Solution quiz-1

 

Solution

Quiz

 

1. Assertion: Molality is a better method to express concentration than molarity
   Reason: Molality is defined in terms of mass of solvent and not mass of solution.
   1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
   2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
   3.   Assertion is correct, but reason is wrong statement.
   4.   Assertion is wrong, but reason is correct statement.
2. Assertion: Soda bottles are sealed under high pressure.
   Reason: High pressure increases the solubility of carbon dioxide gas.
   1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
   2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
   3.   Assertion is correct, but reason is wrong statement.
   4.   Assertion is wrong, but reason is correct statement.
3. Assertion: There will not be any change in concentration of an ethanol and water mixture containing 85% ethanol by volume on boiling.
   Reason: It is because azeotropes boil out in constant composition.
   1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
   2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
   3.   Assertion is correct, but reason is wrong statement.
   4.   Assertion is wrong, but reason is correct statement.
4. Assertion: Benzene and hexane form an ideal solution.
   Reason: Both benzene and hexane are hydrocarbons.
   1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
   2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
   3.   Assertion is correct, but reason is wrong statement.
   4.   Assertion is wrong, but reason is correct statement.
5. Assertion: 1 molar NaCl solution has higher boiling point than one molar urea.
   Reason: NaCl dissociates into ions in solution.
   1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
   2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
   3.   Assertion is correct, but reason is wrong statement.
   4.   Assertion is wrong, but reason is correct statement.
6. Assertion: A raw mango placed in concentrated salt solution loses water shrivel into pickle.
   Reason: The salt solution is hypotonic compared to the raw mango.
   1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
   2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
   3.   Assertion is correct, but reason is wrong statement.
   4.   Assertion is wrong, but reason is correct statement.
7. Assertion: Helium is mixed with nitrogen and oxygen in diving cylinders
   Reason: Helium has comparatively low KH value.
   1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
   2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
   3.   Assertion is correct, but reason is wrong statement.
   4.   Assertion is wrong, but reason is correct statement.
8. Assertion: Ice containing dissolved sugar will melt at a higher temperature than pure ice.
   Reason: Dissolving sugar in water leads to a depression in freezing point.
   1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
   2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
   3.   Assertion is correct, but reason is wrong statement.
   4.   Assertion is wrong, but reason is correct statement.
9. Assertion : Vapour pressure of a solution is more that of the pure solvent.
   Reason: The solute particles occupy certain area of the surface of the solution which reduces the amount of vapour.
   1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
   2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
   3.   Assertion is correct, but reason is wrong statement.
   4.   Assertion is wrong, but reason is correct statement.
10. Which of the following aqueous solutions should have the highest boiling point?
    1.   1.0 M NaOH
    2.   1.0 M Na2SO4
    3.   1.0 M NH4NO3
    4.   1.0 M KNO3
11. KH value for Ar(g), CO2 (g), HCHO (g) and CH4 (g) are 40.39, 1.67, 1.83×10–5 and 0.413 respectively.
    Arrange these gases in the order of their increasing solubility.
    1.   HCHO< CH4 < CO2 <Ar
    2.   HCHO< CO2 < CH4 <Ar
    3.   Ar< CO2 < CH4 < HCHO
    4.   Ar< CH4 < CO2 < HCHO
12. 4.On dissolving sugar in water at room temperature solution feels cool to touch. Under which of the following cases dissolution of sugar will be most rapid?
    1.   Sugar crystals in cold water.
    2.   Sugar crystals in hot water.
    3.   Powdered sugar in cold water.
    4.   Powdered sugar in hot water.
13. Maximum amount of a solid solute that can be dissolved in a specified amount of a given liquid solvent does not depend upon __________.
    
    1.   Temperature
    2.   Nature of solute
    3.   Pressure
    4.   Nature of solvent
14. The molecular weight of benzoic acid in benzene as determined by depression in freezing point method corresponds to :
    1.   Ionisation of benzoic acid
    2.   Dimerisation of benzoic acid
    3.   Trimerisation of benzoic acid
    4.   Solvation of benzoic acid
15. The hard shell of an egg was dissolved in HCl. The egg was then placed in a concentrated solution of NaCl. What will happen?
    1.   The egg will shirnk.
    2.   The egg will swell.
    3.   The egg will become harder.
    4.   No visible change noticed.
16. How many grams of 70% concentrated Nitric acid solution is used to prepare 250mL of 2.0M HNO3?
    1.   45 g
    2.   90.0 g
    3.   70.0 g
    4.   54.0 g
17. Dipole induced dipole interactions are present in which of the following pairs?
    1.   Water and ethanol
    2.   Cl2 and CCl4
    3.   HCl and Iodine molecules.
    4.   SiF4 and He atoms
18. The molarity of solutions obtained by mixing 750 mL of 0.5M HCl with 250 mL of 2M HCl will be:
    1.   0.875 M
    2.   0.01M
    3.   0.001M
    4.   0.1M
19. Which of the following is dependent on temperature?
    1.   Molarity
    2.   Mole fraction
    3.   Mass percentage
    4.   Molality
20. If the molality of the solution is doubled. The value of molal depression constant (kf) will be
    1.   Halved
    2.   Tripled
    3.   Unchanged
    4.   Doubled
21. Which of the following liquid pairs show a positive deviation from Rault’s law-
    1.   Water and HCl
    2.   Benzene and Methanol
    3.   Water and Nitric acid
    4.   Acetone and Chloroform
22. An unripe mango placed in the solution of concentrated NaCl to prepare pickle, shirnks due to :
    1.   It gains water due to reverse osmosis
    2.   It loses water due to reverse osmosis
    3.   It gains water due to osmosis
    4.   It loses water due to osmosis
23. Assertion : When methyl alcohol is added to water, boiling point of water increases.
    Reason : When a volatile solute is added to a volatile solvent elevation in boiling point is observed.
    1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
    2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
    3.   Assertion is correct, but reason is wrong statement.
    4.   Assertion is wrong, but reason is correct statement.
24. Assertion : When NaCl is added to water a depression in freezing point is observed.
    Reason : The lowering of vapour pressure of a solution causes depression in the freezing point.
    
    1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
    2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
    3.   Assertion is correct, but reason is wrong statement.
    4.   Assertion is wrong, but reason is correct statement.
25. Assertion : When a solution is separated from the pure solvent by a semipermeable membrane, the solvent molecules pass through it from pure solvent side to the solution side.
    Reason : Diffusion of solvent occurs from a region of high concentration solution to a region of low concentration solution.
    1.   Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
    2.   Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
    3.   Assertion is correct, but reason is wrong statement.
    4.   Assertion is wrong, but reason is correct statement.
26. The boiling point of an azeotropic mixture of water and ethanol is less than that of water and ethanol. The mixture shows
    1.   no deviation from Raoult’s Law.
    2.   positive deviation from Raoult’s Law.
    3.   negative deviation from Raoult’s Law.
    4.   that the solution is unsaturated.

S-Block elements slide presentation part-2

It is the slide presentation on s-block elements part-2 for class 11. here you can scroll to see all slides.

 

Click here to see slide presentation on s-block elements part -1

pH CHANGE AS THE CAUSE OF TOOTH DECAY

 Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up of calcium hydroxyapatite (a crystalline form of calcium phosphate) is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.

You might have heard that the pH level in the body affects your health. Studies have shown that lower, or acidic, pH levels are associated with a greater risk of serious health conditions including type 2 diabetes, heart disease, and obesity. Studies have also shown that higher, or alkaline, pH levels are linked to improvements in memory and cognition, reduced pain, and lower risk of hypertension (high blood pressure), and stroke.

Another interesting link is pH levels and bone health.  Extensive research has been conducted on the effects of pH on bone health, and studies have discovered that low-acid diets can help improve bone density. According to Dr Sara Gottfried, the Journal of Nutrition published a study that stated that alkaline mineral waters can decrease bone resorption and even lower parathyroid hormone levels which regulate the release of calcium from bone.

An alkaline diet is one that incorporates foods that can increase the pH levels. Interestingly, an alkaline diet is associated with an increase in growth hormone which can burn fat, improve libido, and retain a general sense of well-being.

Maintaining a good pH balance in the mouth allows a healthy balance of good and bad bacteria. Many of the good bacteria in our mouth are harmless and some bacteria, known as probiotics, aid in the digestion of foods. Other good bacteria actually protect our teeth and gums.

Certain foods, such as sugary beverages, snacks, and some grains, increase the acidity in the mouth. The pH of the mouth can change dramatically with the types offoods we eat. Foods that are highly acidic, like lemons, lowers the pH, while foods like melons increases the pH.

The saliva can help neutralize the acid, but eating acidic foods can increase the acidity of the saliva. If the pH takes a long time to neutralize in the mouth, it may give bad bacteria enough time to wreak havoc on the teeth and gums. Typically it may take a few minutes or a few hours for the pH to neutralize. An acidic mouth is an optimal environment for bad bacteria to grow, and if given the time and the ability, it can cause tooth decay.

Question 5.1 The pH of mouth is generally-

(a) Less than 7

(b) Greater than 7

(c) Equal to 7

(d) Cannot be determined.

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

 

Q5.2 The hardest substance in the body has _______________ and __________ elements as the major components.

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

Q5.3 What according to you, could be the reason of not allowing the kids to eat plenty of chocolates?

Q 5.4 Give two benefits of having an alkaline diet.

Answer-key

5.1 (a) less than 7- Full credit.

Any other response- no credit

5.2  Calcium and Phosphorus– Full credit

Calcium, phosphorus and oxygen – Full credit

Any one of Calcium, phosphorus and oxygen – partial credit

Any other response- no credit

5.3 Sugary substances turn into acidic when reacted with saliva in our mouth. This acid decays the teeth and is the reason of cavity in the teeth. – Similar responses – full credit.

Any other response- no credit

5.4Higher, or alkaline, pH levels are linked to improvements in memory and cognition, reduced pain, and lower risk of hypertension (high blood pressure), and stroke. Low-acid diets can help improve bone density. It allows a healthy balance of good and bad bacteria in the mouth and helps prevent tooth decay. – Any two of these responses- full credit.

Any other response – no credit

Refined sugar

 Sucrose is a common sugar. It is a disaccharide, a molecule composed of two monosaccharide units ie glucose and fructose. Sucrose is produced naturally in plants, from which table sugar is refined. It has a molecular formula C₁₂H₂₂O₁₁.‌Refined sugar is made by extracting and processing the sugar naturally found in foods like corn, sugar beets, and sugar cane. This refined sugar is then added to foods for various purposes, such as to boost flavor.

Refined sugar is harmful for health. Children are very fond of ice cream, cold drinks, chocolates, and sweets, etc. which contain refined sugar. Higher intake of refined sugar forms acid in mouth which reacts with calcium phosphate present in enamel and tooth decay starts. These days children have lots of cavities. Lots of people are suffering from diabetes.

Q10.1 The chemical compound present in cane sugar is

     a.      Sucrose

     b.      Glucose

     c.       Fructose

     d.      Lactose

 Q10.2 The molecular mass of sucrose is

     a.      352 u

     b.      342 u

     c.       364 u

     d.      326 u

     Q10.3 If 3.42 gm of sucrose is dissolved in 18gm of water in a beaker. Estimate the number of oxygen atoms in the beaker.

       -------------------------------------------------------------

Q10.4How much do you agree with the following statement?

 

		Strongly Agree	Agree	Disagree	Strongly disagree
a	Refined sugar is the only cause of tooth decay
b	One should always have sugar free diet

Answer Marking Scheme

10.1. Full  credit :2 if response is a  as Sucrose is produced naturally in plants

          No credit :0 if response is b, c, d

10.2). Full  credit :2 if response is b as sucrose has a molecular formula C₁₂H₂₂O₁₁;12 x 12+22 x 1 + 11 x 6 = 342

          No credit :0 if response is a, c, d

10.3) . Full  credit :2 if response is 6.68 x 10²³ :0.01mole of sucrose contains 11 x 6.022 x 10²³ = 6.6242 x 10²² oxygen

    Total oxygen in solution =(6.022+.662) x 10²³ =6.684 x 10²³

    Partial credit :1 for correct formula

        No credit :0 for wrongly calculated

10.4 (a) Full  credit:2 if response is strongly disagree

             Partial credit :1 if response disagree

             No credit :0 other response or missing

   (b)   Full  credit :2 if response is strongly disagree

Partial credit :1 if response disagree

                      No credit :0 other response or missing 

MANUFACTURING PROCESS OF SOAP

 

The fats and oils required for manufacturing soap are extracted from the plants and animals.  To make the fatty acids called triglyceride molecule, 3 fatty acid molecules are bonded to 1 molecule of glycerine. Fatty acids are weak acids composed of 2 parts. A carboxylic acid group having 1  hydrogen atom, 2 oxygen atoms, and 1 carbon atom and a hydrocarbon chain attached to the carboxylic acid group. Earlier the alkali required for making soaps were obtained from the animals but now they are clinically composed. The common alkalis used in soap making are sodium hydroxide and potassium hydroxide.

 

Q4.1 . Why do we consider fatty acid as weak acid?

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

Q4.2. How  are atoms in  “Acid” functional group  bonded together?

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

Q4.3. Each chemical has common name such as sodium chloride known as common salt .Similarly NaOH and KOH also have common names. Give the names.

.................................................................................................................................

Q4.4. Sonali’s mother has cracked hands due to washing clothes regularly. What are the possible  reasons of it ?

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

Answer key-

4.1 full credit : low ionization when dissolve in water  or low conductivity of electricity

       Partial credit: any one given above

4.2 Full credit :  structure  of –COOH

        No credit : other response

4.3 Full credit : caustic soda and caustic potash

     Partial Credit :  Any one of the above

     No credit : other response

4.4 Full credit : Due to soap with high amount of NaOH(base).

      No credit : other response

Valence

Valence, also spelled valency, in chemistry, the property of an element that determines the number of other atoms with which an atom of the element can combine. Introduced in 1868, the term is used to express both the power of combination of an element in general and the numerical value of the power of combination.

The explanation and the systematization of valence was a major challenge to 19th-century chemists. In the absence of any satisfactory theory of its cause, most of the effort centred on devising empirical rules for determining the valences of the elements. Characteristic valences for the elements were measured in terms of the number of atoms of hydrogen with which an atom of the element can combine or that it can replace in a compound. It became evident, however, that the valences of many elements vary in different compounds. The first great step in the development of a satisfactory explanation of valence and chemical combination was made by the American chemist G.N. Lewis (1916) with the identification of the chemical bond of organic compounds with a pair of electrons held jointly by two atoms and serving to hold them together. In the same year, the nature of the chemical bond between electrically charged atoms (ions) was discussed by German physicist W. Kossel. After the development of the detailed electronic theory of the periodic system of the elements, the theory of valence was reformulated in terms of electronic structures and interatomic forces. This situation led to the introduction of several new concepts—ionic valence, covalence, oxidation number, coordination number, metallic valence—corresponding to different modes of interaction of atoms.

Q1. Why do Helium, Neon and Argon have zero valency?

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Q2. Helium has 2 electrons in its valence shell but its valency is not 2. Do you agree?

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Q3. Ramesh answered that ³⁵Cl and ³⁷Cl have different valences. Do agree with his answer, justify.

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Q4. An atom with 3 Protons and 4 Neutrons will have a valency ………………

ANSWER KEY-

(1)Full credit: Helium has 2 electrons in its only energy shell, while Argon and Neon have 8 electrons in their valence shells. As these have maximum number of electrons in their valence shells, they do not have any tendency to combine with other elements. Hence they have a tendency equal to zero.

No credit: Other responses and missing.

(2). Full credit:No.  Its duplet is complete. Hence the valency is zero.

No credit: Other responses and missing.

(3) Full credit:No.³⁵Cl and ³⁷Cl will have same valency. Valency is determined by number of protons or number of electrons. Since the number of protons/electrons are same in both the cases mentioned above, the valencies will be same.

No credit: Other responses and missing.

(4) Full credit:   ANS-1.

No credit: Other responses and missing

Full credit:        ANS-1.

No credit: Other responses and missing