Metals and non metals important questions

Question-1
a) Due to which property of metals are metallic foils prepared?
b) Write uses of aluminium foils
Solution:
a) Metallic foils are prepared, making use of the malleable property of metals.
b) Aluminium foils are used for
(i) wrapping chocolates and food stuff
(ii) to prepare hydrogen.

Question-2
Name one non-metal and one metal, which are in liquid state at room temperature.
Solution:
Bromine is the non–metal and mercury is the metal which are in liquid state at room temperature.

Question-3
Give reasons for the following
i) Zinc oxide is considered an amphoteric oxide.
ii) Non-metals in general do not displace hydrogen from dilute acids.
iii) Metals conduct electricity.
Solution:
i) Zinc oxide is considered an amphoteric oxide because it shows both acidic and basic behaviour.
ii) Non-metals do not react with dilute acids hence do not displace hydrogen from dilute acids.
iii) thatMetals conduct electricity because they contain free electrons which can move easily through the metal and conduct electric current.

Question-4
Identify the following oxides with neutral, acidic, basic and amphoteric oxides.
i) Al2O3 ii) MgO iii) SO2 iv) CO; v) Na2O vi) N2O vii) ZnO viii) CO2 ix) SO3 x) CaO.
Solution:
Neutral oxides: CO; N2O
Acidic oxides: SO2; CO2; SO3
Basic oxides: MgO; Na2O; CaO
Amphoteric oxides: Al2O3 ; ZnO

Question-5
By what processes do you concentrate the following ores:
i) PbS(galena)
ii) Fe2O3(haematite)
iii) Al2O3.2H2O (bauxite).
Solution:
i) PbS (galena) is concentrated by froth floatation method.
ii) Fe2O3 (haematite) is concentrated by magnetic separation.
iii) Al2O3.2H2O (bauxite) is concentrated by leaching process (chemical method).

Question-6
Why is that iron does not occur as a metal in the crust of the earth? What are the common compound forms in which iron occurs? Which of these is more often used for extracting iron? Why are carbon and limestone mixed with iron ore before feeding it into the blast furnace? Write the chemical equations for the reduction step and the slag formation step.
Solution:
Iron is quite reactive and so it does not occur as a metal in the crust of the earth. The common compounds formed are its oxide, a carbonate and a sulphide. The oxide ore of iron called haematite is more often used for extracting iron. The carbon and limestone which is mixed with iron ore is called the charge. This charge is responsible for the formation of iron metal. Coke acts the reducing agent and addition of limestone helps to remove the earthy impurities like sand from the blast furnace by forming fusible slag.
Reduction of Iron(III)oxide or haematite to Iron: carbon monoxide reduces iron(III)oxide to iron metal


Question-7
By what chemical processes do you obtain the following metals?
i) Mercury from HgO ii) Iron from Fe2O3 iii) Manganese from MnO2 iv) Sodium form NaCl v) Aluminium from Al2O3.


Question-8
i) What is the composition of molten slag, formed in the extraction of iron in the blast furnace?
ii) What is the use of slag?

Solution:
i) Molten slag in the extraction of iron is calcium silicate(CaSiO3).
ii) Slag is used for constructions of roads.

Question-9
Write the name of the compound, when iron is corroded?
Solution:
When iron is corroded rust is formed which is hydrated iron (III) oxide (Fe2O3.x.H2O)

Question-10
Give reasons for the following
i. Na, K and Ca metals form hydrides by combination with hydrogen gas, but most other metals do not.
ii. Aluminium easily combines with oxygen but still it can be used for making kitchen utensils.
Solution:
i. Metals like Na, K and Ca can force the hydrogen atoms to accept electrons given by them and form hydrides.
ii. Aluminium forms a protective oxide layer when it combines with oxygen and hence it is used for making kitchen utensils.

Question-11
i) Among iron and aluminium which rusts easily?
ii) What are the conditions, necessary for rusting of iron?
Solution:
i) Among iron and aluminium, iron rusts easily. It forms Al2O3. That is why iron pi

Acids,bases and salts questions -1

1.What is an acid?

An acid is a hydrogen-containing chemical compound which, when dissolved in water, gives hydrogen ion (H+) or hydrated hydrogen ion (H2O. H+) or hydronium ion (H3O+).

2.What are bases and alkalies?

Oxides and hydroxides of metals and metal like radicals (e.g., NH4+ ions) are called bases. Bases ionise to give OH– ions in aqueous solution. Bases may be soluble or insoluble in water. The soluble bases are called alkalies. Thus all alkalies are bases but all bases are not alkalies.
Examples
NaOH and Cu (OH)2 both are bases, but, since NaOH is soluble in water, it is an alkali. On the other hand, since Cu (OH)2 is insoluble in water, it is not an alkali. Other examples of alkalies are KOH, Ca (OH)2 and NH4OH.

3.Define pH.

pH of a given solution is the negative logarithm to the base 10 of the hydrogen ion concentration, [H+] expressed in g ions/lit or moles/lit. Thus
pH=- log1- [H+].

4.What are the practical applications of neutralisation reactions?

Being alkaline in nature, cold milk is used to neutralise the acidity produced by HCl present in the gastric juice in the stomach.
Astronauts in space ships use this reaction to neutralise the dangerous levels of CO2.
Farmers add slaked lime (calcium hydroxide) to reduce acidity of soil.
Sting of ants and bees contains formic acid. This can be neutralised by rubbing soap, which contains free sodium hydroxide.
Persons suffering from acidity are given antacid tablets, containing magnesium hydroxide which neutralises excess HCl produced, in stomach. Alternately, they are advised to sip cold milk, which neutralises HCl.

5.Why the salts solutions of strong acid and strong alkali are neutral?

Let us take the example of potassium sulphate, which is a salt of strong acid [sulphuric acid] and strong base [potassium hydroxide solution].
From the above equation, it is clear that water is always feebly ionised and hence solution of potassium sulphate is neutral in nature.

6.What is an universal indicator?

Universal indicator is a solution, which undergoes several colour, changes over a wide range of pH. The colour is used to ‘indicate’ pH directly. Universal indicators are usually mixtures of several indicators.

7.Why common indicators cannot determine pH value of a solution?

Common indicators, such as litmus; methyl orange and phenolphthalein can easily tell, us whether a solution is acidic or alkaline, but they cannot easily tell how much a given acidic solution is stronger than another acidic solution. It means they cannot really tell us the pH value of different acidic or alkaline solutions.
In case of litmus, we cannot tell about pH values of 5,6 and 7. Similarly, in case of methyl orange pH values between 3 and 8 will not be very accurate.

8.What are the general characteristics of acids?

They have a sour taste
They turn blue litmus to red and methyl orange to red.
They react with active metals to give hydrogen
They decompose carbonates to produced carbon dioxide and water.

9.What is called deliquescent? Give examples.

Compounds that take up enough water from the air to dissolve in the water they have taken up are called deliquescent. Calcium chloride (CaCl2) and Sodium hydroxide (NaOH) are the examples of deliquescent.

10.Write the uses of chlorines.

Chlorine is used in the production of bleaching powder.
Chlorine is used for making solvents for dry cleaning.
Chlorine is used to sterilise drinking water supply, and the water in swimming pools.
It is used in the production of hydrochloric acid.