Required practicals

Question 1

What’s a hypothesis ?

Hint: explain

Answer 1

• a hypothesis, is a proposal that could explain a fact or an observation [it must be testable]

Question 2

What three practicals can be used, to investigate rate of reaction ?

Hint: volume

Answer 2

• the disappearing cross reaction
• measuring [the] gas volume, produced by a reaction
• and, by measuring the loss [change] in mass

Question 3

What’s the method, for the disappearing cross reaction ? ❌

Hint: conical flask, printed black cross, hydrochloric acid into, look and cloudy, stop, different concentrations

Answer 3

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

Question 4

After you’ve repeated the disappearing cross expirement, what should you do next ? ❌

Hint: mean…

Answer 4

• 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

Question 5

What’s the promblem with the disappearing cross experiment ? ❌

Hint: reproducible- why ?

Answer 5

• 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]

Question 6

What’s the solution, to reproducing the disappearing cross experiment ? ❌

Answer 6

• 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

Question 7

When measuring the gas produced by a reaction, what are the two ways this method can be done ? 💉

Answer 7

• 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

Question 8

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 ?

Answer 8

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.]

Question 9

How can a measuring cylinder be inverted ? [2]

Answer 9

• holding a piece of paper towel over the top, inverting the measuring cylinder.
• and then place it under the water, in the trough

Question 10

What’s the practical to measure the volume of a gas produced, using a gas syringe ? 💉 [6]

Answer 10

• 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.

Question 11

What’s the required practical, to measure the loss [change] in mass ? 👛 [5]

Hint: measure, boat, top-pan balance, cotton wool, intervals

Answer 11

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.

Question 12

After you’ve completed the change in mass experiment, what should you do ?

Answer 12

• 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.