Lime water is a saturated solution containing about 1 g of calcium hydroxide per dm3 of solution. Its concentration could be determined by titrating 20 cm3 of lime water with 0.01M hydrochloric acid. Answer questions a-d to help work out a theoretical titre for this titration.
Ar values; Ca=40, O=16, H=1
Eqn: Ca(OH)2(aq) + 2HCl(aq) = CaCl2(aq) + H2O(l)
a) What is the molarity of a lime water solution containing 1g/dm3?
Give your answer to 3 sig fig.
Is this 0.00100?
b) How many moles of Ca(OH)2 are there in 20 cm3 of this solution?
Moles of Ca(OH)2: C x V/1000 = 0.01 x 20/1000 = 0.002 mol ?
c) How many moles of HCl are needed to react with this number of moles of Ca(OH)2?
1:2; Moles of HCl: 0.002 x ½ = 0.001 mol ?
d) What volume of 0.01 M HCl would contain this number of moles?
Volume = Moles/Concentration; 0.01/0.01 = 0.1 dm3 ?
e) i) Why would this not be a suitable volume for the titre?
Help here as well please.
ii) Suggest how this titre value could be reduced by half.
Is this doubling the concentation of HCl?
f) Suggest a suitable indicator for this titration. Give the colour change expected at the end point.
Is this Phenolphthalein? Pink? I don't know much about experiment as I don't get classroom time, so I'm thinking this is more appropriate than methyl orange in this case because this would give a darker pink which would be easier to see than if methyl orange was used?
g) Name the apparatus which you would use to accurately measure the 20 cm3 of calcium hydroxide solution.
Again, I'v got no clue.
Please help me. Thank you.
Originally posted by Tullia:Lime water is a saturated solution containing about 1 g of calcium hydroxide per dm3 of solution. Its concentration could be determined by titrating 20 cm3 of lime water with 0.01M hydrochloric acid. Answer questions a-d to help work out a theoretical titre for this titration.
Ar values; Ca=40, O=16, H=1
Eqn: Ca(OH)2(aq) + 2HCl(aq) = CaCl2(aq) + H2O(l)
a) What is the molarity of a lime water solution containing 1g/dm3?
Give your answer to 3 sig fig.
Is this 0.00100?
b) How many moles of Ca(OH)2 are there in 20 cm3 of this solution?
Moles of Ca(OH)2: C x V/1000 = 0.01 x 20/1000 = 0.002 mol ?
c) How many moles of HCl are needed to react with this number of moles of Ca(OH)2?
1:2; Moles of HCl: 0.002 x ½ = 0.001 mol ?
d) What volume of 0.01 M HCl would contain this number of moles?
Volume = Moles/Concentration; 0.01/0.01 = 0.1 dm3 ?
e) i) Why would this not be a suitable volume for the titre?
Help here as well please.
ii) Suggest how this titre value could be reduced by half.
Is this doubling the concentation of HCl?
f) Suggest a suitable indicator for this titration. Give the colour change expected at the end point.
Is this Phenolphthalein? Pink? I don't know much about experiment as I don't get classroom time, so I'm thinking this is more appropriate than methyl orange in this case because this would give a darker pink which would be easier to see than if methyl orange was used?
g) Name the apparatus which you would use to accurately measure the 20 cm3 of calcium hydroxide solution.
Again, I'v got no clue.
Please help me. Thank you.
a) No, molarity = mole / volume (dm3). You have to calculate the moles of Ca(OH)2 present in 1g, then divide by the 1dm3 volume to obtain molarity.
b) moles (in 20cm3) = 20/1000 x molarity
c) yes, simply twice the moles of Ca(OH)2, since the base is diprotic, while the acid is monoprotic.
d) correct formula used, wrong values (due to error carried forward)
e) the titre value is too large, exceeding the burette capacity.
f) since this is a strong acid against strong base titration, any indicator will do. Just correctly state its end-point colour change.
http://en.wikipedia.org/wiki/PH_indicator
g) pipette