Frequently Asked Logical Questions and their Answers | YT Academy

Frequently Asked Logical Questions and their Answer by YT Academy

Chemistry

Q.1 What are some examples of how intermolecular forces affect the boiling point of a molecule?

Ans: 

Here is the best example:

1. Water has strong Hydrogen bonding (a strong inter-molecular force)therefore its boiling point is higher from those which don’t have H-bonding.
2. For example Bromine water have weak type inter-molecular forces known as London dispersion forces therefore its B.P is 58.8 C which much less than water (100 C ).

Moreover, due to large size of Bromine ,its polarizability is greater , as a result more extensive London dispersion force are present. This factor is responsible for B.p of bromine up to 58.8 C.

Q.2 What does water smell like?

Ans: Pure water is a colorless, odorless (not having any smell) and tasteless liquid.

if there is any smell or color in water, it shows that it is impure.

Q.3 What is most acidic between benzoic and acetic?

Ans: BENZOIC acid is stronger due to its resonance structures. 

Acidic Strength Depends on:

• Stability of conjugate base and Electronegativity
• Resonance Structures of Conjugate Base (formed after losing a proton from Respective acid)

Greater the stability of base formed after donating electron more will be the chance to lose proton which in turn results in more acidic character.

Benzoic acid has more stable resonance structures due to delocalization of electrons in benzene ring which results in rather stable benzoate anion than acetate anion (conjugate base formed after losing a proton from Benzoic acid) and hence Benzoic acid has more tendency to lose proton therefore its acidic strength is more than acetic acid.

Q.4 What are the chemical constituents of chalk?

Ans: Calcium Carbonate (CaCO3).

Q.5 How do you convert pKa to Ka?

Ans: Here ‘p’ means negative logarithm (log) of Ka.

So first we take Antilog of pKa and then multiply the power by ‘-1’ .

for example: pKa = 14

we take antilog of 14.

antilog 14 = 10 raised to the power 14 .

But as ‘p’ is negative log so power will be multiplied by -1 . Hence the Final answer will be : “10 raised to the power -14 or 10e-14.

Q.6 How do I determine which atomic bond is less or more polar?

Ans: By finding the electronegativity difference between bonded atoms we can find polarity of bond. Greater the difference greater will be polarity. 

Generally bonds having difference above 0.5 are considered as polar.

You can guess more or less polarity by considering  following factors:

• Nature of bonded atoms (electropositive and electronegative)
• Geometry of molecules

Q.7 How do I prepare a pH buffer made from citric acid and Na2HPO4?

Ans: Acid buffer from citric acid can be prepared by making a solution of citric acid with its salt with strong base (like Tri-sodium citrate ‘Na3C6H5O7’ )

pH of the solution can be calculated by following formula:

pH = pKa + log [conc. of salt] / [conc. of acid]

Where pKa is negative log of Ka ( dissociation constant of acid)

Q.8 Which has the highest vapor pressure?

Ans: Boiling point is defined as: the temperature at which vapour pressure of liquid becomes equal to atmospheric or external pressue!

Which has low boiling point , it will have greater vapour pressure at a temperature!

Example : boiling points of noble gases increases down the group due to increase in polarizablity .So neon will have low boiling point than krypton, and therefore neon has high Vapour pressure w.r.t krypton at a given temperature.

Mainly Vapour pressure depends upon intermolecular forces between molecules, greater the intermolecular force the greater the lower will be its vapour pressure at a specific temperature.

Best Example: Water has strong Hydrogen Bonding(intermolecular force) between its molecule i.e. 2 H-bonds per molecule but ethanol has only one H-bond per molecule therefore due to greater hydrogen bonding in water it shows less vapour pressure than ethanol at particular temperature.

Q.9 How is an element a pure substance?

Ans: Element is a pure substance because it is made up of same kind of atom which are distinguished and different from all other substance and have its own characteristics and identity in pure form.

For example : gold is an element. In pure form gold contain all atoms having atomic number of ‘79’ there is no other kind of atom which have this atomic number and not any element other than gold that is made up of atoms having atomic number ‘79’.

Actually when we say ‘an element’ we are talking about a specific type of matter which has different identity in this world and has specific chemical as well as physical properties which distinguish it from all other kinds of matter.

‘Name of an element is for their identity.’

If you say ‘gold’ we come know to that you are talking about that particular matter having that kinds of atoms.

Summing up, as element refers to a specific type of matter having specific kind of atoms therefore we say that is pure form of matter.

Q.10 Na^2-  is Acid or Base?

The specie which has the tendency to donate a pair of electron is called base. Na^2-  (if it exists in nature) will easy and readily donate its electrons so it will be a strong base.