full chapter of basic concepts of chemistry using my personal tricks the first topic is matter which is divided into pure substances and impure substances we know that pure substances contain same type of particles for example consider iron sheet and sodium chloride we can see that this iron sheet contain one type of particles these all particles have same properties so we say that iron sheet is a pure substance secondly this sodium chloride also contain one type of particles all the particles have same properties so we say that sodium chloride is a pure substance here let me teach you an exam question why elements and compounds are called pure substances well the answer is simple they both are made up of one type of particles so we say that elements and compounds are pure substances for example like iron sheet gold sodium chloride silver etc on the other hand empire substances are those substances which contain different types of particles for example consider salt solution and salad we can see that salt solution contains two types of particles secondly they have different properties so we say that salt solution is impure substance on the other hand we can see that in salad there are more than two types of particles and these particles have different properties so we also say that salad is impure substance here let me teach you one another exam question why mixtures are called impure substances well mixture are called impure substances because they are made up of different types of particles remember the name of these important mixtures like air sea water solutions suspensions colloids and alloy like steel which are usually asked in mcqs so remember about pure substances and impure substances the second topic is properties of metal like physical properties and chemical properties we can easily observe physical properties without changing the identity of a substance now how we can remember the physical properties of metal well i always use my personal track moving vent should come late here m stands for mass v stands for volume s stands for shape c stands for color l stands for length also remember that all physical changes like melting point boiling point evaporation sublimation and condensation are physical properties we can observe chemical properties when a substance changes at state now how can we remember chemical properties well we say that moving vein should come late in case of chemical property we say that amirbay will come here a stands for acid this s stands for air b stands for base w stands for water c stands for chemical so a reaction of acid reaction of air reaction of base reaction of water and direction of chemicals all possesses chemical properties thus noted down physical properties and chemical properties now let me teach you the third topic physical quantities well anything which we can measure is called physical quantity for example consider 12 kilometer or 12 hours here we can measure the length of anything like 12 kilometer so length is a physical quantity similarly we can also measure the time like 12 hours so time is a physical quantity this topic is divided into three sub topics like best physical quantities derived physical quantities international system of units now what are base physical quantities well the seven physical quantities and terms of which other physical quantities are expressed are called base physical quantities like length time secondly those physical quantities which we can derive from the best physical quantities are called derived physical quantities for example when we divide length by time we get speed here we know that length and time they both are best physical quantities but dividing them we get another physical quantity like speed which is known as derived physical quantity now what is international system of units well in 1960 an international system of units were established for seven base physical quantities which we call international system of units know how to remember best physical quantities and international system of units well i always use my personal trait i say lisa mem turns to a left age here l stands for length m stands for mass t stands for time this t stands for temperature s stands for amount of substance l stands for light intensity e stands for electric current the sa unit of length is meter the sa unit of mass is kg the s unit of time is second the sa unit of temperature is kelvin the s unit of amount of substance is mole the s unit of light intensity is candela and that s a unit of electric current is ampere remember that except these all seven units the rest of units are called derived units also let me teach you one bonus question what is the difference between mass and weight well mass is the amount of matter present in any object while wet is the force between the earth and an object the s unit of mass is kg and the s unit of wet is newton so note it down all these important points now coming to the fourth topic the fourth topic is about prefixes mnemonic that is added to units to show multiples or fractions are called prefixes for example consider 2 kilogram here gram is the unit and kilo is the prefix now how can we remember the list of important prefixes well i use my personal trick i always write 10 to the power 1 2 3 and then i jump 3 times 6 9 12. now i say dead has keeped my great trach this d stands for deca this h stands for hecto this k stands for kilo this m stands for mega this g stands for giga and this t stands for tera secondly i write 10 to the power negative 1 then i write negative 2 negative 3 and then i repeat the previous process jumping 3 times negative 6 negative 9 negative 12. i use the trach that can make me nice person here this d stands for desi this c stands for centi this m stands for milli this m stands for micro this n stands for nano this p stands for pico so this is the list of negative prefixes thus using this trick we can easily learn all the prefixes the fifth topic is scientific notations well a system of writing too big are two small numbers the self-space and time is called scientific notation for example round about the mass of the earth is 6 into 10 to the power 24 kg we can see that it is a very big number so using scientific notation we can easily save space and time to write it also the diameter of the nucleus is 1.7 into 10 to the power -15 meter it is a very small number so using scientific notation we can easily save space and time to write eight the seventh topic is significant figures the certain assure and important digits in any measurement are called significant figures for example consider this number here we know that 205 are certain are important three digits while this zero zero three is uncertain less important three digits so the collection of certain are less important digits are called significant figures now let me teach you the most simple trick to find significant figures i write non-decimal numbers and decimal numbers in case of non-decimal numbers go from non-zero digit to last non-zero digit for example consider this number here the first non-zero digit is one and the last non-zero digit is 2. so i go from this one to this 2. now i count the total digits and this number there are six digits in this number so there are six significant figures similarly consider this number the first non-zero digit is four and the last non-zero digit is five i go from four to five so there are three digits i say there are three significant figures thirdly consider this number here the first non-zero digit is one and the last non-zero digit is three so i go from one to three there are three digits i say there are three significant figures now in case of decimal numbers i go from first non-zero digit to last digit for example consider this number here the non-zero digit is two and the last digit is zero so i go from two to zero we can see that there are three digits in this number so there are three significant figures secondly consider this number the first non-zero digit is one so i go from one to the last there are four digits so there are four significant figures thirdly consider this number the first non-zero digit is five so i go from five to the last there are total five digits so i say there are five significant figures thus using this simple trick we can easily learn significant figures the seventh topic is accuracy and precision accuracy means that how close you are to the actual value for example consider this man that the height of this man is 5 meter let i ask three students to find the height of this man let the first student measured it as a 4 meter the second student measured it as 4.5 meter and the third student measured it is 5 meter now these are the three different measurement we say that this whole measurement is accurate result are we say that high accuracy because the one measurement is exactly 5 meter which is matching the actual height of the man so the actual measurement is also 5 meter and this measurement of the student is also 5 meter so they both are intersecting or touching each other so we say that this measurement is accurate or it has high accuracy on the other hand precision means that how does two or more measurements are close to each other for example consider the man from the previous example we know that the actual height of the man is 5 meter let i again ask three more students to find the height of this man let one student measure the height of this man as 3.5 meter the second student also measured 3.5 meter and the third student measured it as 3.4 meter now let me ask you are these three measurements are accurate your answer is no because the actual measurement is 5 meter and the measurements of the students are totally different from them but wait a minute here we can see that this 3.5 and this 3.5 are close to each other while this 3.5 and this 3.4 are also close to each other the results of students are close to each other so it has high precision so we say that the first measurement of the student is close to the second measurement of the student and the second measurement of the students is close to the third measurement of the students so we say that it has high precision just remember that it has high precision but low accuracy now let me teach you some important mcqs a skill measure the mass of an apple as constantly as 0.5 kg less than the actual mass the options are accurate and precise accurate and non-precise precise but not accurate which one is right well the c option is hundred percent right zero point five is precise because the skill is constantly measuring 0.5 kg 0.5 kg and 0.5 kg but this result is not accurate because it is less than the actual mass the mass of a bag is 10.5 kg a student measured it as 12.5 kg 10.6 kg 9.5 kg the options are precise but not accurate accurate and precise accurate and not precise can you guess the correct option well the correct option is c it is accurate because one measurement of the student is matching the actual measurement on the other hand it is not precise because 9.5 kg is very different from 10.6 kg thus this is all about accuracy and precision remember that we will not discuss topics of nine class which we have already learned like atomic masses relative atomic masses atomic mass unit percentage composition etc so the next important topic is dimensional analysis the process of converting one set of units to another is called dimensional analysis for example convert 3045 meter to kilometer and 35 degree centigrade to kelvin we know that in one kilometer there are 1000 meter so i divide 3045 meter by thousand i get 3.45 kilometer on the other hand in one degree centigrade there are 273 kelvin so 35 plus 273 is equal to 308 kelvin does this process of converting units from one set to another is called dimensional analysis the ninth topic is laws of chemical combination well there are five different laws or five sub topics that describe the basic rules by which atoms and molecules combine together the first law is law of conservation of mars remember that it is all about the mars it states that mass can neither be created nor destroyed in a chemical reaction for example consider 2 grams of hydrogen and 16 grams of oxygen when they both react together they form water now if we measure the mass of the water it would also be 18 grams so we say that the mass of the reactants is 18 grams and the mass of the product is also 18 grams thus the both are equal that's why we say that mass can neither be created nor destroyed in any chemical reaction the second law is law of definite proportion remember that it is based on ratio of masses the word definite proportion means fixed amount it states that chemical substances are made up of elements that are present in fixed ratio by mass for example consider water and hydrogen per oxide in water the ratio of hydrogen to oxygen is two to one while in hydrogen peroxide the ratio of hydrogen to oxygen is one to one it shows that the ratio of oxygen and hydrogen would always be two to one and the water while the ratio of hydrogen and oxygen in hydrogen peroxide would always be one to one therefore we say that chemical substances combine in fixed ratio by mars the third law is law of multiple proportion it is very difficult for students but i will crack it it is also based on ratio of mars now consider two elements like x and y let they form three different compounds x y x y to x y three now we can see that the ratio of x and all these three compounds is one while the ratio of y in all these three compounds is one two and three now listen carefully we say that if i combine with the same element x the ratio of y is whole number like 1 2 3 let me repeat it if y combine with the same element x the ratio of y is the whole number like 1 2 3. this is what the law of multiple proportion explains let me give you one real example consider carbon monoxide and carbon dioxide in carbon monoxide the ratio of masses is 12 to 16 while in carbon dioxide the ratio of masses are 12 to 32 now dividing this whole thing by 12 in carbon monoxide the ratio of carbon is 1 to 1.3 while in carbon dioxide the ratio of carbon is 1 to 2. so the ratio of carbon is 1 in both the compounds but the ratio of oxygen is 1 2 which is again whole number therefore this law states that when two elements like x and y form two different compounds the ratio of the mass of y can be expressed as whole numbers so this is what the law of multiple proportions is the fourth law is gay lusake's law remember that it is based on volume of guesses it states that pressure is directly proportional to temperature for example consider oxygen gas in this cylinder if we increase the temperature of the gas the rate of collision of oxygen molecules on the wall of container is increased as a result of this pressure is increased so we say that pressure is directly proportional to temperature the fifth law is avogadro's law remember that this law is based on volume and mass of a case it states that volume is directly proportional to number of moles or mass of the gas at constant temperature and pressure for example consider these balloons as you fill these balloons with more air or more mess their volume increases remember that we can also write avogadro's law as equal volumes of any two gases at constant temperature and pressure contains the same number of moles or same masses for example consider 2 dm cube hydrogen gas and 2 dm cube of oxygen gas that they both are present at constant temperature and pressure so we say that they both contain equal number of molecules thus noted down these laws of chemical combinations the 10th topic is mole and avogadro's number in our daily life we say that one dozen egg is equal to 12. so we say that one dozen is nothing but just like a number now to learn the concept of mole and avogadro's number we should learn relative atomic mass and molar mass for example the relative atomic mass of carbon is 12 amu remember that there is only one atom of carbon present now we cannot touch we cannot see and we cannot do chemistry with one atom of carbon to solve this issue scientists put forward the idea of molar mass now instead of 12 amu if i take 12 grams of carbon it is known as a molar mass remember that we can touch we can see we can do chemistry with molar mass of carbon we know that in 12 amu there is only one atom of carbon but in 12 grams there are total 6.023 into 10 to the power 23 atoms thus this number is known as avogadro's number just remember that in 12 grams of carbon there are 6.023 into 10 to the power 23 atoms now listen carefully one mole is always equal to molar mass of an atom molecule or formula unit also we know that molar mass of any atom like carbon molar mass of any molecule and molar mass of any formula unit contains 6.023 and to 10 to the power 23 atoms so remember that one dozen of anything is always equal to 12 one mole or molar mass of any atom molecule or formula unit contains 6.023 into 10 to the power 23 particles if you want to learn more about mole concept and avogadro's number we have already uploaded a very dedicated video and its link is given in the description the last topic is molarity and molality no molarity is the number of moles of solute dissolved in one litre solution remember that we do not consider solvent and molarity for example consider some water in this object i add 2 moles sugar to this water after adding 2 moles sugar to this water the volumes of solution becomes one liter so we say that the solute is sugar and we have dissolved two moles of it the solvent is water the volume of solution is one liter so the molarity of this solution is 2m because we have dissolved 2 moles of sugar and 1 liter remember that the formula of molarity is number of moles of solute upon volume of solution on the other hand molality is the number of moles of solute dissolved in 1 kg of solvent remember that we do consider solvent in case of molality for example firstly i take 1 kg of water in this object now let's consider that i add 4 mole of sugar to this 1 kg of water now we know that the solute is sugar and we have dissolved four moles of it the solvent is water and the mass of the solvent is one kg so the molality of this solution is for m because we have dissolved four moles of sugar and 1 kg of solvent remember that molality is denoted by small m and it is equal to number of solute upon mass of the solvent and kg i hope that you have learned the important concepts of first chapter of chemistry