## anonymous 4 years ago molarity and molality !

1. anonymous

See there your question is given like: 2g of a Substance is added to water... Can you tell me what is solute here and what is the solvent here ??

2. anonymous

solvent is water and solute is that 2g substance .. correct ?

3. anonymous

Yes..

4. anonymous

For finding molarity you need number of moles solute.. How will you find number of moles of solute because it is given in 2 grams.. ??

5. anonymous

i dont know !

6. anonymous

For that there is a formula you will use that..

7. anonymous

ah .. that previous one ?

8. anonymous

derived from molarity .. ?

9. anonymous

$Number \; Of \; Moles = \frac{Grams \; Present}{Molecular \; Mass \; Of \; that \; Substance}$

10. anonymous

No no that one.. This one I have written above now..

11. anonymous

how many formulas are there in this chapter ?

12. anonymous

Now let us try to implement this formula on a question so that you can understand it properly. There are as many formulas as there are hairs on your head.. Ha ha ha..

13. anonymous

what if am bald ?? :P

14. anonymous

Wait for one second my mummy is calling me.. Have a look on that formula and try to memorize it and understand it as well..

15. anonymous

okay !

16. anonymous

Then there are as many formulas as there are hairs on my head And I don't like to be bald..

17. anonymous

am not bald either .. i were just kidding :)

18. anonymous

|dw:1345436660852:dw|

19. anonymous

Mention me when you will come.. I am in Mathematics Section..

20. anonymous

yeah back !

21. anonymous

@waterineyes

22. anonymous

I have to go ashna...

23. anonymous

So let us hurry up I can explain you this thing..

24. anonymous

okay

25. anonymous

See you are given with question like this: 2g of a NaCl is dissolved in 4 L of water.. Find the Molarity..

26. anonymous

Hurry up find the molecular mass of NaCl first..

27. anonymous

Because you have to find Number of Moles first..

28. anonymous

23+35.5 ?

29. anonymous

Yep...

30. anonymous

so it is 58.5..

31. anonymous

58.5

32. anonymous

Now 2g you are given with.. Can you find number of moles now ??

33. anonymous

2 / 58.5

34. anonymous

Yep solve it hurry up..

35. anonymous

0.034...

36. anonymous

Yep..

37. anonymous

Now can you find molarity by using its formula ??

38. anonymous

For that you need volume of solution too..

39. anonymous

0.034 / 4

40. anonymous

For that you need volume of solution too..

41. anonymous

No..

42. anonymous

then ?

43. anonymous

I don't know.. Ha ha ha..

44. anonymous

Yes we can ashna..

45. anonymous

okay .. you leave then !

46. anonymous

For that you should know the density of water.. It will be given to you.. I think approximately density of water is 1.. So: $Density = \frac{Mass}{Volume}$

47. anonymous

Oh god what I am doing.. We have to find volume of NaCl not water..

48. anonymous

you better leave water ..

49. anonymous

Yeah but I will explain you after coming for sure.. May be till then others may help you.. Or I think I have written the question wrong...

50. anonymous

hm..

51. anonymous

But the main concept is you got how to find number of moles of solute when it is not given.. Right ??

52. anonymous

yes

53. anonymous

It did increase some knowledge of yours. Okay now I have to leave.. There is work for me from my neighborers.. So I have to go now..

54. anonymous

hm.. bye

55. anonymous

Bye take care as well..