HSC Chemistry Sample Paper 1

HSC Chemistry Sample Paper 1

Chemistry

Section A

Select and write the correct answers to the following questions:

(i) A compound forms hcp structure, number of Octahedral and Tetrahedral voids in 0.5 mole of substance is respectively.

(a)

(b)

(c)

(d)

(ii) In which reaction mechanism carbocation is formed?
(a)
(b)
(c) Both (a) and (b)
(d) None of them

(iii) The solubility product of a sparingly soluble salt is . Its solubility in is:
(a)
(c)
(b)
(d)

(iv) Neutral solutions have the of.
(a) 8
(b) 7
(c) 9
(d) 14

(v) Polonium has the half-life of.
(a) 13.8 days
(b) 12 days
(c) 5 days
(d) 102 days

(vi) Most stable oxidation state of titanium is:
(a) +2
(b) +3
(c) +4
(d) +5

(vii) The number of electrons that have total charge of 965 coulomb is:
(a)
(b)
(c)
(d)

(viii) In which of the following series all the elements are radioactive in nature: (a) lanthanides

(b) actinides

(d) s-block elements

(ix) Pressure cooker reduces cooking time for food because:

(a) boiling point of water involved in cooking is increased

(b) heat is more evenly distributed in the cooking space

(d) cooking involves chemical changes helped by a rise in temperature.

(x) is an example of:

(a) Aldohexose

(b) Aldoheptose

(d) Ketoheptose

Answer the following questions:

(8)

(i) Define Enthalpy of fusion.

(ii) What is rate determining step?

(iii) Name two gases which deplete ozone layer.

(iv) Write examples of addition polymers and condensation polymers.

(v) What are aromatic ketones?

(vi) Write reaction of P-toluenesulfonyl chloride with Diethylamine.

(vii) Which nanomaterial is used for tyres of car to increase the life of tyres?

(viii) How many asymmetrical carbon atoms are present in a molecule of fructose?

Section B

4. Attempt any Eight of the following questions:

A solution has an osmotic pressure of at 300 k. What would be its concentration?
What are bidentate ligands? Give one example.
How nanotechnology plays an important role in water purification techniques?
What is a salt bridge?
What two uses of the alloys.
Why haloarenes are less reactive than halo alkanes?
Acetic acid is ionised in its decimolar solution. Calculate the dissociation constant of acid.
What is entropy? Give its units.
Give two evidences for presence of formyl group in glucose.
What is the standard enthalpy of combustion? Give an example.
Explain the effect of dilution of solution on conductivity.
What is difference between a double salt and a complex? Give one example.

5. Section C

6. Attempt any Eight of the following questions:

While considering boiling point elevation and freezing point depression a solution concentration is expressed in molality and not in molarity. why?
Why aldehydes are more reactive toward nucleophilic addition reactions than ketones?
Why dissociation of is suppressed by the addition of ?
Write structural formulae for:

(i) 3-methoxyhexane

(ii) methyl vinyl ether

(iii) 1-ethylcyclohexanol

One mole of an ideal gas is compressed from against a constant external pressure of . The work involved in the process is . Calculate the final volume.
How catalyst increases the rate of reaction? Explain with the help of potential energy diagram for catalysed and uncatalyzed reactions.
What current strength in amperes will be required to produce of Cu from solution in 1 hour? Molar mass of .
Describe the manufacturing of by contact process.
What is meant by LDD and HDP? Mention the basic difference between the same with suitable examples.
How stability of the coordination compounds can be explained in terms of equilibrium constants?
What is zeroth order reaction? Derive its integrated rate law. What are the units of rate constant?
Draw structures of following compounds.
(i) 2,5-Diethylphenol
(iii) 2-methoxypropane
(ii) Prop-2-en-1-ol

7. Section D

8. Attempt any Three of the following questions:

The density of iridium is . The unit cell of iridium is fcc. Calculate the radius of iridium atom, molar mass of iridium is .
Write reaction showing conversion of -bromoiso-propyl benzene into -isopropyl benzoic acid (3 steps).
Explain optical isomerism in 2-chlorobutane.
What are the differences between cast iron, wrought iron and steel.
Give two reactions showing oxidising property of concentrated . Write the structures of and

A] Answer Key

10. Section A

(i) (a)

(ii) (a)

(iii) (a)

(iv) (b) 7

(v) (a) 13.8 days

(vi) (c) +4

(vii) (c)

(viii) (c) -block elements

(ix) (a) boiling point of water involved in cooking is increased

(x) (d) Ketoheptose

(i) It is defined as change in enthalpy when one mole of solid is converted into liquid without any change in temperature at constant pressure. ( fus )

(ii) The slowest step in the reaction mechansim is called rate determining step.

(iii) Two gases that deplete ozone layer are Nitric oxide (NO), chlorofluro carbons (freons).

(iv) (a) Addition Polymers: Polythene, Teflon, Polyacrylonitrile, Polyvinylchloride (PVC), etc. (b) Condensation Polymers: Terylene, Nylon-6,6, Bakelite, Novolac, etc.

(v) The compounds in which group is attached to either two aryl groups or one aryl and one alkyl group are called aromatic ketones.

e.g.

(vi)

(vii) Carbon black

(viii) 3 (three) Asymmetrical carbon atoms.

Section B

Given: Osmotic pressure

Temperature

Formula:

Bidentate Ligands: The ligands which bind to central metal through two donor atoms are called bidentate ligands.

e.g.,

Ethylenediammine binds to the central metal atom through two nitrogen atoms

Similarly. Oxalate ligand utilises electron pair on each of its negatively charged oxygen atoms on linking with central metal.

Nanotechnology plays an important role in water purification techniques. Some of its uses are:

(i) Water contains waterborne pathogens like viruses, bacteria.

(ii) Cost-effective filter materials coated with silver nanoparticles (AgNps) is an alternative technology and can be used in water purification.

(iii) Silver nanoparticles act as a highly effective antibacterial agent that kills E coli from water.

(i) It provides electrical contact between two solutions and thereby completes the electrical cicrcuit.

(ii) It prevents the mixing of two solutions.

(iii) It maintains electrical neutrality in both the solutions by the transfer of ions.

12. The two uses of alloys are:

(i) Bronze, an alloy of copper and tin is tough, strong and corrosion resistant. It is used for making statues, medals and trophies.

(ii) Cupra-nickel, an alloy of copper and nickel is used for making machinery parts of marine ships, baots. For example, marine condenser tubes.

(i) The low reactivity of aryl halides is due to resonance effect and hybrid state of carbon to which halogen atom is attached.

(ii) In aryl halides, one of the lone pairs of electrons onhalogen atom is in conjugation with p-electrons of the ring. Due to resonance, the bond acquires partial double bond character. Thus, the bond in haloarenes is stronger and shorter than haloalkanes. Hence, it is difficult to break C-X bond in haloarenes. (e.g. bond length in chlorobenzene is as compared to bond length in alkyl chloride which is ).

13. Given:

Percent dissociation Concentration (c)

decimolar

To find: Dissociation constant of acid

Formulae: used

(i) Percent dissociation

(ii)

Calculation: Using formula (i),

Using formula (ii),

The dissociation constant of acid is .

Entropy is a measure of molecular disorder or randomness. An entropy change of a system is equal to the amount of heat transferred to it in a reversible manner divided by the temperature in Kelvin at which the transfer takes place. Thus,

Units of entropy are:

14. Two evidences in favour of the presence of formyl group in glucose are:

(i) Glucose gets oxidised to a six-carbon monocarboxylic acid called gluconic acid on reaction with bromine water which is a mild oxidising agent. Thus, the carbonyl group in glucose is in the form of formyl ( ).

(ii) Hemacetal group of glucopyranose structure is a potential aldehyde (formyl) group. It imparts reducing properties to glucose. Thus, glucose gives positive Tollen’s test or Fehling test.

The standard enthalpy of combustion of a substance is the standard enthalpy change accompanying a reaction in which one mole of the substance in its standard state is completely oxidised.

Consider the reaction,

In the above reaction, the standard enthalpy change of the oxidation reaction, is the standard enthalpy of combustion of (g).

(i) The electrolytic conductivity is the electrical conductance of unit volume of solution. It depends on the number of current-carrying ions present in unit volume of solution.

(ii) On dilution total number of ions increases as a result of an increased degree of dissociation.
(iii) An increase in the total number of ions is not in the proportion of dilution. Therefore the number of ions per unit volume of solution decreases.

(iv) This results in a decrease of conductivity with a decrease in the concentration of the solution.
14. A double salt dissociates in water completely into simple ions, whereas a coordination complex dissociates in water with at least one complex ion.

e.g., Mohr’s salt, is a double salt while is a complex.

Section C

In boiling point elevation and freezing point depression, we deal with the systems whose temperature is not constant. We cannot express the concentration of the solution in molarity because it changes with temperature whereas molality is temperature independent. Hence, while considering boiling point elevation and freezing point depression a solution concentration is expressed in molality and not in molarity.
Reactivity of aldehydes and ketones is due to the polarity of carbonyl group which results in electrophilicity of carbon. In general aldehydes are more reactive than ketones towards the nucleophilic attack. This can be well explained in terms of both the electronics effect and steric effect.

16. (i) Influence of electronic effects:

(a) Alkyl groups have an electron-donating inductive effect (+1). A ketone has two electron-donating alkyl groups bonded to carbonyl carbon which are responsible for decreasing its positive polarity and electrophilicity.

(b) In contrast aldehydes have only one electrondonating groups bonded to the carbonyl carbon. This makes aldehydes more electrophilic than ketones.

(ii) Steric effects:

(a) Two bulky alkyl groups in ketone come in the way of the incoming nucleophile. This is called steric hindrance to nucleophilic attack.

(b) On the other hand, nucleophile can easily attack the carbonyl carbon in aldehyde because it has one alkyl group and is less crowded or sterically less hindered. Hence, aldehydes are more easily attacked by nucleophiles.

and both dissociate to produce ions which are common to both.

is a weak electrolyte. It dissociates to a little extent.

is a strong electrolyte. It undergoes complete dissociation.

both and provide ions.

The concentration of ions in the solution increases due to the complete dissociation of .

According to Le-Chatelier’s principle, the effect of the stress (the addition of ions from ) applied to the ionisation equilibrium of is reduced by shifting the equilbrium in the backward direction.

ions combine with ions to produce unionised . Thus, the dissociation of is suppressed by the addition of .

(ii) Methyl vinyl ether

(iii)

1- Ethylcyclohexanol

Given: Initial volume

External pressure

To find : Final volume

Formula:

Calculation : Initial volume

External pressure bar

Now, from formula,

(i) A catalyst provides an alternative pathway associated with lower activation energy.

Potential energy barriers for catalysed and uncatalysed reactions.

(ii) The potential energy diagram compares the potential energy barries for the catalysed and uncatalysed
reactions. The barrier for uncatalysed reaction is larger than that for the same reaction in the presence of a catalyst

(iii) Consider the decomposition of in aqueous solution catalysed by ions.

. At room temperature, the rate of reaction is slower in the absence of a catalyst with its activation energy being . In the presence of catalyst, iodide ion ( , the reaction is faster since the activation energy decreases to 57 .

Given: of .

Molar mass of

1 hour

To find: Current strength (in amperes)

Formula used:

(i) Mole ratio

(ii) mole ratio molar mass

18. Calculation:

(i) Stoichiometry for the formation of is

Using formula (i),

(ii) Using formula (ii),

mole ratio molar mass

Current strength in amperes required to produce of Cu from is .

Manufacturing of sulphuric acid by contact process is done through following sequential steps:

(a) Preparation of :

(b) Conversion of to (oxidation):

(d) Oleum is diluted with water to get desired concentration of .

The sulphuric acid obtained by contact process is 96 pure.

LDP is a branched polymer of ethene with polymeric chains loosely held. Hence, even though it is tough, it is extremely fiexible. Therefore, LDP is used in producing extruded films, sheets, mainly for packaging and household uses like in preparation of squeeze bottles, attractive containers, etc. where low tensile strength and flexibility is required.

On the other hand, HDP is a linear polymer of ethene with closely packed polymeric chains. Hence, it is much stiffer than LDP and has high tensile strength and hardness. Therefore, HDP is used in the manufacture of toys and other household articles like buckets, dustbins, bottles, pipes, laboratory wares and other objects where high tensile strength and stiffness is required.

The stability of the complex can be explained in terms of equilibrium constant. Higher the value of larger is the thermodynamic stability of the complex. The equilibria for the complex formation with the corresponding values are given below:

Among the above equilibrium constant data, is more stable than and because has higher value of equilibrium constant.

Zero Order Reactions: The rate of zero order reaction is independent of the reactant concentration.

For zero-order reaction, the differential rate law is given by rate

Rearrangement of Eq. (i) gives

Integrating between the limits

at and at gives

Hence,

Units of rate constant of zero order reactions

The units of rate constant of zero order reaction are the same as the rate.

(iii)

(ii)

19. Section D

Given: Type of unit cell is fcc.

Density of iridium

Molar mass of iridium

To find: Radius of iridium atom

Formula used:

(i)

(ii) For fcc unit cell,

Calculation: For fcc unit cell, , using formula (i)

Using formula (ii)

Radius of iridium atom is .

Step 1: Converting – group to :

p-Bromoisopropylbenzene

p-Cyanoisopropyibenzene
Step 2: Converting – group to – :

p-Cyanoisopropylbenzene Amide
Step 3: Converting – group to :

(i) The stereoisomerism in which the isomers have different spatial arrangements of groups/atoms around a chiral atom is called optical isomerism.

(ii) 2-chlorobutane has one chiral carbon atom. The spatial arrangement of the four different groups around the chiral atom is different.

(iii) Structure of 2-chlorobutane and its image can be represented as:

(iv) 2-Chlorobutane cannot superimpose perfectly on its mirror image as shown in the figure. Hence, 2-chlorobutane exhibits optical isomerism.

30.

Cast Iron	Wrought Iron	Steel
1. Hard and brittle	Very soft	Neither too hardnor too soft
2. Contains 4% carbon.	Contains lessthan carbon.	Contains 0.2 to carbon
3. Used for makingpipes, manufacturingautomotive parts,pots, pans, utensils,etc.	Used for makingpipes, bars forstay bolts, enginebolts and rivets,etc.	Used in buildingsinfrastructuretools, ships,automobiles,weapons, etc.