In this lesson we will study what significant figures are and how they work
A significant figure in science is a number that serves for more than just a place holder and that the removal of this number in the problem causes its value to change
Example
33.5648
Has 6 significant digits and the removal of anyone of these causes the value to change
33.56480
still has six because if remove the 0 the value is unchanged
1.001
1.001 has four significant figures
Now there is more to it than just the stated definition that was just the first part if you can change the unit of measurement to remove the zeros then those are not considered significant
Example
.001
According to the first definition this has three SF's but actually it only has one because lets say it were
.001 meter if i change it to millimeters it is 1mm and that only has one significant figure
Basically if there is no numerical value before the zeroes then they are not significant because it is assumed that you could change the measurement to get rid of the zeroes
Here is Some Practice for y'all if you cannot figure out comment I will respond
39.67 = How many Sf's
41.0025= How many sf's
.000237= How many sf's
Monday, January 12, 2015
Volume density and mass
Volume density and mass is one of the most important topics in chemistry as they are crucial that you no how to calculate each one correctly in order to get the correct measurements
Calculations
V=M/D this means volume "V" Equals mass "M" divided by "D" density
One thing you will need to know is that these use the Si unit for there calculation so mass is generally grams volume generally milliliters and density is usually grams per milliliter notice i said generally sometimes volume is in liters and mass is in kilograms and density is kilograms a liter but you can always convert back and forth to get the proper setup
Here is a word problem for real world practicality I have a substance with a mass of twelve grams and a density of 3.43g/ml what is my volume
V= 12/3.43 V= 3.49 milliliters
Now I'll do one showing the need to convert I usually like to deal with the end result in small units so often Iconvert from kg to g and L to ml and Kg/l to g/ml but you may do as you wish it just depends on what one is trying to solve and your professors or teachers views
I have an object that weighs about 3.49 kg and has a density of 4.09 g/ml what is its volume in milliliters
First I need to figure out if my mass and density units match as far as grams and kilograms they do not obviously second now I need to decide which to convert or do I need to convert both since its asked for volume in milliliters I am gonna convert kilograms to grams and just leave my denstiy alone since they will cancel out in the division
3.49*1000 (1000 grams in a kilogram for those of us who need more detail)
Vml= 3490g/4.09gml (grams cancel leaving you with ml)
Vml= 3490/4.09
V= 853.3ml
(please note that i used "Vml" just to remind everyone what the unit of volume was you dont have to do this technically all you have to do is use V)
Now on to mass calculations
the formula for mass is
M= V*D
This formula means Where M= mass V= volume and D= density Mass is equal to the volume of your substance times its density
I will show you a problem without conversion since i did one above and these three equations are all of circular relations
I have a substance with a volume of 168 ml and a density of 3.27 g/ml what is its mass
Your equation should look like this
M= 168ml * 3.27 g/ml (g/ml stands for grams a milliliter) now just multiply
M= 549.4 grams (mass has no volumetric measurement that why milliliters did not carry)
Now for how to calculate density
The formula for density is
D= M/V
Where D is Density and M is Mass and V is Volume
Again I will not show a conversion as i showed one in the first part of this lesson and they are the same for each problem
I have a substance with a mass of 628 grams and a volume of 54.3 milliliters what is its density
D= 628g/54.3ml (since no unity cancel and its division the density unit will be g/ml)
D=11.6 g/ml
Please comment all problems are made up off the top of my head and are subject to human error we are not perfect please notify me by comments and I will correct them I hope this helps if you need clarification please comment
Calculations
V=M/D this means volume "V" Equals mass "M" divided by "D" density
One thing you will need to know is that these use the Si unit for there calculation so mass is generally grams volume generally milliliters and density is usually grams per milliliter notice i said generally sometimes volume is in liters and mass is in kilograms and density is kilograms a liter but you can always convert back and forth to get the proper setup
Here is a word problem for real world practicality I have a substance with a mass of twelve grams and a density of 3.43g/ml what is my volume
V= 12/3.43 V= 3.49 milliliters
Now I'll do one showing the need to convert I usually like to deal with the end result in small units so often Iconvert from kg to g and L to ml and Kg/l to g/ml but you may do as you wish it just depends on what one is trying to solve and your professors or teachers views
I have an object that weighs about 3.49 kg and has a density of 4.09 g/ml what is its volume in milliliters
First I need to figure out if my mass and density units match as far as grams and kilograms they do not obviously second now I need to decide which to convert or do I need to convert both since its asked for volume in milliliters I am gonna convert kilograms to grams and just leave my denstiy alone since they will cancel out in the division
3.49*1000 (1000 grams in a kilogram for those of us who need more detail)
Vml= 3490g/4.09gml (grams cancel leaving you with ml)
Vml= 3490/4.09
V= 853.3ml
(please note that i used "Vml" just to remind everyone what the unit of volume was you dont have to do this technically all you have to do is use V)
Now on to mass calculations
the formula for mass is
M= V*D
This formula means Where M= mass V= volume and D= density Mass is equal to the volume of your substance times its density
I will show you a problem without conversion since i did one above and these three equations are all of circular relations
I have a substance with a volume of 168 ml and a density of 3.27 g/ml what is its mass
Your equation should look like this
M= 168ml * 3.27 g/ml (g/ml stands for grams a milliliter) now just multiply
M= 549.4 grams (mass has no volumetric measurement that why milliliters did not carry)
Now for how to calculate density
The formula for density is
D= M/V
Where D is Density and M is Mass and V is Volume
Again I will not show a conversion as i showed one in the first part of this lesson and they are the same for each problem
I have a substance with a mass of 628 grams and a volume of 54.3 milliliters what is its density
D= 628g/54.3ml (since no unity cancel and its division the density unit will be g/ml)
D=11.6 g/ml
Please comment all problems are made up off the top of my head and are subject to human error we are not perfect please notify me by comments and I will correct them I hope this helps if you need clarification please comment
Tuesday, January 6, 2015
The Atom
The Atom is composed of 3 main particles protons neutrons and electrons.
Protons carry a positive charge and determine the type of elements for example the element with 8 protons in its nucleus is oxygen and it is Atomic number 8 on the periodic table Same with Carbon six protons so its atomic number six on the table.
Neutrons: serve a very big purpose they hold the nucleus together have you ever taken two magnets and stuck both ends together and then tried to do it b north to north pole and south to south pole they repel well so do protons neutrons have no charge so they stick together like glue and hold the protons close and these can be calculated by taking the atomic number and atomic mass and subtract mass from number
electrons: Orbit the outside of the atom and are equivalent to the number of protons they are small very small and move rapidly they carry same charges and want to be as far away from one another as possible and thus have orbits that are spaced so that happens
Protons carry a positive charge and determine the type of elements for example the element with 8 protons in its nucleus is oxygen and it is Atomic number 8 on the periodic table Same with Carbon six protons so its atomic number six on the table.
Neutrons: serve a very big purpose they hold the nucleus together have you ever taken two magnets and stuck both ends together and then tried to do it b north to north pole and south to south pole they repel well so do protons neutrons have no charge so they stick together like glue and hold the protons close and these can be calculated by taking the atomic number and atomic mass and subtract mass from number
electrons: Orbit the outside of the atom and are equivalent to the number of protons they are small very small and move rapidly they carry same charges and want to be as far away from one another as possible and thus have orbits that are spaced so that happens
Balancing an equation
To balance a chemical equation is very difficult at times especially when multiple elements and compounds are involved
First you need to figure out what you have here i will show you a balanced equation and give you step by step instructions on how I got there
2H2+1O2=2H20
pretty simple this is the balanced equation for water now lets do something a bit more tricky I have three molecules of hydrogen a surplus of of chlorine and need to know how much hydrogen chloride i will yield from combining them
3H2+?Cl2=?HCl
First off we need to know how much hydrogen it takes to fulfill chlorine's octet it takes one electron for chlorine to reach and octet be it being a group7 element and hydrogen being group one wants to give one away so they combine on an even ratio meaning it takes 3 molecules of chlorine and you get 6 HCl (wait a minute how did that happen). You see hydrogen and chlorine are both diatomic meaning you rarely find just H or Cl you will mostly find H2 or Cl2 due to their nature so you have to multiply the product result by 2 in order to maintain the law of conservation of matter.
Your end result should be
3H2+3Cl2= 6HCl
what if you have elements with opposing charges though that means you will have to have different coefficients no worries i will show you an example of that
3C+6Cl2=3CCl4
Carbon has a charge of plus or minus 4 chlorine has a charge of -1 it just needs one electron to satisfy its octet carbon needs to give away 4 to satisfy what it needs so it will take 12 Cl atoms to satisy 3 C atoms thus giving you a carbon chlorine ratio of 1/4 which is how i derived CCl4
please comment if you have any questions
First you need to figure out what you have here i will show you a balanced equation and give you step by step instructions on how I got there
2H2+1O2=2H20
pretty simple this is the balanced equation for water now lets do something a bit more tricky I have three molecules of hydrogen a surplus of of chlorine and need to know how much hydrogen chloride i will yield from combining them
3H2+?Cl2=?HCl
First off we need to know how much hydrogen it takes to fulfill chlorine's octet it takes one electron for chlorine to reach and octet be it being a group7 element and hydrogen being group one wants to give one away so they combine on an even ratio meaning it takes 3 molecules of chlorine and you get 6 HCl (wait a minute how did that happen). You see hydrogen and chlorine are both diatomic meaning you rarely find just H or Cl you will mostly find H2 or Cl2 due to their nature so you have to multiply the product result by 2 in order to maintain the law of conservation of matter.
Your end result should be
3H2+3Cl2= 6HCl
what if you have elements with opposing charges though that means you will have to have different coefficients no worries i will show you an example of that
3C+6Cl2=3CCl4
Carbon has a charge of plus or minus 4 chlorine has a charge of -1 it just needs one electron to satisfy its octet carbon needs to give away 4 to satisfy what it needs so it will take 12 Cl atoms to satisy 3 C atoms thus giving you a carbon chlorine ratio of 1/4 which is how i derived CCl4
please comment if you have any questions
The mole
Want to know how scientist calculate how much substance it takes to yield certain products in reactions they use a concept called the mole. One mole of something is 6.022x10^23.
Let's study a basic reaction and determine the yield using the concept called the mole
Water has a molecular formula H2O meaning to hydrogen atoms fused to one oxygen atom
Problem: I need to know the amount of hydrogen needed in moles needed to get 16 moles of water
Work: H2+O2= 16H2O
Answer: It takes 16 moles of hydrogen to make 16 moles of water due to that they both have the same subscripts the "2" in hydrogen and oxygen if this problem were reverse let us say and we wanted to figure out the moles of oxygen it would be 8 due to the fact oxygen is naturally diatomic or has a subscript of two because it hates to be alone and water only needs to be one oxygen per molecule it would only take half the moles of oxygen to water ratio
Now that you can see how moles work in chemical equations how much does a mole weigh.
This is all dependent on the type of element and corresponds directly to the elements atomic mass. For example carbon has an accepted atomic mass of 12.0107 meaning a mole of carbon weighs 12.0107 grams or for most 12 grams so now if you take the equation above and ask how many grams of hydrogen does it take to make 16 moles of water given hydrogen atomic mass is accepted as 1 and 1x16 is 16x2 for the subscript it takes 32 grams of hydrogen to make 16 moles of water
These are the basics if you have questions please comment I will do my best to answer
Let's study a basic reaction and determine the yield using the concept called the mole
Water has a molecular formula H2O meaning to hydrogen atoms fused to one oxygen atom
Problem: I need to know the amount of hydrogen needed in moles needed to get 16 moles of water
Work: H2+O2= 16H2O
Answer: It takes 16 moles of hydrogen to make 16 moles of water due to that they both have the same subscripts the "2" in hydrogen and oxygen if this problem were reverse let us say and we wanted to figure out the moles of oxygen it would be 8 due to the fact oxygen is naturally diatomic or has a subscript of two because it hates to be alone and water only needs to be one oxygen per molecule it would only take half the moles of oxygen to water ratio
Now that you can see how moles work in chemical equations how much does a mole weigh.
This is all dependent on the type of element and corresponds directly to the elements atomic mass. For example carbon has an accepted atomic mass of 12.0107 meaning a mole of carbon weighs 12.0107 grams or for most 12 grams so now if you take the equation above and ask how many grams of hydrogen does it take to make 16 moles of water given hydrogen atomic mass is accepted as 1 and 1x16 is 16x2 for the subscript it takes 32 grams of hydrogen to make 16 moles of water
These are the basics if you have questions please comment I will do my best to answer
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