Question

How many molecules approximately do you expect to be present in

(i) a small sugar crystal weighing 10 mg.

(ii) 1 drop of water with 0.05 cc volume.

Answer 1

For that, you would use molar calculations. A mole is the amount of a substance that contains Avogadro’s number, or 6.022*10^23 molecules. Since that number is well chosen, it’s also quite easily to calculate from molecular weights.The basic atomic mass unit (or Dalton) is the weight of one 12th of a Carbon atom. Which is also almost exactly the weight of one proton or neutron. By looking at a periodic table, you can in fact easily count the atomic weight of one molecule of almost any substance if you have the total formula.Water’s total formula is H20. So there’s two hydrogen atoms and one oxygen atom in a molecule of water. Since oxygen has an atomic weight of 16 and hydrogen one of 1, the atomic weight of water is 16+2*1=18.Now. From the way avogadro’s number is defined, we know that one mole of water, that is 6.022*10^23 molecules of water, weigh exactly 18 grams. Or the other way round, if we have 18 grams of water, we know it’s 6.022*10^23 molecules. (Plus or minus our measuring precision, of course.)Google tells me a drop of water is 0.05 grams. Good enough, I suppose.So, we have, by basic primary school arithmetic:6.022*10^23/18/20 molecules of water in a drop. For that, my calculator gives me:1.67*10^21 grams.4.7k Views · View UpvotersRelated QuestionsMore Answers BelowHow many molecules of water and oxygen atoms are present in 0.9g of water?How many molecules of water are present in a drop of water which has a mass of 50mg?How many molecules of water are present in 0.05 moles?How many neutrons are present in a molecule of heavy water?How many H2O molecules are there in 10 drops of water?Ask New QuestionNeil Menon, Research Scholar - Materials Science and NanotechnologyAnswered Sep 22, 2017 · Author has 923 answers and 12.1m answer viewsOriginally Answered: How many molecules are in one drop of water?Assuming standard temperature and pressure, let’s take the volume of 1 drop of water as 0.05 mL.Given that the density of water is 1g/cc, the mass of 0.05 mL water = 0.05 g (taking 1 cc = 1 mL).The molecular weight of water is about 18g/mol (H22O and all, you know, where H = 1g/mol and O = 16g/mol! Look it up!)Thus, the number of moles in 0.05 mL water = 0.05/18 = 0.00278 moles.Now, 1 mole of anything contains 6.023 x 102323 atoms, molecules, elementary units, whatever!So, 0.00278 moles of water will have 0.00278 * 6.023 * 102323 molecules of water.This is, 1.674 x 102121 molecules.We good?Great! So, now that I’ve done your homework for you, can I go and watch some TV?Please?4.3k Views · View UpvotersX Zhang, DPhil from University of Oxford (2019)Answered Dec 26, 2017Originally Answered: How many water molecules are there in one water drop?

Assuming a drop of water is 0.18g, then since the molar mass of water (chemical formula H2OH2O) is 18g/mol, we have 0.18/18 = 0.01 mol of water in one drop of water. The Avogadro constant gives the number of particles in one mole of substance as NA=6.02×1023NA=6.02×1023 particles/mol (this is the same for any identity of the particle, thus named a constant). Therefore there are roughly 6.02×1023×0.01=6.02×10216.02×1023×0.01=6.02×1021water molecules in a drop of water.

406 ViewsAniruddh Ramanujam, studied at Smt. Ramkuwar Devi Fomra Vivekananda VidyalayaAnswered Jan 16, 2018 · Author has 80 answers and 7.1k answer viewsOriginally Answered: How many molecules are present in 1 drop of water?Volume of 1 drop of water = 0.050.05 ml.Mass of 1 drop of water= 0.05ml×1g/ml0.05ml×1g/ml..= 0.05 g.No. Of molecules = 0.05×6.022×0.05×6.022×10231023/18/18= 1.673×1.673×10211021374 Views · View UpvotersAltuğ Gür, M.Sc. Chemical Engineering, Hacettepe University (1998)Updated Jan 18, 2018 · Author has 701 answers and 1m answer viewsAssuming pure water at 20 °C.1 drop is roughly equal to 1/20 ml = 0.05 ml.Density of water at 20 °C is 0.998 g/ml. So:0.05 x 0.998 = 0.0499 g1 mole of water weighs 18 g. Therefore:0.0499/18 = 0.00277 moles.1 mole of a pure substance contains as many atoms/molecules as Avogadro's number. Hence:0.002770.00277x6.0226.022x 1023=0.01671023=0.0167x 1023=1.67∗10211023=1.67∗1021 molecules of water in one drop.1.8k Views · View UpvotersAnkit Anand, studied at Kendriya Vidyalaya No 1, AFS JodhpurAnswered Mar 11, 2018Originally Answered: How many molecules are in one drop of water?let we suppose volume of water be 0.18 ml( i take 0.18ml bcoz to make my calculation easier) ;no. of moles in 0.18 ml water =0.18/18=0.01;we know no. of mole anything contain=Avogadro no.(6.023 x 10^23)thus,0.01 moles of water will have=0.01*6.023 x 10^23= 6.23*10^216.23*10^21 moles