Required practicals Flashcards
What’s a hypothesis ?
Hint: explain
- a hypothesis, is a proposal that could explain a fact or an observation [it must be testable]
What three practicals can be used, to investigate rate of reaction ?
Hint: volume
- the disappearing cross reaction
- measuring [the] gas volume, produced by a reaction
- and, by measuring the loss [change] in mass
What’s the method, for the disappearing cross reaction ? ❌
Hint: conical flask, printed black cross, hydrochloric acid into, look and cloudy, stop, different concentrations
1) use a measuring cylinder, put 0.5mol/dm^3 of sodium thiosulfate solution, into a conical flask
2) and then place the conical flask, on a printed black cross
3) add 10cm^3 of hydrochloric acid, into the conical flask, then swirl the solution and start a stopwatch.
4) look down through the top of the conical flask, and after a certain time, the solution turns cloudy
5) then stop the clock, as soon as the cross can no longer be seen
6) finally, repeat the experiment; use different concentrations of sodium thiosulfate solution
After you’ve repeated the disappearing cross expirement, what should you do next ? ❌
Hint: mean…
- repeat the whole experiment, and calculate mean values, for each concentration of sodium thiosulfate solution.
- ; when calculating a mean, don’t include any anomalous results
What’s the promblem with the disappearing cross experiment ? ❌
Hint: reproducible- why ?
- it’s subjective because, different people, have different eyesights.
- therefore, the results might not be reproducible because, some people can see the cross for longer than others [meaning they may not get the same results]
What’s the solution, to reproducing the disappearing cross experiment ? ❌
- problem- because the results are subjective as different people have different eyesights, which may affect the reproducibility of the expirement…
- solution- all students should use the same size printed cross
When measuring the gas produced by a reaction, what are the two ways this method can be done ? 💉
- using a gas syringe, to measure the volume of gas produced in a reaction
- and, using a measuring cylinder, to measure the volume of gas produced in a reaction
What’s the practical to measure the volume of a gas produced, using a measuring cylinder ? 🥣 [7]
Hint: hydrochloric acid, attach, trough and water, inverted, weighed calcium carbonate, trapped, measure- until when ?
1) first use a measuring cylinder, to place 50cm^3 of hydrochloric acid, into a conical flask
2) then, attach the conical flask to a bung and delivery tube
3) place the delivery tube into a trough filled with water
4) and, place an inverted measuring cylinder [that’s filled with water] over the delivery tube.
5) then tip 1.00g of the weighed calcium carbonate to the hydrochloric acid, and start a stopwatch [adding the bung immediately]
6) as the reaction produces hydrogen gas, this will be trapped in the measuring cylinder.
7) ; measure the volume of hydrogen gas, every 30 seconds, until there is no further increase in volume
[repeat the experiment, using different concentrations of hydrochloric acid.]
How can a measuring cylinder be inverted ? [2]
- holding a piece of paper towel over the top, inverting the measuring cylinder.
- and then place it under the water, in the trough
What’s the practical to measure the volume of a gas produced, using a gas syringe ? 💉 [6]
- Support a gas syringe with a stand, boss and clamp.
- and using a measuring cylinder, add 50 cm3 of dilute hydrochloric acid to a conical flask.
- then, add 0.4 g of calcium carbonate to the flask.
- Immediately connect the gas syringe and start a stop clock.
- and Every 10 seconds, record the volume of gas produced.
- when the reaction is complete, clean the apparatus, and repeat steps 1 to 5, with different concentrations of hydrochloric acid.
What’s the required practical, to measure the loss [change] in mass ? 👛 [5]
Hint: measure, boat, top-pan balance, cotton wool, intervals
1) measure 25 cm^3 of 1.0 mol/dm^3 of hydrochloric acid, using a 25cm^3 measuring cylinder, and pour it into a 250cm^3 conical flask.
2) weigh out 1.00g of calcium carbonate, using a weighing boat
3) and, place the conical flask on a top-pan balance, quickly adding the calcium carbonate to acid, in the flask.
4) then put a piece of cotton wool, loosely in the mouth of the flask
5) record the mass at 30 second- intervals, until there’s no further change in mass.
After you’ve completed the change in mass experiment, what should you do ?
- plot a graph of total mass in grams [y-axis] against time in seconds [x-axis] and draw a best fit line, through the points.
