Matters- As pure and impure

 

Anything that occupies some space, having mass, volume and can be felt by one or more out of five senses is called matter. The purest form of matter is called an element. An element is a substance which cannot be split up into two or more simpler substances by the usual chemical methods of applying heat, light or electric energy.

A pure substance consists of a single type of particles. All the elements and compounds are pure substances because they contain only one kind of particles. eg. Hydrogen, Carbon, Oxygen, Carbon-monoxide,Copper, Gold, Silver.

 

A pure substance has a fixed composition as well as a fixed boiling point and melting point. The presence of impurities generally increases the melting and boiling point of the pure substances

 

Q: 8.1 Which of the statement is true about pure substances

a.     Homogeneous mixtures are pure as they have same composition throughout.

b.     22 carat goldis pure in nature.

c.     Elements are not pure in nature.

d.     Gold and carbon dioxide both are pure in nature.

 

Q: 8.2 The boiling point of pure water is 100^oC. What likely be the effect on the boiling point of water if 150 gm NaCl is added to one litre of water ?

______________________________________________________________________________________________________________________________.

 

Q: 8.3 Carbonmonoxide gas can be separated into carbon and oxygen gas by ________________.

     a.     Chemical methods

     b.     Applying heat,

     c.     Sunlight or electric energy

     d.     None of the above.

Q: 8.4The melting point of 1 Kg carbon dioxide is –79°C. What will be the melting point of 500gmCarbondioxide?

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Q: 8.5 Why table salt resist free flow and becomes damp during rainy season moisture if exposed to damp air although sodium chloride does not hygroscopic?

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Q: 8.6 Universe is made up of matter justify this statement?

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Answer Key and Credit:

ANSWER 8.1:-

 

Scientific Literacy:

FRAMEWORK	CHARACTERISTICS
Competency	Evaluate and design scientific enquiryExplain the phenomenon scientifically
Knowledge system	Knowledge of science-Physical
Context	Global
Cognitive demand	Low
Item format	Simple Multiple choice question.
Proficiency level	2

 

Credit Pattern:

Full Credit:	2
Partial Credit:	1
Nil Credit:	0

 

Full Credit:	(D)(d) Gold and carbon dioxide both are pure in nature.
Partial Credit:	Only if one factor is mentioned like Gold or Carbonmondioxide
Nil Credit:	Other responses.(A), (B) and (C)

 

ANSWER 8.2:-

Scientific Literacy:

FRAMEWORK	CHARACTERISTICS
Competency	Interpret data and evidencescientificallyEvaluate and design scientific enquiry
Knowledge system	Knowledge of science-Physical
Context	Global
Cognitive demand	Medium
Item format	Closed constructive
Proficiency level	4

Credit Pattern:

Full Credit:	2
Partial Credit:	1
Nil Credit:	0

 

Full Credit:	Boiling point of water will increase.
Partial Credit:	101oC or above
Nil Credit:	Boiling point of water will remains constant or decreasies.

 

ANSWER 8.3:-

Scientific Literacy:

FRAMEWORK	CHARACTERISTICS
Competency	Use scientific evidences to draw conclusion
Knowledge system	Procedural
Context	Global
Cognitive demand	Low
Item format	Simple Multiple choice question.
Proficiency level	2

Credit Pattern:

Full Credit:	2
Partial Credit:	1
Nil Credit:	0

 

 

Full Credit:	(D) None of the above.
Partial Credit:	------
Nil Credit:	Other responses.(A), (B) and (C)

 

ANSWER 8.4:-

Scientific Literacy:

FRAMEWORK	CHARACTERISTICS7
Competency	Interpret Data and Evidence Scientifically
Knowledge system	Physical
Context	Global
Cognitive demand	Low
Item format	Closed constructive
Proficiency level	1

Credit Pattern:

Full Credit:	2
Partial Credit:	1
Nil Credit:	0

 

 

Full Credit:	Same –79°C.
Partial Credit:	------
Nil Credit:	Other responses or missing

 

ANSWER 8.5:-

Scientific Literacy:

FRAMEWORK	CHARACTERISTICS7
Competency	Evaluate and design scientific enquiry
Knowledge system	Earth
Context	Global
Cognitive demand	High
Item format	Closed constructive
Proficiency level	5

Credit Pattern:

Full Credit:	2
Partial Credit:	1
Nil Credit:	0

 

Full Credit:	The presence of CaCl2 and MgCl2 impurities in table salt absorb moisture if exposed to moist air and resist free flow.
Partial Credit:	Due to the presence of impurities.
Nil Credit:	Any other or missing.

ANSWER 8.6:-

Scientific Literacy:

FRAMEWORK	CHARACTERISTICS7
Competency	Evaluate and design scientific enquiry
Knowledge system	Earth
Context	Global
Cognitive demand	High
Item format	Closed constructive
Proficiency level	5

Credit Pattern:

Full Credit:	2
Partial Credit:	1
Nil Credit:	0

 

Full Credit:	Space research have shown that all the star, planet and satellites are very big in size and made up of solid particle and sometimes possess (gaseous) atmosphere. Even our earth planet contains soil, mineral rocks, water and atmosphere therefore according to the definition mentioned anything that occupies some space, having mass, volume and can be felt by one or more out of five senses is called matter.
Partial Credit:	Universe is made up of solid liquid and gases.
Nil Credit:	Any other or missing.

Unit test for class XI Chemistry 2020-21

 

Endoscopy -

John  complained of severe stomach pain and started crying.  His elder brother consoled him and took  him to  gastroenterologist. Doctor advised for endoscopy and asked him to come next day with an empty stomach. John was not for the test he was afraid . However  his elder brother Jim was a medical student, explained the need for the test and told him that it was not a painful experience. He further explained that  a tube containing a fine  glass fibre would be inserted through the food pipe and light through this pipe would allow the doctor to  examine inside the stomach. Endoscopes can be directly  inserted into bladder, colon and other organs for direct visual examination. The test was done  and John felt good after taking medicine for two days .The coloured  X-ray image of a  patient's abdomen shows an endoscope winding through the colon is shown.

 

Question 1. What is the working principle of glass fibre  in the endoscope?

 

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Question 2. What are the two conditions for the light to travel along  the pipe?

 

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.............................,............................................................................................

 

Question 3. The critical angle for glass is ........

               (a) 50°

               (b) 42°

               (c) 45°

               (d) 30°

 

Question 4. The outer concentric shell in the fibre optic is called........

               (a)   Cladding

               (b).   Core

               (c)   Mantle

               (d)    Coating

 

ANSWERS:-

 

1.          Full Credit :-Total Internal Reflection

Nil Credit :- No answer Or any wrong answer

2.          Full Credit :-the two conditions are. 1. light must travel from optically denser medium to optically rare medium  2. the angle of incidence in the denser medium must be greater than the critical angle

Half Credit :- For any one condition

Nil credit :- No answer Or any wrong answer

3.          Full Credit :- (b)42°

Nil Credit. :- No answer Or any wrong answer

            4.    Full Credit :- (a) Cladding

                    Nil Credit. :- No Answer or any other Answer

Metallic Character and Non-Metallic Character- Pisa Based question for cbse exams

 Metallic Character

The ability of an atom to donate electrons and form positive ion (cation) is

known as electropositivity or metallic character. Down the group, metallic

character increases due to increase in atomic size and across the period, from left to right electropositivity decreases due to decrease in atomic size.

Non-Metallic Character

The ability of an atom to accept electrons to form a negative ion (anion) is

called non-metallic character or electronegativity. The elements having high

electro-negativity have a higher tendency to gain electrons and form anion.

Down the group, electronegativity decreases due to increase in atomic size and

across the period, from left to right electronegativity increases due to decrease

in atomic size.

(i). Which of the following correctly represents the decreasing order of metallic

    character of Alkali metals plotted in the graph?

   a) Cs>Rb>Li>Na>K

   b) K>Rb>Li>Na>Cs

   c) Cs>Rb>K>Na>Li

   d) Cs>K>Rb>Na>Li

(ii). Hydrogen is placed along with Alkali metals in the modern periodic table

      though it shows non-metallic character

    a) as Hydrogen has one electron & readily loses electron to form negative

       ion

     b) as Hydrogen can easily lose one electron like alkali metals to form

     positive ion

    c) as Hydrogen can gain one electron easily like Halogens to form

       negative ion

   d) as Hydrogen shows the properties of non-metals

(iii). Which of the following has highest electronegativity?

    a) F

    b) Cl

    c) Br

    d) I

(iv). Identify the reason for the gradual change in electronegativity in halogens

      down the group.

    a) Electronegativity increases down the group due to decrease in atomic

      size

    b) Electronegativity decreases down the group due to decrease in

      tendency to lose electrons

   c) Electronegativity decreases down the group due to increase in atomic

     radius/ tendency to gain electron decreases

   d) Electronegativity increases down the group due to increase in forces of

    attractions between nucleus & valence electrons

(v). Which of the following reason correctly justifies that “Fluorine (72pm) has

     smaller atomic radius than Lithium (152pm)”?

   a) F and Li are in the same group. Atomic size increases down the group

   b) F and Li are in the same period. Atomic size increases across the

   period due to increase in number of shells

  c) F and Li are in the same group. Atomic size decreases down the group

  d) F and Li are in the same period and across the period atomic size/radius

  decreases from left to right.

CLONING

 CLONING

Cloning is a technique scientist use to make exact genetic copies of living things. Genes, cells, tissues, and even whole animals can all be cloned.

Some clones already exist in nature. Single-celled organisms like bacteria make exact copies of themselves each time they reproduce. In humans, identical twins are similar to clones. They share almost the exact same genes. Identical twins are created when a fertilized egg splits in two.

Scientists also make clones in the lab. They often clone genes in order to study and better understand them. To clone a gene, researchers take DNA from a living creature and insert it into a carrier like bacteria or yeast. Every time that carrier reproduces, a new copy of the gene is made.

Animals are cloned in one of two ways. The first is called embryo twinning. Scientists first split an embryo in half. Those two halves are then placed in a mother’s uterus. Each part of the embryo develops into a unique animal, and the two animals share the same genes. The second method is called somatic cell nuclear transfer. Somatic cells are all the cells that make up an organism, but that are not sperm or egg cells. Sperm and egg cells contain only one set of chromosomes, and when they join during fertilization, the mother’s chromosomes merge with the father’s. Somatic cells, on the other hand, already contain two full sets of chromosomes. To make a clone, scientists transfer the DNA from an animal’s somatic cell into an egg cell that has had its nucleus and DNA removed. The egg develops into an embryo that contains the same genes as the cell donor. Then the embryo is implanted into an adult female’s uterus to grow.

In 1996, Scottish scientists cloned the first animal, a sheep they named Dolly. She was cloned using an udder cell taken from an adult sheep. Since then, scientists have cloned cows, cats, deer, horses, and rabbits. They still have not cloned a human, though. In part, this is because it is difficult to produce a viable clone. In each attempt, there can be genetic mistakes that prevent the clone from surviving. It took scientists 276 attempts to get Dolly right. There are also ethical concerns about cloning a human being.

Researchers can use clones in many ways. An embryo made by cloning can be turned into a stem cell factory. Stem cells are an early form of cells that can grow into many different types of cells and tissues. Scientists can turn them into nerve cells to fix a damaged spinal cord or insulin-making cells to treat diabetes.

The cloning of animals has been used in a number of different applications. Animals have been cloned to have gene mutations that help scientists study diseases that develop in the animals. Livestock like cows and pigs have been cloned to produce more milk or meat. Clones can even “resurrect” a beloved pet that has died. In 2001, a cat named CC was the first pet to be created through cloning. Cloning might one day bring back extinct species like the woolly mammoth or giant panda.

 Q1.1.Name the first mammal to be cloned from an adult cell.

(a)  Copy cat

(b)  Dolly

(c)  Snuppy

(d)  None of these

Q1.2. What is Cloning?

……………………………………………………………………………………………………………………………………………………………………………………………………..

Q1.3. Write two applications of animal cloning.

……………………………………………………………………………………………………………………………………………………………………………………………………

Q1.3. Do you think that cloning is good practice? Justify.

……………………………………………………………………………………………………………………………………………………………………………………………………

Catalytic Converter- PISA Competency Based Question in Chemistry

 

                            PISA Competency Based Question in Chemistry

Catalytic Converter

Most modern cares are fitted with a catalytic converter that makes the exhaust fumes of the car less harmful to people and to the environment.

pic-1

pic-2

About 90% of harmful gases are converted into less harmful ones. Here are some of the gases that go into the converter and how they come out of it.

Catalytic Converter

Question 1 : Catalytic Converter

Use the information in the diagram above to give an example of how the catalytic converter makes exhaust fumes less harmful.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

CATALYTIC CONVERTER SCORING 1

Full credit

·       The conversion of carbon monoxide or nitrogen oxides, to other compound is mentioned.

·       Carbon Monoxide is changed into carbon dioxide.

·       Nitrogen oxides are changed into nitrogen.

·       It changes harmful fumes into non-harmful fumes. E.g. CO into CO2 (90%).

·       Carbon dioxide and nitrogen are not as harmful as carbon monoxide and nitrogen oxides.

No credit

·       Other responses.

·       The gases become less harmful.

·       It purifies the carbon monoxide and nitrogen oxides.

PLASTICS- PISA Competency Based Question in Chemistry

 

PLASTICS

The advent of fuel-based plastics has revolutionized the industrial world and there is no area of manufacturing which is untouched by plastics. Convenience and cost factors have pitch forked plastics as the most preferred material of choice till recently, a rethinking about its impact on environment and sustainability is slowly putting a brake on its continued use. While cheap petroleum fuels from which most plastics are derived was once justified to introduce them in place of traditional materials like glass and metals, this plea cannot hold any more since the cost of non-renewable fossil fuels increased several folds during the last 3 decades. 

Research based on plastics proves their injurious nature towards human health in many direct or indirect ways. Phthalates or phthalate esters are esters of phthalic acid mainly used as plasticizers (substances added to plastics to increase their flexibility) in Poly Vinyl Chloride (PVC). PVC is a widely used material, including extensive use in toys and other children's products such as chewy teethers, soft figures and inflatable toys. Di (2-ethylhexyl phthalate (DEHP), dibutyl phthalate (DBP), di-isononylphthalate (DINP), di-isodecyl phthalate (DIDP), benzyl - butyl - phthalate (BBP) and di-n- octyl- phthalate (DNOP) are phthalates mainly used in converting polyvinyl chloride (PVC) from a hard plastic to a flexible plastic. Phthalates migrate into the air, into food and into people including babies in their mother's wombs. Phthalates can be released from soft PVC by surface contact, especially where mechanical pressure is applied e.g., during chewing of a PVC teether). Release of phthalates during manufacture, use and disposal of PVC products, in addition to their use as additives in ink, perfumes etc. has lead to their ubiquitous distribution and abundance in the global environment.[1]

Growing literature links many of the phthalates with a variety of adverse outcomes, including increased adiposity and insulin resistance,[2] decreased anogenital distance in male infants,[3] decreased levels of sex hormones,[4] and other consequences for the human reproductive system, both for females and males,[5] Infants and children may be especially vulnerable to the toxic effects of phthalates given their increased dosage per unit body surface area, immature metabolic system capability and developing endocrine and reproductive system.

Question 1.1

 

Mention two reasons of popularity of plastics.

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--------------------------------------------------------------.  

Question intent:

Context: Science and Technology

Situation: Global

Process: Identifying plastics

Theme: Ill effects of plastic 

Level: Medium

Question format: short constructed response

 

Full credit: mentioning two reasons

Partial credit: mentioning one reason

No credit: For no reason or wrong answer

 

Question 1.2 

 

Plasticizers are used to -

1. make plastic strong
2. make plastic flexible
3. make plastic durable
4. make plastics colour

 

Question intent:

Context: Science and Technology

Situation: Global

Process: Demonstrating knowledge and understanding plastic

Theme: plastic 

Level: Medium

Question format: MCQ type.

 

Full credit: B. make plastic flexible

No credit: For other responses or missing

Question 1.3

Plastic has ill effects specially in human

A. Respiratory system

B. Circulatory system

C. Reproductive system

D. Excretory system

Question intent:

Context: Science and Technology

Situation: Global

Process: Demonstrating knowledge and understanding plastic

Theme: plastic 

Level: Medium

Question format: MCQ type.

 

Full credit: C Reproductive system

No credit: For other responses or missing

 

Question 1.4

Name two phthalates used to make PVC flexible.

 

-------------------- & ----------------------------.

 

Question intent:

Context: Science and Technology

Situation: Global

Process:  understanding plastics

Theme: Ill effects of plastic 

Level: Medium

Question format: short response

 

Full credit: mentioning two

Partial credit: mentioning one

 No credit: for no answer or wrong answer 

Question 1.5

Phthalates migrate into –--------, ----------– and in human body to make its distribution global.

Question intent:

Context: Science and Technology

Situation: Global

Process:  understanding plastics

Theme: Ill effects of plastic 

Level: Medium

Question format: fill in the blanks

Full credit: mentioning two (air, food)

Partial credit: mentioning one (air or food)

No credit: for no answer or wrong answer