If an atom contains one electron
[question] Question. If an atom contains one electron and one proton, will it carry any charge or not? [/question] [solution] Solution: An electron is a negatively charged particle, where as a proton is a positively charged particle. The magnitude of their charges is equal. Therefore, it will be a neutral atom. [solution]...
Read More →Draw the structure for the following
[question] Question. Draw the structure for the following compounds : (i) Ethanoic acid (ii) Bromopentane (iii) Butanone (iv) Hexanal [/question] [solution] solution: (i) Ethanoic acid $\longrightarrow \mathrm{CH}_{3} \mathrm{COOH}$ (ii) Bromopentane $\longrightarrow \mathrm{C}_{5} \mathrm{H}_{11} \mathrm{Br}$ (iii) Butanone $\longrightarrow \mathrm{CH}_{3} \mathrm{COC}_{2} \mathrm{H}_{5}$ <img src="/media/uploads/2021/12/Draw-the-structure-for-the-following-compounds-03.png" alt="Draw the struc...
Read More →What are canal rays?
[question] Question. What are canal rays? [/question] [solution] Solution: Canal rays are beams of positive ions that are created by certain types of gas discharge tubes. They were first observed in Crookes tubes during experiments by the German scientist Eugen Goldstein, in 1886. Later work on anode rays by Wilhelm Wien and J. J. Thomson led to the development of mass spectrometry [/solution]...
Read More →Prove that the following are irrationals :
[question] Question. Prove that the following are irrationals : (i) $\frac{1}{\sqrt{2}}$ (ii) $7 \sqrt{5}$ (iii) $\mathbf{6}+\sqrt{\mathbf{2}}$ [/question] [solution] Solution: (i) Let us assume, to the contrary, that $\frac{1}{\sqrt{2}}$ is rational. That is we can find coprime integers a and $b(b \neq 0)$ such that, $\frac{1}{\sqrt{2}}=\frac{\mathbf{P}}{q}$ Therefore, $q=\sqrt{\mathbf{z}_{\mathbf{p}}}$ Squaring on both sides, we get $\mathrm{q}^{2}=2 \mathrm{p}^{2}$ ...(1) Therefore, 2 divides...
Read More →Calculate the number of aluminium ions present
[question] Question. Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.(Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of Al = 27 u) [/question] [solution] Solution: 1 mole of aluminium oxide $\left(\mathrm{Al}_{2} \mathrm{O}_{3}\right)=2 \times 27+3 \times 16=102 \mathrm{~g}$ i.e., $102 \mathrm{~g}$ of $\mathrm{Al}_{2} \mathrm{O}_{3}=6.022 \times 10^{23}$ molecules of $\mathrm{Al}_{2} \mathrm{O}_{3}$ Then, $0.051 \mathrm{~g}$ ...
Read More →What will be the formula and electron
[question] Question. What will be the formula and electron dot structure of cyclopentane? [/question] [solution] solution: Cyclopentane $\mathrm{C}_{5} \mathrm{H}_{10}$ Electron dot structure [/solution]...
Read More →What are the two properties of carbon which led
[question] Question. What are the two properties of carbon which led to the huge number of carbon compounds we see around us? [/question] [solution] solution: (i) Catenation (ii) Tetravalency [/solution]...
Read More →Calculate the number of molecules of sulphur
[question] Question. Calculate the number of molecules of sulphur $\left(\mathrm{S}_{8}\right)$ present in $16 \mathrm{~g}$ of solid sulphur. [question] [solution] Solution: 1 mole of solid sulphur $\left(\mathrm{S}_{\mathrm{o}}\right)=8 \times 32 \mathrm{~g}=256 \mathrm{~g}$ i.e., $256 \mathrm{~g}$ of solid sulphur contains $=6.022 \times 10^{23}$ molecules Then, $1 \mathrm{~g}$ of solid sulphur contains $=\frac{6.02 \times 10^{23}}{256}$ $16 \mathrm{~g}$ of solid sulphur contains $=\frac{6.02 ...
Read More →How many structural isomers
[question] Question. How many structural isomers can you draw for pentane? [/question] [solution] solution: [/solution]...
Read More →What is the mass
[question] Question. What is the mass of : (a) 0.2 mole of oxygen atoms ? (b) 0.5 mole of water molecules ? [/question] [solution] Solution: (a) Mass of one mole of oxygen atoms $=16 \mathrm{~g}$ mass of $0.2$ mole of oxygen atoms $=0.2 \times 16 \mathrm{~g}=3.2 \mathrm{~g}$ (b) Mass of one mole of water molecule $=18 \mathrm{~g}$ mass of $0.5$ mole of water molecules $=0.5 \times 18 \mathrm{~g}=9 \mathrm{~g}$ [/solution]...
Read More →Prove that $3+2 \sqrt{5}$ is irrational.
[question] Question. Prove that $3+2 \sqrt{5}$ is irrational. [/question] [solution] Solution: Let us assume, to the contrary, that $3+2 \sqrt{5}$ is rational. That is, we can find coprime integers a and $b(b \neq 0)$ such that $3+2 \sqrt{5}=\frac{\mathbf{a}}{\mathbf{b}}$ Therefore, $\frac{\mathbf{a}}{\mathbf{b}}-3=2 \sqrt{\mathbf{5}}$ $\Rightarrow \frac{\mathbf{a}-\mathbf{3} \mathbf{b}}{\mathbf{b}}=2 \sqrt{\mathbf{5}}$ $\Rightarrow \frac{a-3 b}{2 b}=\sqrt{5} \Rightarrow \frac{a}{2 b}-\frac{3}{2...
Read More →What would be the electron dot structure of a molecule of sulphur
[question] Question. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? [solution] solution: The eight atoms of sulphur are joined together in the form of a puckered ring (crown shape). [/solution]...
Read More →Convert into mole
[question] Question. Convert into mole. (a) 12 g of oxygen gas (b) 20 g of water (c) 22 g of carbon dioxide [/question] [solution] Solution: (a) $32 \mathrm{~g}$ of oxygen gas $=1$ mole Then, $12 \mathrm{~g}$ of oxygen gas $=\frac{12}{32}$ $=0.375 \mathrm{~mole}$ (b) $18 \mathrm{~g}$ of water $=1 \mathrm{~mole}$ Then, $20 \mathrm{~g}$ of water $=\frac{18}{20}$ $=1.11$ moles (approx) (c) $44 \mathrm{~g}$ of carbon dioxide $=1$ mole Then, $22 \mathrm{~g}$ of carbon dioxide $=\frac{22}{44}$ $=0.5$ ...
Read More →What would be the electron dot structure
[question] Question. What would be the electron dot structure of carbon dioxide which has formula $\mathrm{CO}_{2}$ ? [solution] solution: In carbon dioxide molecule, the two oxygen atoms are bonded on either side with carbon atom by double bonds. Thus there are 2 double bonds in $\mathrm{CO}_{2}$. Carbon share its two electrons in the formation of a double bond with one oxygen atom and another two electrons with another oxygen atom. In this process, both the oxygen atoms and the carbon atom acq...
Read More →Prove that $\sqrt{\mathbf{5}}$ is irrational.
[question] Question. Prove that $\sqrt{5}$ is irrational. [/question] [solution] Solution: Let us assume, to the contrary, that $\sqrt{5}$ is rational. So, we can find coprime integers a and $b(\neq 0)$ such that $\sqrt{5}=\frac{a}{b}$ $\Rightarrow \sqrt{5} b=a$ Squaring on both sides, we get $5 b^{2}=a^{2}$ Therefore, 5 divides $\mathrm{a}^{2}$. Therefore, 5 , divides a So, we can write a = 5c for some integer c. Substituting for a, we get $5 \mathrm{~b}^{2}=25 \mathrm{c}^{2}$ $\Rightarrow \mat...
Read More →What is the mass
[question] Question. What is the mass of (a) 1 mole of nitrogen atoms? (b) 4 moles of aluminium atoms (Atomic mass of aluminium = 27)? (c) 10 moles of sodium sulphite $\left(\mathrm{Na}_{2} \mathrm{SO}_{3}\right)$ ? [/question] [solution] Solution: (a) The mass of 1 mole of nitrogen atoms is $14 \mathrm{~g}$. (b) The mass of 4 moles of aluminium atoms is $(4 \times 27) g=108 g$ (c) The mass of 10 moles of sodium sulphite $\left(\mathrm{Na}_{2} \mathrm{SO}_{3}\right)$ is $10 \times[2 \times 23+32...
Read More →Give reasons why copper is used to make hot
[question] Question. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron). [/question] [solution] solution: Copper does not react with cold water, hot water, or steam. However, iron reacts with steam. If the hot water tanks are made of steel (an alloy of iron), then iron would react vigorously with the steam formed from hot water. [/solution]...
Read More →Calculate the molar mass
[question] Question. Calculate the molar mass of the following substances (a) Ethyne, $\mathrm{C}_{2} \mathrm{H}_{2}$ (b) Sulphur molecule, $S_{8}$ (c) Phosphorus molecule, $\mathrm{P}_{4}$ (atomic mass of phosphorus $=31$ ) (d) Hydrochloric acid, $\mathrm{HCl}$ (e) Nitric acid, $\mathrm{HNO}_{3}$ [/question] [solution] Solution: (a) Molar mass of ethyne, $\mathrm{C}_{2} \mathrm{H}_{2}=2 \times 12+2 \times 1=26 \mathrm{~g}$ (b) Molar mass of sulphur molecule, $\mathrm{S}_{\mathrm{g}}=8 \times 32...
Read More →Explain why $7 \times 11 \times 13+13$ and $7 \times 6 \times 5 \times 4$ $\times 3 \times 2 \times 1+5$ are composite numbers.
[question] Question. Explain why $7 \times 11 \times 13+13$ and $7 \times 6 \times 5 \times 4$ $\times 3 \times 2 \times 1+5$ are composite numbers. [/question] [solution] Solution: (i) $7 \times 11 \times 13+13=(7 \times 11+1) \times 13$ $=(77+1) \times 13$ $=78 \times 13=(2 \times 3 \times 13) \times 13$ So, $78=2 \times 3 \times 13$ $78 \times 13=2 \times 3 \times 13^{2}$ Since, $7 \times 11 \times 13+13$ can be expressed as a product of primes, therefore, it is a composite number. (ii) $7 \t...
Read More →Give the names of the elements
[question] Question. Give the names of the elements present in the following compounds: (a) Quick lime (b) Hydrogen bromide (c) Baking powder (d) Potassium sulphate [/question] [solution] Solution: [/solution]...
Read More →Differentiate between metal and non-metal on the
[question] Question. Differentiate between metal and non-metal on the basis of their chemical properties. [/question] [solution] solution: Metals (i) Metals are electropositive. (ii) They react with oxygen to form basic oxides. (iii) These have ionic bonds. (iv) They react with water to form oxides and hydroxides. Some metals react with cold water, some with hot water, and some with steam. (v) They react with dilute acids to form a salt and evolve hydrogen gas. However, $\mathrm{Cu}$, Ag, Au, Pt...
Read More →Write the chemical formulae
[question] Question. (a) Magnesium chloride (b) Calcium oxide (c) Copper nitrate (d) Aluminium chloride (e) Calcium carbonate [/question] [solution] Solution: (a) Magnesium chloride: $\quad \mathrm{MgCl}_{2}$ (b) Calcium oxide : $\mathrm{CaO}$ (c) Copper nitrate: $\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}$ (d) Aluminium chloride : $\mathrm{AlCl}_{3}$ (e) Calcium carbonate: $\mathrm{CaCO}_{3}$ [/solution]...
Read More →Check whether $6^{\mathrm{n}}$ can end with the digit 0 for any natural number $\mathrm{n}$.
[question] Question. Check whether $6^{\mathrm{n}}$ can end with the digit 0 for any natural number $\mathrm{n}$. [/question] [solution] Solution: If the number $6^{\mathrm{n}}$, for any natural number $\mathrm{n}$, ends with digit 0 , then it would be divisible by 5 . That is, the prime factorisation of $6^{\mathrm{n}}$ would contain the prime number 5 . This is not possible because $6^{\mathrm{n}}=(2 \times 3)^{\mathrm{n}}=2^{\mathrm{n}} \times 3^{\mathrm{n}} ;$ so the only primes in the facto...
Read More →The above frequency distribution table represents the blood groups of 30 students of a class.
[question] Question. The above frequency distribution table represents the blood groups of 30 students of a class. Use this table to determine the probability that a student of this class, selected at random, has blood group AB. [/question] [solution] Solution: Number of students having blood group AB = 3 Total number of students = 30 Hence, required probability, $\mathrm{P}=\frac{3}{30}=\frac{1}{10}$ [/solution]...
Read More →You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice.
[question] Question. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels. [/question] [solution] solution: Copper reacts with moist carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tamarind neutralises the basic copper carbonate and dissolves the lay...
Read More →