0
Q:

Leakage in LP gas cylinders is easily detected by adding

 A) mercaptans B) propylene C) carbon disulphide D) phosgene

Explanation:

mercaptans (or thioalcohols) have a foul odour

Subject: Chemistry
Q:

Which structural formula represents a dipole?

 A) 4 B) 3 C) 2 D) 1

Explanation:

What is Dipole :

when two atoms in a molecule have substantially different electronegativity: One atom attracts electrons more than another, becoming more negative, while the other atom becomes more positive.

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0 22
Q:

Which of the following elements is a metal?

 A) Se B) I C) Zn D) S

Explanation:

In chemistry, a metal is an element that readily forms positive ions (cations) and has metallic bonds. Metals are opaque, lustrous elements that are good conductors of heat and electricity. Most metals are malleable and ductile and are, in general, denser than the other elemental substances.

Examples of metals are aluminium, copper, iron, tin, gold, lead, silver, titanium, uranium, and zinc.

Here Se - Selenium is an element but is not a metal, S - Sulphur is not a metal and I - Iodine is also not a metal.

Hence, Zn - Zinc is the only metal in the given options.

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2 21
Q:

What is the gram formula mass of ${\mathbf{Li}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$?

 A) 101.2487 B) 109.9446 C) 111.2687 D) 106.5871

Explanation:

The term gram formula mass is synonymous with molecular mass. So, to get this, we must add molar mass of all the elements in this compound.

Given compound is Lithium Sulphate - ${\mathbf{Li}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$

Elemental calculation ::

Li  -  Lithium   -   6.941    -     2   -   13.88200 %
S  -  Sulfur     -    32.065   -    1   -   32.065 %
O  -  Oxygen   -   15.9994  -    4   -   63.9976 %

Now, total = 12.6264 + 29.1647 + 58.2090 = 109.9446

Hence, the gram formula mass of Li2SO4 = 109.9446.

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1 66
Q:

Which formula represents a nonpolar molecule?

 A) H2O B) CF4 C) HCl D) H2S

Explanation:

You have to consider three things.

1. First, are the bonds polar?

Look at differences in electronegativity and if  it is >0.5, bonds are polar.

2. Second, does the molecule have unshared electron pairs?

If so, they generally lead to a polar molecule.

3. Third, is the molecule symmetric?

If so, then although the bonds may be polar, the symmetry cancels out the individual bond polarity and the molecule is non polar.

CF4 follows all the rules above and has a symmetric distribution of charge, making it nonpolar. The others all have asymmetric charge distributions.

Hence, CF4 represents a Non-polar molecule.

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1 40
Q:

Order of basicity of amines in gaseous state?

 A) 2'> 1'> 3' > NH3 B) 3' > 2' > 1'> NH3 C) 1' > 2' > 3'> NH3 D) 2'> 3'> 1' > NH3

Explanation:

The order of basicity in ammonia is different in gaseous phases vs. aqueous phases due to hydrogen bonding.

So in gaseous phases it's the well known: 3' > 2' > 1'> NH3. Just so we're on the same page, this is due to the inductive effect of electron donating alkyl groups--they destabilize the lone pair on nitrogen atom, making nitrogen more basic.

But in aqueous phase, the order is slightly different: 2'> 1'> 3' > NH3.

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0 250
Q:

Which of the following is not an allotrope of carbon?

 A) Diamond B) Graphene C) Ethylene D) Buckminsterfullerene

Explanation:

Allotropes are different structural modifications of an element, that is, each of two or more different physical forms in which an element can exist.

Carbon is capable of forming many allotropes due to its valency. Well-known forms of carbon include charcoal, diamond, graphite, buckminsterfullerene and graphene.

Hence, Ethylene is not an allotrope of Carbon.

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1 88
Q:

Which compound matches the IR Spectrum?

 A) 1, 5 – hexadiene B) 3 – Hexanol C) Trans – 4 – octene D) None of the above

Explanation:

3 – Hexanol:

There is no alcohol stretch present in the spectrum. Therefore, the above structure is not suitable for the given spectrum.

Trans – 4 – octene:

There is no vinyl bending present in the spectrum. Therefore, the above structure is not suitable for the given spectrum.

The vinyl bending and other stretches were matched with the above structure.

Hence, the c = c stretch, vinyl bending and stretch were matched with the above structure.

Therefore, the given spectrum belongs to 1, 5 – hexadiene.

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0 123
Q:

Which of these molecules are polar? Check all that apply.

 A) SO2 B) CH2Cl2 C) PCl3 D) All the above

Explanation:

1) SO2                  2) CH2Cl2                3) PCl3

How to check the given molecules are polar or non polar :

If the electronegativity of the two bonded atoms are different then the bond is polar. Although, some molecules contain polar bonds, the molecule may be non-polar. If the polarity of all the bonds present in the molecule are cancel each other then molecule is non-polar.

In the given options,

SO2  is polar because the dipole moments on the O do not cancel.

PCl3  is polar because the P-Cl bonds do not cancel out.

CH2Cl2  polar because the C-Cl bonds do not cancel.

Hence, in brief, Polar molecules are molecules with net dipole due to the presence of partial positive and partial negative charge.

For example, water is a polar molecule that has partial positive and partial negative charge on it. CO2 is a non polar compound.

Therefore, all the given options SO2, CH2Cl2 and PCl3 are Polar molecules.