AS Level Chemistry Questions and Answers

AS Level Chemistry Questions and Answers Atomic number Number of protons in an element Mass number Number of protons and neutrons Ion Electrically charged particle formed by the loss/gain of electrons Relative masses of P,N and E 1,1, 1/2000 (respectively) Isotopes Atoms of the same element with different number of neutrons but same number of protons. What are steps of mass spectroscopy? Ionisation, Acceleration, Deflection, Detecting Ionisation A gaseous sample is bombarded with high energy electrons to create 1+ ions Acceleration They are accelerated through magnetic/electric field Deflection Ions are deflected through magnetic field according to mass (heavy - deflect least)(light - deflect most) Detection A calibrated detector records degree of deflection and interprets this into mass What does mass spectroscopy provide? Information about masses of particles inside machine and how often it's detected. What is shown on mass spectrum? Different isotopes relative abundance and molecular peak is furthest to right Molecular ion peak Peak corresponding to relative molecular mass of the compound (parent peak) Why are there sometimes line after the parent peak? They are a result of carbon 13 isotope and isn't considered when identifying a compound 1st Ionisation energy The energy change when 1 mole of electrons is removed from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ions Nth Ionisation energy Energy required to remove 1 electron feom each (n-1)+ ion in 1 mole of gaseous (n-1)+ ions to form 1 mole of gaseous n+ions Ground state Natural state of existence with electrons in lowest energy position Orbital Region around atom nucleus which can hold maximum of 2 electrons What's responsible for trends of 1st IE in first 20 elements? Sub-shells Describe an S-orbital Simplest of all, is spherical. The quantum number dictates how far away from the nucleus it is. Describe P-orbital Elongated dumbbell shape vary in charge density with area of greatest concerned increasing with distance from nucleaus due to principle quantum number. Have 3 different orientation of spaces. (x,y,z) Electron configuration points to consider S-orbital have less energy than d orbitals of principle quantum numbers. Always fill orbital with 1 electron first before pairing. Electrons have different directions of spin. Why do you fill each orbital with one electron before adding in pairs? Two electrons in same orbital experience some repulsion making pairing less favourable Valency Number of electrons involved in characteristic properties of element (reactions) What are the main ionic compounds to know? SO4(2-), NO3(-),NH4 (+), CO3 (2-), OH (-), Zn (+), Ag (+) Halide ion test with NaCl (Ionic equation) Ag (+)(aq) + Cl (-)(aq) AgCl (s) Relative atomic mass The weighted mean mass of an atom of an element compared to 1/12 of the mass of carbon 12. Relative Isotopic mass The mass of an isotope of an element compared to 1/12 of the mass of carbon 12 Relative molecular mass The weighted mean mass of a molecule compared to 1/12 of the mass of carbon 12. Relative formula mass The weighted mean mass of a formula unit compared to the mass of 1/12 of the mass of carbon 12. 1 mole The amount of substance that contains as many elementary particles as there are in 12 of carbon 12. Avogadro's constant (Number of particles per mole) 6.02e^23 Molar mass The mass of one mole of a substance. (g mol-1) Relationship between mass, Molar Mass and Moles M=m/n Empirical formula The simplest whole number ratio. Molecular mass The number and different type of atoms of each element in a molecule. Water of crystallisation Salts with water present in crystal form Anhydrous A compound with no waters of crystallisation. Hydrated A compound with water in its structure. Avogadro's law Equal volumes of gases measured at the same temperature and pressure will contain the same number of molecules. What are standard conditions? 0°C (273°K) and 100kPa. Molar volume= 22.1dm3 What are conditions at RTP? 25°C (298°K) and 100kPa Molar volume= 24dm3 Relationship between moles of gas and gas volume n (mol)=V(cm3/dm3)/molar volume (cm3/dm3) Ideal gas equation PV=nRT Conditions in ideal gas equation T=°K V=dm3=P=kPa V=cm3=P=Pa Relationship between Temp, pressure and volume P1V1/T1 = P2V2/T2 Relationship between concentration, moles and volume n (moles)=Conc(mol dm-3)×Vol(dm-3) What are cations? Positive ions What are anions? Negative ions What's a precipitate A solid formed when two liquids react Oxidation Loss of electrons Reduced Gain of electrons Rules of Oxidation numbers Natural elements=0 Oxi no total 0 Oxi no of ion totals ionic charge. Priorities of Oxidation states Groups 1,2&3 have Oxi no of +1,+2&+3 respectively. Flourine=-1 Hydrogen~+1 Oxygen ~-2 Chlorine~-1 Oxidising agent Is reduced in itself (gains electrons easily) {Flourine} Reducing agent Is oxidised itself (loses electrons readily) {Ba} Acid Proton donor Strong acids Completely disassociates into ions in water. (HCl, HNO3, H2SO4, H3PO4) Weak acid Partially disassociates in water. (CH3COOH) Base Proton acceptor. Alkali SOLUBLE BASE (NaOH, KOH, NH3) Neutralisation reaction H+ + OH- = H20 Water in acid base reactions Acids & alkalis will not behave as their meant to unless in the presence of water Acid + Base neutralisation Acid + Base Salt + Water Acid + Ammonia Acid + Ammonia Ammonium Salt Acid + Carbonate Acid + Carbonate Salt + Water + Carbon Dioxide Acid + Metal Acid + Metal Salt + Hydrogen (REDOX) Salt Formed when 1 or more Hydrogens of acid is replaced by metal ion or ammonium ion Carbonate ion test CO3 (2-)+DILUTE ACID= Salt+Water+CO2. Effervescence of CO2 gas proves carbonate present Sulfate ion test Adding Barium Chloride to SO4 (2-) leads to white precipitate. Halide ion test Add AgNO3 which forms silver halide which is a ppt. Cl=white (dilute NH3) Br=Cream (Conc NH3) I=Yellow (Insoluble) Ammonium ion test Warm NH4+ with NaOH producing NH3 gas which turns MOIST RED LITMUS- BLUE Ionic bond Electrostatic attraction between oppositely charged, which acts in all directions in lattice. Between a metal and non metal Ionic compound Properties Giant ionic lattices. High mpt&bpt- due to electrostatic attraction. Poor conductors (solid)- no mobile ions. Conductors (liquid/molten)- ions are mobile Soluble H2O- polar solvents dissolve polar compunds Solubility of ions Water is polar and so binds to ions (hydration) and is able to overcome ionic bond to disassociate the ionic compound. Covalent bond Strong electrostatic attraction between shaired pair of electrons and nuclei bonded. Between 2 non metals Lone pair of electrons Can form Dative bonds Affect molecule shape Important in chemical reactions. Behave as nucleophile Non bonded pair of electrons Dative (coordinate) bond Two electrons are provided from 1 atom. Electrostatic attraction between electron pair and nuclei if bonded atoms makes the covalent bond.