1) Define "mole". 2) How many moles are present in 34 grams...

1) Define "mole". 2) How many moles are present in 34 grams of Cu(OH)2? 3) How many moles are present in 2.45 x 1023 molecules of CH4? 4) How many grams are there in 3.4 x 1024 molecules of NH3? 5) How much does 4.2 moles of Ca(NO3)2 weigh? 6) What is the molar mass of MgO? 7) How are the terms "molar mass" and "atomic mass" different from one another? 8) Which is a better unit for expressing molar mass, "amu" or "grams/mole"?

Transcript

00:01 Let us have this question, in the first part we have to define mole, so that is idea, mole can be defined as the amount of substance that contains the same number of chemical species that are atoms, molecules, ions, etcetera as the number of atoms in 12 gram of carbon 12 isopores and it is considered as 1 mole, so this is the definition of mole, let us calculate the second part of the question, we have to find the number of moles in 34 grams of carbon, copper hydroxide, so we are given mass of cu, os whole twice and that is equals to 34 grams, so now let us write the molar mass, the molar mass of copper hydroxide is 97 .57, so the moles are equals to mass divided by molar mass, so it will be equals to 34 divided by 97 .57 and the moles comes out 0 .348, this is the number of moles.

02:37 Now, let us calculate the number of atoms, so we have to calculate the number of moles in 2 .45 multiplied by 10 raised to the power 23 molecules of ch4, so let us write here number of molecules first and that are equals to 2 .45 multiplied by 10 raised to the power 23, so in order to calculate the number of moles, moles here will be equals to number of molecules divided by the number of atom number that is 6 .022 multiplied by 10 raised to the power 23, so let us write here, it will be 2 .45 multiplied by 10 raised to the power 23 divided by 6 .022 multiplied by 10 raised to the power 23, so from here 10 raised to the power 23 cancels each other and the answer will be 0 .406 moles, these are the number of moles of d10 that is ch4.

04:14 Now, let us calculate the fourth part of the question and in this part we have to calculate the mass of ammonia and the molecules given to us are 3 .4 multiplied by 10 raised to the power 23.

04:42 So, first let us calculate the moles which will be equals to number of molecules that is 3 .4 multiplied by 10 raised to the power 23 divided by avogadro number that is 6 .022 multiplied by 10 raised to the power 23, so this is the number of moles.

05:11 Now, let us calculate the mass, since moles equals to the mass divided by molar mass, therefore the mass will be equals to moles multiplied by molar mass.

05:39 So, the mass will be equals to 3 .4 multiplied by 10 raised to the power 23 divided by 6 .022 multiplied by 10 raised to the power 23 and it is multiplied by again molar mass that is 17 .031 and the mass comes out 96 .1 grams, this is the mass of ammonia that is nh3...

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