviewed it it is your
29:57responsibility to make sure that your
29:59your submission is done correctly all
30:02right so once you have done that um you
30:06can go ahead and pop into chapter 2 and
30:08start taking notes on that or you can um
30:12get into Wy plus and look at the
30:16homework set for chapter 1 and start
30:17working on that um up to you how you
30:21want to do that but take a look at that
30:22schedule look at when things are due to
30:24kind of help pace yourself through out
30:27this
30:29semester