11th Class Chemistry Chapter 1 Basic Concepts Short Question Answers

Chemistry short QA

11th Class Chemistry Chapter 1 Basic Concepts Short Question Answers Below

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1.What is atomic mass unit?
It is unit of mass used for atoms and molecules and is equal to the 1/12 of the mass of an atom of carbon -12.It is obtained by dividing the unity by Avogadro’s number (6.02×1023). one a.m.u= 1.6603×10-27kg=1.6603×10-24g.
2.Whenever an electron is removed from the atom a cation is produced and the formation of the cation is an endothermic process.Comment?
The number of electrons and protons in an atom are equal.When the electron is removed from the atom energy has to be supplied.So it is an endothermic process.The ion develops the positive charge and is called cation.
3.What do you mean by molecular ions?
Any molecular species having positive or negative charge is called molecular ion.They are mostly produced when a beam of electrons having energy between 10 to 15eV is bombarded on molecules of a compound in the vapour phase.The examples may be CO+,N2+,C2H4+,O2+,CH4+,
4.The atomic masses may be in fractions.Why?
Most of the elements have isotopes.Each isotopes contributes its atomic masses.Hence the average of atomic masses of isotopes will be definitely in fractions.Anyhow the monopolistic elements have also fractional atomic masses.
5.Why positively charged ions of isotopes are passed through magnetic field in the mass spectrometer?
The positively charged ions bend perpendicular to the joining lines of the two poles when passed through the magnetic field.In this way magnetic field gives semicircular path to ions scatters them onn the basis of m/e values and compels them to fall on the electrometer. Electrometer records them.
6.What is the function of electrometer in separation of isotopes in mass spectrometer?
When positively charged ions of different isotopes fall upon the electrometer then current is produced proportional to the number of ions falling upon that.In this way the relative abundance of these isotopes can be recorded in the form of peaks on the graph.
7.What is mass spectrum or mass spectrograph?
It is a graph which is plotted between m/e of the positive ions on x-axis and the relative abundance of the isotopes on y-axis.This graph is plotted with the eletrometer and system is computerized.
8.How does the change of either electric field or magnetic field help us to record the isotopic separation by mass spectrometer?
ans of q no 8 ch 1
9.Why the isotopes have the same chemical properties?
The isotopes of an element have same the number of electrons in different orbitals.They have the same number of unpaired electrons in the outermost orbitals.The number of unpaired electrons in the outermost orbitals determine the chemical properties of elements.
10.One hundred ions of No3- and fifty ions of SO4-2 have equal number of charges but they have unequal masses and unequal number of atoms in them individually.Justify it?
100 No3 ions have 100 negative charges.50 SO4-2 have 100 negative charges.Their ionic masses are respectively 62 and 96g/mole.So even if the number of ions are same then the have unequal masses.Each ion has different number of atoms in them so there will be 400 atoms in 100 NO3-1and 250 atoms in 50 SO4-2.
11.In the mass spectrum of isotopes of oxygen the highest peak is due to 168O,the second highest is of 8O18 while 8O17 has the smallest peak.Why?
The relative abundance of various isotope is determined by the height of the peak in mass spectrometer.8O16 has 99.759% of relative abundance.8O18has 0.204% while 8O17has  0.037% of relative abundance.So the height of the peak due to 8O17 will be smallest.
12.The ratio of heights of the peaks for the isotopes of chlorine is 3:1 but in case of bromine two peaks of equal heights are obtained.Why?
The height of the peak depends upon the relative abundance of isotopes of that element.Chlorine has two isotopes 17CI35= 75.53 % and 17CI36=24.47%. The intensities of these two peaks are in the ratio of 3:1 In the case of bromine the relative abundance are 50.54% for 35Br80 and 49.46% for 35Br81.These two percentages are almost 50:50.
13.What is the reason for two equally strong peaks in the mass spectrum for bromine;while for iodine only one peak at 127 a.m.u.is indicated?
Bromine has two isotope which are almost equally abundant.Therefore mass spectrometer gives two equally strong peaks.Iodine is mono-isotopic so only one peak is obtained in the mass spectrum.
14.No individual neon atom in the sample of the element has a mass of 20.18 a.m.u.Why?
Neon has three isotopes of atomic masses 20.21 and 22 with relative abundances as 90.92%,0.26 and 8.82%.The relative atomic mass of neon comes out to be 20.18 a.m.u.is the average atomic mass of all the three isotopes and there is no atom of Ne with this atomic mass.
15.Define empirical formula and how it is related to molecular formula?When they are same for a molecule?
The simplest formula of a substance which tells us the ratio of atoms in the molecule of a substance is called empirical formula.
E.F.of benzene is CH,but M,F is C6H6.Therefore M.F =6(E,F)
H2O,CO2,H2SO4,KmnO4,have same molecular are empirical are empirical formulas and their n value is one.
16.One mole of H2SO4 should completely react with two moles of NaOH.How does Avogadro’s number help to explain it?
The balanced chemical equation between H2SO4 and NaOH.
H2SO4+2NaSO…………………. Na2SO4+2H2O
one mole of H2SO4 releases two moles of H+ in the solution.It needs two moles of OH ions for complete neutralization.
17. NaCI has 58.5 amu as formula mass and not the molecular mass justify it?
NaCI is a ionic compound.It has no molecules in the crystal structure.So 58.5 amu cannot be called as its molecular mass.Its formula is NaCI because for one Na+ there is one CI in the crystal.Here 58.5 amu is its formula mass.
18.Molecular formula is multiple of empirical formula.Give an example?
The empirical formula is the simplest whole number ratio of atoms of different elements present in a compound.Molecular formula tells us the actual number of atoms of each element in a molecule.Hence the empirical formula has to be multiplied with a suitable digit to get the molecular formula.
19.Circulate the mass in grams of 10-3 mole of water?
Mass of water = No.of moles × molar mass
= 10-3×18g =1.8×10-2g
= 0.018g
20.Mg atom is twice heavier than that of carbon atom.How?
The atomic mass of Mg is 24g mol-1 which is twice in mass as compared to the atomic mass of C i.e. 12g mol-1.So Mg atom is twice heavier than that a carbon.
21.180 grams of glucose and 342 grams of sucrose have same number of molecules but different number of atoms present in them. justify it?
180 grams of glucose and 342 grams of sucrose are one mole of each.One mole of various substance contain equal number of molecules i.e.6.02×1023.
22.What is the number of H+ ions in 9.8g of H3PO4?
The molar mass of H3PO4 is 98 g of H3PO4 is 0.1 moles.1 molecule of H3PO4 has 3H+. Hence the number of H+ ions in 0.1 moles of H3PO4 is 1/10th  of Avogadro’s number multiplied 3.i.e…3×6.02×1022=1806×1023.
23.What is the mass and number of molecules of CO2 in 0.224 dm3 of CO2 at S.T.P?
0.224 is 1/100th of one molar volume at S.T.P.Hence the number of molecules will be 1/100th of Avogadro’s number i.e.6.02×1021 and mass will be 44/100=0.44 g.
24.Define Avogadro’s number?How does it relate to the masses of chemical substances?
It is the number of atoms molecules or ions in one gram mole of an element compound and ion.One gram mole of the substance is the atomic mass molar mass  or ionic mass taken in grams.It means that the  number of the species is related with the masses of the species.23 g of Na and 238g of U have equal number of atoms in them.
25.What is the number of covalent bonds in 8 g of Ch4?
8 g of CH4 is 0.5 moles of CH4.It has 3.01×1023molecules of CH4. Each molecule has four bonds.So the total number of bonds is 4×3.01×1023=12.04×1023=1.204×1024.
26.Two grams of H2,16g of Ch4 and 44g of CO2 occupy separately the volumes of 22.414 dm3at STP although the sizes and masses of molecules of three gases are very different from each other.Give reason?
One mole of an ideal gas at S.T.P.occupies a volume of 22.414 dm3 sizes and masses of molecules of different gases do not affect the velum.Normally it is know that in the gaseous state the distance between the molecules is 300 times greater than their diameter.Therefore two grams of H2 16g of CH4 and 44g of CO2 separately occupy a volume of 22.4 dm3.This is called molar velum.
27. 4.9 g of H2SO4,when completely ionized in water have equal number of positive and negative charge but number of positively charged ions are twice the number of negatively charged ions.Give reason?
When one molecule of H2SO4 ionizes  it produce two H+ and one SO42-ion.Hydrogen ion contains +1 charge while suphate ion has -2charge.The ions produced by complete intuition of 4.9grams of H2SO4 in water will have equal +ve and –ve charges but the number of H+ ions is twice than number of negatively charged sulphate ions.Similarly 1mg of K2cro4 will have thrice the number of ions(2k+ + CrO4-2).If the number of formula units is X then ions will be 3X
28. 96 gm of SO4-2 has Avogadro’s number of SO4-2 ions twice the Avogadro’s number of negative charges 4NA as oxygen atoms and 5NA as total number of atoms.How?
The ionic of SO4-2 is 96 a.m.u.So in 96 gms of SO4-2 there is one mole of SO4-2 and one mole of the species have Avogadro’s number of particles.i.e. 6.02×1023.Each so SO4-2 ion has two negative charges so total negative charges are 2NA.Each SO4-2 ions has four oxygen atoms so there are total 4NA. Oxygen atoms in 96 gms of SO4-2.Each SO4-2 has five atoms.So one mole of SO4-2 has total 5NA atoms.
29.One mole of H2O has two moles of bonds three of atoms ten moles of electrons and twenty –eight moles of the total fundamental particles present in it.Justify?
The molecule of H-O H has two bonds in it.Therefore one mole of H2O contains two moles of bonds and three moles of atoms. Similarly there are eight electrons in oxygen and one electron in each of the two H atoms.One molecule of H2O has 10 electrons.So one mole of water contais  10 moles of electrons.There are 28 moles of all fundamental particles in one mole of water 10 moles of electrons 10 moles of protons 8 moles of neutrons.
30.Prove that one mole of each N2,Co2,and H2 contain equal number of molecules?
This is according to Avogadro’s law that one mole of a substance has 6.02×1023 molecules in it.So 28g of H2,44g of CO2and 2 g of H2 have 6.02×1023 molecules in each.
31.N2 and CO have same number of electrons protons and neutrons.Justify?
No.of electrons in N2= 7+7=14 number of protons in N2= 7+7=14 and number of neutrons.
In Co number of electrons in C=6 number of electrons in O=8 total number of electrons=6+8=14.
Number of protons in C=6 number of protons in O=8 total number of protons = 6+8=14.
Number of neutrons in C=6,number of neutrons in 0=8 total number o neutrons=6+8=14.
32.Calculate the mass in kg of 2.6×1023 molecules of SO2?
33.How many water molecular are there in 10 g of ice?
34.How can the efficiency of a chemical reaction be expressed?
35.11g of carbon is reacted with 32 g of oxygen to give CO2.Which is the limiting reactant?
According to the balanced chemical equation.12g  of carbon should completely react with 32 g of oxygen to gives 44grams of Co2.So32 grams of oxygen will be in excess in comparison to 11 grams of carbon.SO carbon is the limiting reactant.
36.Concept of limiting reactant is not applicable to the reversible reactions?
In the case of reversible reactions certain amounts of the reactants are left behind at the equilibrium stage.In the case of reaction having one of the substance as limiting one of the substance has to be consumed completely.So the reversible reactions do not help us to understand the concept of limiting reactant.
37.Distinguish between actual and theoretical yield. Calculate efficiency of a reaction?
38.What is limiting reagent?How it helps to control the reaction?
A limiting reactant is that one which is in lesser quantity and it is consumed earlier.Whenever it is consumed then the further formation of the product stops although the excess reagent is lying in the vessel.If the limiting reagent is not available to the excess reagent then product cannot be formed further.
39.Why the experimental yield is mostly less than the theoretical yield?

Experimental yield is mostly less than theoretical yield due to the following  reasons.
(1)Mechanical loss of products due to:
(i)filtration (ii)separation by distillation (iii)separating by separating funnel (iv) washing (v) drying (vi) crystallization
(2). Side reaction (3) Reversibility of reaction.

40.Law of conservation of mass has to be obeyed in stiochimetric calculations?
Total mass of reactants must be equal to total mass of product in a chemical reaction.So the calculation can be done for relative amounts of reactants and products in a chemical reaction.
41.Define storchiometry.What are its basic assumptions?
The branch of chemictry which deals with quantitative relationships between reactants and products in a balanced chemical equation is called stoichiometry.To perform stoichiometric calculations following assumptions are necessary:
(i) All the reactants are completely converted into products.
(ii)No side reaction is taking place.
(iii)Law of conservation of mass and law of definite proportions are obeyed.
42.The reaction of combustion in atmosphere consumes O2,which is in excess.What is limiting reactant?
Since O2 is always excess and is left  over in the atmosphere.A small part of total O2 can burn the whole material.So burning material is limiting reactant.This is one of the best example of a reaction which is frequent in our surrounding in which one substance is limiting.One of the reactants should be taken  in large excess to consume other material completely.
43. 23g of NA and 238g of U have equal number of atoms in them.How?
23g of Na is 1 mole of U.one mole of  element has 6.02×1023 atoms in that.
44.Calculate the number of moles of o-atoms in 9 g of Mg(NO3)?

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