3. equations,calculations + electrolysis
balancing equations
equations show reactants+ products of reaction e.g magnesium reacts with oxygen produce magnesium oxide word equation; magnesium+ oxygen-> magnesium oxide.symbol equation 2Mg+O2-> 2MgO
symbol equation
need to be balanced .same number of atoms each side of equation
relative formula mass
relative formula mass Mr is all relative atomic mass(Ar) lf atoms added together
moles
unit for amount of substance 1 mole of atoms or molecules of any substance will have a mass in grams equal to particle mass (Ar or Mr) for that substance.carbon Ar of 12 1 mole carbon weighs 12g .all contain same n.o particles,1 mole or 6.02x10 23 of atoms or molecules.molar mass of substance mass of 1 mole meassured in grams
calclutation of number of moles
number of moles=mass(g) element or compound/ Mr(element or compound
calculating masses in reactions
1) write balanced equation
2) work out relative formula mass (Mr) of reactant + product
3) find how many moles of substance
4) balanced equation how many moles of substance
5) use number of moles calculate mass
percentage yield
percentage yield compare actual+ theoretical yield.more reactant start with higher the yield.percentage yield doesnt depend on amount of reactants is a percentage .percentage yield = actual yield(g)/ theoretical yield(g) x100 .100 percent all product
empirical + molecular formuale
empirical formula gives you smalles number of ratio.
1) list all elements in compound
2) underneath write experiment of masses
3) find number of moles of each element by dividing each mass by relative atomic mass(Ar) for particular element
4) turn numbers in simpler ratio by dividing by smallest number of moles
5) get ratio in smalles whole number form
molecular formulae
tells you actual n.o atoms of each element in single molecule .molecule formular are whole number multiples of empirical formulae e.g molecule has empirical formula C4H3O2 relative molecular mass 166 work at molecula formula 1) find mass of empirical formula(4x12)+(3x1)+(2x16)=83g
2) relative molecular mass is 166/83=2 empirical units in molecule
3) molecular formula must be empirical frmula x2 C8H6O4
combustion
subtance reacts with oxygen burned in air
empirical formula using combustion
magnesium oxide:1)crucible heat until red hot
2)leave cruicible to cool weigh with lid
3) add clean magnesium ribbon to cruicible reweigh cruicible,lid+magnesium ribbon .mass of magnesium using is reading minus intial reading for mass of cruicible+lid
4)heat cruicible containing magnesium put lid on cruicible to stop bits solid escaping small gap leave 02 to enter cruicible
5) heat cruicible 10 mins till magnesium turns white
6) allow crucible to cool+reweigh with lid+ content.mass of magnesium oxide-intial reading of mass with lid
magnesiun of oxygen is magnesium oxide is difference between mass kf magnesium+ oxygen is magnesium oxide
reduction
loss of oxygen from a subtance
empirical formula using reduction
1) place rubber bung into test tube weigh usijg mass balance
2) bung out of test tube +soread small amount copper (ii) oxide in middle of tube
3) reinsert bung+weigh test tube.set uo experiment .
4) expel air from test tube gently turning on gas.after 5 seconds light gas by holding burning splint next to hole in test tube
5) bunsen burner heat copper(ii) oxide 10 mins
6) turn of bunsen vurner allow testube to cool
7) weigh test tube with bung+ contents
water of crystalisation
water molecules have smal s+ charge on hydrogen atoms+ small negative(s-) charge on oxygen stoms means they are attracted to ions in lattice + held in place
salts
anhydrous ir hydrated .all solid salts consist if lattice of positive+negative ions.in some salts water molecules are incoperated in lattice water in lattice called water of crystalisation is hydrated.if salt doesnt contain any water of crystalisation called anydrous
moles of salt
1 mole of hydrated salt has particular n.o moles of water of crystalisation hydrated copper sultate has 5 moles lf water for every 1 mole salt hydrated salt ions lose water lf crystalisation when heated to befome anhydrous
moles+ crystalisation
concentration- amount of stuff per unit
volume measured in moles per dm3
concettation = n.o moles (mol)/ volume of solution (dm3)