Chemistry moles?

i dont get any of this... how do i do it? show your work plz





how many moles in each of the following? use correct significant digits





25g of SO22





219g of HCl





35g of CO2








and part two


how many grams in each of the following


0.035 moles of KOH








and party three


calculate the molar mass of each of the following





0.0025moles weighs 0.40g





3.9 *10^3 moles weighs 117kg

Chemistry moles?
The mole is a measure of the amount of a substnace that is present. It is a measure of the number of molecules or atoms that are present, therefore for atoms or molecules that have a greater atomic weight, it takes more mass for there to be a mole of material present. For example, on the periodic table you will see helium have an atomic number of 2 and an atomic weight of 4. This atomic weight of 4 means that for there to be 1 mole of helium present, there must be 4 g. Likewise, for lead, Pb, the atomic weight is 207.2, so there must be 207.2 g present for 1 mole of lead to be there. The mole is an absolute measure, meaning it is an absolute measure of the number of molecules or atom in a sample. In the above examples, if there are 4 g of He present and there are 207.2 g of Pb present, then they both have the same number of atoms present in the sample. I hope this explains the concept of the mole. Now to answer a couple of your questions.





I think you mean SO2 (not SO22). To get the atomic weight of SO2 you need to add the atomic weights of each element present to get the atomic (or molar) mass of the molecule. In this case 1 sulphur and 2 oxygens. The atomic weight of sulphur is 32 and the atomic weight of oxygen is 16 so:





Molecular weight of SO2 = (1*32) + (2*16) = 64 g/mol of SO2


now to determine the number of moles present in 25 g, you just need to use the molecular weight of SO2 as a conversion:





25 g * (1 mol/64 g) = 0.39 mol of SO2





THe other ones are done the same way, by adding the atomic weights of each element to ge tthe molecular weight of the molecule, then using that as a conversion to moles.





The strategy for part two is the same except that you are now converting from moles into grams.





Part three is where you need to be aware of the units on the numbers and be sure that you know what you are after as an answer. THe molar mass is expressed in grams/mole, so you have the mass in grams and the number of moles for each of these and you just need to set up the numbers and units to give you the units in the order that is needed. The first one is:





You need to get grams/mole, therefore, set up the numbers just like that:





0.40 g/0.0025 mole = molar mass of substance





Now just divide this out





0.40 g/0.0025 mol = 160 g/mol





The last one is done the same way, but you are working with different numbers.





Hope this helps
Reply:Just think this way: a dozen means 12. Half a dozen means 6. Likewise, a Mole means 6.022 x 10e+23 ( or an Avogadro's number). The weight of ONE mole of a given substance is called the Molar mass (common symbol Mw). One mole weighs one times the molar mass. 2 moles weigh 2 times the molar mass.


I'll solve the first one for you, approximately. 1 mole of SO2 weighs [32+(2x16)], which means in approximately 64 g of SO2, there's one mole of SO2. So, if 64g contains one mole, how many moles are there in 25g?


(25/64) moles (approximately).
Reply:1) moles = grams/Molar Mass





Molar mass is the mass in grams of the sum of the atomic masses of all the atoms in a formula.


Ex. CO2: 1C x 12. + 2 O x 16 = 12 + 32 = 44grams/1mol





Find mol:= 35g/44g/mol = 0.80 mol CO2





2) mol = g/MM





to find g, rearrange the formula: g = mol x MM





KOH: find MM = 1 K x 39.1 + 1 O x 16 + 1 H x 1.01 = 56.1g/mol





g = mol x MM = 0.035 mol KOH x 56.1 = 2.0 g KOH





3) mol = g/MM





to find MM, rearrange the formula: MM = g/mol





MM = 0.40g/0.0025mol = 160g/mol or 1.6 x 10^2g/mol