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# C2 calculations

work out the formula mass of NaCl. Na=23; Cl=35.5 Formula Mass of NaCl = 1xMass Na + 1xMass Cl = 23 + 35.5 =58.5
CHALLENGE work out the formula mass of (NH4)2SO4; N=14; H=1; S=32; O=16 Formula mass of (NH4)2SO4= (massN x1 + mass H x4)x2 + massS x1 + massO x4= (14x1 + 1x4)x2 + 32x1 + 16x4 = 132
work out the formula mass of MgSO4; Mg=24; S=32; O=16 Formula mass MgSO4 = MassMg x1 + MassS x1 + MassO x4= 24x1 + 32x1 + 16x4 = 120
work out the % by mass of Aluminium in Aluminium Oxide, Al2O3; Al=27; O=16 nb of atoms of Aluminium x mass of Aluminium x 100 / Formula mass of Al2O3 = 2 x 27 x 100 /102 = 57%
work out the % by mass of Oxygen in Magnesium Sulfate, MgSO4; Mg=24; S=32; O=16 nb of atoms of Oxygen x mass of Oxygen x 100 / Formula mass of MgSO4 = 53.3%
work out the % by mass of Aluminium in Aluminium Oxide, Al2O3; Al=27; O=16 nb of atoms of Aluminium x mass of Aluminium x 100 / Formula mass of Al2O3 = 2 x 27 x100 / 102 = 57%
how do you work out the formula mass of a compound? multiply the mass of each element by the subscript that follows; then add the masses together; MgCl2
how do you work out the % by mass of an Element in a compound Work out the formula mass; then check the number of atom of your element; %by mass= number of atoms x RAM of element x 100 / formula mass
work out the formula mass of NH4NO3 14*1 + 1*4 + 14*1 + 16*3 = 80
what is the empirical formula for the compound that has 2.4g of Magnesium and 1.6g of Oxygen? Mg=24 and O=16 Work out the moles of Mg=2.4/24=0.1 and moles of Oxygen=1.6/16=0.1; divide both numbers by the smallest: Mg=0.1/0.1=1 and O=0.1/0.1=1; the empirical formula is Mg1O1
what is the empirical formula for the compound that has 4.6g of Sodium and 1.6g of Oxygen? Na=23 and O=16 Work out the moles of Na=4.6/23=0.2 and moles of Oxygen=1.6/16=0.1; divide both numbers by the smallest: Na=0.2/0.1=2 and O=0.1/0.1=1; the empirical formula is Na2O1
CHALLENGE: 239g of a Lead Oxide contains 32g of Oxygen. what is the empirical formula? Pb=207; O=16 You must have the mass of each ELEMENT: here mass of Lead is 239-32=207; Then as usual, Work out the moles of Pb=207/207=1 and moles of Oxygen=32/16=2; divide both numbers by the smallest: Pb=1/1=1 and O=2/1=2; the empirical formula is Pb1O2
how do you work out the empirical formula, given the mass of each element? set up one column for each element; on the first line, work out mass/RAM (ie the moles); on the second line divide the moles by the smallest number; remember to show the elements for the empirical formula (and not only the ratio)
what is the relative atomic mass of Chlorine, knowing that it has two isotopes: Chlorine with mass 35 and an abundance of 75% and Chlorine with mass 37 and an abundance of 25% (35*75 + 37*25)/100= 35.5
Boron has two isotopes of mass 10 and 11. The relative atomic mass of Boron is 10.8. What does it tell you about the abundance of each isotope? There is more isotope of Mass 11, because the RAM is closer to 11 than 10
CHALLENGE Fe2O3 + 3 CO -> 2 Fe + 3 CO2; what mass of iron is produced when 80g of Iron(III)oxide is reacted? (Fe=56; O=16) Formula mass Fe2O3=56x2+3x16=160; moles Fe2O3=mass/formula mass=80/160=0.5; ratio of BIG numbers says moles Fe= 2x molesFe2O3 =0.5x2=1; mass Fe=moles Fe x formula mass=1x56=56g; remember to use BIG numbers in ratio ONLY
2 KClO3 -> 2 KCl + 3 O2; What mass of KCl is produced when 122.5g of KClO3 reacts completely? (K=39; Cl=35.5; O=16) Formula mass KClO3=39+35.5+3x16=122.5; form.mass KCl=39+35.5=74.5; moles KClO3=mass/formula mass=122.5/122.5=1; ratio of BIG numbers says moles KCl= moles KClO3 =1; mass KCl=moles KCl x formula mass=1x74.5=74.5g
CuCO3 -> CuO + CO2; What mass of Carbon Dioxide is produced when 12.4g of CuCO3 reacts completely? (Cu=64; C=12; O=16) Formula mass CuCO3=64+12+3x16=124; form mass CO2=12+16x2=44; moles CuCO3=mass/formula mass=12.4/124=0.1; ratio of BIG numbers says moles CO2=moles CuCO3 =0.1; mass CO2=moles CO2 x formula mass=0.1x44=4.4g
Gallium has two isotopes of mass 69 and 71. The relative atomic mass of Gallium is 69.8. What does it tell you about the abundance of each isotope? There is more isotope of Mass 69, because the RAM is closer to 69 than 71
How do you work out the relative atomic mass, given the mass of each isotope and the % abundance of each isotope? for each isotope, multiply the percentage by the mass of the isotope; add all the numbers; then divide by 100.
how do you work the mass of a compound, given the equation for the reaction and the mass of the reactant? set up the calculations under the equation: first line is mass; second line is formula mass; bottom line is moles; then go down (divide mass by formula mass); across (look at the BIG numbers); and up (multiply moles by formula mass)
In an experiment 2.4g of Magnesium is burned; and 3.6g of Magnesium Oxide is collected. What is the yield of Magnesium Oxide? 3.6g (what you should collect)
The theoretical yield of Magnesium Oxide is 4.0g. But only 3.6g is collected. What is the %yield? 3.6/4.0*100=90%
Created by: UrsulineChem