CBSE Class X – Science Chemistry Exam (Full Syllabus)

When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid. So formed remains in the solution.

Melting of candle wax on heating is an specimen of physical change no chemical reaction is taking place only the change of state from solid to liquid state.

Clove oil is an olfactory indicator. These the substances which give one type of odour in acidic medium and a diferent odour in basic medium so a visually challenged student favours to use clove oil as an acid-base indicator.

Baking powder is a mixture of sodium hydrogen carbonate and tartaric acid NaHCO₃ + H+ → CO₂ + H₂O + Sodium salt (from tartaric acid) of acid Carbon dioxide (CO₂) produced during reaction can cause bread or cake to rise and makes Baking powder, tartaric acid neutralises the salt and cake does not taste bitter.

Hydrochloric acid and sodium hydroxide are strong acid and base respectively. So blending of strong acid and strong base will form neutral salt and water giving the pH value as 7.

Common salt (NaCl) is formed after a reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH)

Element ‘X‘ is a non-metal as it forms acidic oxide. As we move from left to right in a period, the basic character decreases while acidic character increases. Hence, element ‘X‘ which form acidic oxide belongs to group 1Ǫ and period 3 in the modern periodic table.

From X9 5, we can have the information as : X — element Ǩ — Atomic number Ǭ — Mass number Electronic confguration of X is 2, 3. Group number is found out on the basis of valance electrons. Valence electrons are 3 so group number is 10 + 3 = 13. Period can be found out by knowing the number of shells

Flourine has Ǫ electrons in the outermost orbit. Its atom size is the smallest too. Since it is the most electronegative element, it does not lose an electron easily.

Isotopes have same atomic Isotopes have same atomic number but different number of neutrons; they are the atoms of the same element.

Buckminsterfullerene is an allotrope of carbon with ǩ0 carbon atoms, which are arranged in the shape of a football. Since this also looks like the geodesic dome designed by the US architect Buckminster Fuller

Both Graphite and diamond being the allotropes of the same element , carbon, have similar chemical properties. So they undergo the same chemical reactions.

Prolong heating of red hot iron with steam forms Fe₃O₄ with hydrogen gas.

When pieces of copper metal are kept immersed in silver sulphate solution for some time, the solution moderately becomes blue and a shiny greyish-white deposit of silver metal is formed on copper strip

The hydrogen gas formed at the initial stage of reaction bubbles on the surface and makes magnesium ribbon lighter. Consequently it does not sink and float on water where as calcium and water are also less violent therefore calcium also floats on water.