PAG 01 - Moles Determination Flashcards
(14 cards)
Describe how to set up apparatus to measure vol of gas produced in a reaction
Gas syringe or an upside-down water-filed measuring cylinder in a trough of water may be used to collect the gas
What’s used to accurately measure mass
A digital balance that records mass to 2 dp
Write chemical equation for reaction that occurs when Mg reacts with H2SO4
Mg + H2SO4 —> MgSO4 + H2
How can measuring vol of gas produced during reaction between Mg and H2SO4 be used to determine the relative atomic mass of Mg
- Measure the mass of some magnesium then react it with sulfuric acid
- Measure the volume of hydrogen gas produced in a gas syringe or an upturned water-filled measuring cylinder
- Calculate the number of moles of H, produced (number of moles = volume / 24 dm3)
- Use the ratio in the chemical equation to find the number of moles of magnesium
- Since original mass of magnesium is known, relative atomic mass can be calculated by dividing mass of magnesium by number of moles
Give 2 possible sources of error in this experiment
Some H2 gas may escape before the bung is put in conical flask
Some Mg may no react
Why is it important to rapidly put the bung in the conical flask after adding the sulfuric acid
Reaction starts as soon as acid is added so H2 will start to be produced.
To reduce amount of H2 that escapes, bung should be inserted rapidly
What equation links moles, Mr and mass
n = m/Mr
What safety precautions should be taken when conducting an experiment with Mg and H2SO4
Sulfuric acid cause skin and eye irritation so wear safety goggles and avoid contact with skin
Magnesium is highly flammable so keep away from naked flames
How can number of moles of CO2 be calculated from vol of CO2 collected during an experiment
If at room temp and press (RTP), use equation
n=V/24 [v=volume in dm^3]
If not at RTP, rearrange ideal gas law pV=nRT
And plug in numbers R= 8.31, T in kelvin, p in pascals and V in m^3
CuCO3 react with HCl to produce 15 mol of CO2
How many mol of CuCO3 reacted
CuCO3 + 2HCl —> CuCl2 + H2O + CO2
Ratio of CuCO3:CO2 is 1:1
15 mol of CuCO3 reacted
How could you find the % mass of CuCO3 in CuCO3.Cu(OH)2
- Record the mass of CuCO. Cu(OH)2
- React with acid and measure the volume of CO, collected. Use this to work out the number of moles of CO2 produced (number of moles = volume in dm3/ 24)
- Use the ratio in the chemical equation to work out the number of moles of CuCO, that reacted.
- Calculate the mass of CuCO, (number of moles = mass/Molar mass)
- Calculate the percentage of mass of CuCO, in the original sample:
(mass of CuCO3/mass of CuCO3. Cu(OH)2) × 100
Why is it important to rapidly put bung into conical flask after adding H2SO4 to CuCO3.Cu(OH)2
Reaction starts as soon as acid is added so CO2 will start to be produced
To reduce amount of CO2 that escapes, the bung should be inserted rapidly
Give 3 possible sources of error when investigating vol of gas produced in reaction
Some of gas could have escaped before bung is put in conical flask
Reaction may be incomplete
Some gas may dissolve in water meaning a smaller volume would collected than was released
What safety precautions should be taken when conducting an experiment with CuCO3.Cu(OH)2 and H2SO4
CuCO3.Cu(OH)2 is harmful if swallowed so avoid putting it near your face and wash hands after use. It is also an irritant so wear safety goggles and avoid contact with skin
H2SO4 causes skin and eye irritation so wear safety goggles and avoid contact with skin
