## ashna Group Title molarity and molality ! 2 years ago 2 years ago

1. waterineyes

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. ashna

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

3. waterineyes

Yes..

4. waterineyes

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. ashna

i dont know !

6. waterineyes

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

7. ashna

ah .. that previous one ?

8. ashna

derived from molarity .. ?

9. waterineyes

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

10. waterineyes

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

11. ashna

how many formulas are there in this chapter ?

12. waterineyes

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. ashna

what if am bald ?? :P

14. waterineyes

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. ashna

okay !

16. waterineyes

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

17. ashna

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

18. ashna

|dw:1345436660852:dw|

19. waterineyes

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

20. ashna

yeah back !

21. ashna

@waterineyes

22. waterineyes

I have to go ashna...

23. waterineyes

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

24. ashna

okay

25. waterineyes

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

26. waterineyes

Hurry up find the molecular mass of NaCl first..

27. waterineyes

Because you have to find Number of Moles first..

28. ashna

23+35.5 ?

29. waterineyes

Yep...

30. waterineyes

so it is 58.5..

31. ashna

58.5

32. waterineyes

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

33. ashna

2 / 58.5

34. waterineyes

Yep solve it hurry up..

35. ashna

0.034...

36. waterineyes

Yep..

37. waterineyes

Now can you find molarity by using its formula ??

38. waterineyes

For that you need volume of solution too..

39. ashna

0.034 / 4

40. waterineyes

For that you need volume of solution too..

41. waterineyes

No..

42. ashna

then ?

43. waterineyes

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

44. waterineyes

Yes we can ashna..

45. ashna

okay .. you leave then !

46. waterineyes

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. waterineyes

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

48. ashna

you better leave water ..

49. waterineyes

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. ashna

hm..

51. waterineyes

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

52. ashna

yes

53. waterineyes

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. ashna

hm.. bye

55. waterineyes

Bye take care as well..