Physics, Chemistry, Mathematics Forums

Well friends i have something for you over here. You see when we write the Ksp of a compound such as PbS for example we say its Ksp is about 10^(-40), but practically speaking when i have a concentation of the order of 10^(-10) In a litre flask for the sulphide ion[ which can be easily attained] ,I need to have a concentration of 10^(-30) for the lead ion in the same litre but practically speaking the lowest concentration for a litre of any solution is when 1 atom of it is dissolved in a litre i.e 1/N where N is the avagadro number. so how do i acheve it .

Q. Which of the following are true about phenol??

a) It can be oxidised more readily than ethanol.
b) it is basic in aqueous soln.
c) it forms picric acid on nitration
d) it gives purple colour when treated with aq. FeCl₃

It is a more than one correct ques.
Please again tell me your suggested answers... i will confirm the answer in a few days....
I marked it as acd.
My friends have raised doubts about a). What say???

Q. Increasing amount of solid HgI₂ is added to an aqueous solution containing 0.1 mol of KI. Which of the following graphs does represent the variation of depression in freezing point of the resulting solution with the amount of HgI₂ added???
For all graphs, delta T_f is represented on Y-axis and moles of HgI₂ added on X-axis:

a) A straight line inclined to the axis at an angle b/w 0^o and 90^o lying in the 1st quadrant having +ve y-intercept and -ve x-intercept, having no breaks and increasing as x increases.
b) A similar line as in a) but this time the line becomes parallel to x-axis beyond x = 0.05
c) A similar line as in a) but this time having a negaive slope and becomes parallel to x-axis beyon x = 0.05
d) A similar line as in c) but this time it becomes parallel to x-axis beyond x = 0.1.

See for the uploaded picture file if it gets uploaded. I hope u can imagine the graphs.... Plz tell me the answer somebody and along with reasoning...

An unbiased die with faces marked 1,2,3,4,5 & 6 is rolled four times. Out of four face values obtained, the probability that the minimum face value is not less than 2 and the maximum face value is not greater than 5 is then

(a) 16/81   (b) 1/81  (c) 80/81  (d) 65/81

Ans as given is (a)16/81.

Find the chance of throwing at least one ace in a single throw with two dice.

[Ref:- Hall & Knight , Pg 374, Example 3 ]

 I dont understand the question itself. How is an ace related to a die?

I was not getting the correct ans. to the following three questions, Please answer them.

1.The no. of solutions of the equation x⁶- x⁵+ x⁴- x³+ x²- x + 3/4 = 0 is ....
The ans. is given as zero...Please explain.
2.The no. of ordered pairs (a,b,c) such that L.C.M (a,b) = 1000, L.C.M (b,c) = 2000, L.C.M (c,a) = 2000 is....
The ans. is given as 70. Please try and explain if u get it.
3.If alpha is a real root of x³+ 2x² + 10x - 20 = 0, then
a. alpha is rational
b.(alpha)² is rational
c. alpha is irrational
d. (alpha)² is irrational
ans. is given as c,d. Please explain me the ans.

Q. If same quantity of electricity is passed through three electrolytic cells containing FeSO₄, Fe₂(SO₄)₃ and Fe(NO₃)₃, then
A) The amounts of iron deposited in FeSO_{4 and} Fe₂(SO₄)₃, are equal.
B) The amounts of iron in FeSO₄ is 1.5 times of the amt. of iron deposited in Fe(NO₃)_3.
C) The amounts of iron deposited in Fe₂(SO₄)₃ and Fe(NO₃)₃ are equal.
D) The same amount of gas is evolved in all the three cases at the anode.

It is again a more than one correct ques.
I got the answer as BC.
But my friends are saying for D also.
What do you say? Please reply soon

Could anyone please explain LCR circuit to me? I find it a bit hard .

According to Huygen's principle, every point becomes a source of secondary wavelets sending such wavelets in all directions when reached by a progressive wave travelling in that elastic medium and at any instant, the shape of the new wave can be found out by drawing a surface enveloping all the secondary wavelets.

I have seen in all the books, that the secondary wavelets travel only in forward direction through, according to Huygen's Principle, they should travel backwards too. Can anyone please point out the reason behind it?

Can someone please clear these doubts?

1. P(x,y) is a point on the curve y² = 2x³ , such that the tangent is perpendicular to the line 4x-3y+2=0. Then, 1/x - 1/y =__________

a) 24

b) 50

c) 8

d) 4

Ans. : a)

2. Let f be the function defined by f(x) = cos x - 1 + x²/2. Then

a) f(x) is increasing on the real line

b) f(x) is decreasing on the real line

c) f(x) increases in (-infinity,0] and decreases in [0, infinity)

d) f(x) decreases in (-infinity,0] and increases in [0, infinity)

Ans. : d)

Please give the explanation as well. Thnx!