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Such substances are also referred to as associated colloids. These sols are quite stable because of the strong attractive forces between the particles of dispersed phase and dispersion medium. These sols are less stable than the lyophilic sols. Explain what is observed when : i a beam of light is passed through colloidal sol ii an electrolyte NaCl is added to ferric hydroxide sol iii electric current is passed through a colloidal sol?
Delhi , ; Outside Delhi, , Solution: i The path of light as well as the colloidal particles become visible because of Tyndall effect. When a beam of light is passed through a true solution, no scattering of light takes place. When the same beam of light is passed through a colloidal solution, scattering of light takes place. The visibility of dust particles in a semi darkened room, when a beam of sunlight enters or when a beam of light is thrown from a projector, are familiar examples of this scattering.
As a result, they get coagulated. What are emulsions? What are their different types? Give example of each type. Solution: Emulsions: It is a colloidal system in which both the dispersed phase and the dispersion medium are liquids, e. Types of emulsions: a Oil-in-water type in which small droplets of an oil are dispersed in water, e. How do emulsifires stabilise emulsion?
Name two emulsifiers. Solution: The role of an emulsifier in stabilising an emulsion can be explained in two ways: a It is believed that an emulsifier gets concentrated at the oil-water interface i. It forms a protective coating around each drop of oil and thus, prevents the oil drop from coming in contact with one another.
The oil drops remain suspended in water and are not coagulated. Just as a lubricant reduces the friction in the various parts of machine, an emulsifier also tries to reduce the interfacial tension between oil and water by suitable means.
Thus, oil and water remain in company of each other and do not get separated. The commonly used emulsifying agents are soaps, detergents, lyophilic colloids, proteins, gums, gelatin, caesin, agar etc. Action of soap is due to emulsification and micelle formation. The RCOO � ions are, therefore, present on the surface with their COO � groups in water and the hydrocarbon chains R staying away from it and remain at the surface.
But at critical micelle concentration, the anions are pulled into the bulk of the solution and aggregate to form a spherical shape with their hydrocarbon chains pointing towards the centre of the sphere with COO � part remaining outward on the surface of the sphere. The cleansing action of soap is due to the fact that soap molecules form micelle around the oil droplet in such a way that hydrophobic part of the stearate ions is in the oil droplet and hydrophilic part projects out of the grease droplet like the bristles.
Since the polar groups can interact with water, the oil droplet surrounded by stearate ions is now pulled in Water and removed from the dirty surface. Thus soap helps in emulsification and washing away of oils and fats.
The negatively charged sheath around the globules prevents them from coming together and forming aggregates. Give four examples of heterogeneous catalysis. Solution: In heterogeneous catalysis, the catalyst is present in a different phase than that of the reactants,e.
What do you mean by activity and selectivity of catalysts? Solution: Important features of solid catalyst: a Activity: The activity of a catalyst is its ability to accelerate chemical reactions.
It depends upon the strength of chemisorption to a large extent. The catalytic activity of a metal for hydrogenation increases as we move from Group 5 metals to Group The maximum activity is shown by metals of Groups 7, 8 and 9. It mean a substance which acts as a catalyst in one reaction may not act as a catalyst Ncert Solutions Class 10th Chemistry Chapter 4 Journal in other reaction e.
Question Describe some features of catalysis by zeolites. Solution: a Zeolites are hydrated aluminosilicates which have a three dimensional network structure containing water molecules in their pores. What is shape selective catalysis? Solution: The catalytic reaction that depends upon the pore structure of the catalyst and the size of the reactant and product molecules is called shape-selective catalysis. Zeolites are good shape-selective catalysts because of their honeycomb-like structures.
They are microporous aluminosilicates with three dimensional network of silicates in which some silicon atoms are replaced by aluminium atoms giving Al-O-Si framework. The reactions taking place in zeolites depend upon the size and shape of reactant and product molecules as well as upon the pores and cavities of the zeolites.
They are found in nature as well as synthesised for catalytic selectivity. Solution: i Electrophoresis : Refer answer number 15 iii. If somehow, the charge is removed, the particles will come nearer to each other to form aggregates or coagulate and settle down under the force of gravity.
The process of settling down of colloidal particles is called coagulation. Since particles ions or smaller molecules in a true solution can pass through animal membrane bladder or parchment paper or cellophane sheet but not the colloidal particles, the membrane can be used for dialysis.
The apparatus used for this purpose is called dialyser. A bag of suitable membrane containing the colloidal solution is suspended in a vessel through which fresh water is continuously flowing. The molecules and ions diffuse through membrane into the outer water and pure colloidal solution is left behind. Give four uses of emulsions. What are micelles? Give an example of a micelle system. Solution: Micelles are substances that behave as normal strong electrolytes at low concentration but at high concentrations behave as colloids due to formation of aggregates.
They are also called associated colloids, e. They can form ions and may contain or more molecules to form a micelle.
Question 8 How does the electronic configuration of an atom relate to its position in the Modern Periodic Table? Answer: Modern periodic table is based on the atomic number and atomic number is directly related to the electronic configuration. One can find the group number and period number of an element on the basis of electronic configuration. For example, if an element has 1 or 2 electrons in its outermost shell, then it would belong to group 1 or group 2.
And if it has 3 or more electrons in its outermost shell, then it would belong to group 10 4- the number of electrons in the outermost shell. All the alkali metals have one electron in their outermost shell, so they are placed in group 1. Thus, all the group 2 elements have 2 electrons in their outermost shell. In group 15 elements, there are 5 electrons in their outermost shell. Similarly, the number of shells in an element indicates its period number.
For example, the atomic number of magnesium is 12 and its electronic configuration is 2, 8, 2. Thus it is an element of 3rd period. Question 9 In the Modern Periodic Table, calcium atomic number 20 is surrounded by elements with atomic number 12, 19, 21 and Which of these have physical and chemical properties resembling calcium?
Periodic classification of elements: Needs for classification, Modern Periodic table, gradation in properties, valency, Ncert Solutions Class 10th Chemistry Chapter 1 Date atomic number, metallic and non-metallic properties. Formulae Handbook for Class 10 Maths and Science. Solution: All the known elements could not be arranged in the form of triads. Take the example of F, Cl and Br. Atomic mass of Cl is not an arithmetic mean of atomic masses of F and Br. Solution: It was not valid for elements that had atomic masses higher than Ca.
When more elements were discovered, such as elements from the noble gases such as He, Ne, Ar, they could not be accommodated in his table. Question 5 Besides gallium, which other elements have been left by Mendeleev in his periodic table, since the time they were discovered?
Any two Solution: Scandium and Germanium. Question 6 What were the criteria used by Mendeleev in creating his periodic table? Solution: He observed the relationship between the atomic masses of the elements and their physical properties. Among chemical properties, he concentrated on the compounds formed by elements with oxygen and hydrogen. Question 7 Why do you think, the noble gases are placed in a separate group?
Solution: Due to its inert and low concentration in our atmosphere, they could be placed in a new group without disturbing the existing order. For example, Position of isotopes: All the isotopes of an element have the same number of protons, so their atomic number is also the same. Since all the isotopes of an element have the same atomic number, they can be put at one place in the same group of the periodic table.
Question 9 Name two elements, which you would expect to show chemical reactions similar to magnesium. Solution: Calcium and Beryllium are the elements that will show chemical reactions similar to magnesium. This is because beryllium and calcium belong to the same group of periodic table as magnesium.
All of them have similar electronic configurations with 2 valence electrons each. Question 10 Name: a. Three elements that have a single electron in their outermost shell. Two elements that have two electrons in their outermost shell.
Three elements with filled outermost shell. Solution: a. Three elements that have a single electron in their outermost shell are: 1. Lithium 2. Sodium 3. Potassium b.
Two elements that have two electrons in their outermost shell are: 1. Magnesium 2. Calcium c. Three elements with filled outermost shell are: 1.
Argon 2. Helium 3. Question 11 a. Lithium, sodium, potassium are metals that react with water to liberate hydrogen. Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common Solution: a.
These elements are alkali metals and they have 1 valence electron in their outermost shell and are therefore very unstable and reactive. These elements each have full outermost subshell, which results in high stability. They only react with other elements in extreme circumstances, the trait for which they are named. Question 12 In the Modern periodic table, which are the metals among the first ten elements? Solution: The metals are Lithium and Beryllium. Question 13 By considering their position in the periodic table, which one of the following elements would you expect to have maximum metallic characteristic?
Question 14 Which of the following statements is not a correct statement about the trends when going from left to right across the periods of the periodic table? Question 15 Element X forms a chloride with the formula XCl 2 , which is a solid with a high melting point.
X would most likely be in the same group of the periodic table as a. Si Solution: b. Question 16 Which element has? Two shells, both of which are completely filled with electrons? The electronic configuration of 2,8,2? A total of three shells, with four electrons in its valence shell?
A total of two shells, with three electrons in its valence shell? Twice as many electrons in its second shell, as in its first shell? Neon 2,8 b. Magnesium 2,8,2 c. Silicon 2,8,4 d. Boron 2,3 e. Carbon 2,4. Question 17 What property do all elements in the same column of the periodic table as fluorine have in common?
Solution: These elements all have 7 electrons in their outermost shells and these often exist as salts, combined with elements from the Alkali metal group. Question 18 An atom has electronic configuration 2,8,7.
What is the atomic number of this element? Question 19 Which type of ion, cation or anion, will be formed by element A? Anion will be formed by element A. Question 20 Nitrogen atomic number 7 and phosphorus atomic number 15 belong to group 15 of the periodic Table.
Solution: Electronic configuration � Nitrogen � 2s 2 2p 3 and Phosphorus � 1s 2 2s 2 2p 6 3s 2 3p 3. Nitrogen will be more electronegative; this is because its atom has small size due to which the attraction of its nucleus for the incoming electron is more. Corrosion is the process in which metals are eaten up gradually by the action of air, moisture or a chemical on their surface. Corrosion is caused mainly by the oxidation of metals by the oxygen of air.
Example: Rusting of iron is the most common form of corrosion. This is called rusting of iron. The condition produced by aerial oxidation of fat and oil in food which is marked by an unpleasant smell and taste is called rancidity. Example: Rancidity can be retarded by keeping food in a refrigerator. The refrigerator has a low temperature inside it. When the food is kept in a refrigerator, the oxidation of fat and oil in it is slowed down due to low temperature.
So, the development of rancidity due to oxidation is retarded. Question 20 Why should a magnesium ribbon be cleaned before burning in air? Solution: To remove the oxide layer and facilitates rapid burning. Question 21 Write the balanced equation for the following chemical reactions.
Question 22 Write a balanced chemical equation and state symbols for the following reactions. Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride b. Sodium hydroxide solution in water reacts with hydrochloric acid solution in water to produce sodium chloride solution and water.
Question 24 Why does the colour of copper sulphate solution change when an iron nail is dipped into it? Solution: In this reaction, iron displaces copper from copper sulphate solution.
The deep blue colour of copper sulphate solution fades due to the formation of light green solution of iron sulphate. A red-brown coating of copper metal is formed on the surface of the iron metal.
This displacement reaction occurs because iron is more reactive than copper. Question 25 Identify the substances that are oxidised and the substances that are reduced in the following reactions. The addition of oxygen is Called oxidation.
So the substance that is oxidized is sodium Na. In this reaction, copper oxide CuO gives the oxygen required for the oxidation of hydrogen; therefore, copper oxide is the oxidizing agent. Hydrogen is responsible for removing oxygen from copper oxide; therefore, hydrogen is the reducing agent here. Question 1. When crystals of lead nitrate are heated strongly in a dry test tube a crystals immediately melt b a brown residue is left c white fumes appear in the test tube d a yellow residue is left Answer: b Pungent smelling, brown fumes are evolved due to NO 2 gas and brown coloured residue of lead oxide PbO is left.
Question 2. A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation? In acidic medium, KMnO 4 oxidises ferrous sulphate to ferric sulphate. Question 3. Dilute hydrochloric acid is added to granulated zinc taken in a test tube.
The following observations are recorded. Point out the correct observation. HCl to form zinc chloride and bubbles of colourless and odourless hydrogen gas is evolved. Question 4.
When a magnesium ribbon is burnt in air, the ash formed is a black b white c yellow d pink Answer: b When a Mg ribbon is burnt in air, the ash formed is of magnesium oxide which is white in colour. Question 5. Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhyd. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B whereas, in case of beaker C, the temperature of the solution falls.
In beakers A and B, exothermic process has occurred. In beakers A and B, endothermic process has occurred. In beaker C, the exothermic process has occurred. In beaker C, endothermic process has occurred. Question 6. Which of the following will be required to identify the gas evolved when dilute hydrochloric acid reacts with zinc metal? HCl, zinc metal forms zinc chloride and hydrogen gas is evolved. Presence of hydrogen gas can be checked by a burning splinter because H 4 gas burnt in a splinter with a pop sound.
Question 7. And the colour of the solution fades away. This is an example of displacement reaction. Question 8. What happens when ferrous sulphate crystals are heated? Question 9. The colour of the precipitate formed when barium chloride solution is mixed with sodium sulphate solution is [CCE ] a blue b black c white d green Answer: c This is an example of a double displacement reaction and a white precipitate of barium sulphate is formed.
Question How the colour changes when the gases after thermal decomposition of ferrous sulphate come in contact with an acidified solution of potassium dichromate? Answer: c The color changes from orange to green due to the formation of iron III sulphate. The representation of chemical reaction by means of symbols of substances in the form of formulae is called chemical equation. Balanced Chemical Equation. A balanced chemical equation has equal number of atom of each element participating in the reaction on both left and right hand sides of the reaction.
According to Law of Conservation of Mass, total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the element present in the reactants.
Rusting When iron reacts with oxygen and moisture it forms a red substance called rust. Corrosion Metals on coming in contact with oxygen, water, acids or gases presents in air changes its surface. This is called corrosion for e. Prevention � painting, galvanization, oiling, greasing. Rancidity Oil and fats on exposure to air show a change in taste and smell.
This property is known as rancidity. Prevention � adding antioxidants, Vacuum packing, refrigeration, flushing food with nitrogen.
The transformation of chemical substance into a new chemical substance by making and breaking of bonds between different atom is known a chemical reaction. Combination Reaction When two elements or one compound and one element or two compounds combine to form a new product. Exothermic Reactions Reactions producing energy are called exothermic reactions. Most of the combination reactions are exothermic in nature.
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