Required practicals

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

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

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

• 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

• 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]

• 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

• 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

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.]

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

• 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.

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.

• 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.