SUBJECT – SCIENCE (CHEMISTRY)
CLASS – X (10th)
QUESTION FROM – CHEMICAL REACTIONS & EQUATIONS
ALL EXTRA & IMPORTANT QUESTION ANSWER FOR 2019 EXAMS
Science – Chapter 1 (Chemical Reactions And Equations) Important Questions For 2019 Board Exams – Class 10 (CBSE & All State Boards Questions)
Q1. What is meant by thermal decomposition ? (1)
Answer – It is defined as the decomposition of chemical compounds after absorption of heat.
Q2. How does the food become rancid ? (1)
Answer – Food becomes rancid when fat and oils present in the food get oxidized.
Q3. On what chemical law, balancing of chemical equations is based ? (1)
Answer – Balancing of chemical equation is based on the law of conservation of mass.
Q4. What is lime -water test for the detection of carbon dioxide ? (2)
Answer – When carbon dioxide gas passes through lime water it turns milky due to the formation of milky suspension (precipitate) of calcium carbonate. Carbon dioxide is produced by the action of dilute HCl on sodium carbonate.
Q5. A copper coin is kept in a solution of silver nitrate for some time. What will happen to the coin and the colour of the solution ? (2)
Answer – We know that copper is more reactive than silver, so it will displace silver from its salt solution – Cu(S)+2AgNO3(aq) –> Cu(NO3)2(aq) + 2Ag(s)
Q6. (A) Why can a chemical change not be normally reversed ? (1)
Answer – In chemical change some bonds breaks and some bonds form. The products are quite different from the reactants. Therefore normally some chemical reactions can’t be reversed.
(B) Why does AgCI keep in dark place ? (1)
Answer – Because in presence of sunlight it decomposes.
(C) Represent decomposition of ferrous sulphate with the help of balanced chemical equation. (1)
Answer – 2FeSO4(s) –> Fe2O3(s)+SO2(g)+SO3(g)
(D) Can rusting of iron take place in distilled water ? (1)
Answer – No rusting of iron cannot take place in distilled water because it neither contains dissolved oxygen nor CO2, both are essential for rusting of iron.
(E) Name the chemical present in photographic film ? (1)
Answer – AgBr.
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