Core practical 1 Flashcards
measure the molar volume of a gas
Equation for moles of gases
volume/ 24,000 cm3
Equipment for practical
Balance
test tube
boiling tube
bung fitted with delivery tube that fits boiling tube
water bath for gas collection
1 molar ethanoic acid
powdered CaCO₃
100 cm³ measuring cylinder
50 cm³ measuring cylinder
clamp and stand
spatula
Method
- Set up water bath by:
(+filling medium size container, half way with water.
+ Filling 100cm³ measuring cylinder with water and
flipping upside down into the container of water
+ use a clamp stand to hold the measuring cylinder in
+ place
+ put the opening end of the deliver tube into the
100cm³ cylinder ) - Measure 30 cm³ (excess volume) of 1 Molar ethanoic acid into a measuring cylinder and pour into boiling tube
- On a top pan balance, weight 0.05g of CaCO₃ into a test tube, recording the weight of the test tube before adding CaCO₃ and after adding it to the test tube
- Gently tip the contents (CaCO₃) of the test tube into the boiling tube, attaching a bung on the boiling tube quickly, reducing gas lost
- once the reaction is over, measure the volume of gas collected in the measuring cylinder
- reweight mass of test tube containing CaCO₃
- repeat 6 more times, increasing mass of CaCO₃ by 0.05g not exceeding 0.40g
how to record data
Before practical:
- create a table showing mass of CaCO₃ used and volume of CO₂ produced
During practical:
- record mass of CaCO₃ and the corresponding volume of gas produced
After Practical;
- create a graph for the data, with volume of gas produced on y-axis (dependent variable) and mass of calcium carbonate powder on x-axis (dependent variable)
- draw a line of best fit through origin and you can use it to find the volume of gas produced with 0.25g of CaCO₃…
(find the moles of CaCO₃ when there is 0.25g of it… Mass/Mr. The moles of CaCO₃ and CO₂ are in a 1:1 ratio. Use the moles in the gas equation moles = vol/24,000 to find vol of CO₂ produced)
- axis of graph MUST TAKE UP HALF OF SHEET
equation for this equation
CaCO₃ + 2CH₃COOH → Ca(CH₃COO)₂ + CO₂ + H₂O
Why do we reweight the mass of the test tube ?
- there will be transference error of the CaCO₃
- finding the mass of the test tube when it contained CaCO₃ and after it it tipped out allows you to find the difference, meaning you can calculate the actual mass of CaCO₃ used in the reaction
Why is a weak acid used ?
- only ionizes 10% = reacts slower
- gives more time to attach bung to boiling tube with reduced loss of CO₂
how to properly measure the mass of CaCO₃ on the balance ?
- first place a 250cm³ beaker onto the balanced, set the palace to zero
- then place the test tube into the beaker and pour in your CaCO₃ with a spatula, measure the mass if both the test tube and powder
How else could you make the test tube and boiling tube easier to handle ?
placing both into a test tube rack
Safety hazards
- Ethanoic acid: can cause stinging if it enters cuts or eyes
+ wear eye protection, f in cuts, rise immediately under cold water and seek medical attention
Why is there a limit on CaCO₃ used ?
will produce more than 100cm³ of gas
- therefore, if more calcium carbonate is used or a balance only rounds to 1 decimal place, use a larger measuring cylinder to collect all the gas
The major errors in the practical
- gas lost before bung is applied to boiling tube
- CO₂ is slightly soluble so the entire volume of gas produced isn’t measured
