Very Short Answer-Class 10 – Science -Chemistry -Chapter 1 – Chemical Reaction and Equation

Class 10 – Science -Chemistry -Very Short Answer -Chapter 1 – Chemical Reaction and Equation

Q1. Why does not silver evolve hydrogen on reacting with dill H2SO4

Ans. Silver do not evolve hydrogen on reacting with dil. H2SO4 as silver is less reactive metal than hydrogen.

Q2. Giving an example list two important information which makes a chemical equation more useful (informative). [CBSE 2015]

Ans : a. It should include physical states of reactants and products.

b. It should specify conditions under which reaction takes place e.g.,

$$2Na(s)+2H_{2}O(l)\rightarrow 2NaOH(aq)+H_{2}(g)$$

$$H_{2}(g)+Cl_{2}(g)\overset{sunlight}{\rightarrow}2HCl(g)$$

Q3.Way do diamond and graphite, the two allotropic forms of carbon evolve different amounts of heat on combustion?

Ans. Diamond and graphite are the two allotropes of carbon but they do not evolve same amount of heat on combustion because they differ in the arrangement of carbon atoms and also their shapes one different.

Q4.What is the sole of oxidizing agent is a reaction?

 Ans. The oxidizing agent supply the oxygen in a reaction or it removes the hydrogen.

 Q5.What happens chemically when quick lime is added to water?

Ans. When quick lime is added to water calcium hydroxide (slaked lime) is formed with a hissing sound and lot of heat is evolved during the reaction.The reaction involved is

$$CaO(s)+H_{2}O(Quick Lime)\rightarrowCa(OH)_{2}(s)+Heat(Shaked Lime)$$

Q6. Distinguish between a displacement reaction and a double displacement reaction. Identify the displacement and the double displacement reaction from the following reactions: [CBSE 2009]

$$a.Hcl(aq)+NaOH(aq)\rightarrow Nacl(aq)+H_{2}O(l)$$

$$b.Fe(s)+CuSO_{4}(aq)\rightarrow FeSO_{4}(aq)+Cu(s) $$

Ans : Displacement Reaction: When a more reactive metal displaces a less reactive metal from its salt solution. Double displacement reaction: When two compounds exchange their ions to form two new compounds.

a. Double displacement reaction. b. Displacement reaction. 

Q7. A zinc plate was put into solution of copper sulphate kept in a glass container. It was found that blue colour of the solution gets fader and fader with passage of time. After few days when zinc plate was taken out of the solution, a number of holes were observed on it.

a. State the reason for the changes observed on zinc plate.

b. Write the chemical equation for the reaction involved.

Ans : 

a. Zinc displaces copper from copper sulphate solution to form colourless ZnSO4 and copper metal is deposited. Zinc gets consumed due to which holes are formed. 

\(b.Zn(s)+CuSO_{4}(aq)\rightarrow ZnSO_{4}(aq)+Cu(s)\)

Q8. When the powder of common metal is heated in open china dish its colour turns black. However, when hydrogen is passed over the hot black substance so formed, it regains its original colour. Based on the above information answer the following questions:[CBSE 2010]

 a. What type of chemical reaction takes place in each of the two given steps?

b. Name the metal initially taken in powdered form. Write balanced equations for both the reactions.

Ans :  

a. Oxidation reaction, Redox reaction

b. Copper metal was present initially

$$2Cu(s)+O_{2}(g)\overset{Heat}{\rightarrow} CuO(s)$$

$$CuO(s)+H_{2}(g)\overset{Heat}{\rightarrow} Cu(s)+H_{2}O(l)$$

Q9. What do you mean by a precipitation reaction? Explain by giving examples.

Ans. A chemical reaction in which an insoluble substance (precipitate) is formed is called precipitation reaction. For example

$$AgNO_{3}+NaCl\rightarrow AgCl+NaNO_{3}$$

Q10. A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.

Ans. The brown coloured element‘X‘ is copper. On heating in air it forms copper oxide, which is black in colour.$$2CuS+O_{2}\rightarrow 2CuO$$

Q11. What is redox reaction? When a magnesium ribbon burns in air with a dazzling flame and forms a white ash, is magnesium oxidised or reduced. Why?  [CBSE 2010, 2009]

Ans : Redox reaction is a reaction in which oxidation and reduction takes place simultaneously. Mg is getting oxidised because it is gaining oxygen to form magnesium oxide.

Q12. Identify the type of each of the following reactions:[CBSE 2012] 

 a. A reaction in which a single product is formed from two or more reactants.

b. The reaction mixture becomes warm.

c. An insoluble substance is formed.

d. External surface of the container in which reaction takes place becomes cold.

Ans : a. Combination reaction

b. Exothermic reaction

c. Precipitation reaction (Double displacement reaction)

d.  Endothermic reaction

Q13. When a metal X is added to salt solution of metal Y, the following chemical reaction takes place:  [CBSE 2012]

$$Metal X + Salt solution of Y\rightarrow Salt solution of X + Metal Y$$

Mention the inference you draw regarding the reactivity of metal X and Y and also the type of reaction. State the reason of your conclusions.

 Ans : X is more reactive than Y because , X displaces Y from its salt solution. Hence, this reaction is an example of displacement reaction.