What volume of 75% alcohol by weight (d=0.80g/cm3) must be used to prepare 150cm3 of 30% alcohol by weight (d=0.90g/cm3)?

As par question mass of alcohol is same in both solutions. Consider V ml of alcohol required.

Then 

75​/100×0.8×V=30/100 ×0.9×150

V=67.5mL

ILLUSTRATIVE EXAMPLES:

(1):Calculate the mole fraction of solute in the 12 molal aqueous solution of CaCO3.

(2):The mole fraction of glucose in aqueous solution is 0.2 , The molality of solution will be.

(3):If the mole fraction of a solute is changed from 1/4 to 1/2 in the 800 gm of solvent . then the ratio of molality will be .

(4):Mole fraction of I2 (iodine) in benzene (C6H6) is 0.2 . Calculate the molality of iodine (I2) in benzene.

(5):Calculate the amount of water that should be added to 16 gm methanol to make mole fraction of methanol as 0.25.?

Calculate the average atomic weight of an element (X) containing three isotopes X56, X57 and X59 and natural occurrence of these isotopes are 90%, 8% and 2% respectively.

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What is the misconceptions about resonance?

Many misconceptions are associated with resonance and the same need to be dispelled. 

You should remember that : 

(1) The cannonical forms have no real        existence.

(2)The molecule does not exist for a       certain fraction of time in one     cannonical form and for other       fractions of time in other cannonical       forms.

(3) There is no such  equilibrium between the cannonical forms as we have between tautomeric forms (keto and enol) in tautornerisrn. 

(4) The molecule as such has a single       structure which is the resonance       hybrid of the cannonical forms and       which cannot as such be depicted by     a single Lewis structure.

(5) Resonance is a theoratical concept. The resonating structure have no physical reality, i.e., they do not actually exist. Only the hybrid structure exists. The hybride structure can not be represented on the paper but resonating structure can be represented.

Releted Questions:

(1) What is the structure of Blue vitriol (CuSO4) .5H2O also represent the H-Bond with water molecules?

(2) Why bond angle of hydrides of group 15, decreases down the group?

(3) Why SF6 behave inert towards hydrolysis?

(4) What are the SESQUI OXIDES ? give the examples.

(5) Arrange in increasing order of extent of hydrolysis [ CCI4, MgCI2, AICI3, PCl5, SiCI4].

(6) Why SF6 behave inert towards hydrolysis?

(7) Although Sulphur contain vacant d-orbital but SF6 does not under go hydrolysis. Why ?

(8) Phosphorus can form PCl5 but nitrogen can not form NCl5 why?

(9) Why PCl3 hydrolysed while NCl3 can not be hydrolysed?

(10) CCl4 can not be hydrolysed but SiCl4 can be. Why?

(11) Silianol (SiH3OH) is more acidic than methanol (CH3OH) why?