# First Year Chemistry Basic Concepts Select the most suitable answer from the given ones in each question.The mass of one mole of electrons is:(a) 1.008 \mathrm{mg} (b) 0.55 \mathrm{mg} (c) 0.184 \mathrm{mg} (d) 1.673 \mathrm{mg}

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##### Select the most suitable answer from the given ones in each question.The mass of one mole of electrons is:(a) 1.008 \mathrm{mg} (b) 0.55 \mathrm{mg} (c) 0.184 \mathrm{mg} (d) 1.673 \mathrm{mg}

Q.16 Ethylene glycol is used as automobile antifreeze. It has 38.7 \% carbon 9.7 \% hydrogen and 51.6 \% oxygen. Its molar mass is 62.1 \mathrm{~g} \mathrm{~mol}^{-1} . Determine its empirical formula.?(Ans: \mathrm{CH}_{3} \mathrm{O} )

Q.7 Boron with atomic number 5 has two naturally occurring isotopes. Calculate the percentage abundance of { }^{10} \mathrm{~B} and { }^{11} \mathrm{~B} from the following information.Average atomic mass of boron =10.81 \mathrm{amu} Isotopic mass of { }^{10} \mathrm{~B} =10.0129 \mathrm{amu} Isotopic mass of { }^{\prime \prime} \mathrm{B} =11.0093 \mathrm{amu} (Ans: 20.002 \% 79.992 \% )

Q.5(a) What are isotopes? How do you deduce the fractional atomic masses of elements from the relative isotopic abundance? Give two examples in support of your answer.

Q.25 Explain the following with reasons.i) Law of conservation of mass has to be obeyed during stoichiometric calculations.

Calculate the number of grams of \mathrm{K}_{2} \mathrm{SO}_{4} and water produced when 14 \mathrm{~g} of \mathrm{KOH} are reacted with excess of \mathrm{H}_{2} \mathrm{SO}_{4} . Also calculate the number of molecules of water produced.

Define the following terms and give three examples of each.(i) Gram atom

A sample of liquid consisting of carbon hydrogen and oxygen was subjected to combustion analysis. 0.5439 \mathrm{~g} of the compound gave 1.039 \mathrm{~g} \mathrm{of} \mathrm{CO}_{2} 0.6369 \mathrm{~g} \mathrm{of} \mathrm{}_{2} \mathrm{O} . Determine the empirical formula of the compound.

The combustion analysis of an organic compound shows it to contain 65.44 \% carbon 5.50 \% hydrogen and 29.06 \% oxygen. What is the empirical formula of the compound? If the molecular mass of this compound is 110.15 gmol ^{-1} . Calculate the molecular formula of the compound.

Q.13 In each pair choose the larger of the indicated quantity or state if the samples are equal.a) Individual particles: 0.4 \mathrm{~mol} of oxygen molecules or 0.4 \mathrm{~mol} of oxygen atoms.(Ans: both are equal)b) Mass: 0.4 \mathrm{~mol} of ozone molecules or 0.4 \mathrm{~mol} of oxgen atoms.(Ans: ozone)

Define the following terms and give three examples of each.(ii) Gram molecular mass

Q.25 Explain the following with reasons.iii) No individual neon atom in the sample of the element has a mass of 20.18 amu.

Q.11 Aspartame the artificial sweetner has a molecular formula of \mathrm{C}_{14} \mathrm{H}_{12} \mathrm{~N}_{2} \mathrm{O}_{5} . .a) What is the mass of one mole of aspartame?(Ans: 294 \mathrm{~g} \mathrm{~mol}^{-1} )b) How many moles are present in 52 \mathrm{~g} of aspartame?(Ans: 0.177 \mathrm{~mol} )c) What is the mass in grams of 10.122 moles of aspartame? (Ans: 2975.87 \mathrm{~g} )d) How many hydrogen atoms are present in 2.43 \mathrm{~g} of aspartamẹ?

Q.18 An unknown metal M reacts with S to form a compound with a formula \mathrm{M}_{2} \mathrm{~S}_{3} . If 3.12 \mathrm{~g} of M reacts with exactly 2.88 \mathrm{~g} of sulphur what are the names of metal M and the compound \mathrm{M}_{2} \mathrm{~S}_{3} ?(Ans: \mathrm{Cr} ; \mathrm{Cr}_{2} \mathrm{~S}_{3} )

Fill in the blanksThe unit of relative atomic mass isThe exact masses of isotopes can be determined byspectrograph.The phenomenon of isotopy was first discovered byEmpirical formula can be determined by combustion analysis for thosecompounds which have and in them.A limiting reagent is that 1 mole of glucose has of oxygen and of hydrogen. atoms molecules of \mathrm{CH}_{4} . 4 \mathrm{~g} of \mathrm{CH}_{4} at 0^{\circ} \mathrm{C} and \mathrm{latm} pressure has Stoichiometric calculations can be performed only when is obeyed.

Define the following terms and give three examples of each.(viii) Percentage yield

Q.5(a) What are isotopes? How do you deduce the fractional atomic masses of elements from the relative isotopic abundance? Give two examples in support of your answer.

Justify the following statement:e) One \mathrm{mg} of \mathrm{K}_{2} \mathrm{CrO}_{4} has thrice the number of ions than the number of formula units when ionized in water.

b. What is a limiting reactant? How does it control the quantity of the product formed? Explain with three examples.

Justify the following statement:a) 23 \mathrm{~g} of sodium and 238 \mathrm{~g} of uranium have equal number of atoms in them.

Q.17 Serotenin (Molar mass =176 \mathrm{~g} \mathrm{~mol}^{-1} ) is a compound that conducts nerve impulses in brain and muscles. It contains 68.2 \% C. 6.86 \% \mathrm{H} 15.09 \% \mathrm{~N} and 9.08 \% \mathrm{O} . What is its molecular formula?(Ans: \mathrm{C}_{10} \mathrm{H}_{12} \mathrm{~N}_{2} \mathrm{O} )

Q.6 Silver has atomic number 47 and has 16 known isotopes but two occur naturally i.e. Ag-107 and \mathrm{Ag}-109 . Given the following mass spectrometric data calculate the average atomic mass of silver.\begin{tabular}{|l|c|c|}\hline Isotopes & Mass (\mathrm{amu}) & Percentage abundance \\\hline { }^{107} \mathrm{Ag} & 106.90509 & 51.84 \\ { }^{100} \mathrm{Ag} & 108.90476 & 48.16 \\\hline\end{tabular}

Select the most suitable answer from the given ones in each question.The mass of one mole of electrons is:(a) 1.008 \mathrm{mg} (b) 0.55 \mathrm{mg} (c) 0.184 \mathrm{mg} (d) 1.673 \mathrm{mg}

Select the most suitable answer from the given ones in each question.(a) Isotopes with even atomic masses are comparatively abundant.(b) Isotopes with odd atomic masses are comparatively abundant.(c) Isotopes with even atomic masses and even atomic numbers are comparatively abundant.(d) Isotopes with even atomic masses and odd atomic numbers are comparatively abundant.

Calculate the number of grams of \mathrm{K}_{2} \mathrm{SO}_{4} and water produced when 14 \mathrm{~g} of \mathrm{KOH} are reacted with excess of \mathrm{H}_{2} \mathrm{SO}_{4} . Also calculate the number of molecules of water produced.

\mathrm{NH}_{3} gas can be prepared by heating together two solids \mathrm{NH}_{4} \mathrm{Cl} and \mathrm{Ca}(\mathrm{OH})_{2} . If a mixture containing 100 \mathrm{~g} of each solid is heated then(a) Calculate the number of grams of \mathrm{NH}_{3} produced.(b) Calculate the excess amount of reagent left unreacted. 2 \mathrm{NH}_{4} \mathrm{Cl}(\mathrm{s})+\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{~s}) \longrightarrow \mathrm{CaCl}_{2}(\mathrm{~s})+2 \mathrm{NH}_{3}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})

Q.23a. What is stoichiometry? Give its assumptions? Mention two important laws which help to perform the stoichiometric calculations?

10.0 \mathrm{~g} of \mathrm{H}_{3} \mathrm{PO}_{4} has been dissolved in excess of water to dissociate it completelyinto ions.Calculatea) Number of molecules in 10.0 \mathrm{~g} \mathrm{of} \mathrm{}_{3} \mathrm{PO}_{4} .b) Number of positive and negative ions in case of complete dissociation in water.c) Masses of individual ions.d) Number of positive and negative charges dispersed in the solution.

Q.19 The octane present in gasoline burns according to the following equation. 2 \mathrm{C}_{\mathrm{z}} \mathrm{H}_{\mathrm{l8}}(\mathrm{l})+25 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 16 \mathrm{CO}_{2}(\mathrm{~g})+18 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) d) If this reaction is to be used to synthesize 8 moles of \mathrm{CO}_{2} how many grams of oxygen are needed? How many grams of octane will be used?