20 quastions-quantative chem and science skills Flashcards
state the law of conservation of mass
the mass of reactants is always equal to the total mass of products
calculate the relative formula mass of calcium carbonate CaC03
40+12+(16x3)=100
why must symbol equations balance
because no atoms are lost of made since the products are made from exactly the same atoms as the reactants
when metals form metal oxide ,why does the mass increase
because oxygen atoms have chemically bonded to the metal atoms
calculate the relative formula mass of water
h20=(2x1)+16=18
what does the state symbol aq stand for
aqueous (dissolved in water)
whats avogadros number (number of atoms in a mole)
6.02 x 10^23
whats the equation that links moles mass and mr
mass=mr X moles
69g of sodium reacts with sodium chlorine to produce sodium chloride 2na+Cl2->2NaCL. calculate the moles of sodium present
69/23=3 moles of Na
calculate the moles of chlorine requireed to react exactly woth sodium in 2na+Cl2->2NaCL.
from the eqation you get NA:CL ratio is 2:1 but we have 3 moles not 2 so 3;1.5 is required
whats the equation we use to find the concentration of a liquid
conc=mass or moles/volume in dm
whatre the units of concentration
g/dm^3 or moles/dm^3
1.5 moles of solute are dissolced in 1 dm of solvent,whats the concentration of solution formed
1,5 moles.1.00 dm=1.50 mol/dm cubed
2 g of solute are dissolved in 2 dm of solvent,whats the concentration of solution formed
2/2=1 g/dm cubed
0.2 moles of solute are dissolved in 500cm of solvent whats the concentration of the solution formed
0.2/0.5dm=0.4 mol/dm cubed
why might actual yields of reactions be less than the theoretical yield of a reaction
some product is lost when its seperated from the reaction, if reactions are reversable when it may not complete and some reactants react in diff ways than the expected reaction
a reaction has a theoretical yield of 13g but an actual yield of 8.5g whats the percentage yield of this reaction
(8.5/13)x100=65.4%
why are reactions that have high atom economy good for the environment
they produce less waste that could damage the environment like co2 and global warming
the equation to form ammonia is NH3, is: N2 + 3H2 → 2NH3, whats the percentage atom economy of this reaction
100 percent cayse theres only 1 product
whats a limiting reactant
A reaction finishes when one of the reactants is all used up. The
other reactant has nothing left to react with, so some of it is left over:
the reactant that is all used up is called the limiting reactant
