Question 12 Marks
Draw a labelled diagram in proper sequence to show budding in hydra.
Answer
View full question & answer→Budding in Hydra:
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Question 22 Marks
A student is observing the temporary mount of a leaf peel under a microscope. Draw labelled diagram of the structure of stomata as seen under the microscope.
Answer
View full question & answer→Structure of stomata:
Question 32 Marks
In three test tubes A, B, and C, three different liquids namely, distilled water, underground water and distilled water in which a pinch of calcium sulphate is dissolved, respectively are taken. Equal amount of soap solution is added to each test tube and the contents are shaken. In which test tube will the length of the foam (lather) be longest? Justify your answer.
Answer
Test tube A contains distilled water which is considered as soft water, free from ions like $Mg ^{2+}, Ca ^{2+}$, etc. So, in this case, the length of foam will be the longest(maximum).
Test tube B contains underground water which contains ions like $Mg ^{2+}, Ca ^{2+}$, etc. which react with soaps to form salts of fatty acids called scum, which are insoluble in water. So, in this case, the length of form will be the less in comparison to test tube $A$.
Test tube C contains distilled water with $CaSO _4$, which contains $Ca ^{2+}$ ions which react with soaps to form salts of fatty acids called scum, which are insoluble in water. So, in this case also, the length of foam will be the less in comparison to test tube $A$.
View full question & answer→Test tube A contains distilled water which is considered as soft water, free from ions like $Mg ^{2+}, Ca ^{2+}$, etc. So, in this case, the length of foam will be the longest(maximum).
Test tube B contains underground water which contains ions like $Mg ^{2+}, Ca ^{2+}$, etc. which react with soaps to form salts of fatty acids called scum, which are insoluble in water. So, in this case, the length of form will be the less in comparison to test tube $A$.
Test tube C contains distilled water with $CaSO _4$, which contains $Ca ^{2+}$ ions which react with soaps to form salts of fatty acids called scum, which are insoluble in water. So, in this case also, the length of foam will be the less in comparison to test tube $A$.
Question 42 Marks
Draw the electron-dot structure of a hydrogen chloride molecule:
- Which inert gas does the H atom in HCl resemble in electron arrangement?
- Which inert gas does the Cl atom in HCl resemble in electron arrangement?
Answer
View full question & answer→
- Helium.
- Argon.
Question 52 Marks
The atomic number of an element X is 12.
- What must an atom of X do to attain the nearest inert gas electron configuration?
- Which inert gas is nearest to X?
Answer
View full question & answer→- An atom of X loses 2 electrons to attain the nearest gas electron configuration (2, 8).
- Neon.
Question 62 Marks
Explain how, mercury is extracted from its sulphide ore (cinnabar). Give equations of the reactions involved.
Answer
View full question & answer→Mercury (II) sulphide ore is roasted in air when mercury (II) oxide is formed.$\ \ \ \ \ \ \ \ \ \ 2\text{HgS}\text{(s)}\ \ \ \ \ \ \ \ \ \ \ \ \ +\ \ \ \ \ \ \ \ \ \ \ 3\text{O}_2\text{(g)}\xrightarrow{\ \ \ \ \text{Rcesting}\ \ \ }2\text{Hg(l)}\ \ \ \ \ \ \ \ \ \ \ +\ \ \ \ \ \ \ \ \ \ \ \ \text{2SO}_2\text{(g)}\\\text{Mercury (II) Sulphide}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Oxygen}\ \ \ \ \ \ \ \ \ \ \ \ \text{Mercury (II) Oxide}\ \ \ \ \ \ \ \ \text{Sulphur dioxide}$
When this mercury (II) oxide is hearted to about 300°C, it decomposes to form mercury metal. $\ \ \ \ \ \ \ \ \ \ 2\text{HgS}\text{(s)}\ \ \ \ \ \ \ \ \ \ \ \ \xrightarrow[\ \ \ \ \text{Rcesting}\ \ \ ]{\text{Heat}}\ \ \ \ \ 2\text{Hg(l)}\ \ \ \ \ \ \ \ \ \ \ +\ \ \ \ \ \ \ \ \ \ \ \ \text{O}_2\text{(g)}\\\text{Mercury (II) oxide}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Mercury metal}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Oxygen}$
When this mercury (II) oxide is hearted to about 300°C, it decomposes to form mercury metal. $\ \ \ \ \ \ \ \ \ \ 2\text{HgS}\text{(s)}\ \ \ \ \ \ \ \ \ \ \ \ \xrightarrow[\ \ \ \ \text{Rcesting}\ \ \ ]{\text{Heat}}\ \ \ \ \ 2\text{Hg(l)}\ \ \ \ \ \ \ \ \ \ \ +\ \ \ \ \ \ \ \ \ \ \ \ \text{O}_2\text{(g)}\\\text{Mercury (II) oxide}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Mercury metal}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Oxygen}$
Question 72 Marks
Non-metals do not evolve hydrogen gas when react with water, steam or dilute acids. Why?
Answer
View full question & answer→Except Carbon (C), all other non-metals are below Hydrogen {H} in the Activity Series. So they cannot displace Hydrogen from the dilute acids in any chemical reaction.
Question 82 Marks
What is meant by 22 carat gold? Name the metals which are usually alloyed with gold to make it harder.
Answer
View full question & answer→It means that 22 parts pure gold is alloyed with 2 parts of either silver or copper for making ornaments; Silver and copper are usually alloyed with gold to make it harder.
Question 92 Marks
What happens when calcium reacts with chlorine? Write an equation for the reaction which takes place.
Answer
View full question & answer→Calcium reacts vigorously with chlorine to form an ionic chloride called calcium chloride.$\text{Ca(s)}\ \ \ \ \ \ +\ \ \ \ \ \ \text{Cl}_2(\text{g})\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ \ }\text{CaCl}_2(\text{s})\\\text{Calciam}\ \ \ \ \ \ \ \ \ \text{Cholorine}\ \ \ \ \ \ \ \ \ \text{Calcium chloride}$
Question 102 Marks
What is meant by saying that the metals are malleable and ductile? Explain with examples.
Answer
View full question & answer→Metals are malleable i.e. they can be beaten into thin sheets with a hammer.
Example: Aluminium.
Metals are ductile i.e. they can be drawn into thin wires.
Example: Copper.
Example: Aluminium.
Metals are ductile i.e. they can be drawn into thin wires.
Example: Copper.
Question 112 Marks
Show the formation of $Na _2 O$ by the transfer of electrons between the combining atoms.
View full question & answer→Question 122 Marks
Name one metal and one non-metal that exist in liquid state at room temperature. Also name two metals having melting point less than 310K (37°C).
Answer
View full question & answer→Metal in liquid state is mercury, non-metal in liquid state is bromine.
Gallium (Ga) and Cesium (Cs) have melting point below 310K.
Gallium (Ga) and Cesium (Cs) have melting point below 310K.
Question 132 Marks
Name two ores of zinc. Write the names of the chemical compounds present in them and give their chemical formulae.
Answer
View full question & answer→i. Calamine; Zinc carbonate, $ZnCO _3$.
ii. Zinc blende; Zinc sulphide, ZnS.
ii. Zinc blende; Zinc sulphide, ZnS.
Question 142 Marks
The electronic configurations of two elements A and B are given below:
A 2, 6
B 2, 8, 1
What type of chemical bond is formed between the two atoms of A?
What type of chemical bond will be formed between the atoms of A and B?
A 2, 6
B 2, 8, 1
What type of chemical bond is formed between the two atoms of A?
What type of chemical bond will be formed between the atoms of A and B?
Answer
View full question & answer→- Covalent bond.
- Ionic bond.
Question 152 Marks
Which of the following will conduct electricity and which not?
$MgCl _2, CCl _4, NaCl _2, CS _2, Na _2 S$ Give reasons for your choice.
$MgCl _2, CCl _4, NaCl _2, CS _2, Na _2 S$ Give reasons for your choice.
Answer
View full question & answer→Conduct electricity: $MgCl _2, NaCl ^2, Na _2 S$ (lonic compounds)
Do not con duct electricity: $CCl _4, CS _2$ (Covalent compounds).
Do not con duct electricity: $CCl _4, CS _2$ (Covalent compounds).
Question 162 Marks
What chemical process is used for obtaining a metal from its oxide?
Answer
View full question & answer→solution Metal oxides can be converted to metal by a process called reduction. For example, Zinc oxide is reduced to metallic zinc by heating with carbon.
$ZnO(s)+C(s) \rightarrow Zn(s)+CO(g)$
Besides carbon, highly reactive metals like sodium, calcium, aluminium etc. are used as reducing agents. These displace metals of low reactivity from their oxide, e.g.,
$Fe_2 O_3(s)+2 Al(s) \rightarrow 2 Fe(l)+Al_2 O_3(s)+\text { Heat }$
$ZnO(s)+C(s) \rightarrow Zn(s)+CO(g)$
Besides carbon, highly reactive metals like sodium, calcium, aluminium etc. are used as reducing agents. These displace metals of low reactivity from their oxide, e.g.,
$Fe_2 O_3(s)+2 Al(s) \rightarrow 2 Fe(l)+Al_2 O_3(s)+\text { Heat }$
Question 172 Marks
Name one ionic compound containing chlorine and one covalent compound containing chlorine.
Answer
View full question & answer→Ionic co mpound: Sodium chloride, NaCl.
Cova lent c ompound: Carbon tetrachloride, $CCl_4.$
Cova lent c ompound: Carbon tetrachloride, $CCl_4.$
Question 182 Marks
Explain why, carbon cannot reduce oxides of sodium or magnesium.
Answer
View full question & answer→Carbon cannot reduce oxides of sodium or magnesium because carbon is less reactive than magnesium or sodium. Carbon, which is a non-metal, is more reactive than zinc and can be placed just above Zn in the reactivity series. Hence, carbon can reduce the oxides of zinc and all other metals below zinc to form metals.
Question 192 Marks
In a solution of lead acetate, a strip of metal M was dipped. After some time, lead from the solution was deposited on the metal strip. Which metal is more reactive, M or lead?
Answer
View full question & answer→The metal M is more reactive than lead because M displaces lead from lead acetate solution, which can be done only by an element that is more reactive lead.
Question 202 Marks
Why are aqueous solutions of ionic compounds able to conduct electricity?
Answer
View full question & answer→An aqueous solution of an ionic compound conducts electricity because there are plenty of free ions in the solution which are able to conduct electric current.
Question 212 Marks
What are metalloids?
Answer
View full question & answer→A metalloid is a chemical element that exhibits some properties of metals and some of nonmetals. In the periodic table metalloids form a jagged zone dividing elements that have clear metallic properties from elements that have clear nonmetallic properties. Boron, silicon, germanium, arsenic, antimony, tellurium, and polonium are metalloids.
Question 222 Marks
Give one example, with equation, of the displacement of hydrogen by a metal from an acid.
Answer
View full question & answer→Magnesium reacts with very dilute nitric acid to form magnesium nitrate and hydrogen gas.$\text{Mg(s)}\ \ \ \ \ +\ \ \ \ \ 2\text{HNO}_3\text{(aq)}\xrightarrow{\ \ \ \ }\text{Mg(NO}_3)_2\text{(aq)}\ \ \ \ \ +\ \ \ \ \text{H}_2\text{(g)}\\\text{Magnesium}\ \ \ \ \ \text{Nitric acid}\ \ \ \ \ \ \ \text{Magnesiumnitrate}\ \ \ \ \ \ \ \text{Hydrogen}$
Question 232 Marks
What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer
View full question & answer→Amphoteric oxides are the oxides, which react with both acids and bases to form salt and water.
E.g. ZnO and $Al _2 O _3$.
E.g. ZnO and $Al _2 O _3$.
Question 242 Marks
With the help of examples, describe how metal oxides differ from non-metal oxides.
Answer
View full question & answer→Metal oxides are basic in nature and turn red litmus blue. For example: Magnesium oxide. Non-metal oxides are acidic or neutral in nature. The acidic oxides turn blue litmus red.
For example: Carbon dioxide.
For example: Carbon dioxide.
Question 252 Marks
Some metals melt on keeping them on palm. Why? Also give an example.
Answer
View full question & answer→Gallium and cesium are the metals that melt when kept on palm. because they have very low melting point and just the heat in our palm can melt them easily.
Question 262 Marks
- Copper.
- Zinc.
- Nickel.
- Gold.
- Silver.
Answer
View full question & answer→Anode – Thick block of i mpure metal M.
Cathode – Thin strip of p ure metal M.
Electrolyte – Water soluble salt (of metal M).
Cathode – Thin strip of p ure metal M.
Electrolyte – Water soluble salt (of metal M).
Question 272 Marks
Write the product by giving balanced chemical equation.
When sulphur reacts with conc. nitric acid.
When sulphur reacts with conc. nitric acid.
Answer
View full question & answer→1 mole of elemental Sulfur reacts with nitric acid to produce Sulfuric acid, Nitrogen dioxide gas and water. The balanced chemical equation is:$\text{S(s)}+6\text{H NO}_3(\text{aq.})+6\text{N O}_2(\text{g})+2\text{H}_2\text{O(l)}$
Question 282 Marks
What is an alloy? Give two examples of alloys.
Answer
View full question & answer→An alloy is a homogeneous mixture of two or more metals (or a metal and small amounts of non-metals).
Steel and Brass are examples of alloys.
Steel and Brass are examples of alloys.
Question 292 Marks
Giving one example each, state what are (i) ionic compounds, and (ii) covalent compounds.
Answer
View full question & answer→i. The compounds containing ionic bonds are known as ionic compounds. They are formed by the transfer of electrons from one atom to another.
Example: Sodium chloride, NaCl .
ii. The compounds containing covalent bonds are known as covalent compounds. They are formed by the sharing of electrons between atoms.
Example: Methane, $CH _4$.
Example: Sodium chloride, NaCl .
ii. The compounds containing covalent bonds are known as covalent compounds. They are formed by the sharing of electrons between atoms.
Example: Methane, $CH _4$.
Question 302 Marks
An element X is soft and can be cut with a knife easily. This is very reactive with air and cannot be kept open with air. It reacts vigorously with water. Name the element X.
Answer
View full question & answer→An element which is soft and can be cut easily with a knife is SODIUM Or POTASSIUM. These metals are very reactive and cannot be kept open in d air. Thus they are found in combined state. They are kept with kerosene oil in order to prevent any sort of explosion due to their reactive nature.
Question 312 Marks
How does the painting of an iron object prevent its rusting?
Answer
View full question & answer→When a coat of paint is applied to the surface of an iron object, it prevents air and moisture to come in contact with the object; hence no rusting takes place.
Question 322 Marks
State reasons for the following observations:
Metal sulphides occur mainly in rocks but metal halides occur mostly in sea and lake waters.
Metal sulphides occur mainly in rocks but metal halides occur mostly in sea and lake waters.
Answer
View full question & answer→It is because sea water contains sodium chloride due to which metal halides are formed, whereas sulphur is found below rocks. Therefore, metal–sulphides are formed in rocks.
Question 332 Marks
Four elements A, B, C and D have the following electron arrangements in their atoms:
A 2, 8, 6
B 2, 8, 8
C 2, 8, 8, 1
D 2, 1
A 2, 8, 6
B 2, 8, 8
C 2, 8, 8, 1
D 2, 1
- What type of bond is formed when element C combines with element D?
- Which element is an inert gas?
- What will be the formula of the compound between A and C?
Answer
View full question & answer→- Ionic bond will be formed; element C donates its electron to element D.
- B is an inert gas; has complete octet configuration.
- C 2 A; element A needs two electrons to complete its octet.
Question 342 Marks
Why has sodium chloride a high melting point?
Answer
View full question & answer→Sodium chloride has a high melting point because it is an ionic compound and these compounds are made of up of positive and negative ions. There is a strong force of attraction between the oppositely charged ions, so, a lot of heat energy is required to break this force of attraction and melt or boil the ionic compound.
Question 352 Marks
Explain why, metals usually do not liberate hydrogen gas with dilute nitric acid.
Answer
View full question & answer→Metals do not liberate hydrogen gas with nitric acid because nitric acid is a strong oxidizing agent. So, as soon as hydrogen gas is formed in the reaction between a metal and dilute nitric acid, the nitric acid oxidises this hydrogen to water.
Question 362 Marks
Why does aluminium not corrode right through?
Answer
View full question & answer→Aluminium does not corrode right through because aluminium is more reactive than iron and it forms a layer of aluminium oxide as soon as it comes in contact with moist air.
This aluminium oxide layer is very tough and prevents the aluminium underneath from corroding.
This aluminium oxide layer is very tough and prevents the aluminium underneath from corroding.
Question 372 Marks
Give the formulae of the stable binary compounds that would be formed by the combination of following pairs of elements.
1. Mg and $N _2$
2. Li and $O _2$
3. Al and $Cl _2$
4. K and $O _2$
1. Mg and $N _2$
2. Li and $O _2$
3. Al and $Cl _2$
4. K and $O _2$
Answer
View full question & answer→1. Magnesium nitride - $\left( Mg _3 N_2\right)$
2. Lithium oxide - $\left( Li _2 O \right)$
3. Aluminium chloride - $\left( AlCl _3\right)$
4. Potassium oxide - $\left( K _2 O \right)$
2. Lithium oxide - $\left( Li _2 O \right)$
3. Aluminium chloride - $\left( AlCl _3\right)$
4. Potassium oxide - $\left( K _2 O \right)$
Question 382 Marks
Why does a new aluminium vessel lose shine so soon after use?
Answer
View full question & answer→A new aluminium vessel lose shine so soon after use due to the corrosion of aluminium metal when exposed to moist air. This happens because the oxygen of air reacts with aluminium toform a thin, dull layer of aluminium oxide all over the vessel.
Question 392 Marks
Give an example of a non-metal which is:
- Hardest known substance.
- A good conductor of heat and electricity.
Answer
View full question & answer→- Diamond is one of the strongest known substances.
- Graphite, a form of carbon which is a good conductor of electricity.
Question 402 Marks
Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer
View full question & answer→Copper does not react with cold water, hot water, or steam. However, iron reacts with steam. If the hot water tanks are made of steel (an alloy of iron), then iron would react vigorously with the steam formed from hot water. $3 Fe +4 H _2 O \rightarrow Fe _3 O _4+ H _2 O$
That is why copper is used to make hot water tanks, and not steel.
That is why copper is used to make hot water tanks, and not steel.
Question 412 Marks
Which one of the methods given in column I is applied for the extraction of each of the metals given in column II:
|
Column I
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Column II
|
|
Electrolytic reduction.
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Aluminium.
|
|
Reduction with Carbon.
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Zinc.
|
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Reduction with Aluminium.
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Sodium.
|
|
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Iron.
|
|
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Manganese.
|
|
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Tin.
|
Answer
View full question & answer→|
Column I
|
Column II
|
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Electrolytic reduction.
|
Aluminium and Sodium.
|
|
Reduction with Carbon.
|
Zinc, Iron and Tin.
|
|
Reduction with Aluminium.
|
Manganese.
|
Question 422 Marks
$\text{CuSO}_4\text{(aq)}+\text{Fe(s)}\xrightarrow{\ \ \ \ }\text{FeSO}_4\text{(aq)}+\text{Cu(s)}$$\text{FeSO}_4\text{(aq)}+\text{Zn(s)}\xrightarrow{\ \ \ \ \ }\text{ZnSO}_4\text{(aq)}+\text{Fe(s)}$
On the basis of the above reactions, indicate which is most reactive and which is least reactive metal out of zinc, copper and iron.
On the basis of the above reactions, indicate which is most reactive and which is least reactive metal out of zinc, copper and iron.
Answer
View full question & answer→In the first reaction, Fe displaces Cu from $CuSO _4$ solution. So Fe is more reactive than Cu .
In the second reaction, Zn displaces Fe from $FeSO _4$ solution. So Zn is more reactive than Fe .
Hence it can be concluded that Zn is the most reactive metal and Cu is the least reactive metal out of zinc, copper and iron.
In the second reaction, Zn displaces Fe from $FeSO _4$ solution. So Zn is more reactive than Fe .
Hence it can be concluded that Zn is the most reactive metal and Cu is the least reactive metal out of zinc, copper and iron.
Question 432 Marks
What is meant by corrosion? Name any two methods used for the prevention of corrosion.
Answer
View full question & answer→Corrosion is General destruction of metals due to chemical reaction with water and oxygen. Prevention can be through oiling and Greasing.
Question 442 Marks
What is meant by the ‘concentration of ore’?
Answer
View full question & answer→Before extracting metal from an ore, it is necessary to remove these impurities (gangue) from it. By removing the gangue, we get a concentrated ore containing a much higher percentage of metal. This is called concentration of ore; also known as enrichment of ore.
Question 452 Marks
Silver metal does not combine easily with oxygen but silver jewellery tarnishes after some time. How?
Answer
View full question & answer→The silver articles combine slowly with the hydrogen sulphide gas present in air to form a black coating of silver sulphide. The tarnishing of the silver objects is due to this silver sulphide coating on the object’s surface.
Question 462 Marks
What is the nature of the oxide SO? What happens when it is dissolved in water ? Write the chemical equation of the reaction involved.
Answer
View full question & answer→$SO_2$ is acidic in nature. When dissolved in water, it produces sulphurous acid.$\text{SO}_2(\text{g})\ \ \ \ \ \ \ \ \ \ \ \ \ \ +\ \ \ \ \ \ \ \ \ \ \ \ \ \text{H}_2\text{O(l)}\ \ \ \xrightarrow{\ \ \ \ \ \ \ }\ \ \ \ \ \text{H}_2\text{SO}_3\text{(aq)}\\\text{Sulphurdioxide}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Water}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Sulphurcus acid}\\\text{(Acidic oxide)}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{(Acid)}$
Question 472 Marks
Which of the following elements would yield:
- An acidic oxide.
- A basic oxide.
- A neutral oxide.
Answer
View full question & answer→- Acidic oxide: S, C
- Basic oxide: Na, K
- Neutral oxide: H
Question 482 Marks
What is an ionic bond? What type of bond is present in oxygen molecule?
Answer
View full question & answer→The chemical bond formed by the transfer of electrons from one atom to another is known as an ionic bond.
Covalent bond is present in an oxygen molecule.
Covalent bond is present in an oxygen molecule.
Question 492 Marks
Which metal becomes black in the presence of hydrogen sulphide gas in air?
Answer
View full question & answer→Silver metal when exposed to the hydrogen sulphide turns blackish grey. It is because it consequently reacts with the gas and forms silver sulphide. Due to the traces of $H _2 S$ in the air, this sulphide layer is formed thus turning the silvery and shiny grey colour into black or grey.
Question 502 Marks
Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer
View full question & answer→Iron and aluminium will displace hydrogen from dilute acids as they more reactive then hydrogen. Mercury and copper cannot displace hydrogen from dilute acids as they are less reactive than hydrogen.