Chemistry: Q1. Name and state the law which is kept in mind while we balance a chemical equation. Q2. State the one basic difference between a physical change and a chemical change. Q3. Is burning of candle, a physical change or a chemical change?
Q4. What happens when: (a) dilute hydrochloric acid is added to solid sodium carbonate. (b) Quicklime is treated with water. (c) Sodium chloride solution is added to lead nitrate solution. Also write the chemical equation in each case Q5. Write the chemical equation of the reaction with an example each in which the following change have taken place: (a) Change in color (b)Change in temperature (c) Formation of precipitate. Q6. A metal ‘ x ’ available in the form of ribbons burns in air with a dazzling white light, once heated to its ignition temperature. It leaves a white powder ‘ y ’ which dissolves in water. The solution so formed turns red litmus blue. Identify ‘ x ’ and ‘ y ’ and write the balance chemical equation of the reaction. Q7. Why do fire flies glow at night? Q8. Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is I a chemical change? Q9. Why do silver articles become black after sometime when exposed to air? Q10. Give reasons why chips manufacturers usually flush bags of chips with gas such as nitrogen. Q11. State the type of chemical reaction used for the extraction of metals from their naturally occurring chlorides or oxides. Q12. Why is hydrogen peroxide kept in colored bottles? Q13. State reason for the following: (a) Potato chips manufactures fill the packet of chips with nitrogen gas. (b) Iron articles are shining when new, but get coated with a reddish brown powder, when left for some time. Q14. A solution of substance ‘X’ is used for white washing: (a)Name the substance ‘X’ and write its formula. (b)Express the reaction of ‘X’ with water in the form of a balanced chemical equation. Q15. Give reason for the following: (a) All decomposition reactions are endothermic reactions. (b) Color of copper sulphate solution changes when an iron nail is dipped in it. Q16. A. Solid calcium oxide was taken in a container and water was added slowly to it: (i) Write the observation, (ii) Write the chemical formula of the product formed. B. What happens when carbon dioxide gas is bubbled through lime water? i. In small amount, ii. In excess? C. Why do we apply paint on iron articles? Q17. A substance ‘x’ displace ‘y’ from its solution in water. It is called displacement reaction. What other chemical name can be given to such type of reactions? Explain giving an example. Q18. Given the following reaction:
2Al + Fe2O3 → 2Fe + Al2O3 + heat. Answer the following:” (a) Name of the oxidizing agent. (b) Name the reducing agent. (c) Name of the substance oxidized. (d) Name the substance reduced. What is one commercial application of this process? Q19. A yellowish colored compound ‘x’ is a photosensitive material. On exposure to sunlight, it gives a grayish substance ‘y’ and brown fumes of a gas ‘z’. Identify x, y, z. How will you obtain ‘x’ from the nitrate salt of ‘y’? Q20. Why respiration is considered as an exothermic reaction? Explain
6] X - Mg Y- MgO 2Mg +O2 --- 2MgO
8] becoz fermentation only takes place when yeast is available n during anaerobic respiration
10] to prevent rancicdity
12] Hydrogen peroxide is stored in coloured bottles because coloured bottles do not allow the light to enter the bottle so it prevents hydrogen peroxide from decomposing into water and oxygen.
13] a] to prevent rancidity
b] to prevent corrosion
14] a] x- slaked lime Ca(OH)2
b] CaO + H2O ----------> Ca(OH)2
15] A] The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing decomposition.
B] AS IRON IS MORE REACTIVE THAN COPPER
16] a] a lot of heat is given out
slaked lime
b] in small amounts the milkiness appears In excess it turns clear
c] to prevent from corrosion
18] c] aluminium
d] iron
20] An exothermic reaction gives off heat. Endothermic reactions are the opposite, they take in heat. Respiration is an exothermic reaction. When humans or other animals respire, they take in sugar and oxygen and release energy (heat) and carbon dioxide.
8] becoz fermentation only takes place when yeast is available n during anaerobic respiration
10] to prevent rancicdity
12] Hydrogen peroxide is stored in coloured bottles because coloured bottles do not allow the light to enter the bottle so it prevents hydrogen peroxide from decomposing into water and oxygen.
13] a] to prevent rancidity
b] to prevent corrosion
14] a] x- slaked lime Ca(OH)2
b] CaO + H2O ----------> Ca(OH)2
15] A] The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing decomposition.
B] AS IRON IS MORE REACTIVE THAN COPPER
16] a] a lot of heat is given out
slaked lime
b] in small amounts the milkiness appears In excess it turns clear
c] to prevent from corrosion
18] c] aluminium
d] iron
20] An exothermic reaction gives off heat. Endothermic reactions are the opposite, they take in heat. Respiration is an exothermic reaction. When humans or other animals respire, they take in sugar and oxygen and release energy (heat) and carbon dioxide.