Chemical Reactivity: Solved Exercise and Think-Tank

Question 2short answer

I. The reactivity of metals with oxygen increases in a group. Give examples.

Answers. The increase in reactivity of metals with oxygen increases in the group due to increase in electropositivity. For example alkali metals show increase in affinity for oxygen as we go down the group.

Lithium forms normal oxide.

Li + O2 -------------> Li2O

Sodium forms per oxide.

Na + O2 -------------> Na2O2

K, Rb and Cs form superoxides.

M + O2 -----------------> MO2 ( M = K, Rb, Cs)

ii. Which element is more metallic Mg or Al? Explain.

Answer. Mg is more metallic than Al. The property of an element that makes it metal is its ability to lose the electron. As atomic size of Mg is greater than Al, Therefore, Mg has greater ability to lose the electrons so it is more metallic (electropositive) than Al.

iii. What is the importance of Mg?

Answer. Magnesium has relatively low density and it is used in making light weight alloys with aluminium. These alloys are used for making frames of automobiles, aircrafts, spaceships cameras etc.

As Mg burns brilliantly, so it is used in photo flash guns.

Mg is used to prepare milk of magnesia (Mg(OH)2 ) that is commonly used as an acid.

iv. Arrange the following in order of increasing acidic strength HF, HI, HBr, HCl

Answer. HF<HCl<HBr<HI

v. Can F2 oxidise all halides ions to free halogen?

Answer. Yes. Oxidizing power of F2 is highest among all halogens. Due to relatively higher oxidizing power, F2 can oxidise all the halide ions to free halogen. For example

F2 + 2KCl ------------> 2KF + Cl2

F2 + 2KBr ------------> 2KF + Br2

F2 + 2KI ------------> 2KF + I2

Question 3: Arrange the following oxidise in order of decreasing basic character. BeO, CaO, MgO, SrO.

Answer.

SrO>CaO>MgO>BeO

Question 4: Rank the each set of elements in order of increasing metallic character.

a. Al, Na, Mg

b. Na, Li, K

Answer.

a. AL<Mg<Na

b. Li<Na<K

Question 5: Which of the following displacement reaction will not occur?Give reason.

a. Cl2 + 2NaF --------------> NaCl + F2

b. Br2 + 2KI ----------------> 2KBr + I2

c. I2 + 2KBr ---------------> 2KI + Br2

Answer.

Reason: This is because electronegativity F is higher than Cl. So Cl2 can't replace F in NaF.

Question 6: Give some important applications of platinum.

Answer. Platinum has important applications which are given below.

I. Platinum is widely used as catalyst in many types of industrial process.

For example, 100% pure sulphuric acid by contact process. In this process, platinum is used as catalyst.

ii. Pl is used as an electrode (hydrogen electrode) and in fuel cells.

iii. Pt is used as catalyst in catalytic converter equipped with automobile exhaust. These converter catalyse complete combustion of CO and hydrocarbons.

iv. A platinum compound known as Cis platinum is used as anti cancer.

Question 7: What is a half reaction?

Question 8. What is aqua reggio?

Think Tank

Question 1: it is advisable not to pick sodium metal with fingers justify this statement.

Question 2: how do electrons participate in half reaction?

Question 3: design and experiment to show that iron is more active than copper.

Question 4: how are voltage cells and electrolytic cells like and how are they different?

Question 5: and iron bar is to be silver plated which metal would be the anode and which is the cathode?

Question 6: compare Korean of aluminium and iron.

Question 7: compare and contrast alkali and alkaline earth metals.

Question 8: choose three metals that would not be suitable for coinage. eEaborate your choice.

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