2.1 Atoms And Reactions
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Define Isotope
Atoms of the same element with different number of neutrons but same number of protons
Define relative isotopic mass
The mass of an isotope compared to 1/12th the mass of carbon-12
Define relative atomic mass
The weighted average mass of an atom compared to 1/12th the mass of carbon-12
What’s the relative mass of an electron?
1/2000
Ar formula?
((Isotope mass x %)+(isotope mass x %))/100
Number of particles formula?
Moles x avogadros constant
What does mass spectrometry tell us?
Determine the relative abundances of each isotope of an element Identified unknown substances Provide structural information about a molecule
How do you use mass spectra to work out relative atomic masses of different elements?
Step 1. Mulitply each relative isotopic mass by its relative isotopic abundance, and add up the results Step 2. Divide by the sum of the isotopic abundances (x * y) + (x * y) + (x * y)=z (y + y + y=u) z/u=answer
What’s the formula to finding the number of moles? when you have mass
no. of moles (mol) = mass (g) / Mr (g mol-1)
Why do different isotopes of the same element react in the same way?
• Chemical reactions involve ELECTRONS, and isotopes have the same number and arrangement of electrons. • Neutrons make no difference to chemical reactivity.
What is the Avogadro’s constant?
The number of atoms per mole of the carbon-12 isotope (6.02 x 10^23 mol-1)
What are the steps to calculate the empirical formula?
• Find the moles of the element • Divide the answer for each element by the smallest number • If necessary, multiply the answer by a suitable value to make sure the ratio is in whole number only.
Define molecular formulae
Tells you the number of each type of atom that make up a molecule
What are the steps to calculate the molecular formulae? Q. A molecule has an empirical formula of C4 H3 02, and a molecular mass 166g mol-1 Work out the its molecular formula
• Work out the empirical formula mass (same as relative formula mass) of the compound. • Given molecular mass/the empirical formula mass= No. of empirical units in the molecule • empirical formula x No.^ A. (4 x 12)+(3 x 1.0)+(2x16.0)=83.0g/mol 166/83 = 2 empirical units in the molecule so molecular formula is: C8H604
How do you write an ionic equation? Q. What’s the ionic equation for the reaction of Nitric acid with sodium hydroxide
• Write out a full balanced equation • Rewrite the equation showing all the ions that are in the reaction mixture (only aqueous compounds, leave solids and gasses as is) • Cross out ions that appear on both side of the equation A. HNO3 (aq) + NaOH(aq) –> NaNO3(aq) + H2O(l) H+ + NO3- + Na+ OH- —> Na+ + NO3- + H2O H+ + OH- —> H20
What’s the formula to finding the number of moles? when you have volume of gas
n=v/24
What’s the formula to finding the number of moles? when you have solution volume and concentration
n=C x V
what’s the ideal gas equation?
pV=nRT p in pa V in m^3 n is no. of moles R is gas constant 8.314 J/K/mol T is temperature in k
What’s the molar volume?
The molar volume is the volume per mole of gas. At room temperature and pressure it is 24.0 dm3/mol
What’s a hydrated salt?
A hydrated salt is one which contains water of crystallisation e.g. MgSO4·7H2O. It is water that trapped inside the ionic lattice
What’s an anhydrous salt?
An anhydrous salt is one with no water of crystallisation e.g. MgSO4.
How do you work out the amount of water of crystallisation in a salt Q. Heating 3.210g of hydrated magnesium sulfate, MgS04,XH20, Forms 1.567g of anhydrous magnesium sulfate. Find the value of X and write the formula of the hydrated salt.
-From the Mr Find the Mr of the anhydrous salt and subtract it from the hydrated Mr then divide the remainder by the Mr of water -From experimental results Find the moles of water lost when a hydrated salt is heated in a crucible and the number of moles of anhydrous salt left at the end A. Mass of water lost: 3.210-1.567=1.643g Moles of water lost: 1.643/18 (ar of water) = 0.09127 Mr of MgSO4 is 120.4 no. of moles: 1.567/120.4=0.01301 0.01301 moles of salt : 0.09127 moles of water 1mol of salt: 0.09127/0.01301=7.015 SO ITS MgSO4.7H2O
What are acids?
Proton donors. They release h+ ions when mixed with water
What are bases?
Proton acceptors. They want to grab H+ ions in solution Bases that are soluble in water are alkalis.