Carry out a practical Chemistry investigation with direction

Target Language or Knowledge:

The Disappearing 'X' Experiment investigates the reaction between thiosulfate and hydrochloric acid. We want to see how a change in concentration of sodium thiosulfate affects the rate at which it reacts with hydrochloric acid. The sodium thiosulfate reacts with the hydrochloric acid to form a yellow cloudy solution. The X as shown in the image, will disappear when the solution becomes very dense. We are going to change the amount of the thiosulfate and see how that changes the time needed for the X to become too faint to see.
we shall be adding sodium _thiosulphate_ to _hydrochloric_ acid together and placing a drawn cross _underneath_ and seeing how long the rate of reaction lasts until you _cannot_ see this cross. Before the reaction starts, the liquids are both clear. When added they turn _cloudy_ and milky with a yellow tinge to it, due to the _sulphur_ released.
Hypothesis/Purpose of experiment
The factor we are concentrated on was changing the _concentration_ of the thiosulfate solution. How does this affect the _time_ taken for the X to disappear? To understand this we use collision theory as follows. All chemicals are made from _particles_ (atoms/Molecules) 2) The particles have _energy_ and can move 3) Chemical reactions only happen when particles _collide_ 4) Some collisions are not _successful._ 5)They must have _enough_ energy to react with each other and not just collide. 6) They _must_ be oriented correctly when they collide.
How will the independent variable be changed? That is the one YOU CHANGE.
The independent _variable_ is the _concentration_ of the acid. I will adjust the _amount_ of water in the acid, so there is the same _volume_ of 20mls but different amounts of the _acid_ and water in the 20mls. Give a suitable range of values for this variable. 20mls acid and no _water._ 15mls _acid_ and 5mls water 10mls acid and _10mls_ water _ 5mls_ acid and 15mls water no mls acid and _20mls_ water Why did I chose this range? a. Minimum; I want the _biggest_ range that gives results that I can _measure_ in the time I have to do the experiment.
Which is the DEPENDENT VARIABLE (the one that will be measured each time the independent variable is changed).
My dependent variable is the _change_ that I measure. In this experiment, that will be _time._ The time taken for the reaction between the acid and the _thiosulfate_ solution to _finish;_ the observed variable will be the time taken for and _'X'_ under the beaker to _disappear._ How will it be measured or observed? The _time_ taken to for the cloudy yellow solution to become too thick to see the _X_ under the _beaker._ This time will be _measured_ with a _stopwatch._
What happens when the concentration of the acid is changed?
The increase in _concentration_ of the acid means there is an _increase_ in the amount of _particles_ of acid in the same volume of solution. This means there will be more particles of acid in the solution that can _collide_ with the thiosulfate particles. That means there will be more _successful_ collisions too. This leads to a _faster_ reaction rate, so the X will disappear more _quickly._