Title: What is the effect of concentration of acid on the rate of diffusion in agar blocks? Aim: To investigate how the concentration affects the rate of diffusion of hydrochloric acid through agar blocks Research Question: To determine how will different concentrations (0.1M, 0.2M, 0.3M, 0.4M, 0.5M) of hydrochloric acid affect the rate of diffusion of sodium chloride through agar blocks? Introduction-include prediction; information you have researched before Diffusion refers to the passive movement of molecules along the concentration gradient. In this case we will be looking at the diffusion of acid in agar blocks. Agar is a jelly like substance and the indicator methyl orange is added which will turn red in the presence of acid. Hence we can measure the time taken for the colour change to calculate the rate of diffusion of hydrochloric acid in agar blocks.
1. Volume of hydrochloric acid
The volume of acid should be kept constant to ensure a fair experiment (cm³).
The same volume of acid of 25ml will be used for all experiments
2. Temperature of surroundings
Since temperature is a factor affecting diffusion, this should be kept constant when investigating the rate of diffusion.(°C) All experiments will be conducted at 40°C temperature-controlled water bath(±0.1°C)
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3. Type of acid used
The type of acid used could affect the results of the experiment. Hydrochloric acid provided by the lab from the same standard stock will be used
4. Type of agar block used
To keep the type of agar block the same will cause less differentiation in results and thus it is fairer. The agar blocks will be cut from the same standard stock provided by the lab
Step wise procedure
1. Cut the agar block into the size 1cm by 1cm by 1 cm (length, width, height respectively)
2. Add methyl orange indicator to the agar blocks.
3. Use the 10.0 cm³ measuring cylinder to measure 2.5ml of hydrochloric acid and add it to 22.5ml of water to get 0.1M of acid which you add to the beaker
4. Heat the solution with a Bunsen burner till it is at 40°C by checking the reading with the thermometer
5. Add the agar block into each beaker and record the time taken for the block to turn red completely
6. Repeat steps 1-5 but change the concentration in step 3 to 0.3M of hydrochloric acid
7. Repeat Steps 1-5 but change the concentration in step 3 to 0.4M of hydrochloric acid
8. Repeat Steps 1-5 but change the concentration in step 3 to 0.5M of hydrochloric acid
9. Record the time in a table
10. Repeat steps 1-9 five more times
Diagrams/ Photographs of set up
10. Risk assessment/safety precautions
1) Ensure that table top is cleared especially when heating to prevent flammable objects from coming in contact with flame 2) Hair of long haired students should be tied up as well to prevent any accidents 3) Gloves should be worn by student to prevent solutions from causing any damage in case of spillage and also prevent any injuries when slicing agar blocks